Primary prevention of sudden cardiac death in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) has been regarded as the most common non-trauma-related cause of sudden cardiac death (SCD) in young people, including competitive athletes. The traditional clinical profile of HCM patients at highest risk of SCD is largely comprised of young asymptomatic patients, particularly children and adolescents. Prophylactic drug treatment to prevent SCD is ineffective and obsolete whereas the introduction of implantable cardioverter defibrillators (ICD) has changed the clinical course and natural history of the disease. The ICDs are largely responsible for reducing HCM-related mortality to 0.5%/year and have been shown to be effective despite the often complex HCM phenotype, including extreme and diverse patterns of left ventricular hypertrophy, dynamic subaortic obstruction, microvascular ischaemia, and diastolic dysfunction. An important principle related to ICD decisions in HCM patients surrounds the unpredictable nature of the arrhythmic substrate, often associated with substantial delays of 5–10 years between implant and initial intervention. Selection of patients most likely to benefit from primary prevention ICD therapy is based on non-invasive testing including echocardiography or cardiac magnetic resonance imaging, history taking, exercise testing, and ambulatory electrocardiogram (ECG). Conventional risk markers are (1) family history (one or more HCM-related SCDs in close relatives); (2) recent unexplained syncope; (3) multiple repetitive (or prolonged) non-sustained ventricular tachycardia on ambulatory ECG; (4) massive left ventricular hypertrophy (wall thickness ≥30 mm); and (5) hypotensive blood pressure response to exercise, although this is not a sole indication for ICD implants. ICD decisions within current risk stratification guidelines can be challenging, particularly in patients with just one risk factor or when available evidence is ambiguous or insufficient to assign SCD risk level with confidence.