A regular narrow rhythm may stop when you interrupt the AV node. An irregular, pre-excited rhythm can become more dangerous with that same drug. Start with the tissue and the tracing. The drug names will have somewhere to land.
Read the map. Compare the families. Make the decision. Try the cases.
01 / The electrical map
Which part of the signal changed?
The AV node and ventricular muscle do not use the same upstroke. That difference explains why diltiazem can slow the ventricular response to atrial fibrillation, yet is dangerous as an experiment in an unexplained wide complex tachycardia.
Working myocardium
Phase 0 uses Na⁺. Class I drugs slow the upstroke in atrial muscle, ventricular muscle and the His-Purkinje system. Ventricular conduction slowing widens the QRS.
SA and AV nodes
Phase 0 uses Ca²⁺. Verapamil and diltiazem slow nodal conduction. Beta blockers lower cAMP, reducing pacemaker current and calcium entry. The rate falls and PR may lengthen.
Conceptual traces, not patient recordings. Height represents membrane voltage. Navy identifies working muscle; purple identifies nodal tissue. The numbered phases and text carry the same meaning without color.
In ventricular muscle, phase 1 is the early notch. During phase 2, inward calcium and outward potassium currents sustain a plateau. Phase 3 returns the cell toward rest as outward potassium current predominates. Phase 4 is comparatively flat. In nodal tissue, phase 4 rises spontaneously; the funny current, If, helps set that pace. IK1 helps stabilize resting voltage in working muscle.
PR, QRS and QT answer different questions
PR · Getting through
Atrial activation plus conduction to the ventricles. AV nodal slowing commonly lengthens it. It is not a pure measurement of the AV node alone.
QRS · Spreading through
Ventricular depolarization. Sodium channel block can widen this part of the tracing, particularly with class Ic drugs.
QT · Activating and recovering
Depolarization plus repolarization. QTc adjusts for rate. A longer QT may reflect a wider QRS, delayed repolarization, or both.
A wider QRS can make the measured QT longer without a comparable increase in repolarization time.
Flecainide is the useful example. Its QT increase is largely explained by QRS widening. The JT interval, QT minus QRS, helps separate the components, although wide or paced complexes need experienced interpretation. Do not dismiss a long measured QT, and do not equate every increase with isolated potassium channel block. DailyMed flecainide label
Three ways an arrhythmia can sustain itself
Automaticity
A pacemaking focus fires more readily. Sympathetic stimulation can steepen phase 4. Beta blockade reduces that adrenergic drive.
Triggered activity
An afterdepolarization follows a preceding action potential. Early afterdepolarizations occur before repolarization finishes and can initiate torsades in long QT. Delayed afterdepolarizations occur after repolarization and often reflect calcium overload, as with digoxin toxicity or catecholamine-sensitive outflow tract arrhythmias.
Reentry
An impulse returns to tissue that has recovered enough to conduct again. A loop needs a suitable pathway and timing. Blocking a necessary limb or making it refractory can stop the loop. Slowing conduction alone can also favor reentry in diseased tissue, which is why an antiarrhythmic can be proarrhythmic.
Use dependence means greater drug effect with repeated activation. Class Ic sodium block can become more pronounced as rate rises because the drug dissociates slowly. Class Ib drugs dissociate more readily and favor inactivated channels in depolarized tissue. Ischemic tissue does not need to fire more often to be preferentially affected.
Reverse use dependence means a greater repolarization effect at slower rates, characteristic of several IKr blockers. Long pauses, bradycardia, low potassium and interacting drugs can reduce the margin for safe repolarization. EHRA practical compendium
Try it here · Checkpoint 1 of 3
Make your prediction before reading the choices. A first attempt is just a starting point.
Case 01
The ventricular rate falls, but AF remains
A 72-year-old woman develops palpitations while gardening and comes to the emergency department two hours later. She has no chest pain, syncope or history of heart failure. Blood pressure is 136/78 mmHg. ECG shows an irregular narrow complex rhythm at 148/min without discrete P waves; echocardiography shows an EF of 60%. After IV diltiazem, the ventricular rate falls to 92/min while the atrial rhythm remains disorganized. Which action best explains this response?
Answer and all four rationales
A. Blockade of ventricular sodium channels Sodium block can widen QRS by slowing ventricular depolarization. The useful effect here is reduced transmission of atrial impulses through the AV node, whose upstroke depends mainly on calcium.
B. Blockade of L-type calcium channels in the AV node · Best answer Diltiazem slows calcium-dependent AV conduction. Fewer atrial impulses reach the ventricles, so the ventricular rate falls even though AF continues. That is rate control.
C. Selective IKr blockade restoring atrial refractoriness This describes dofetilide more closely. Repolarization-prolonging drugs may support rhythm control; diltiazem's nodal action does not require conversion of AF to explain the observed rate reduction.
D. Selective inhibition of sinus-node funny current Ivabradine targets the funny current. The sinus node is not controlling the atrial rhythm during AF, so slowing its automaticity does not explain this ventricular rate response.
Vaughan-Williams is a starting map. A drug can act on several channels, and drugs in one class can have very different uses.
Class I · Sodium channel blockers
Ia Intermediate dissociation
Quinidine, procainamide, disopyramide. Sodium block slows conduction; additional effects on repolarization lengthen the action potential. Watch both QRS and QT.
Quinidine has specialist uses in selected atrial and ventricular arrhythmias, including some inherited arrhythmia syndromes. Tinnitus, headache, hearing or visual disturbance and gastrointestinal symptoms suggest cinchonism. QT prolongation, torsades and immune thrombocytopenia matter too. DailyMed quinidine label · EHRA practical compendium
Procainamide is an IV option for selected stable wide complex tachycardia and stable pre-excited AF. Monitor blood pressure, QRS and QT. Its active metabolite NAPA adds repolarization effects; renal impairment can increase exposure to both. Longer exposure can cause a lupus-like syndrome or serious blood dyscrasias. Arthralgia and serositis with ANA and anti-histone antibodies support drug-induced lupus in the right setting. Anti-histone antibodies are not specific, and a negative anti-dsDNA test does not by itself exclude idiopathic SLE. DailyMed procainamide label · 2023 AF guideline · Rubin et al. procainamide serology
Disopyramide has strong negative inotropic and anticholinergic effects. Dry mouth, constipation and urinary retention distinguish its adverse-effect pattern. Glaucoma, obstructive urinary symptoms and impaired ventricular function require particular care. Specialist treatment of obstructive hypertrophic cardiomyopathy uses its negative inotropy deliberately. Pfizer NORPACE label · EHRA practical compendium
Ib Rapid dissociation
Lidocaine and mexiletine. Their ventricular effects are useful in selected arrhythmias, especially where depolarized tissue is involved. They often shorten action potential duration with little QRS effect at usual rates. They are not routine AF drugs.
Lidocaine is given IV for cardiac arrhythmias. It is an option in shock-refractory VF or pulseless VT and some ischemia-associated ventricular arrhythmias. Confusion, perioral sensory symptoms, tremor or seizures suggest toxicity. Low hepatic blood flow and liver dysfunction can impair clearance. It is not routine prophylaxis for every patient after MI. DailyMed IV lidocaine label · 2025 AHA adult ALS
Mexiletine provides oral class Ib treatment for selected ventricular arrhythmias, sometimes as an adjunct. Gastrointestinal intolerance, tremor and coordination problems often limit it. Hepatic function and interactions matter. The EHRA correction identifies no currently available IV formulation in its formulary row. DailyMed mexiletine label · EHRA 2026 correction
Phenytoin has historical use for digitalis-associated ventricular arrhythmias. It does not replace digoxin immune Fab for life-threatening digoxin toxicity. EHRA practical compendium · FDA DigiFab label
Ic Slow dissociation
Flecainide and propafenone. Substantial sodium block slows conduction, with prominent QRS widening and relatively little direct ventricular repolarization prolongation. Measured QT can still increase.
