Hypertrophic cardiomyopathy (HCM) is thickening of the left ventricular wall caused by a disease of the sarcomere, the contractile apparatus of the muscle cell, rather than by a load imposed on the heart. The hypertrophy is usually asymmetric, and it can be substantial without producing any symptom at all.
How it comes to attention
Many patients live asymptomatically for decades and surface incidentally — sport screening or an abnormal ECG.
Symptoms, when they come, follow from what the thickened ventricle does. Exertional syncope is a red flag that must prompt exclusion of HCM. Palpitations and arrhythmias including atrial fibrillation occur, and heart failure symptoms come predominantly from diastolic dysfunction, the poor relaxation and filling of a stiff ventricle. Stroke follows from atrial fibrillation or from thrombus in a dilated atrium or an apical aneurysm.
Sudden death can be the first manifestation, classically collapse during sport in the young.
The murmur
Only obstructive HCM produces a systolic murmur, and its behaviour is diagnostic: manoeuvres that reduce preload or afterload, such as Valsalva or standing, intensify it, while squatting softens it. This fits an obstruction that is dynamic and grows with lower preload.
The ECG
The ECG is abnormal in most patients with pronounced disease, and a normal tracing does not exclude the diagnosis — mild disease can still show a normal ECG. Characteristic features include:
- high QRS voltage (the QRS complex is the ventricular depolarisation) with the tallest R waves inferolaterally
- deep giant negative precordial T waves
- ST abnormalities in either direction
- left axis deviation
- small notches or fragmentation within the QRS from disorganised depolarisation
- broad notched P waves of left atrial enlargement
Electrical change can precede visible hypertrophy, which is why ECG screening before competitive sport in the young is the most effective case-finding tool.
A thick ventricle in a young athlete raises a further question, because physiological hypertrophy from training looks much like mild HCM, and separating the two decides both the diagnosis and the advice about sport.