1. A 58-year-old man with paroxysmal atrial fibrillation and stage 3b chronic kidney disease (creatinine clearance 34 mL/min) is referred for rhythm control. His cardiologist considers sotalol. Which of the following correctly applies sotalol's pharmacokinetic profile to determine whether it can be used?
A) Sotalol requires hepatic dose adjustment in renal impairment because reduced renal blood flow secondarily impairs CYP2D6 metabolism: a 50% dose reduction is appropriate at this creatinine clearance
B) Sotalol can be used at a standard dose of 80 mg twice daily because the renal dosing restriction applies only when creatinine clearance falls below 20 mL/min
C) Sotalol is contraindicated because it is eliminated entirely unchanged by the kidneys, at a creatinine clearance below 40 mL/min, drug accumulation extends the half-life, amplifies QTc prolongation, and creates an unacceptable torsades de pointes risk
D) Sotalol requires an extended dosing interval of every 48 hours, which is appropriate for any creatinine clearance below 60 mL/min and provides adequate safety when combined with weekly outpatient QTc monitoring
E) Sotalol can be initiated with a reduced dose of 40 mg twice daily and in-hospital monitoring for 24 hours, at this dose the torsades de pointes risk is negligible regardless of renal function
ANSWER: C
Rationale:
Sotalol is eliminated entirely unchanged by the kidneys with no meaningful hepatic metabolism. Its half-life of 12 to 18 hours in normal renal function extends proportionally as creatinine clearance falls, because plasma levels rise directly as renal elimination slows. At a creatinine clearance below 40 mL/min the resulting drug accumulation amplifies QTc prolongation and creates an unacceptable torsades de pointes risk, sotalol is contraindicated below this threshold. This patient's CrCl of 34 mL/min falls below the 40 mL/min contraindication threshold.
Option A: Option A incorrectly attributes sotalol's renal dependence to secondary impairment of CYP2D6 hepatic metabolism, sotalol undergoes no hepatic metabolism; its elimination is entirely renal.
Option B: Option B incorrectly states the contraindication threshold as CrCl below 20 mL/min: the established threshold is below 40 mL/min, and standard dosing at CrCl 34 mL/min would cause clinically significant accumulation.
Option D: Option D describes interval extension, which applies to patients with CrCl between 40 and 60 mL/min: this patient's CrCl of 34 mL/min is below the absolute contraindication threshold, making interval extension an insufficient safeguard.
Option E: Option E incorrectly states that low-dose sotalol carries negligible TdP risk in renal impairment, accumulation raises effective plasma levels regardless of the starting dose, and 24-hour monitoring does not satisfy the minimum 3-day in-hospital initiation requirement even for patients who are eligible.
2. A patient with atrial fibrillation maintained on warfarin (target INR 2.0 to 3.0, currently 2.4) is started on amiodarone 200 mg daily for rhythm control. Eight weeks later her INR is 5.6. Which of the following correctly identifies the mechanism of this interaction, explains the 8-week delay in INR elevation, and states the appropriate management?
A) Amiodarone inhibits CYP2C9, reducing metabolism of S-warfarin (the active enantiomer), and displaces warfarin from albumin binding sites: the delay reflects amiodarone's extraordinary tissue accumulation kinetics as CYP2C9 inhibition builds gradually; management is to reduce the warfarin dose by one-third to one-half and monitor INR closely for 4 to 8 weeks
B) Amiodarone induces CYP2C9, initially increasing warfarin metabolism and then causing an unpredictable rebound elevation in INR after 6 to 8 weeks as enzyme induction plateaus, management is to discontinue warfarin and switch to a direct oral anticoagulant
C) Amiodarone displaces warfarin from its vitamin K epoxide reductase binding site, producing a delayed competitive inhibition of clotting factor synthesis that develops proportionally to amiodarone tissue loading over 6 to 8 weeks
D) Amiodarone inhibits intestinal P-glycoprotein, progressively increasing warfarin oral bioavailability as amiodarone accumulates in enterocytes over 6 to 8 weeks, management is to separate the doses by 4 hours
E) Amiodarone's active metabolite desethylamiodarone directly inhibits vitamin K-dependent clotting factor synthesis; the delay reflects the time required for desethylamiodarone to reach tissue steady state in the liver
ANSWER: A
Rationale:
Amiodarone inhibits CYP2C9, the primary enzyme responsible for metabolism of S-warfarin: the pharmacologically active enantiomer. Additionally, amiodarone displaces warfarin from albumin binding sites, raising free warfarin concentration. The 8-week delay before the full INR elevation is seen reflects amiodarone's extraordinary tissue accumulation kinetics: with a volume of distribution of 60 to 100 L/kg and a half-life of 40 to 55 days, amiodarone accumulates slowly in tissues, and CYP2C9 inhibition builds gradually as tissue levels rise. Management requires reducing the warfarin dose by one-third to one-half when amiodarone is started, with close INR monitoring for 4 to 8 weeks. The interaction persists for months after amiodarone is stopped due to its prolonged tissue half-life. Option C is pharmacologically incorrect: amiodarone does not bind to vitamin K epoxide reductase; its interaction with warfarin is entirely pharmacokinetic through CYP2C9 inhibition and albumin displacement.
Option B: Option B inverts the mechanism: amiodarone inhibits CYP2C9, it does not induce it, induction would reduce warfarin effect, not produce a delayed elevation. Switching to a DOAC is not the standard initial management.
Option D: Option D incorrectly describes the mechanism as intestinal P-glycoprotein inhibition affecting warfarin bioavailability, warfarin's interaction with amiodarone is a hepatic metabolic interaction, not a bioavailability interaction, and dose separation does not resolve it.
Option E: Option E incorrectly attributes the interaction to desethylamiodarone inhibiting vitamin K-dependent clotting factor synthesis: this is not an established mechanism; the interaction operates through CYP2C9 inhibition of warfarin metabolism.
3. A patient with heart failure with reduced ejection fraction (EF 36%) and persistent atrial fibrillation has been stable on dofetilide 500 mcg twice daily for 6 months. He is admitted with worsening angina and his cardiologist recommends adding verapamil for rate control during an anginal episode. Which of the following correctly identifies the risk of this combination?