For AF, these are options only after assessing prior MI, significant structural heart disease, ventricular scar and systolic function. CAST showed that suppressing ventricular ectopy after MI did not establish safety or improve survival. Class Ic treatment increased mortality in that setting. A normal echocardiogram also does not eliminate every proarrhythmic risk. DailyMed flecainide label · 2023 AF guideline
AF can organize into atrial flutter with one-to-one AV conduction. A concomitant AV nodal blocker reduces that risk when class Ic treatment is used for ordinary AF. Propafenone also has beta-blocking activity; its label excludes bronchospastic disorders and severe obstructive pulmonary disease. DailyMed propafenone label
Class II · Reduce adrenergic drive
Metoprolol, esmolol, propranolol and atenolol slow sinus activity and AV conduction through beta blockade. Esmolol's short action makes IV titration useful in monitored care. Propranolol is nonselective; metoprolol is relatively beta-1 selective, with selectivity diminishing at higher exposure.
These drugs commonly control the ventricular rate in AF or flutter and help with selected supraventricular or catecholamine-sensitive arrhythmias. Bradycardia, AV block, hypotension and bronchospasm can limit treatment. Combining nodal blockers compounds those effects. EHRA practical compendium · 2023 AF guideline
Chronic benefit is different from an acute bolus. In stable HFrEF, evidence-based beta blockers such as carvedilol can improve outcomes over time. Carvedilol also blocks alpha-1 receptors. Its long-term benefit does not make abrupt additional beta blockade appropriate during cardiogenic shock or active decompensation. DailyMed carvedilol label
Class III · Extend recovery time
Amiodarone
Multiple sodium, potassium, calcium and adrenergic effects explain its broad activity. It is useful in selected AF and ventricular arrhythmias, including patients with reduced EF. Tissue accumulation means effects and interactions can persist for weeks to months after stopping.
QT prolongation occurs, but torsades is less frequent than with several other class III agents. It is still possible. Pulmonary injury, hypo- or hyperthyroidism, liver injury, photosensitivity, blue-gray pigmentation, neuropathy and ocular effects require attention. DailyMed amiodarone label
Dronedarone
A noniodinated relative of amiodarone with a shorter persistence and generally less rhythm-control efficacy. It is not a toxicity-free substitute. Hepatic and pulmonary injury can occur.
Do not use it for permanent AF or recent symptomatic HF decompensation requiring hospitalization or NYHA class IV HF. The AF guideline also advises against use in NYHA III or IV HF or decompensation within four weeks. ANDROMEDA and PALLAS identify harmful populations; ATHENA studied a different AF population. Check rhythm at least every three months under the label. DailyMed MULTAQ label · 2023 AF guideline
Sotalol
Nonselective beta blockade plus IKr block. The beta-blocking effect slows rate; IKr blockade prolongs repolarization. It is used to maintain sinus rhythm in selected symptomatic AF or flutter and to treat selected life-threatening ventricular arrhythmias. Bradycardia can increase, rather than reliably offset, the danger of acquired torsades. Kidney function determines the dosing interval.
The oral BETAPACE label calls for hospitalization for initiation or reinitiation for at least three days or until steady state, with continuous ECG and resuscitation capability. Check QT, creatinine clearance, potassium and magnesium. For AF or flutter, do not initiate with a QT above 450 ms. A QT of 500 ms or greater during treatment requires dose reduction, a longer dosing interval or discontinuation. Serum potassium below 4 mEq/L, decompensated heart failure, cardiogenic shock and bronchial asthma or related bronchospastic conditions are contraindications. Avoid casual substitution for an ordinary beta blocker. DailyMed BETAPACE label
Dofetilide
A selective IKr blocker used for AF or flutter conversion and maintenance. It can be considered in HFrEF, but renal accumulation and drug interactions can cause excessive QT prolongation.
Initiation and reinitiation require a monitored facility and a specific QT and creatinine clearance algorithm. A reassuring pulse or a pacemaker does not replace that protocol. Pfizer TIKOSYN dosing
Ibutilide is the mechanism exception
IV ibutilide can convert AF or flutter, particularly flutter. Its label describes activation of a slow inward current, predominantly sodium, that delays repolarization. Calling it simply a pure potassium blocker misses this distinction. Correct low potassium and magnesium; monitor continuously for at least four hours after infusion and longer if QTc has not returned to baseline or arrhythmias occur. Reduced EF increases concern for proarrhythmia. DailyMed CORVERT label
Class IV · Slow calcium-dependent nodal conduction
Verapamil and diltiazem can slow the ventricular response in AF or flutter and terminate selected AV node dependent SVTs. Expect PR prolongation, bradycardia, AV block or hypotension. Their negative inotropy makes them unsuitable in significant LV systolic dysfunction. For acute AF rate control, the guideline specifies EF above 40% for these drugs. Do not use in sick sinus syndrome or second- or third-degree AV block without a functioning ventricular pacemaker. Marked hypotension is another important exclusion. 2023 AF guideline · DailyMed diltiazem label
Amlodipine and nifedipine are dihydropyridines used mainly for vascular effects. They do not substitute for verapamil or diltiazem in nodal rhythm treatment. Confirmed fascicular VT is an important specialist exception to the usual nodal use of verapamil. Do not generalize that exception to undifferentiated wide complex tachycardia. EHRA practical compendium · 2025 AHA adult ALS
Agents outside the traditional four classes
Adenosine
A1 receptor activation opens potassium channels and reduces cAMP-dependent calcium entry, briefly suppressing AV conduction. Its blood half-life is under ten seconds. A rapid IV bolus followed by saline flush can stop AVNRT or orthodromic AVRT. Flushing, chest discomfort and dyspnea can occur; explain these before administration when possible. Adenosine can cause severe bronchospasm and is contraindicated in asthma under AHA ALS guidance. Second- or third-degree AV block and sick sinus syndrome are contraindications unless a functioning pacemaker is present. Caffeine and theophylline can blunt the effect; dipyridamole can enhance it. DailyMed adenosine label · 2025 AHA adult ALS
Digoxin
Na⁺/K⁺-ATPase inhibition increases intracellular sodium and reduces calcium extrusion, increasing available intracellular calcium. Vagal effects slow AV conduction. It can assist AF rate control, especially with HF or when other agents are unsuitable, but controls exertional rate less reliably. Kidney dysfunction, low potassium, low magnesium, high calcium and interacting drugs raise toxicity concerns. In the DIG trial, HF hospitalization decreased without an overall mortality benefit. It is not a substitute for HF therapies with demonstrated survival benefit or a treatment for routine PVC suppression. DailyMed digoxin label · 2023 AF guideline
Magnesium
IV magnesium can suppress recurrent torsades associated with prolonged QT even when the measured magnesium is normal. Sustained polymorphic VT still needs immediate defibrillation. Magnesium is not routine treatment for every polymorphic VT with a normal QT. 2025 AHA adult ALS
Ranolazine
Late sodium current inhibition can reduce intracellular sodium and calcium loading. It also inhibits IKr and can prolong QT. Its US indication is chronic angina; antiarrhythmic use is off-label and specialist-directed. Do not promise freedom from torsades. With diltiazem or verapamil, the label limits it to 500 mg twice daily. DailyMed ranolazine label
Ivabradine
Selective If inhibition slows the sinus node. It requires an appropriate sinus-rhythm indication and is not a substitute for AV nodal rate control during AF. EHRA practical compendium
Try it here · Checkpoint 2 of 3
Make your prediction before reading the choices. A first attempt is just a starting point.
