There are 4 common causes for a big heart – by which I mean a big LEFT heart. They are ISHCAEMIC (or if you’re not British, ISCHEMIC) HEART DISEASE, HYPERTENSION, CARDIAC VALVE DISEASE, CARDIOMYOPATHIES. Rarely, things like infection (‘MYOCARDITIS’) cause a big heart but these are the big 4.
ISCHAEMIC HEART DISEASE (IHD) is a term that is often written on certificates of the cause of death. It’s a catch-all term for what happens to the heart when ATHEROMA (that thing again) narrows the arteries that supply blood to the heart muscle (the CORONARY ARTERIES supplying blood to the MYOCARDIUM, as doctors put it). The heart muscle cells (the MYOCYTES) die and the heart muscle scars (FIBROSES). The surviving myocytes have to do more work and the heart becomes less efficient; moreover, the beat of the heart becomes more likely to be disrupted. People die suddenly and the pathologist finds only a big heart and coronary artery atheroma, and no other likely cause of death. The pathologist writes the cause of death as Ischaemic Heart Disease because that is the likeliest.
HYPERTENSION is high blood pressure. Most times, there is no known cause, when it’s called ESSENTIAL (medicalese again). To get the blood around the body, the heart has to work harder because it has to push blood out against a higher pressure. Like all muscles, the heart muscle over time becomes larger. Unfortunately, larger hearts require more blood to feed them via the coronary arteries. When the blood supply is insufficient, myocytes die and the heart muscle scars. Sudden death because of terminal arrhythmia may occur.
A big heart because of CARDIAC VALVE DISEASE is usually because of abnormalities of the MITRAL VALVE (between the left atrium and the left ventricle) or the AORTIC VALVE (where the left ventricle meets the aorta). As previously discussed, the abnormality may be regurgitation (also called INCOMPETENCE) when the valve allows blood to go backwards, or stenosis (when the valve becomes narrowed). Either way the heart has more work to do, and becomes larger, etc. etc..
CARDIOMYOPATHY is in intrinsic abnormality of the heart muscle itself – ie the myocardium is diseased. There are various types of cardiomyopathy, but the main ones are HYPERTROPHIC (aka HOCM, pronounced ‘hokum’) or CONGESTIVE (aka COCM, pronounced ‘cokum’). HOCM is usually an inherited disease; COCM is usually a result of lifestyle (‘ACQUIRED’ is the medicalese). Either way, the heart doesn’t behave normally when it comes to beating and terminal arrhythmia my occur. The pathologist can only diagnose it as a cause of death if there’s no other evidence of hypertension, IHD or cardiac valve disease.