GPAtlas🧭 When to suspect
Hypertrophic cardiomyopathy (HCM) is a genetic disorder of the heart muscle in which the left ventricular wall becomes abnormally thickened in the absence of another cause (such as hypertension or aortic stenosis). It is the most common inherited cardiac condition, affecting around 1 in 500 of the UK population, and is inherited in an autosomal dominant pattern – most often through mutations in the sarcomeric genes MYBPC3 and MYH7, giving a 50% chance of transmission to each child. Hypertrophic obstructive cardiomyopathy (HOCM) is the subtype in which the thickened septum produces dynamic left ventricular outflow tract obstruction (LVOTO); obstruction at rest or on provocation is present in the majority of patients.
The clinical importance lies in sudden cardiac death (SCD): HCM is the leading cause of sudden death in young people and athletes, and there is often a long pre-symptomatic phase. The single most important red flag is a family history of HCM or premature sudden death. The key task in primary care is threefold: suspect it in the right patient, recognise the red flags (above all exertional syncope), and know which drugs to avoid.
| Feature | Threshold / significance |
|---|---|
| Diagnostic wall thickness (adult) | ≥ 15 mm in one or more left ventricular segments, not explained solely by loading conditions – classically asymmetrical septal hypertrophy. |
| Diagnostic threshold in first-degree relatives | ≥ 13 mm – a lower cut-off applies when a relative has unequivocal disease. |
| LVOT obstruction | Peak Doppler gradient > 30 mmHg at rest or on physiological provocation. |
| Haemodynamically significant LVOTO | ≥ 50 mmHg – the threshold above which intervention is considered if symptoms persist. |
Raise suspicion in a patient – often young – presenting with exertional breathlessness, chest pain, palpitations, or syncope (especially during or just after exertion). Other triggers are an incidental heart murmur, an abnormal ECG, a family history of HCM or sudden death under 40, or a relative already told they have a “thickened heart muscle”.
Source: ESC 2023 · NHS Genomic Medicine Service
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