Case 10
A quieter monitor is not the outcome
A 67-year-old man attends follow-up three months after an anterior MI. He walks daily without palpitations, syncope or angina. Echocardiography shows an EF of 35%, and ambulatory monitoring records frequent ventricular premature complexes without sustained VT. A clinician proposes flecainide solely to suppress the ectopy. Which finding from antiarrhythmic evidence most directly argues against this plan?
Answer and all four rationales
A. Post-MI class Ic treatment suppressed ectopy but increased mortality · Best answer CAST separates a monitor finding from a patient outcome. Class Ic suppression of ventricular ectopy after MI increased mortality, supporting avoidance in prior MI and significant structural heart disease.
B. Flecainide cannot reduce ventricular ectopy It can suppress ectopy. The problem is that this electrical effect does not establish clinical benefit, and in the post-MI substrate it accompanied worse survival.
C. A normal potassium value would make flecainide safe Correcting electrolytes is important, but it does not erase infarct scar or LV dysfunction. The substrate-related contraindication remains even with normal potassium and magnesium.
D. An ICD would eliminate the contraindication A device may treat some malignant arrhythmias, but its presence does not make a proarrhythmic drug appropriate in an otherwise excluded substrate. It does not reverse the CAST lesson.
Before choosing a drug, identify the pulse, hemodynamic effect, regularity, QRS width and baseline QT. Correct reversible causes alongside rhythm treatment.
Pulseless VF or VT. CPR and defibrillation are central. Amiodarone or lidocaine may be considered when shocks have not terminated the rhythm. Drug preparation must not interrupt compressions or delay shocks.
Unstable tachycardia with a pulse. Hypotension, shock, altered mental status, ischemic discomfort or acute HF attributable to the rhythm calls for electrical treatment. Use synchronized cardioversion for appropriate organized rhythms.
Sustained polymorphic VT. Give an immediate unsynchronized shock, meaning defibrillation. Changing QRS morphology prevents reliable synchronization. This applies even if a pulse was initially palpable.
Regular, usually narrow. The ventricle is activated through the normal conduction system. Vagal maneuvers and monitored adenosine can interrupt the AV nodal limb.
Pre-excited atrial fibrillation
Irregular, often wide and variable. The accessory pathway can conduct dangerously short atrial intervals. AV nodal block does not protect the ventricles.
In pre-excited atrial fibrillation, avoid adenosine, beta blockers, verapamil, diltiazem, digoxin and IV amiodarone. These can worsen the ventricular response or precipitate VF. Unstable patients need electrical cardioversion. Stable patients may receive IV procainamide or ibutilide with appropriate monitoring and expertise. Catheter ablation addresses the accessory pathway. 2023 AF guideline
A history of WPW does not turn every regular narrow SVT into pre-excited AF. Conversely, a wide rhythm is not automatically antidromic AVRT. Antidromic AVRT conducts forward through the accessory pathway and is usually regular and wide. If the mechanism is uncertain, use the wide complex tachycardia pathway and obtain expert help. Adenosine is reserved for selected stable, regular, monomorphic wide complex rhythms; never use it in irregular or polymorphic wide complex tachycardia. 2025 AHA adult ALS · EHRA practical compendium
Stable AF and flutter · Rate is different from rhythm
Rate control limits the ventricular response while the atrial arrhythmia may continue. A beta blocker or, with suitable EF, diltiazem or verapamil often serves that purpose. Digoxin is useful when other agents are unsuitable or insufficient, especially with HF. Selected critically ill or decompensated patients may receive IV amiodarone under monitored care; conversion and stroke implications must be considered.
Rhythm control aims to restore or maintain sinus rhythm using cardioversion, drugs or ablation. For AF with HFrEF, amiodarone or dofetilide can be reasonable drug choices. For appropriate patients without prior MI or significant structural disease, flecainide or propafenone can be considered. A pill-in-the-pocket plan uses a tested flecainide or propafenone regimen with an AV nodal blocker after a supervised first attempt. It is not a generic instruction to take any antiarrhythmic when palpitations start.
Sinus rhythm does not cancel stroke prevention. For elective cardioversion when AF has lasted at least 48 hours, the guideline calls for three weeks of therapeutic anticoagulation or imaging to exclude intracardiac thrombus beforehand. Anticoagulation is established before and continued for at least four weeks after cardioversion; longer treatment depends on stroke risk. Shorter-duration AF still needs individualized risk assessment. 2023 AF guideline
Ventricular rhythms · Separate the exceptions
Stable monomorphic wide complex tachycardia warrants continuous monitoring and a 12-lead ECG when feasible. IV procainamide, amiodarone or sotalol may be considered with attention to HF, QT and contraindications. Prepare for cardioversion if drugs fail or instability develops. Avoid combining antiarrhythmics casually. Verapamil and diltiazem should not be given to an undifferentiated wide complex rhythm. 2025 AHA adult ALS
Confirmed fascicular VT
Often has a right bundle branch block pattern with axis deviation. A calcium-dependent portion of the reentry circuit makes verapamil useful when the diagnosis is established and the patient is stable. The morphology alone is insufficient permission to give it to any wide rhythm.
Idiopathic outflow tract arrhythmia
Often involves catecholamine-sensitive triggered activity. Beta blockers, selected calcium channel blockers and ablation have roles. Adenosine can terminate some outflow tract VT. Selected patients may receive class Ic therapy after appropriate evaluation; normal imaging does not mean zero risk.
Long-QT torsades · Terminate, then prevent recurrence
Sustained polymorphic VT needs a shock. Recurrent long-QT torsades also needs its trigger addressed.
After termination, magnesium can help suppress recurrence. Stop the offending QT-prolonging drug, correct potassium and magnesium deficits, and assess bradycardia or pauses. Refractory, pause-dependent acquired torsades may require expert-directed pacing or isoproterenol. Isoproterenol is not a universal treatment for congenital long QT or ischemic arrhythmias.
For recurrent polymorphic VT with a normal baseline QT, investigate ischemia and other causes; lidocaine or amiodarone may be considered. Routine magnesium has no established benefit in that group. 2025 AHA adult ALS
Inherited syndromes also differ. LQT1 commonly involves KCNQ1 and reduced IKs, often with exertional triggers. LQT2 involves KCNH2 and reduced IKr, with sudden sound or emotional triggers in some patients. LQT3 can involve increased late sodium current from SCN5A variants and events at rest. These are associations, not diagnostic tests; congenital long-QT care is genotype- and patient-specific. EHRA practical compendium
Monitoring is part of choosing the drug
Before treatment, review the ECG, ventricular function, renal and hepatic function, electrolytes, interacting medicines and any implanted device. Recheck when doses change, an illness alters clearance, or a new drug is added.
Amiodarone follow-up has a schedule and symptom triggers
Thyroid and liver
The 2023 AF guideline recommends baseline TSH and AST/ALT, repeat testing at three to six months, then every six months. Additional thyroid testing follows an abnormal TSH.