A) Verapamil is acceptable in this patient because its negative inotropic effect will partially offset dofetilide's positive inotropic action, producing a balanced hemodynamic profile in the setting of HFrEF
B) Verapamil and dofetilide can be co-administered safely provided the QTc is rechecked within 24 hours of starting verapamil and does not exceed 500 ms
C) Verapamil prolongs the QT interval independently through L-type calcium channel blockade in ventricular myocardium, and this additive QT prolongation with dofetilide creates a risk of torsades de pointes requiring immediate drug discontinuation of both agents
D) Verapamil reduces dofetilide's antiarrhythmic efficacy by competing for IKr channel binding sites, increasing the risk of atrial fibrillation recurrence without affecting the QTc
E) Verapamil is contraindicated with dofetilide because it inhibits renal organic cation transporter 2 (OCT2), reducing dofetilide renal tubular secretion and substantially raising plasma dofetilide levels, increasing QTc prolongation and torsades de pointes risk
ANSWER: E
Rationale:
Dofetilide is 80% renally eliminated via OCT2-mediated tubular secretion. Verapamil is an explicit OCT2 inhibitor: it reduces dofetilide renal clearance, causing drug accumulation, amplified QTc prolongation, and substantially elevated TdP risk. Verapamil is listed as a contraindicated combination in dofetilide prescribing guidelines, alongside trimethoprim, cimetidine, ketoconazole, and megestrol. The appropriate management in this patient is to avoid verapamil entirely and use an alternative rate control agent, beta-blockers would generally be avoided in HFrEF with acute ischemia, and non-DHP CCBs are contraindicated in HFrEF regardless, so amiodarone for acute rate control or reassessment of the rate control strategy would be appropriate. Option D is pharmacologically incorrect: verapamil does not compete with dofetilide at IKr channel binding sites, and the interaction does not reduce dofetilide efficacy: it raises dofetilide levels.
Option A: Option A is incorrect on multiple levels: dofetilide is not a positive inotrope, verapamil is contraindicated in HFrEF due to negative inotropy, and the combination with dofetilide is explicitly contraindicated via the OCT2 interaction.
Option B: Option B incorrectly states the combination can be safely managed with QTc monitoring: the OCT2 interaction raises dofetilide levels substantially regardless of monitoring, and the prescribing contraindication is not waived by monitoring alone.
Option C: Option C incorrectly identifies the mechanism as additive QT prolongation from verapamil's ventricular ICaL blockade, while verapamil does affect repolarization, the primary concern with this combination is the pharmacokinetic OCT2 interaction raising dofetilide plasma levels, not direct additive QT effects.
4. A 62-year-old man with recent-onset atrial flutter (confirmed on 12-lead ECG, onset 6 hours ago) and no structural heart disease presents for pharmacologic cardioversion. IV ibutilide is selected. Which of the following correctly describes the expected efficacy, administration protocol, and mandatory post-infusion monitoring requirement?
A) Ibutilide achieves cardioversion in approximately 20 to 30% of atrial flutter cases and 50 to 60% of atrial fibrillation cases; it is administered as a single 2 mg IV bolus over 2 minutes and requires 1 hour of post-infusion monitoring
B) Ibutilide achieves cardioversion in approximately 65 to 70% of atrial flutter cases and 40 to 60% of atrial fibrillation cases, reflecting flutter's more organized re-entrant circuit; it is administered as 1 mg IV over 10 minutes (repeated once if needed) and requires continuous cardiac monitoring for at least 4 hours post-infusion due to a 4 to 8% torsades de pointes risk
C) Ibutilide achieves cardioversion in approximately 90% of both atrial flutter and atrial fibrillation cases due to its dual IKr and slow inward sodium current mechanism; standard monitoring is 30 minutes post-infusion once QTc has returned to within 10% of baseline
D) Ibutilide achieves cardioversion in approximately 65 to 70% of atrial flutter cases but requires oral loading for 24 hours before the IV infusion to achieve adequate tissue concentrations for reliable arrhythmia termination
E) Ibutilide is equally effective for atrial flutter and atrial fibrillation (60 to 65% for both) and can be safely administered without post-infusion monitoring in patients with a normal baseline QTc, as the TdP risk is confined to patients with QTc above 440 ms at baseline
ANSWER: B
Rationale:
Ibutilide's cardioversion success rate for atrial flutter is approximately 65 to 70%, which is higher than its success rate for atrial fibrillation (40 to 60%). This difference reflects the organized, single-circuit nature of flutter: a re-entrant arrhythmia with a discrete excitable gap that is highly susceptible to termination by refractoriness prolongation, compared to the multiple disorganized wavelets of atrial fibrillation. The standard dosing is 1 mg IV over 10 minutes, with a second 1 mg dose given if the arrhythmia has not terminated after 10 minutes. Because TdP occurs in 4 to 8% of patients, continuous cardiac monitoring with resuscitation equipment immediately available is mandatory for at least 4 hours post-infusion.
Option A: Option A inverts the efficacy figures: ibutilide achieves higher rates in flutter than AF, not the reverse, and both the dose and monitoring duration are incorrect.
Option C: Option C overstates efficacy: ibutilide does not achieve 90% cardioversion rates for either arrhythmia, and 30-minute monitoring is dangerously inadequate given the 4 to 8% TdP risk that can manifest up to 4 hours post-infusion.
Option D: Option D incorrectly states that oral loading is required before the IV infusion, ibutilide is an IV-only acute agent used without any prior loading phase; oral dosing formulations do not exist.
Option E: Option E incorrectly states equal efficacy for flutter and AF and incorrectly limits the TdP risk to patients with baseline QTc above 440 ms: TdP can occur in patients with normal baseline QTc, and post-infusion monitoring is mandatory for all patients regardless of baseline QTc.
5. A 71-year-old woman has been on amiodarone 200 mg daily for 3 years for ventricular arrhythmia suppression. She presents with a 6-week history of progressive dyspnea on exertion and nonproductive cough. Her chest X-ray shows new bilateral interstitial infiltrates. Which of the following best describes the diagnosis, the monitoring protocol that should have detected this earlier, and the appropriate management?
