What are the indications for an Implantable Cardioverter-Defibrillator (ICD) in patients with Hypertrophic Obstructive Cardiomyopathy (HOCM)?

ICD Indications for Hypertrophic Obstructive Cardiomyopathy (HOCM)

ICD placement is strongly recommended for HOCM patients with prior documented cardiac arrest, ventricular fibrillation, or hemodynamically significant ventricular tachycardia, as these patients have the highest risk of sudden cardiac death. 1

Primary Prevention Indications

Class I (Recommended)

• Prior documented cardiac arrest, ventricular fibrillation, or hemodynamically significant VT 1

Class IIa (Reasonable)

• Family history of sudden death due to HCM in first-degree relatives 1
• Maximum LV wall thickness ≥30 mm 1
• Recent unexplained syncope 1
• High-risk children with HCM based on unexplained syncope, massive LV hypertrophy, or family history of SCD 1

Class IIa (Can be useful)

• Nonsustained ventricular tachycardia (NSVT) with other risk factors, particularly in patients <30 years of age 1
• Abnormal blood pressure response with exercise plus other risk factors 1
• Left ventricular ejection fraction <50% 1
• Apical aneurysm 1

Risk Stratification Approach

The 2020 AHA/ACC guidelines provide a structured algorithm for ICD patient selection 1:

1. Prior event (SCD, VF, sustained VT): ICD recommended (Class I)
2. At least one of the following:
   • Family history of SCD
   • Massive LVH
   • Unexplained syncope
   • Apical aneurysm
   • EF <50%
   • NSVT plus other risk factors

The European Society of Cardiology (2014) uses a quantitative approach with the HCM Risk-SCD score to estimate 5-year risk 1:

• High risk (≥6% 5-year risk): ICD should be considered
• Intermediate risk (4-<6% 5-year risk): ICD may be considered
• Low risk (<4% 5-year risk): ICD generally not indicated

Important Clinical Considerations

• The rate of appropriate ICD discharges is approximately 11% per year for secondary prevention and 3.6-5% per year for primary prevention 2, 3
• Even patients with only a single risk factor may benefit from ICD implantation, with similar rates of appropriate discharges compared to those with multiple risk factors 3
• Time to first appropriate discharge can be up to 10 years, with a 27% probability at 5 years or more after implantation 3

Device Selection

For patients receiving an ICD:

• Either a single-chamber transvenous ICD or subcutaneous ICD is recommended after shared decision-making (Class I) 1
• Single-coil ICD leads are preferred over dual-coil leads (Class I) 1
• Dual-chamber ICDs are reasonable for patients needing atrial or AV sequential pacing (Class IIa) 1

Cautions and Complications

• ICD complications include inappropriate shocks (reported in 25-27% of patients) 2, 3
• Patients with massive LV hypertrophy (>45 mm) or on amiodarone therapy may have high defibrillation thresholds, potentially requiring epicardial lead placement 4
• ICD placement as a routine strategy in patients without risk factors is potentially harmful 1
• ICD placement to permit competitive athletics participation is potentially harmful 1
• ICD placement in patients with only an identified HCM genotype without clinical manifestations is potentially harmful 1

The decision for ICD implantation should involve thorough discussion of benefits and risks, allowing for informed patient participation in decision-making, but should always prioritize prevention of sudden cardiac death in appropriate candidates.