ECG and examination
Baseline ECG and annual ECG follow-up. Assess skin and neurologic symptoms clinically. Review interacting medicines, especially warfarin, digoxin and other nodal or QT-prolonging drugs.
Lungs
The AF guideline recommends a baseline chest radiograph and repeat radiography for unexplained cough, dyspnea or other suspicion of pulmonary toxicity. CT follows symptoms or radiographic findings when indicated. Routine CT screening is not recommended.
Eyes
New visual symptoms need evaluation, particularly for optic neuropathy. Asymptomatic corneal microdeposits alone do not require stopping treatment. The AF guideline does not require universal annual slit-lamp screening.
The product label differs. The cited oral amiodarone label calls for baseline pulmonary function testing including diffusion capacity and a chest radiograph, followed by history, examination and chest radiography every three to six months. It also recommends regular ophthalmic assessment. Its approved indication centers on life-threatening ventricular arrhythmias. Use the applicable label, indication and clinical plan; do not substitute a universal annual scan bundle. DailyMed amiodarone label
New cough and reduced oxygenation warrant assessment for drug injury, infection and HF. Stopping amiodarone does not clear it overnight. Perioperative teams need to know about exposure because anesthetic and cardiac depressant effects can add to hypotension or bradycardia.
Dofetilide · Clearance plus QT, every time
Use calculated creatinine clearance under the label's Cockcroft-Gault method, not an unexamined eGFR substitution. Starting doses are 500 micrograms twice daily above 60 mL/min, 250 micrograms twice daily at 40 to 60, and 125 micrograms twice daily at 20 to below 40. Below 20 mL/min, dofetilide is contraindicated.
Baseline QTc above 440 ms excludes initiation, with a 500 ms threshold for ventricular conduction abnormalities. Use QT when the rate is below 60/min. Check QT after dosing; after the second dose, QTc or QT above 500 ms requires discontinuation, with a 550 ms threshold for conduction abnormalities. Monitoring lasts at least three days and at least twelve hours after conversion, whichever is longer. These are selected checkpoints, not the complete dosing algorithm. Follow the linked label for first-dose adjustments and repeat checks. Pfizer TIKOSYN dosing
Trimethoprim, hydrochlorothiazide and verapamil are among the contraindicated combinations. Interaction review is required even when electrolytes look normal. Pfizer TIKOSYN contraindications
After initiation, the TIKOSYN label calls for renal function and QT reassessment every three months or sooner when clinically warranted. A new illness, renal deterioration or interacting prescription can invalidate a previously appropriate dose. Sotalol likewise needs ongoing ECG, electrolyte and renal surveillance, particularly after dose or clinical changes. Pfizer TIKOSYN dosing · DailyMed BETAPACE label
Digoxin · Read the patient, not just the level
Nausea, anorexia, confusion, visual disturbance and a new arrhythmia can indicate toxicity. Atrial tachycardia with AV block is suggestive, not uniquely diagnostic. Low potassium increases susceptibility; severe acute poisoning may instead produce hyperkalemia. Check renal function, electrolytes and a correctly timed drug level, generally at least six hours after the last dose.
Life-threatening ventricular arrhythmias, severe symptomatic bradyarrhythmia or other severe poisoning may require digoxin immune Fab. Obtain toxicology support. Monitor potassium after Fab because it can fall, and do not interpret a routine total digoxin assay after Fab as free active drug. DailyMed digoxin label · FDA DigiFab label
Pacemakers · Verify the electrical response
A stimulus is not the same as capture. Flecainide can raise the capture threshold above the programmed output, so a pacing spike may fail to produce ventricular depolarization. Its label calls for threshold checks before treatment, after one week and regularly thereafter. Poor thresholds or a nonprogrammable device require particular caution and suitable rescue capacity. DailyMed flecainide label
A pacemaker may limit pauses when appropriately programmed and functioning, but it does not eliminate torsades risk. QT assessment, renal dosing and electrolyte monitoring still apply. Device presence also does not make class Ic therapy appropriate in prior MI or significant structural disease. EHRA practical compendium · 2023 AF guideline
Find the rhythm. Identify the tissue. Check the substrate. Choose the intervention. Plan the monitoring.
Try it here · Checkpoint 3 of 3
Make your prediction before reading the choices. A first attempt is just a starting point.
Case 05
The same pathway, now with shock
A 31-year-old woman with known ventricular pre-excitation arrives after ten minutes of palpitations and near-syncope. She is confused, cool and diaphoretic, with blood pressure 74/46 mmHg. ECG shows irregular wide complex tachycardia with variable QRS morphology at approximately 240/min, identified as pre-excited AF. A pulse is present, and a defibrillator with synchronization capability is ready. What is the most appropriate immediate treatment?
Answer and all four rationales
A. A procainamide infusion before considering electrical treatment Procainamide is an option in stable pre-excited AF. This patient's hypotension and altered mental status show severe instability, so waiting for a drug infusion delays the indicated intervention.
B. IV metoprolol followed by reassessment of blood pressure Beta blockade is inappropriate in pre-excited AF and can worsen perfusion in shock. The ventricular response is not safely controlled by treating the AV node alone.
C. IV digoxin because it supports contractility Digoxin's inotropic effect does not solve this electrical emergency. It can be dangerous in pre-excited AF, and its use would delay treatment of rhythm-related hemodynamic collapse.
D. Immediate electrical cardioversion with synchronization when feasible · Best answer Unstable pre-excited AF requires electrical cardioversion. Use appropriate sedation if feasible without delaying treatment. If synchronization cannot be achieved in a deteriorating patient, do not allow that difficulty to delay a needed shock.
Each case stands on its own. Choose an answer, then compare all four explanations. You can change a choice and revisit any case. There is no timer or required order.
Open “Answer and all four rationales” whenever you want to compare the explanations.
Case 02
An SVT stops, then starts again
A 29-year-old woman develops abrupt palpitations while sitting at work. After 40 minutes, ECG shows regular narrow complex tachycardia at 188/min; blood pressure is 122/76 mmHg and she has no wheezing or chest pain. Modified Valsalva does not terminate it. A monitored adenosine bolus produces transient AV block and sinus rhythm. Twenty seconds later, a premature atrial complex initiates the same tachycardia. What best explains the recurrence?
Answer and all four rationales
A. The drug briefly interrupted reentry without eliminating its substrate · Best answer Adenosine has a very short blood half-life. It can interrupt an AV node dependent circuit, but the pathways remain available. A new premature impulse can initiate another episode after conduction recovers.
B. The initial dose failed to reach the AV node Delivery failure can explain no response. Here, recorded AV block and termination demonstrate a nodal effect. The later restart is a separate event, not evidence that the first dose never arrived.
C. The rhythm was AF with temporary ventricular slowing Adenosine may reveal atrial activity by slowing AV conduction. This tracing instead documents regular tachycardia, a period of sinus rhythm, and reinitiation by a premature atrial complex.
D. Adenosine produced persistent sodium channel blockade Persistent sodium block would not match the brief AV block and recovery. Adenosine acts through A1 receptors and nodal signaling; it is not a long-acting class I drug.
A 34-year-old man awaiting accessory-pathway ablation has 25 minutes of palpitations after climbing stairs. His prior electrophysiology study documented orthodromic AVRT. He is alert, with blood pressure 128/80 mmHg, clear lungs and no asthma. The current ECG matches his prior regular narrow complex tachycardia at 196/min; there is no irregularity. Vagal maneuvers fail. Which intervention is appropriate with monitoring and resuscitation equipment available?
