What is the best course of action for a patient with Hypertrophic Cardiomyopathy (HCM) and apical aneurysm, who had catheter ablation for sustained conscious Ventricular Tachycardia (VT) a few months ago, has a Cardiac Resynchronization Therapy-Defibrillator (CRT-D) pacing their heart fully, and has been on Amiodarone (anti-arrhythmic medication) since the initial VT termination, now presenting with palpitations?

Management of Palpitations in HCM Patient Post-VT Ablation on Amiodarone with CRT-D

The immediate priority is to interrogate the CRT-D device to determine if palpitations represent recurrent ventricular arrhythmias, atrial fibrillation, or are device-related, as this will fundamentally direct all subsequent management decisions. 1

Device Interrogation and Rhythm Assessment

• Device interrogation is the critical first step to review stored electrograms, assess for appropriate/inappropriate shocks, evaluate antitachycardia pacing episodes, and confirm pacing parameters 1
• Specifically assess for:
  • Recurrent VT episodes (monomorphic or polymorphic) 1
  • New-onset atrial fibrillation or flutter (common in HCM and associated with high stroke risk) 1
  • Inappropriate shocks from lead malfunction or oversensing 1
  • Pacing-induced arrhythmias from CRT settings 1

If Recurrent Ventricular Arrhythmias Are Identified

Continue amiodarone and optimize the dose to 400-600 mg/day, as lower maintenance doses (<400 mg/day) are associated with higher recurrence rates in sustained VT. 2, 3

• Amiodarone remains the most effective antiarrhythmic for VT in HCM despite its toxicity profile 1
• Ensure antitachycardia pacing is optimally programmed in the CRT-D, as this minimizes shock burden and is specifically recommended for HCM patients with ICDs 1
• If VT recurs despite optimal amiodarone dosing:
  • Consider adding mexiletine (50-200 mg three times daily) as adjunctive therapy 1
  • Evaluate for repeat catheter ablation, particularly if monomorphic VT with identifiable substrate 1
  • If refractory to maximal medical therapy and repeat ablation, refer for heart transplantation evaluation 1

Critical Caveat on Amiodarone Timing

• The patient received a "full loading" several months ago, but amiodarone has a very long half-life (40-55 days) 2
• If maintenance dosing was reduced too aggressively or discontinued, recurrence can occur 15-60 days after dose reduction 2
• Verify current amiodarone dose and plasma levels if available 3

If Atrial Fibrillation Is Detected

Initiate anticoagulation immediately with a DOAC (apixaban, rivaroxaban, or dabigatran) regardless of CHA₂DS₂-VASc score, as HCM patients with AF have a 27% thromboembolism risk independent of traditional scoring systems. 1

Rate Control Strategy

• Beta-blockers are first-line for rate control in HCM with AF 1
• If beta-blocker is insufficient, add diltiazem or verapamil (high doses often required) 1
• Avoid relying solely on digoxin for rate control, though it can be added as adjunctive therapy 1

Rhythm Control Strategy

• Amiodarone is the preferred antiarrhythmic for AF rhythm control in HCM (already on board for VT suppression) 1
• Disopyramide combined with beta-blocker is an alternative if amiodarone toxicity develops 1
• Dofetilide, sotalol, and dronedarone are Class IIb alternatives but less well-studied in HCM 1, 4
• Consider AF catheter ablation if symptoms persist despite antiarrhythmic therapy, though success rates are lower in HCM (44% freedom from AF at 1 year) and repeat procedures are frequently needed 1

If No Arrhythmia Is Documented on Device Interrogation

• Obtain 12-lead ECG during symptomatic episodes if possible 5
• Consider extended ambulatory monitoring (30-day event monitor) to capture symptomatic episodes 5
• Evaluate for:
  • Pacing-induced symptoms (adjust CRT settings, consider reducing pacing percentage if appropriate) 1
  • Anxiety or panic disorder (common in patients with ICDs and prior cardiac arrest) 5
  • Medication side effects (amiodarone can cause thyroid dysfunction leading to palpitations) 4, 3

Amiodarone Monitoring and Toxicity Considerations

Given several months of amiodarone therapy, assess for organ toxicity that could necessitate drug discontinuation: 4, 3

• Check liver function tests (hepatotoxicity is a key reason to discontinue) 4
• Thyroid function tests (both hypo- and hyperthyroidism can occur and exacerbate arrhythmias) 4, 3
• Pulmonary function tests and chest imaging if respiratory symptoms present 3
• Ophthalmologic examination for corneal deposits 3
• If amiodarone must be discontinued due to toxicity, dofetilide is the preferred alternative in structural heart disease 4

Key Pitfalls to Avoid

• Do not assume palpitations are benign without device interrogation – recurrent VT in HCM with apical aneurysm carries high mortality risk 1
• Do not reduce or discontinue amiodarone without careful consideration – recurrence of VT can occur weeks after dose reduction 2, 6
• Do not delay anticoagulation if AF is detected – stroke risk in HCM with AF is 27% and independent of CHA₂DS₂-VASc score 1
• Do not overlook the possibility of amiodarone-induced thyroid dysfunction as a cause of new palpitations 4, 3
• Sudden death can occur in HCM patients on amiodarone despite VT suppression on monitoring, particularly in the first 6 months of therapy 6