• hypertrophic cardiomyopathy
• sudden cardiac death
• ventricular tachycardia
• ventricular fibrillation

Hypertrophic cardiomyopathy (HCM) is an inherited disease (or perhaps more correctly, in view of its genetic heterogeneity it should be considered as a group of diseases). It exhibits pronounced phenotypic variability, including extent of hypertrophy, presence and severity of symptoms, and natural history. The early literature, derived from a small group of tertiary referral centres, suggested that it was a relatively uncommon but extremely malignant disorder, with annual mortality rates of 2–4% in adults and 6% in adolescents and children, the majority of these deaths being sudden.^w1 More recently it has become apparent that HCM is in fact a common disorder, with a prevalence estimated from echocardiographic population screening of 0.2%.^w2 However, it is also now clear that HCM is overall much more benign than these earlier studies had suggested, with an annual mortality rate in large unselected series of approximately 1%, at least half of these deaths being sudden, and the remainder principally caused by heart failure and stroke.¹

Nevertheless, HCM is an important cause of sudden cardiac death (SCD); in most (but not all) series it is the most important cause of SCD in young adults and in athletes.² Many of these deaths occur in patients with minimal or no symptoms (indeed the diagnosis of HCM is sadly often made first at the postmortem examination, following the sudden cardiac death of a previously healthy individual). With the development of automatic implantable cardioverter-defibrillators (AICDs), effective preventive therapy is now available. The challenge is to distinguish high risk from low risk patients with HCM in order to target prophylactic therapies (AICD ± amiodarone) to those at risk. The need for such risk stratification is more than simply one of health economics. Compared with patients with coronary artery disease who undergo AICD implantation, HCM patients who are …