Answer and all four rationales
A. IV digoxin to slow accessory-pathway conduction Digoxin primarily slows AV nodal conduction and is not an acute accessory-pathway blocker. Its hazards in pre-excited AF also make it a poor substitute for the indicated acute SVT strategy.
B. IV amiodarone as the first pharmacologic treatment Amiodarone is used for selected atrial and ventricular arrhythmias, but monitored adenosine is the targeted acute drug after vagal maneuvers fail in this documented stable AV node dependent SVT.
C. IV adenosine to interrupt the AV nodal limb · Best answer Orthodromic AVRT conducts forward through the AV node. Brief nodal block can terminate it. WPW history alone does not prohibit this use, although adenosine can provoke AF and requires appropriate readiness.
D. Immediate unsynchronized shock solely because WPW is present A stable, regular narrow rhythm is not an indication for automatic defibrillation. Electrical cardioversion may be needed if the clinical situation changes, but the current findings support monitored SVT treatment.
A 26-year-old man with a prior ECG showing a short PR interval and delta wave develops palpitations during dinner. Thirty minutes later he is alert, with blood pressure 126/74 mmHg and no chest pain or pulmonary edema. ECG shows a markedly irregular tachycardia, varying QRS widths and ventricular rates reaching 230/min. The electrophysiologist identifies pre-excited atrial fibrillation. Which IV drug is a guideline-supported option in this stable monitored setting?
Answer and all four rationales
A. Diltiazem Diltiazem is familiar for ordinary AF rate control. In pre-excited AF, AV nodal block can permit a more dangerous ventricular response through the accessory pathway and precipitate VF.
B. Procainamide · Best answer Procainamide affects conduction and refractoriness in the accessory pathway. It is an option for stable pre-excited AF, with ECG and blood pressure monitoring. Instability would change the priority to electrical cardioversion.
C. Adenosine Adenosine may terminate regular orthodromic AVRT, but this rhythm is irregular pre-excited AF. Transient AV block does not protect the ventricles from atrial impulses using the bypass pathway.
D. Amiodarone Its broad antiarrhythmic reputation is tempting. The AF guideline includes IV amiodarone among drugs to avoid in pre-excited AF because worsening conduction through the pathway or VF can occur.
A 68-year-old man hospitalized after an acute coronary syndrome suddenly becomes pale and poorly responsive. Telemetry shows a sustained wide complex tachycardia with continuously changing QRS morphology. A weak pulse is initially felt at the femoral artery. The defibrillator repeatedly fails to place reliable synchronization markers on the complexes. Which action should occur immediately?
Answer and all four rationales
A. Deliver an unsynchronized high-energy shock · Best answer Sustained polymorphic VT requires immediate defibrillation. Changing morphology makes synchronization unreliable. An initially palpable pulse does not justify delaying the shock while trying to synchronize.
B. Continue adjusting synchronization until every complex is marked Synchronization is useful for appropriate organized rhythms, including monomorphic VT with a pulse. In sustained polymorphic VT it may never become reliable, and continued adjustment delays treatment.
C. Give magnesium first and await its effect Magnesium may help prevent recurrence in long-QT torsades, but it does not replace the immediate shock for sustained polymorphic VT. The prior QT should guide later treatment after termination.
D. Give adenosine as a diagnostic trial Adenosine is not used in polymorphic wide complex tachycardia. Its selected diagnostic role in stable regular monomorphic rhythms does not apply to this electrical emergency.
A 63-year-old woman receiving sotalol has two brief self-terminating runs of polymorphic VT overnight. She is now alert in sinus rhythm at 48/min, with blood pressure 116/68 mmHg and a QTc of 565 ms. Potassium is 3.1 mmol/L and magnesium is 2.0 mg/dL. Sotalol is held, potassium replacement begins, and defibrillation pads are applied. Which additional drug is appropriate to help suppress recurrence?
Answer and all four rationales
A. IV ibutilide Ibutilide can cardiovert AF or flutter but also prolongs repolarization. Adding it in marked acquired QT prolongation can worsen the substrate responsible for torsades.
B. Another dose of sotalol Sotalol is a likely contributor to the prolonged QT and bradycardia. Its beta-blocking component does not reliably neutralize its torsades risk; restarting it now would compound the problem.
C. IV magnesium sulfate · Best answer Magnesium can suppress recurrent polymorphic VT associated with long QT despite a normal serum magnesium value. Continue correction of causes. If polymorphic VT becomes sustained, defibrillate immediately.
D. IV amiodarone Amiodarone is useful in other ventricular arrhythmias but can prolong QT. In this long-QT, pause-associated pattern, magnesium and correction of the provoking conditions are the appropriate focus.
A 70-year-old man with symptomatic persistent AF elects dofetilide treatment after a rhythm-control discussion. He is admitted for initiation. He has no interacting medicines, potassium is 4.4 mmol/L, magnesium is 2.1 mg/dL, heart rate is 76/min and baseline QTc is 425 ms with QRS 94 ms. The label's calculation gives creatinine clearance of 32 mL/min. Which starting dose matches the renal portion of the algorithm?
Answer and all four rationales
A. 500 micrograms twice daily That is the renal starting dose above 60 mL/min. At 32 mL/min, reduced clearance increases exposure and the risk of excessive QT prolongation; the highest dose is inappropriate.
B. 125 micrograms twice daily · Best answer The 20 to below 40 mL/min band starts at 125 micrograms twice daily. This does not replace serial QT assessment or inpatient observation. Renal function and QT both determine treatment safety.
C. 250 micrograms twice daily That dose belongs to the 40 to 60 mL/min band. Using it merely because the patient is an adult ignores the lower calculated clearance supplied in the stem.
D. No treatment because all creatinine clearances below 40 exclude it The renal contraindication is below 20 mL/min, not below 40. This patient falls into a lower-dose band, assuming the other initiation criteria and monitoring requirements remain satisfied.
A 64-year-old woman is undergoing monitored dofetilide initiation for AF. Her pretreatment QTc was 421 ms and creatinine clearance was 56 mL/min. After the third dose, a 12-lead ECG shows sinus rhythm at 72/min, QRS 92 ms and QTc 526 ms. She feels well, potassium is 4.3 mmol/L and magnesium is 2.2 mg/dL. Which action best follows the prescribing algorithm?
Answer and all four rationales
A. Continue because she has no symptoms QT prolongation may be silent until proarrhythmia occurs. A normal examination and absence of palpitations do not override the post-dose discontinuation threshold.
B. Continue because the conduction-abnormality threshold is 550 ms The higher threshold applies to ventricular conduction abnormalities. Her QRS is narrow, so applying 550 ms would use an exception that the ECG does not support.
C. Add hydrochlorothiazide and repeat the ECG tomorrow Hydrochlorothiazide is contraindicated with dofetilide and can increase QT-related risk. It neither corrects this adverse response nor substitutes for following the dosing algorithm.
D. Discontinue dofetilide and continue monitored assessment · Best answer After the second dose, QTc or QT above 500 ms requires discontinuation in a patient without a ventricular conduction abnormality. Observation and reassessment remain necessary while drug effects resolve.