A) This presentation is most consistent with amiodarone-induced hypothyroidism causing pleural effusions: TSH and free T4 should be checked immediately, and amiodarone should be continued while thyroid replacement is initiated
B) This presentation is most consistent with amiodarone-induced hepatotoxicity causing transudative pleural effusions, liver function tests and abdominal ultrasound are the priority investigations, and amiodarone dose should be halved
C) This presentation is most consistent with amiodarone-induced corneal microdeposit progression to optic neuropathy with secondary visual-cortex-mediated dyspnea, ophthalmology referral and drug discontinuation are required
D) This presentation is most consistent with amiodarone pulmonary toxicity: the standard monitoring protocol requires baseline and annual chest X-ray and pulmonary function tests, with high-resolution CT and drug discontinuation when toxicity is confirmed; corticosteroids are used in severe cases
E) This presentation is most consistent with amiodarone-induced peripheral neuropathy affecting the phrenic nerve, nerve conduction studies are required and amiodarone should be continued at a reduced dose of 100 mg daily
ANSWER: D
Rationale:
Progressive dyspnea, nonproductive cough, and new bilateral interstitial infiltrates after 3 years of amiodarone therapy is the classic presentation of amiodarone pulmonary toxicity, interstitial pneumonitis is the most serious and most common form of amiodarone pulmonary injury, with an incidence of approximately 1 to 5% per year that increases with cumulative dose and duration. The monitoring protocol requires baseline and annual chest X-ray and pulmonary function tests throughout therapy; when symptoms develop, high-resolution CT of the chest is indicated to characterize the pattern and extent of infiltrates. Once pulmonary toxicity is confirmed, amiodarone must be discontinued. Corticosteroids are used in severe or rapidly progressive cases.
Option A: Option A incorrectly identifies the syndrome as hypothyroidism causing pleural effusions, amiodarone hypothyroidism presents with weight gain, fatigue, cold intolerance, and elevated TSH, not progressive dyspnea with interstitial infiltrates; bilateral pleural effusions from hypothyroidism would be transudates and would not produce the clinical picture described.
Option B: Option B incorrectly identifies the syndrome as hepatotoxicity, amiodarone hepatotoxicity presents with elevated liver enzymes and, in severe cases, signs of hepatic failure, not interstitial lung infiltrates.
Option C: Option C incorrectly attributes the presentation to phrenic nerve involvement from peripheral neuropathy: this is not an established mechanism of amiodarone-related dyspnea and does not explain bilateral interstitial infiltrates.
Option E: Option E incorrectly attributes the presentation to corneal microdeposit progression to optic neuropathy, optic neuropathy causes visual loss, not dyspnea or pulmonary infiltrates.
6. A 74-year-old man with permanent atrial fibrillation, hypertension, and preserved ejection fraction (EF 58%) is seen by a new cardiologist who proposes adding dronedarone for rate control. His current medications include metoprolol, ramipril, and apixaban. Which of the following correctly identifies the concern with this proposal and the trial evidence supporting it?
A) Dronedarone is acceptable in this patient because the ATHENA trial demonstrated cardiovascular benefit with dronedarone in patients with atrial fibrillation and preserved ejection fraction: the PALLAS trial findings do not apply to patients with preserved EF
B) Dronedarone is acceptable because his heart failure risk is low with a preserved EF: the ANDROMEDA contraindication applies only to patients with EF below 35% and does not extend to patients with permanent AF
C) Dronedarone is contraindicated in permanent atrial fibrillation: the PALLAS trial enrolled patients with permanent AF at cardiovascular risk and was stopped early due to excess stroke, cardiovascular death, and arrhythmia events in the dronedarone arm, regardless of ejection fraction
D) Dronedarone can be used cautiously in permanent AF provided the ventricular rate remains below 90 bpm on concurrent beta-blocker therapy: the PALLAS mortality signal applied only to patients with inadequate rate control at baseline
E) Dronedarone is acceptable because its primary indication is rate control, and the PALLAS contraindication applies only when dronedarone is used for rhythm control in permanent AF, rate control use is not restricted by that trial
ANSWER: C
Rationale:
The PALLAS trial enrolled patients with permanent AF and additional cardiovascular risk factors and was stopped early due to a significant increase in stroke, cardiovascular death, and arrhythmia-related events in the dronedarone arm. The contraindication to dronedarone in permanent AF is absolute and applies regardless of ejection fraction. This patient has permanent AF, dronedarone must not be used.
Option A: Option A incorrectly states that ATHENA evidence overrides PALLAS, ATHENA enrolled patients with non-permanent AF and demonstrated cardiovascular benefit in that population; it does not provide a basis for using dronedarone in permanent AF, and the PALLAS mortality signal specifically in permanent AF is the governing evidence.
Option B: Option B incorrectly conflates the ANDROMEDA contraindication (HFrEF) with the PALLAS contraindication (permanent AF): these are two distinct contraindications, and the permanent AF contraindication from PALLAS applies regardless of ejection fraction.
Option D: Option D incorrectly states that the PALLAS mortality signal was limited to patients with inadequate rate control, PALLAS did not identify a rate-control threshold below which dronedarone is safe in permanent AF; the contraindication is absolute for permanent AF.
Option E: Option E incorrectly states that the PALLAS contraindication applies only to rhythm control use, dronedarone's contraindication in permanent AF is categorical and not limited by the intended therapeutic goal.
7. A 78-year-old man with atrial fibrillation and heart failure with reduced ejection fraction (EF 32%) is on digoxin 0.125 mg daily (serum level 0.7 ng/mL) and metoprolol for rate control. Amiodarone is started for rhythm control. Three weeks later he presents with nausea, anorexia, and a ventricular rate of 42 bpm. His digoxin level is 2.6 ng/mL. Which of the following correctly identifies the mechanism and appropriate immediate management?
