A heart muscle that grows too thick can hide for years, then strike
Up to one in 500 people have hypertrophic cardiomyopathy, a mostly inherited thickening of the heart's walls. Many feel nothing at all. Others get breathlessness, chest pain or fainting, and a few face sudden cardiac death. With modern treatment, though, the yearly risk of dying from it falls below one percent.
In this condition the heart muscle, usually the wall between the ventricles and the ventricles themselves, thickens without an obvious reason such as high blood pressure. A stiff, bulky left ventricle fills poorly, so pressure builds and blood can back up into the lungs, which explains the breathlessness. The thick muscle also demands more oxygen than narrowed, thick-walled coronary vessels can deliver, producing chest pain on exertion. Dehydration can make symptoms worse.
In the obstructive form, the swollen septum narrows the exit route from the left ventricle. Blood rushing through the gap speeds up and its pressure drops, a Venturi effect that can tug a mitral valve leaflet into the channel and block it further. Obstruction is sometimes hidden at rest, which is why doctors may scan the heart after exercise or even after a meal, when symptoms often flare. A related variant, apical HCM or Yamaguchi syndrome, first described in people of Japanese descent, carries a gentler outlook and is commoner in Asian populations.
Genetics drives most cases. The pattern is autosomal dominant, so a child of one affected parent has a 50 percent chance of inheriting the mutation. More than 1,400 mutations are known, mostly in genes for the sarcomere, the heart's contractile machinery, and about 40 to 60 percent of patients carry an identifiable change in one of nine such genes. Carrying a mutation does not guarantee visible disease, and testing cannot forecast severity or age of onset, but it can flag relatives who need monitoring.
Donald Teare wrote the first modern description in 1958. Diagnosis draws on family history, ECG, which is the most sensitive test, echocardiography and cardiac MRI. Drug options include beta blockers, verapamil, disopyramide and the newer mavacamten and aficamten. People with dangerous rhythms may receive an implanted defibrillator, and those who do not improve may need septal myectomy surgery or a heart transplant.
Source: Hypertrophic cardiomyopathy