A 46-year-old woman with paroxysmal AF and no prior MI or structural heart disease returns after starting flecainide. She has mild dizziness but no syncope. At the same sinus rate of 70/min, QRS duration has increased from 90 to 112 ms and measured QT from 400 to 423 ms. Electrolytes are normal. Which interpretation best explains the interval pattern while her clinician evaluates tolerability?
Answer and all four rationales
A. Class Ic drugs cannot increase measured QT, so the ECG must be wrong QT includes QRS. Sodium channel blockade can therefore lengthen measured QT through slower ventricular depolarization. The tracing should be assessed, not dismissed because of an oversimplified class rule.
B. The entire QT change proves marked IKr blockade The QRS increase nearly accounts for the QT increase. QT alone cannot assign the change to repolarization, especially when depolarization time has visibly changed.
C. Most of the QT increase is explained by QRS widening · Best answer QT minus QRS is almost unchanged in these measurements. Flecainide's measured QT effect is often largely due to QRS widening. Symptoms, conduction effects and dosing still require clinical assessment.
D. The longer QRS shows improved His-Purkinje conduction A wider QRS indicates slower or altered ventricular activation, not improved conduction. That is consistent with flecainide's sodium channel effect and warrants comparison with baseline.
A 51-year-old man taking flecainide for paroxysmal AF has missed his prescribed metoprolol for three days. During a brisk walk he develops palpitations. Blood pressure is 118/72 mmHg. A 12-lead ECG and atrial electrogram reviewed by electrophysiology show atrial flutter at 220/min with one-to-one ventricular conduction and QRS widening. What best explains the role of the omitted medicine?
Answer and all four rationales
A. Metoprolol prevents flecainide-related QRS widening by shortening ventricular repolarization Metoprolol is not paired with flecainide to shorten ventricular repolarization. Its relevant effect is limiting AV nodal transmission when class Ic treatment organizes AF into flutter.
B. AV nodal blockade reduces the risk of one-to-one flutter conduction · Best answer Class Ic treatment can organize AF into slower flutter that the AV node may transmit one-to-one. A prescribed nodal blocker reduces this risk. The electrogram establishes flutter here; wide tachycardia otherwise needs diagnostic caution.
C. Metoprolol is the primary drug that chemically cardioverts AF Metoprolol primarily controls ventricular rate. Flecainide supplies the rhythm-control action in this regimen. Attributing conversion to metoprolol reverses their principal roles.
D. Metoprolol is needed because flecainide directly accelerates AV nodal conduction The danger does not require a direct acceleration of AV nodal conduction. Flecainide can slow and organize the atrial rhythm enough to permit one-to-one transmission through the node.
A 43-year-old woman with asthma and symptomatic paroxysmal AF develops wheezing within a week of starting propafenone at an outside clinic. Symptoms worsen after each dose. She has no fever, edema or chest pain. Oxygen saturation is 94% on room air, expiratory wheezing is diffuse, and chest radiography shows no infiltrate. Which property of propafenone most directly explains the concern?
Answer and all four rationales
A. Antimuscarinic activity reducing airway secretions Antimuscarinic effects suggest a drug such as disopyramide, with dry mouth, constipation and urinary retention. They do not best explain dose-associated bronchospasm in a patient taking propafenone.
B. Iodine accumulation causing pulmonary fibrosis That association belongs more closely to amiodarone's toxicity discussion. The short course, wheezing and asthma history favor bronchospasm rather than fibrotic interstitial lung disease.
C. Adenosine A1 receptor activation Adenosine can provoke bronchospasm, but propafenone is not an A1 agonist. Similar adverse symptoms can arise from different mechanisms; the drug's additional beta blockade is the relevant one here.
D. Beta-adrenergic blocking activity · Best answer Propafenone has beta-blocking activity in addition to class Ic effects. Its label contraindicates bronchospastic disorders or severe obstructive pulmonary disease. The medication needs prompt reassessment while the respiratory problem is treated.
A 58-year-old man receiving specialist-supervised quinidine for recurrent ventricular arrhythmia reports three days of tinnitus, headache and blurred vision. He also has diarrhea but no pleuritic pain, arthritis or urinary difficulty. Blood pressure is 124/70 mmHg. His ECG shows sinus rhythm with QTc 502 ms, increased from 438 ms before treatment. Which toxicity pattern best fits the symptoms?
Answer and all four rationales
A. Cinchonism with additional quinidine-related QT risk · Best answer Tinnitus, headache, visual disturbance and gastrointestinal symptoms fit cinchonism. Quinidine also prolongs repolarization, so the QT finding warrants attention independently of the sensory symptoms.
B. Procainamide-type drug-induced lupus A lupus-like syndrome often includes arthralgia, serositis and a compatible exposure history. The sensory and gastrointestinal cluster here is a much closer match to quinidine's characteristic toxicity.
C. Disopyramide-type anticholinergic toxicity Dry mouth, constipation and urinary retention would support a strong anticholinergic pattern. Diarrhea and tinnitus with quinidine point elsewhere, even though both drugs belong to class Ia.
D. Expected benign effects that require no medication review Recognizing a known adverse-effect pattern is not permission to ignore it. The symptoms suggest intolerance or toxicity, and QT prolongation adds a separate proarrhythmic concern.
A 62-year-old man who received prolonged procainamide treatment abroad for a refractory arrhythmia develops six weeks of symmetric hand pain and pleuritic chest discomfort. He has no prior autoimmune illness, focal neurologic symptoms or hematuria. ANA and anti-histone antibodies are positive, anti-dsDNA is negative, complement is normal and urinalysis shows no protein or blood. Which diagnosis best integrates the exposure and findings?
Answer and all four rationales
A. New systemic lupus is proven by the positive ANA ANA is not specific enough to prove idiopathic SLE. The drug exposure, serositis, arthralgia and relative absence of renal or neurologic disease support a medication-associated syndrome in this setting.
B. Quinidine-associated cinchonism Cinchonism would suggest tinnitus, headache and sensory or gastrointestinal symptoms, with quinidine exposure. It does not best explain this procainamide-associated autoimmune pattern.
C. Procainamide-associated drug-induced lupus · Best answer The exposure and syndrome fit drug-induced lupus. Anti-histone positivity supports it but is not unique to it. Normal complement and absent renal findings are compatible; negative anti-dsDNA alone does not exclude idiopathic SLE.
D. Viral pleuropericarditis with an incidental positive ANA Viral disease can cause pleuritic symptoms, and ANA can be incidental. The prolonged procainamide exposure, persistent symmetric arthralgia and anti-histone result together favor a medication-associated lupus syndrome.
A 69-year-old man with symptomatic obstructive hypertrophic cardiomyopathy starts disopyramide under specialist care. A week later he develops dry mouth, constipation and inability to urinate for ten hours. He previously had a weak urinary stream. He is afebrile, with blood pressure 128/76 mmHg and a tender distended bladder; bladder ultrasound shows 780 mL of retained urine. Which drug effect best explains the new symptoms?
Answer and all four rationales
A. Alpha-1 receptor stimulation increasing bladder-neck tone An alpha agonist can aggravate urinary outflow obstruction, but that is not disopyramide's characteristic effect. Its muscarinic antagonism explains the retention together with dry mouth and constipation.
B. Muscarinic antagonism aggravating urinary outflow symptoms · Best answer Disopyramide has strong anticholinergic effects. Preexisting obstructive urinary symptoms increase concern for retention. The beneficial negative inotropy in selected obstructive HCM does not prevent this separate adverse effect.