A) Amiodarone inhibits P-glycoprotein and reduces digoxin renal tubular clearance, approximately doubling digoxin serum levels, digoxin should be withheld, digoxin-specific antibody fragments (DigiFab) administered given the symptomatic toxicity and level above 2.0 ng/mL, electrolytes corrected, and amiodarone continued with digoxin dose halved when restarted
B) Amiodarone induces P-glycoprotein at the renal tubule, increasing digoxin clearance and paradoxically causing digoxin toxicity through a rebound pharmacokinetic effect, digoxin should be increased by 50% to compensate
C) Amiodarone competitively inhibits digoxin binding to Na+/K+-ATPase in cardiac tissue, displacing digoxin from its receptor and paradoxically increasing free serum digoxin levels while reducing its inotropic effect, calcium gluconate IV is the treatment of choice
D) Amiodarone reduces hepatic CYP3A4 activity, impairing digoxin conversion to its inactive cardiotoxic metabolite: the resulting accumulation of the active parent drug is managed by dose reduction alone without antibody therapy
E) Amiodarone reduces gastrointestinal motility, increasing digoxin intestinal absorption and raising plasma levels, dose separation by 6 hours and a reduced oral dose of 0.0625 mg daily are sufficient management
ANSWER: A
Rationale:
Amiodarone inhibits P-glycoprotein (P-gp) at both the intestinal and renal tubular level and additionally reduces digoxin renal tubular secretion, together raising digoxin serum levels by approximately 70 to 100%, roughly doubling exposure. This patient's digoxin level has risen from 0.7 to 2.6 ng/mL, and he has symptomatic toxicity: nausea, anorexia, and profound bradycardia at 42 bpm. At a level above 2.0 ng/mL with clinical toxicity, digoxin-specific antibody fragments (DigiFab) are indicated. Digoxin should be withheld, electrolytes corrected (hypokalemia and hypomagnesemia worsen toxicity), and when digoxin is eventually restarted, the dose should be halved to account for the ongoing amiodarone interaction. Option C is pharmacologically incorrect: amiodarone does not competitively displace digoxin from Na+/K+-ATPase; the toxicity reflects genuine pharmacokinetic accumulation with full receptor occupancy. Calcium gluconate is contraindicated in digoxin toxicity as it worsens intracellular calcium overload.
Option B: Option B inverts the mechanism: amiodarone inhibits P-gp, it does not induce it: the result is raised, not lowered, digoxin levels, and increasing the digoxin dose would be dangerous.
Option D: Option D is incorrect: digoxin is not significantly metabolized by CYP3A4: it is eliminated primarily by renal tubular secretion via P-gp, and there is no inactive cardiotoxic metabolite described in established digoxin pharmacology.
Option E: Option E incorrectly attributes the interaction to reduced GI motility increasing absorption: the interaction is a pharmacokinetic one involving P-gp inhibition and reduced renal clearance, not altered GI absorption, and dose separation does not resolve a systemic pharmacokinetic interaction of this magnitude.
8. A pharmacology fellow asks why dofetilide, despite being a highly selective and predictable IKr blocker, has a higher torsades de pointes risk per unit of QT prolongation than amiodarone, which prolongs the QT interval more. Which of the following best explains this apparent paradox in terms of the pharmacodynamic property responsible?
A) Dofetilide has a shorter half-life than amiodarone, producing larger peak-to-trough plasma level fluctuations that create intermittent periods of exaggerated QT prolongation between doses: it is the pharmacokinetic variability rather than any channel property that explains the higher TdP risk
B) Dofetilide blocks IKr more potently than amiodarone at equivalent plasma concentrations because it has higher receptor affinity: this greater potency at the channel level directly correlates with higher TdP risk independent of heart rate
C) Dofetilide lacks amiodarone's concurrent ICaL blockade, which in amiodarone suppresses the inward trigger current for early afterdepolarization formation, without this counter-regulatory mechanism, dofetilide's APD prolongation generates EADs and TdP more readily
D) Dofetilide is eliminated renally and accumulates in patients with renal impairment, whereas amiodarone is hepatically eliminated: the renal accumulation risk rather than any intrinsic channel property accounts for the higher per-unit TdP risk
E) Pure IKr blockers such as dofetilide exhibit reverse use-dependence, APD prolongation is greatest at slow heart rates, the condition that most favors early afterdepolarization formation, while amiodarone's multi-channel profile reduces this rate-dependent vulnerability, contributing to its lower TdP incidence across heart rates
ANSWER: E
Rationale:
The paradox has two complementary explanations, and Option E captures one of the most mechanistically important. Pure IKr blockers exhibit reverse use-dependence: APD prolongation is greatest at slow heart rates because IKr channels spend more time in the closed drug-accessible state during bradycardia. Slow rates are precisely the condition that most favors early afterdepolarization (EAD) formation: the trigger for TdP. Amiodarone's multi-channel profile, including IKs blockade and other actions, reduces reverse use-dependence and produces more uniform APD prolongation across heart rates, lowering the bradycardia-specific TdP vulnerability. Option C also captures a valid complementary explanation (ICaL blockade suppressing EAD trigger) but Option E is the more complete answer to the specific question asked, which concerns the pharmacodynamic property responsible.
Option A: Option A incorrectly attributes the difference to pharmacokinetic variability, while dofetilide does have a shorter half-life, this is not the primary explanation for higher TdP risk per unit of QT prolongation; the rate-dependent channel pharmacodynamics are the more fundamental answer.
Option B: Option B incorrectly identifies receptor affinity as the explanation, higher IKr potency does not directly correlate with TdP risk in the manner described; TdP risk depends on the rate-dependent profile and the presence or absence of compensating mechanisms.
Option D: Option D incorrectly attributes the difference to renal accumulation risk, while renal impairment does amplify dofetilide's TdP risk in individual patients, it does not explain the higher per-unit TdP risk of pure IKr blockers versus amiodarone at equivalent QT prolongation as a pharmacodynamic class property.
9. A 69-year-old woman on sotalol 160 mg twice daily for atrial flutter develops recurrent torsades de pointes on telemetry. Each episode is preceded by a compensatory pause following a premature ventricular beat. The episodes are self-terminating but she has had four in the past 2 hours. Her serum potassium is 3.2 mEq/L and magnesium is 1.6 mg/dL. What is the correct sequence of management?
