BIG HEARTS

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.

HEART VALVES

There are 4 heart valves, 2 on the right side and 2 on the left. There is one between the two chambers on the right (the tricuspid valve), and one between the two chambers on the left (the mitral valve). There is one at the exit of the right heart (the pulmonary valve) and one at the exit of the left heart (the aortic valve).

Three of the valves (the tricuspid, the pulmonary and the aortic) have 3 leaflets, one (the mitral) has two. As with all valves, the role of the heart valves is to ensure that the blood goes in one direction and one direction only.

The valves may be INCOMPETENT (meaning that they leak, ie that they don’t seal properly) or STENOSED (which is medicalese for narrowed). Reasons for heart valve problems are most often due to infection (bugs in the blood), but can be congenital. The problem is that narrowing of the valve or leaking of the valve results in blood going the wrong way. Effectively, then, the bit of the heart behind the valve has to work harder. Eventually, that hard work causes the heart muscle to give up (or fail).

Valve replacements can be entirely artificial (ie metal, usually titanium because it’s hard and doesn’t tarnish) or biological (from another human being who, of course, is dead) or even from another animal (usually a pig because pigs and humans have a lot in common).

Heart Failure

Heart failure is a mode of death and not, in itself, a natural disease. As such, it must be followed on a Death Certificate by what disease caused it. It merely means that the heart can no longer fulfill its function as well as it should. If it causes death, the failure is obviously profound.

But what does ‘failure’ mean? It doesn’t usually mean the heart stops, although technically it could. It usually means that its pumping action is no longer efficient and the heart’s output is reduced. People can live with cardiac failure for a long time.

Since the heart is in fact 2 pumps, heart failure can affect just the right side, or just the left side, or most commonly both. Because the ventricle(s) is/are no long pushing out the blood as well as it/they should, it/they dilate(s) (because blood is left in them when the heart beats) and there is a rise in upstream pressure. This is why the lungs fill with water in left or biventricular failure (the atria don’t contribute a great deal to the act of pushing blood out of the heart), because the pressure in the veins of the lungs increases. The blood coming out of the lungs is slightly thicker because water has been pushed out of the blood vessel walls.

This is also why ankles swell in biventricular or right side heart failure. it also affects internal organs such as the liver and can be so severe that the liver scars (‘cardiac cirrhosis’) and may even fail itself.

The water causes breathlessness (aka DYSPNOEA). It’s worse if the patient lies flat, which is why people with cardiac failure sleep with multiple pillows propping them up.

And if the heart is not pushing out blood as it should, arteries constrict to keep up blood pressure, and the heart enlarges because blood is not being ejected but it is still coming in from the veins. The kidneys need blood pressure because they are essentially just high pressure filters; they have their own mechanisms for making sure that the pressure of blood remains reasonable.

But why? Why does it fail?

It might be for one or more of a variety of reasons. Intrinsic problems with the heart muscle (reduced blood supply causing death of myocytes and fibrosis of the heart muscle due to coronary atheroma), myocarditis (where the heart muscle is inflamed, perhaps due to an infection), cardiomyopathy (in which the heart muscle is not normal), etc; or extrinisic problems such as hypertension. If the heart has to push blood out against raised blood pressure, it has to do more work, and eventually that tells.

THE HEART

The heart is not a pump.

It is TWO pumps.

You do not have a single circulation.

you have TWO (THREE, if you count the portal venous circulation as a separate circulation).

What the heart does is really very simple. The right side pumps blood around the lungs; the left side pumps it around the rest of the body. Those two circulations never mix, but they are linked. They may sit side by side, but essentially the left side of the heart is a pumping station downstream of the right side.

Each pump – the right side and the left side – is two chambers. An atrium (or ‘hallway’) and a ventricle (or ‘stomach’). There is a valve between the atrium and ventricle on either side, and a valve where the ventricle meets its circulation. The work of the valves is the same as all valves, to make sure that the pumped liquid goes in only one direction.

So, two pumps, each with 2 chambers and 2 valves. Simple.

Except that, for some reason, the heart is twisted around in the body, which makes it look more complex than it really is.

The right side of the heart only has to pump blood through the lungs (where it gets oxygenated), this then returns to the heart (the left side) which pumps it around the body where the oxygen is required for the cells to live.

Because the right side of the heart has relatively little work to do compared with the left, it is not as muscular. In fact, the thickness of the myocardium on the right is only a third that of the left in the normal heart.

What of the heart in the unborn baby? What of congenital abnormalities? More of these in later posts.