C. Increased vagal activity at the bladder Increased parasympathetic activity would generally support detrusor contraction and bladder emptying. The retention and dry mouth point in the opposite direction.
D. A lupus-like inflammatory obstruction Procainamide has the classic lupus-like association. This rapid cluster after disopyramide is better explained by its anticholinergic pharmacology than by a new inflammatory urinary disorder.
A 74-year-old man with a recent MI and recurrent ventricular arrhythmia receives a monitored lidocaine infusion. He has low cardiac output and chronic liver disease. After several hours he develops perioral numbness, slurred speech, tremor and increasing drowsiness. Glucose is 104 mg/dL, oxygen saturation is 97%, and there is no unilateral weakness. What is the most appropriate immediate medication response while assessing other causes?
Answer and all four rationales
A. Increase lidocaine because neurologic symptoms predict recurrent VT These symptoms can reflect systemic lidocaine toxicity rather than undertreatment of arrhythmia. Increasing exposure can worsen neurologic depression or seizures, particularly when clearance is impaired.
B. Continue unchanged because class Ib drugs have no systemic toxicity Class Ib agents can cause neurologic and cardiovascular adverse effects. Relative tissue selectivity at therapeutic concentrations is not protection from toxicity when the drug accumulates.
C. Continue the infusion until a serum lidocaine concentration confirms toxicity A level can assist assessment, but progressive neurologic symptoms during exposure require an immediate medication response. Waiting for laboratory confirmation permits further accumulation in a patient with impaired clearance.
D. Stop the infusion and assess for lidocaine toxicity with supportive care · Best answer The symptom pattern and impaired hepatic clearance make lidocaine toxicity a leading concern. Stop the drug, monitor cardiac and respiratory status, and treat complications while evaluating alternative neurologic causes.
A 60-year-old woman with an ICD and recurrent ventricular arrhythmias has her regimen revised by electrophysiology. Mexiletine is added as an oral adjunct. Three days later she reports nausea after doses and a fine hand tremor without syncope, rash or fever. ECG and device checks show no new arrhythmia. Which explanation best fits this treatment and adverse-effect pattern?
Answer and all four rationales
A. Dose-related gastrointestinal and neurologic effects of an oral sodium-channel blocker · Best answer Mexiletine is an orally active class Ib agent. Nausea and tremor are recognized dose-related problems. The prescriber should assess tolerability, hepatic function and interactions rather than assuming symptoms are unrelated.
B. Potassium-channel blockade with dose-dependent repolarization prolongation That describes the principal effect of several class III drugs, not the class Ib profile of mexiletine. Nausea and tremor with a reassuring rhythm assessment fit the recognized gastrointestinal and neurologic adverse effects more closely.
C. Renal accumulation is usually the dominant determinant of mexiletine exposure Unlike a predominantly renally cleared drug such as dofetilide, mexiletine is largely metabolized hepatically. Hepatic function, dose and interactions deserve review when neurologic or gastrointestinal effects appear.
D. Early thyroid dysfunction caused by an iodine-containing antiarrhythmic Iodine-related thyroid injury is an important association with amiodarone, not mexiletine. This new oral class Ib exposure and its recognized nausea-tremor pattern are a better fit than an unrelated thyroid mechanism.
A 71-year-old man taking amiodarone for recurrent VT reports two months of progressive exertional dyspnea and dry cough. He has no fever, orthopnea or recent weight gain. Oxygen saturation is 90% on room air and fine inspiratory crackles are present. CT shows bilateral ground-glass and interstitial opacities, and diffusion capacity has fallen from baseline. His EF and volume assessment are unchanged. Which of the following is the most likely explanation?
Answer and all four rationales
A. Acute decompensated left ventricular failure HF can cause dyspnea and bilateral opacities and must be considered. The unchanged volume assessment, absent orthopnea and weight gain, and progressive interstitial pattern make pulmonary drug injury a stronger concern here.
B. Amiodarone pulmonary toxicity · Best answer The drug, progressive cough, hypoxemia and interstitial findings raise concern for pulmonary injury. Evaluate infection and cardiac causes as well; suspected toxicity warrants prompt drug and specialist review rather than a diagnosis by imaging alone.
C. Atypical community-acquired pneumonia Atypical pneumonia can produce dry cough and diffuse pulmonary findings. Here the prolonged course, treatment exposure and declining diffusion capacity make pulmonary drug injury the stronger explanation, while infection still needs exclusion.
D. Idiopathic pulmonary fibrosis Idiopathic pulmonary fibrosis can present with progressive exertional dyspnea, crackles and impaired diffusion. A known pneumotoxic medication is a competing explanation that must be evaluated before the disease can be called idiopathic.
A 66-year-old woman with AF is three months into oral amiodarone treatment. She has no cough, dyspnea or visual symptoms; oxygen saturation is 98% and examination is unchanged. Baseline TSH, liver enzymes, ECG and chest radiograph were documented. Her clinician is using the 2023 AF guideline's follow-up table while also considering the product label. Which statement accurately describes that guideline table?
Answer and all four rationales
A. Every patient needs an annual screening chest CT The AF guideline does not recommend routine CT screening. Chest imaging beyond baseline follows suspicion of pulmonary toxicity; the oral product label has additional pulmonary surveillance recommendations that should be considered separately.
B. Thyroid and liver tests need repeating only when symptoms appear Thyroid and hepatic abnormalities may be detected before obvious symptoms. The AF guideline recommends scheduled biochemical follow-up in addition to symptom-triggered assessment.
C. Repeat thyroid and liver tests at three to six months, then every six months · Best answer This matches the guideline's biochemical schedule. It also includes ECG follow-up and symptom-directed evaluation. It should not be conflated with every detail of the product label's monitoring instructions.
D. Asymptomatic corneal microdeposits require automatic discontinuation Corneal microdeposits alone are not an automatic reason to stop amiodarone. New visual impairment is different and needs evaluation, including consideration of optic neuropathy.
A shorter-lived relative is not automatically safer
A 73-year-old man with persistent AF was hospitalized ten days ago for pulmonary edema and worsening systolic HF. EF is 28%. At follow-up he remains breathless with ordinary activity despite improving edema. A medication list proposes dronedarone to maintain sinus rhythm after a planned cardioversion. Which feature most directly makes that proposal inappropriate?
Answer and all four rationales
A. Atrial fibrillation itself always prohibits dronedarone Dronedarone has a role in selected patients with paroxysmal or persistent AF. The critical issue here is recent symptomatic HF decompensation, not AF as a blanket diagnosis.
B. Absence of iodine makes its antiarrhythmic effect unreliable Iodine is not required for an antiarrhythmic effect. Dronedarone's distinct toxicities and contraindications must be assessed from outcome evidence, not inferred from its lack of iodine.
C. A pacemaker has not yet been implanted A pacemaker is not a routine prerequisite for dronedarone, nor would one correct the increased risk associated with recent decompensated HF.
D. Recent hospitalization for symptomatic decompensated heart failure · Best answer Dronedarone is contraindicated in this setting because of adverse outcomes in recently decompensated HF. Permanent AF is another distinct contraindication; a future cardioversion plan does not remove the present HF concern.
A 55-year-old woman with stable HFrEF begins low-dose carvedilol after congestion has resolved. Over four months it is gradually titrated alongside her other guideline-directed medicines. She now walks farther, has no edema and her EF has increased from 27% to 39%. She asks how a medicine that initially reduces contractile force can help. Which explanation best distinguishes its long-term role?