A) Administer IV amiodarone 150 mg over 10 minutes to provide counter-regulatory multi-channel blockade, then discontinue sotalol and correct electrolytes over the following 24 hours
B) Administer IV magnesium sulfate 2 g over 1 to 2 minutes as first-line treatment, discontinue sotalol, correct hypokalemia and hypomagnesemia, and if TdP remains recurrent and pause-dependent, increase heart rate with IV isoproterenol or temporary overdrive pacing at 90 to 110 bpm to suppress the pauses that trigger EAD formation
C) Perform immediate synchronized DC cardioversion for each episode of TdP, discontinue sotalol, and initiate amiodarone for ongoing rhythm suppression
D) Administer IV lidocaine 1.5 mg/kg to shorten ventricular APD and reduce the QT prolongation driving TdP, then reduce sotalol to 80 mg twice daily and continue with monitoring
E) Administer IV adenosine 6 mg to terminate the re-entrant circuit sustaining TdP, then discontinue sotalol and initiate dofetilide at a reduced dose for ongoing rhythm control
ANSWER: B
Rationale:
This is pause-dependent TdP: each episode is triggered by the post-extrasystolic pause that follows a premature ventricular beat, which maximally prolongs APD at the slow effective rate during the pause, generating EADs. The correct management sequence is: IV magnesium sulfate 2 g over 1 to 2 minutes as first-line (suppresses EADs by blocking ICaL regardless of serum magnesium level), discontinuation of sotalol (the offending QT-prolonging agent), and aggressive electrolyte correction (hypokalemia and hypomagnesemia both amplify IKr blockade-driven APD prolongation). If TdP is recurrent and specifically pause-dependent, increasing the heart rate with IV isoproterenol or temporary overdrive pacing at 90 to 110 bpm eliminates the pauses that trigger EAD formation: this is the definitive short-term management for pause-dependent TdP.
Option A: Option A is incorrect: amiodarone further prolongs QT and would worsen the proarrhythmic substrate; it is contraindicated in QT-prolongation-driven TdP.
Option C: Option C incorrectly prioritizes DC cardioversion for each self-terminating episode, cardioversion is appropriate for sustained hemodynamically unstable TdP, but recurrent self-terminating pause-dependent TdP is managed with magnesium, electrolyte correction, and heart rate acceleration, not repeated shocks.
Option D: Option D is incorrect: lidocaine may have a minor role in shortening APD but is not the established first-line treatment for TdP, and reducing sotalol rather than stopping it does not address the acute risk.
Option E: Option E is incorrect: adenosine acts on the AV node and is ineffective for ventricular arrhythmias; TdP is not an AV nodal re-entrant tachycardia, and initiating dofetilide, another IKr blocker, in the setting of active TdP from sotalol would be contraindicated.
10. A 65-year-old man on amiodarone 200 mg daily for 4 years presents with a 3-month history of weight loss, heat intolerance, tremor, and palpitations. His TSH is suppressed at 0.02 mU/L and free T4 is markedly elevated. Thyroid ultrasound shows a nodular gland with increased vascularity on Doppler. Which of the following correctly identifies the most likely diagnosis, distinguishes it from the alternative form of the same complication, and describes the treatment implications?
A) This presentation is consistent with amiodarone-induced hypothyroidism type 1: the nodular gland and elevated T4 reflect iodine-mediated suppression of TSH and secondary thyroid enlargement; treatment is levothyroxine supplementation while continuing amiodarone
B) This presentation is consistent with amiodarone-induced hypothyroidism type 2, free T4 elevation occurs as a compensatory response to peripheral thyroid hormone resistance induced by amiodarone's structural similarity to thyroxine; no treatment is required
C) This presentation is consistent with amiodarone-induced pulmonary toxicity with secondary thyroid involvement: HRCT of the chest is the diagnostic priority and amiodarone should be discontinued regardless of thyroid status
D) This presentation is most consistent with amiodarone-induced thyrotoxicosis type 1 (AIT-1), driven by iodine-induced autonomous hormone overproduction in an abnormal (nodular) gland, distinguished from type 2 (destructive thyroiditis) by the nodular gland and Doppler vascularity; AIT-1 is treated with thionamides (carbimazole or propylthiouracil) while AIT-2 is treated with corticosteroids
E) This presentation is consistent with amiodarone-induced thyrotoxicosis, but the distinction between type 1 and type 2 is not clinically relevant because both are treated identically with potassium iodide loading to block further iodine-driven hormone synthesis
ANSWER: D
Rationale:
Amiodarone-induced thyrotoxicosis (AIT) occurs in 2 to 3% of patients on long-term amiodarone. Two mechanistically distinct forms exist. AIT type 1 occurs in patients with pre-existing abnormal thyroid tissue (multinodular goiter or latent Graves disease): the iodine load from amiodarone drives autonomous hormone overproduction in susceptible tissue. AIT type 2 is a destructive thyroiditis in a previously normal gland, where direct amiodarone toxicity causes follicular cell destruction and hormone release. This patient has a nodular gland with increased Doppler vascularity, indicating type 1: autonomous functioning nodular tissue stimulated by excess iodine. AIT-1 is treated with thionamides (carbimazole or propylthiouracil) to block hormone synthesis. AIT-2 is treated with corticosteroids to suppress the destructive inflammatory process. The distinction matters because thionamides are largely ineffective in type 2 (no active synthesis to block) and corticosteroids are unnecessary in type 1.
Option A: Option A incorrectly identifies the syndrome as hypothyroidism: this patient has a suppressed TSH and elevated free T4, indicating hyperthyroidism, not hypothyroidism; levothyroxine would be harmful.
Option B: Option B incorrectly identifies the syndrome as hypothyroidism type 2 and mischaracterizes amiodarone's thyroid effects as peripheral hormone resistance: this patient has biochemical hyperthyroidism with a suppressed TSH, not hypothyroidism.
Option C: Option C incorrectly attributes the presentation to pulmonary toxicity with secondary thyroid involvement, pulmonary toxicity presents with dyspnea, cough, and interstitial infiltrates, not thyrotoxicosis with suppressed TSH.
Option E: Option E incorrectly states that the distinction between AIT-1 and AIT-2 is clinically irrelevant: the distinction is precisely what determines whether thionamides or corticosteroids are the primary treatment.
11. A 72-year-old woman with heart failure with reduced ejection fraction (EF 31%) and persistent atrial fibrillation is being initiated on dofetilide during an in-hospital stay. Her baseline QTc is 428 ms and her creatinine clearance is 48 mL/min. Which of the following correctly identifies the appropriate starting dose and mandatory initiation requirements?
A) Dofetilide 250 mcg twice daily (dose-adjusted for CrCl 40 to 60 mL/min), initiated in hospital with continuous telemetry for a minimum of 3 days, with QTc checked 2 to 3 hours after each dose, reduce dose or discontinue if QTc exceeds 500 ms
B) Dofetilide 500 mcg twice daily (standard dose), initiated in hospital with 24-hour monitoring, her baseline QTc of 428 ms indicates low TdP risk and the full dose is appropriate given HFrEF requires maximum antiarrhythmic effect
C) Dofetilide 125 mcg twice daily (dose for CrCl 20 to 40 mL/min), initiated in hospital with 5-day monitoring, in HFrEF, the lowest available dose is always used regardless of creatinine clearance to minimize TdP risk
D) Dofetilide is contraindicated in this patient because her CrCl of 48 mL/min falls below the 50 mL/min threshold required for standard dofetilide dosing and no dose adjustment is available for this creatinine clearance range
E) Dofetilide 500 mcg once daily (reduced frequency rather than reduced dose) with outpatient QTc monitoring at 48 hours, once-daily dosing eliminates the peak-concentration TdP risk while maintaining adequate 24-hour IKr blockade
ANSWER: A
Rationale:
Dofetilide has a mandatory four-tier renal dose adjustment based on creatinine clearance, reflecting its 80% renal elimination unchanged. For CrCl greater than 60 mL/min, the standard dose is 500 mcg twice daily. For CrCl 40 to 60 mL/min: this patient's range at 48 mL/min: the dose is reduced to 250 mcg twice daily. For CrCl 20 to 40 mL/min, the dose is 125 mcg twice daily. For CrCl below 20 mL/min, dofetilide is contraindicated. All patients must be initiated in a facility capable of continuous monitoring for at least 3 days, with QTc checked 2 to 3 hours after each dose; the dose must be reduced or discontinued if QTc exceeds 500 ms during initiation.
Option B: Option B incorrectly prescribes the standard 500 mcg twice daily dose without renal adjustment, at CrCl 48 mL/min this dose would produce drug accumulation, excessive QTc prolongation, and elevated TdP risk.
Option C: Option C incorrectly applies the 125 mcg dose, which corresponds to CrCl 20 to 40 mL/min: this patient's CrCl of 48 mL/min falls in the 40 to 60 range requiring 250 mcg, not the lower tier.
Option D: Option D incorrectly states a contraindication threshold of 50 mL/min: the contraindication threshold is CrCl below 20 mL/min; a CrCl of 48 mL/min is within the dose-adjustable range requiring 250 mcg twice daily.
Option E: Option E incorrectly proposes once-daily dosing as a dose-reduction strategy, dofetilide's renal dose adjustment is by concentration reduction (lower dose), not by extending the interval; once-daily dosing is not an established or approved regimen.
12. A 63-year-old man with ischemic cardiomyopathy (EF 29%), NYHA Class II symptoms, and paroxysmal atrial fibrillation has had three electrical cardioversions in the past 18 months, each relapsing to AF within 6 weeks. His cardiologist considers several antiarrhythmic options for rhythm maintenance. Which of the following correctly identifies the agents available for this patient and the trial evidence constraining each choice?
A) Flecainide is the preferred agent because its sodium channel blockade stabilizes the myocardium against triggered activity in structural heart disease, and Class Ic agents are contraindicated only in patients with active ischemia, not in stable ischemic cardiomyopathy
B) Sotalol is the optimal choice because its combined Class II and III activity provides superior efficacy in HFrEF and its safety in patients with EF below 35% was established by the DIAMOND-CHF trial
C) Only amiodarone and dofetilide are appropriate choices, flecainide and propafenone are contraindicated by CAST evidence in structural heart disease, sotalol should be avoided with EF below 40%, and dronedarone is contraindicated by ANDROMEDA in HFrEF
D) Dronedarone is the preferred agent because its non-iodinated structure eliminates the thyroid and pulmonary toxicity risks of amiodarone, and the ANDROMEDA contraindication applies only to patients hospitalized for heart failure decompensation within the preceding 30 days
E) Any Class III agent is appropriate provided the baseline QTc is below 450 ms: the contraindications in structural heart disease are specific to Class I agents and do not extend to the broader Class III category
ANSWER: C
Rationale:
In heart failure with reduced ejection fraction, antiarrhythmic drug selection is severely restricted. Flecainide and propafenone are contraindicated in structural heart disease: the CAST trial demonstrated increased mortality with Class Ic agents in patients with structural heart disease, and this contraindication is not limited to the post-MI period but extends to any significant structural heart disease including HFrEF. Sotalol should be avoided in patients with EF below 40% due to its beta-blocking negative inotropy and the mortality signal from the SWORD trial with d-sotalol in LV dysfunction. Dronedarone is contraindicated in this patient: the ANDROMEDA trial demonstrated excess mortality in patients with severe HFrEF or recently decompensated HF, and guidelines extend this to NYHA Class III-IV or any recent decompensation. Only amiodarone (broad efficacy, safe in structural heart disease) and dofetilide (DIAMOND-CHF: neutral mortality in EF below 35%) are appropriate.
Option A: Option A incorrectly states that flecainide is acceptable in stable ischemic cardiomyopathy: the CAST contraindication applies to all structural heart disease with impaired LV function, not only to patients with active ischemia.
Option B: Option B incorrectly credits DIAMOND-CHF to sotalol, DIAMOND-CHF established dofetilide's safety in HFrEF; sotalol was not studied in that trial and should be avoided with EF below 40%.
Option D: Option D incorrectly characterizes the ANDROMEDA contraindication as limited to patients hospitalized within the preceding 30 days: the contraindication applies to HFrEF with NYHA Class III-IV symptoms or any recent decompensation, with no 30-day specificity in current guidelines.
Option E: Option E incorrectly generalizes that all Class III agents are safe in HFrEF when QTc is acceptable, sotalol and dronedarone carry specific mortality signals in HFrEF that are independent of baseline QTc.
13. A 58-year-old man with ischemic cardiomyopathy is in the ICU with hemodynamically stable but symptomatic sustained monomorphic ventricular tachycardia at 148 bpm, refractory to two attempts at overdrive pacing. IV amiodarone is selected. Which of the following correctly describes the IV amiodarone loading protocol, a key administration precaution, and its evidence base for this indication?