Answer and all four rationales
A. Chronic adrenergic blockade can reduce harmful sympathetic effects and support reverse remodeling · Best answer Evidence-based beta blockade improves outcomes in stable HFrEF over time. This chronic benefit differs from its acute negative inotropic effect, which is why treatment starts carefully and is titrated to clinical status.
B. Carvedilol immediately increases intracellular calcium as a positive inotrope That would resemble an inotropic mechanism such as digoxin's indirect calcium effect. Carvedilol acutely reduces adrenergic stimulation rather than directly increasing contractile force.
C. The improvement proves that a large IV beta-blocker dose is appropriate during shock Stable chronic treatment and cardiogenic shock are different physiologic settings. Acute additional blockade can worsen perfusion when the circulation depends on adrenergic support.
D. Every drug that suppresses ventricular ectopy provides the same survival benefit Electrical suppression is not a surrogate for survival. The class Ic experience after MI demonstrates why clinical outcome evidence and substrate selection are essential.
A 79-year-old woman taking digoxin develops vomiting and poor intake during a gastrointestinal illness. Two days later she is confused and sees yellow halos. Blood pressure is 82/48 mmHg. ECG shows atrial tachycardia with high-grade AV block and recurrent ventricular ectopy; symptomatic bradycardia persists after atropine. Creatinine has risen from 1.0 to 2.4 mg/dL and potassium is 5.8 mmol/L. Which treatment most directly addresses the suspected life-threatening toxicity?
Answer and all four rationales
A. An additional digoxin dose for inotropic support Renal deterioration and the gastrointestinal, visual and electrical findings suggest accumulated digoxin. Further dosing could worsen both triggered activity and conduction impairment despite its therapeutic inotropic role.
B. Digoxin immune Fab with close potassium and ECG monitoring · Best answer Severe suspected digoxin toxicity with hemodynamic compromise and refractory bradyarrhythmia supports Fab treatment. Potassium can fall after reversal, and routine total digoxin levels become difficult to interpret after Fab.
C. IV verapamil to treat the atrial tachycardia Additional nodal suppression can worsen the high-grade block and hypotension. Treat the toxic exposure rather than isolating the atrial tachycardia from the rest of the syndrome.
D. Phenytoin as a substitute for antidotal treatment Phenytoin has historical use for digitalis-associated ventricular arrhythmias. It is not a substitute for Fab in this severe poisoning presentation with unstable conduction disease.
A 32-year-old man with previously documented left posterior fascicular VT returns with 45 minutes of palpitations. His ECG matches the prior electrophysiology-confirmed rhythm, showing a right bundle branch block pattern and left axis deviation at 172/min. Blood pressure is 124/78 mmHg, he is alert and has no chest pain. Prior imaging showed no structural disease. Which drug targets the characteristic calcium-dependent portion of this known circuit?
Answer and all four rationales
A. Digoxin Digoxin is used for selected HF and AF rate-control situations. Its vagal AV nodal action is not the targeted treatment for this established fascicular ventricular circuit.
B. Amlodipine Amlodipine is a dihydropyridine with mainly vascular clinical effects. Membership in the broad calcium channel blocker family does not make it interchangeable with verapamil for this rhythm.
C. Verapamil · Best answer Confirmed fascicular VT may respond to verapamil through calcium-dependent slow conduction within the circuit. This is a diagnosis-specific exception; it does not justify verapamil for an unexplained wide complex tachycardia.
D. IV magnesium for presumed torsades This is a stable, documented monomorphic rhythm, not a twisting polymorphic rhythm associated with a long baseline QT. Magnesium's torsades role does not explain the targeted treatment here.
A 61-year-old man taking diltiazem for AF rate control has persistent stable angina despite his current regimen. He has no resting pain, syncope or recent acute coronary syndrome. A proposed prescription lists ranolazine 1000 mg twice daily. His pharmacist requests clarification before dispensing. Which statement best explains the needed review?
Answer and all four rationales
A. Ranolazine is a beta blocker, so the only concern is duplicate beta blockade Ranolazine is not a beta blocker. Its late sodium and potassium current effects and CYP3A-related exposure are relevant; the concern cannot be reduced to duplicate beta blockade.
B. Late sodium current inhibition guarantees that QT cannot increase Ranolazine also inhibits IKr and can prolong QT. A potentially useful late sodium effect does not justify promising an absence of repolarization risk.
C. Ranolazine is approved as a universal replacement for AF rhythm-control drugs Its US indication is chronic angina. Antiarrhythmic applications are off-label and specialist-directed, so its presence in a pharmacology lesson does not make it a routine AF substitute.
D. Diltiazem increases exposure, and the label limits ranolazine to 500 mg twice daily · Best answer Diltiazem is a moderate CYP3A inhibitor. The ranolazine label specifies a lower maximum dose with this combination. QT effects and the broader medication list also need review.
A 76-year-old woman with complete AV block and a permanent pacemaker starts flecainide after specialist evaluation for symptomatic AF. One week later she develops presyncope. ECG shows intermittent pacing spikes without subsequent QRS complexes. Device interrogation finds no lead displacement but a ventricular capture threshold above the programmed output. Creatinine has increased during a recent dehydrating illness. Which interpretation is most appropriate?
Answer and all four rationales
A. Flecainide-associated threshold rise can cause loss of capture despite a pacemaker · Best answer A pacemaker only captures if its stimulus exceeds the effective threshold. Flecainide can raise that threshold, so urgent device and drug assessment is needed. The label specifically calls for baseline, one-week and ongoing threshold checks.
B. The visible pacing spikes prove adequate ventricular capture A spike shows stimulus delivery, not successful depolarization. The absent following QRS and measured threshold explain why a functioning generator can still fail to produce ventricular activation.
C. AV nodal slowing alone explains absent paced QRS complexes Ventricular pacing bypasses the AV node. In this patient, the problem is the relation between delivered output and capture threshold, not simply conduction through an already blocked node.
D. Once output is adjusted, all QT-prolonging drugs become risk-free Restoring capture addresses this immediate device problem. It does not eliminate drug-induced torsades, renal accumulation or the need to assess QT and other contraindications.
Sinus rhythm returns before observation is complete
A 57-year-old woman with symptomatic atrial flutter receives IV ibutilide after appropriate thromboembolic assessment and correction of electrolytes. EF is 58%. She converts to sinus rhythm and feels well 30 minutes after infusion. Blood pressure is 126/72 mmHg, but QTc remains 482 ms compared with a baseline of 430 ms. She asks to leave. What is the most appropriate response?
Answer and all four rationales
A. Discharge because successful conversion ends the proarrhythmic period Successful conversion does not immediately end drug effects. Ibutilide-related ventricular proarrhythmia may occur after the atrial rhythm has normalized, so symptoms alone cannot determine discharge timing.
B. Continue ECG monitoring for at least four hours and until QTc returns to baseline · Best answer The label requires at least four hours of postinfusion observation, extended when QTc has not returned to baseline or arrhythmias occur. Conversion alone does not satisfy those monitoring requirements.
C. Give sotalol immediately to shorten the remaining QT prolongation Sotalol also prolongs repolarization and is not a QT-shortening rescue drug. Adding another class III agent can increase proarrhythmic risk; the ibutilide label warns against close coadministration.
D. Replace ECG observation with a single serum magnesium measurement Normal magnesium does not prove the absence of ibutilide-related electrical risk. Electrolyte assessment and rhythm monitoring answer different questions, and both matter after conversion.