A) IV amiodarone is administered as a single bolus of 300 mg over 3 minutes for rapid termination of VT, followed by oral loading at 600 mg three times daily, central line access is not required and peripheral IV is preferred to allow rapid bolus delivery
B) IV amiodarone is administered as 75 mg over 30 minutes followed by a 12-hour infusion at 0.25 mg/min: the slow initial infusion is required to prevent the hypotension seen with faster loading rates, and the maximum 24-hour dose is 1.0 g
C) IV amiodarone is administered as 360 mg over 6 hours followed by oral transition, no central line is needed as the dilute concentration used for VT does not cause phlebitis, and total 24-hour IV dosing should not exceed 1.5 g
D) IV amiodarone is administered as 150 mg over 10 minutes for acute VT, followed by 1 mg/min for 6 hours, then 0.5 mg/min maintenance; central line access is preferred due to phlebitis risk with peripheral IV; maximum dose is 2.2 g in 24 hours; evidence from the ALPS trial supports its superiority over lidocaine for shock-refractory ventricular fibrillation
E) IV amiodarone is administered as 150 mg over 10 minutes, then 1 mg/min for 6 hours, then 0.5 mg/min, central line is preferred due to phlebitis risk with peripheral IV; the maximum dose is 2.2 g in 24 hours; the ALPS trial demonstrated that both amiodarone and lidocaine improved return of spontaneous circulation versus placebo in shock-refractory VF but neither improved neurologically favorable survival in the overall population
ANSWER: E
Rationale:
The standard IV amiodarone protocol for hemodynamically stable VT or acute VF is: 150 mg IV over 10 minutes (the loading bolus), followed by a maintenance infusion of 1 mg/min for 6 hours, then 0.5 mg/min thereafter, with a maximum cumulative dose of 2.2 g in 24 hours. Administration via central line is preferred because amiodarone is highly lipophilic and causes phlebitis with prolonged peripheral IV infusion; if only peripheral access is available, the most proximal vein should be used. The ALPS (Amiodarone, Lidocaine, or Placebo) trial demonstrated that both amiodarone and lidocaine improved return of spontaneous circulation (ROSC) compared to placebo in shock-refractory VF, but neither agent improved neurologically favorable survival in the overall trial population. Both remain guideline-supported for this indication. Option D correctly describes the protocol and ALPS trial but mischaracterizes the ALPS finding:
Option A: Option A incorrectly describes a single rapid bolus for VT and oral loading: the IV protocol for stable VT uses the structured infusion regimen described above, not a single bolus, and peripheral IV is not preferred.
Option B: Option B incorrectly describes a slower initial infusion rate and an incorrect maximum dose of 1.0 g per 24 hours: the correct maximum is 2.2 g in 24 hours.
Option C: Option C incorrectly omits the initial 10-minute loading bolus, incorrectly states that peripheral IV does not cause phlebitis, and uses an incorrect maximum dose of 1.5 g.
Option D: Option D states amiodarone is superior to lidocaine for shock-refractory VF, whereas ALPS demonstrated that both improved ROSC versus placebo without a significant difference between amiodarone and lidocaine.
14. Which of the following correctly identifies all the major patient factors that amplify torsades de pointes risk during sotalol initiation and that must be assessed before and during the mandatory in-hospital monitoring period?
A) Advanced age, hepatic impairment, concurrent use of CYP2D6 inhibitors, and left ventricular hypertrophy: these factors reduce sotalol metabolism and raise peak plasma levels, directly correlating with QTc prolongation and TdP risk
B) QTc prolongation at any point during initiation, bradycardia, hypokalemia, hypomagnesemia, renal impairment (through drug accumulation), and female sex: all of these amplify the IKr-blocking effect of sotalol or the myocardial vulnerability to EAD formation
C) Active smoking, concurrent use of caffeine-containing beverages, male sex, and exercise-induced tachycardia: these factors shorten the QTc through adrenergic stimulation and paradoxically reduce sotalol's IKr-blocking effect during initiation
D) Hyponatremia, hypocalcemia, concurrent use of loop diuretics, and diabetes mellitus: these metabolic factors directly prolong the action potential duration in ventricular myocardium and amplify sotalol-driven QT prolongation
E) Concurrent use of Class Ia antiarrhythmics and left bundle branch block: these factors produce transmural APD heterogeneity that combines with sotalol's IKr blockade to generate the conditions for TdP specifically in structurally abnormal ventricular tissue
ANSWER: B
Rationale:
Sotalol's TdP risk during initiation is amplified by several well-defined patient factors. QTc prolongation, either pre-existing or developing during initiation, increases the APD prolongation beyond the threshold for EAD formation. Bradycardia amplifies reverse use-dependence, maximizing IKr blockade at slow rates. Hypokalemia and hypomagnesemia both impair repolarizing currents and lower the EAD threshold independently of sotalol. Renal impairment causes drug accumulation (sotalol is 100% renally eliminated), raising effective plasma levels and amplifying all IKr-mediated effects. Female sex is an independent risk factor: women have a longer baseline QTc and greater sensitivity to IKr-blocking drugs, explaining why TdP from Class III agents occurs disproportionately in women. Option C identifies factors that reduce TdP risk rather than amplify it, and incorrectly lists male sex as a risk factor when female sex is the established risk factor for drug-induced TdP. Option D identifies metabolic factors that are not primary TdP risk amplifiers for sotalol, hyponatremia, hypocalcemia, and diabetes are not established sotalol-specific TdP risk factors in prescribing guidelines.
Option A: Option A incorrectly identifies hepatic impairment and CYP2D6 inhibitors as risk factors, sotalol undergoes no hepatic metabolism; its clearance is entirely renal. Left ventricular hypertrophy may affect arrhythmia substrate but is not a primary TdP risk factor in the context of sotalol initiation.
Option E: Option E incorrectly limits TdP risk amplification to structural conduction abnormalities and concurrent Class Ia agents: the established patient factors are those in Option B, and left bundle branch block is not itself a listed TdP risk amplifier for sotalol.
15. A cardiology resident asks why amiodarone, which prolongs the QT interval more than dofetilide in absolute terms, has a torsades de pointes incidence below 1% while dofetilide has a TdP rate of 1 to 3%. Which of the following provides the most mechanistically complete explanation?
A) Amiodarone has a longer half-life of 40 to 55 days, producing stable plasma levels without the trough-related QTc fluctuations that trigger TdP in patients on dofetilide, pharmacokinetic stability rather than any ion channel difference accounts for the lower TdP incidence
B) Amiodarone is administered at lower total daily doses than dofetilide when expressed in molar equivalents, and the absolute degree of IKr blockade achieved at standard maintenance doses is less than that produced by dofetilide, lower IKr occupancy directly correlates with lower TdP incidence
C) Amiodarone blocks IKs in addition to IKr, producing more uniform action potential prolongation across ventricular layers and eliminating the transmural repolarization gradient that drives the TdP re-entrant wavefront, dofetilide's pure IKr blockade leaves IKs intact, preserving a proarrhythmic transmural gradient
D) Amiodarone's concurrent ICaL blockade reduces the primary inward trigger current for early afterdepolarization formation, directly counteracting the proarrhythmic effect of APD prolongation, pure IKr blockers such as dofetilide lack this mechanism, leaving EAD formation unopposed despite equivalent or lesser QT prolongation
E) Amiodarone's non-competitive beta-blocking activity maintains a higher baseline heart rate than dofetilide, preventing the bradycardia-associated pauses that trigger pause-dependent EAD formation: it is the rate effect rather than any direct membrane action that accounts for the low TdP incidence
ANSWER: D
Rationale:
EADs arise when inward currents overcome outward currents during a prolonged action potential plateau or late phase 3. The primary inward trigger current for EAD generation is ICaL (L-type calcium channel current). Amiodarone's concurrent ICaL blockade directly reduces this trigger current, suppressing EAD formation despite prolonging APD. Pure IKr blockers such as dofetilide prolong APD without any compensating reduction in ICaL, leaving the inward EAD trigger current unopposed. This mechanistic difference is the most complete and direct explanation for amiodarone's paradoxically low TdP incidence despite producing greater absolute QT prolongation. Option C correctly identifies that IKs blockade reduces transmural APD heterogeneity and may contribute to lower TdP risk, but this is a less complete mechanistic explanation than ICaL blockade suppressing the EAD trigger, Option D captures the primary direct mechanism. Option E has partial validity, beta-blockade prevents bradycardia-associated pauses, but this is a secondary contributing factor and does not account for amiodarone's low TdP rate across all heart rates; the ICaL mechanism is the more complete and direct explanation.
Option A: Option A incorrectly attributes the difference to pharmacokinetic stability, stable plasma levels reduce peak toxicity but do not explain why amiodarone generates fewer EADs per unit of QT prolongation; the channel-level mechanism is the more fundamental answer.
Option B: Option B incorrectly proposes that lower IKr occupancy at standard doses explains the difference, amiodarone produces substantial QT prolongation consistent with significant IKr blockade, so the lower TdP rate is not simply a matter of lesser IKr blockade.
16. A 70-year-old woman with ischemic cardiomyopathy (EF 27%), NYHA Class II heart failure, paroxysmal atrial fibrillation, and creatinine clearance of 55 mL/min presents for rhythm control initiation. Her baseline QTc is 436 ms. Which of the following correctly selects the most appropriate antiarrhythmic agent and justifies the exclusion of each alternative?
A) Flecainide 100 mg twice daily, most effective Class Ic agent for paroxysmal AF, and the CAST contraindication applies only to patients with EF below 25% or active ischemia, not to stable ischemic cardiomyopathy with compensated heart failure
B) Dofetilide 250 mcg twice daily (renal-adjusted for CrCl 40 to 60 mL/min) with mandatory in-hospital initiation, amiodarone and dofetilide are the only agents safe in HFrEF; flecainide and propafenone are contraindicated by CAST, sotalol is avoided with EF below 40%, and dronedarone is contraindicated by ANDROMEDA
C) Dronedarone 400 mg twice daily, preferred over amiodarone because it lacks iodine-related organ toxicity, and the ANDROMEDA contraindication applies only to patients hospitalized for heart failure decompensation within 6 months, not to compensated Class II patients
D) Sotalol 80 mg twice daily with in-hospital initiation: the DIAMOND-CHF trial demonstrated sotalol's safety in patients with EF below 35% and the combined Class II and III mechanism provides superior rate and rhythm control in HFrEF
E) Propafenone 150 mg three times daily: its mild beta-blocking activity provides additional benefit in ischemic cardiomyopathy, and Class Ic contraindications in structural heart disease were established only for encainide and flecainide in CAST, not for propafenone
ANSWER: B
Rationale:
In HFrEF, antiarrhythmic drug selection is restricted to amiodarone and dofetilide by trial evidence and guideline contraindications. Dofetilide at 250 mcg twice daily (renal-adjusted for CrCl 55 mL/min, which falls in the 40 to 60 range) with mandatory in-hospital initiation and QTc monitoring is appropriate: DIAMOND-CHF established neutral mortality in EF below 35%, and her baseline QTc of 436 ms is below the 440 ms initiation threshold. Flecainide and propafenone are contraindicated: the CAST trial established that Class Ic agents increase mortality in structural heart disease, and this applies to all structural heart disease with impaired LV function, not only to post-MI patients with EF below 25%. Sotalol is avoided with EF below 40% due to its beta-blocking negative inotropy and the SWORD trial mortality signal with d-sotalol in LV dysfunction, DIAMOND-CHF studied dofetilide, not sotalol. Dronedarone is contraindicated by ANDROMEDA in patients with HFrEF and NYHA Class III-IV or recent decompensation, and guidelines apply this broadly to significant LV dysfunction rather than only to actively decompensated patients.
Option A: Option A incorrectly limits the CAST contraindication to EF below 25% or active ischemia: it applies to all structural heart disease with LV dysfunction.
Option C: Option C incorrectly characterizes the ANDROMEDA contraindication as limited to patients hospitalized within 6 months, guidelines apply it to NYHA Class III-IV or any recent decompensation without a specific 6-month restriction.
Option D: Option D incorrectly credits DIAMOND-CHF to sotalol, that trial studied dofetilide; sotalol is avoided in significant LV dysfunction.
Option E: Option E incorrectly states that the CAST Class Ic contraindication was established only for encainide and flecainide and does not extend to propafenone: the contraindication is applied to the Class Ic drug class in structural heart disease based on CAST mechanism and clinical extrapolation.
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