I have danced around this subject for a long time – as regular readers may have noticed. One of the problems in this area is that you have to start with definitions. Which is somewhat tedious, but also rather necessary? Last week, for example, I read someone argue that we should not use the word cancer, we should talk about cancers. Which is true. Multiple myeloma and pancreatic cancer are both usually called cancers, but they don’t have a great deal in common.
Heart disease is also a pretty meaningless term. Do you mean pericarditis, hypertrophic obstructive cardiomyopathy, aortic stenosis, coronary artery disease etc. et bleeding cetera. In fact, in 1948 the World Health Organisation, recognising the need for accurate definitions, made the first stab at creating an international disease classification (ICD) system. Prior to this, for example, Ischaemic heart disease did not exist. Which meant that you could die of a myocardial infarction in the US, but you could not do so in France – because the French had no term for such an event.
Issues such as this mean that trying to look back in time to ascertain death rates from specific diseases in different countries is a fairly pointless exercise. The French, just to pick on them again, did not accept the ICD system until 1968 – typical, you might say. Even when countries do accept the ICD system, it is difficult to be certain that people are using it in the same way. When I started in medicine a very common diagnosis at death, in the elderly, was bronchopneumonia. ‘The old man’s friend.’
Essentially, when an old person died, and you weren’t really sure what they died of, you put down bronchopneumonia. Try doing that today and the local coroner will be on the phone before you can say Harold Shipman. Now you have to die of something rather more specific – even if the patient is a hundred and two and have been going downhill for the last year.
‘I think they died of old age, Mr Coroner sir. But please sir can I write bronchopneumonia.’
‘Bronchopneumonia! You want more bronchopneumonia!’
In the UK we have now conquered bronchopneumonia. Today, the scourge that used to wipe out millions of elderly people, hardly kills anyone at all. Hooray, great celebrations, all around. My goodness it is a miracle of modern medicine… or not.
Yes, be very careful with medical definitions, and not just because they can often just follow the fashion of the day. Also, because, once you think you have defined something this can constrain your thinking to a painful degree.
Ischaemic heart disease would be what most people think of as heart disease. But just for starters, it is not a disease of the heart; it is a disease of the arteries supplying blood to the heart – through the coronary arteries. The ‘disease’ itself is atherosclerosis (thickening and narrowing of the arteries), and the condition underlying this atherosclerotic plaque development.
This is, sort of covered by ICD 414.0
414.0 Coronary atherosclerosis
Atherosclerotic heart disease
Coronary (artery) sclerosis
But is 414.0 what actually kills you? You can have coronary arteries blocked up to 70:80:90 even 100% without having a heart attack a.k.a. a myocardial infarction:
‘We conclude that total occlusion of the major coronary artery occurs commonly in patients with chronic coronary disease, but is associated with myocardial infarction in only 65%.’2
On the other hand you can find people with completely clear coronary arteries who have died of – what has been clearly diagnosed as – a myocardial infarction. Here is a paper from the European Heart Journal published last year, entitled: ‘Acute myocardial infarction with no obstructive coronary atherosclerosis: mechanisms and management.’
‘Myocardial infarction with no obstructive coronary atherosclerosis (MINOCA), a syndrome with several causes, is frequent in patients admitted with the diagnosis of M (myocardial infarction ‘heart attack’ my words). An accurate and systematic diagnostic work-up, is crucial for the identification of the cause of MINOCA in each individual patient, and then for risk stratification and for the implementation of the most appropriate forms of treatment. Yet, patients with MINOCA, in particular those with angiographically normal-coronary arteries, are frequently labelled as ‘non-cardiac patients’, thus missing the opportunity to appropriately treat patients with an outcome worse than previously believed.’1
In this study they found that about 5 – 25% of those admitted with ‘infarctions’ had no coronary atherosclerosis. So ischaemic heart disease/MI can very frequently occur without the presence of any atherosclerotic plaques at all.
Unfortunately, the plot thickens even further. In many cases it can be found that a large blood clot (thrombus) can form in an artery days or weeks before the myocardial infarction actually occurs.
Here is an interesting little section from an article with a very boring title: ‘The temporal relationship and clinical significance of plaque substrate in healing coronary thrombi from sudden deaths attributed to rupture and erosion.’
‘Although the morphology of the culprit plaque has been extensively studied, especially rupture, relatively little is known about the temporal relationship between the onset of acute coronary events and thrombus maturation. The occurrence of nonlethal ruptures recognized by accumulated fibrous tissue at healed repair sites suggests that healing thrombi represent an episodic cycle of lesion progression. Moreover, thrombi from fatal plaques are in various stages of healing, further suggesting that death might not necessarily coincide with the initial onset of thrombus formation.’3
Now, in English.
The thrombus ‘clot’ formation – the thing that is supposed to kill you within minutes of hours after forming – may well not actually occur shortly before you die. It can occur days or ever weeks earlier. Which mean that, in many cases the thrombus forms, the artery blocks, and nothing happens until – in some cases – weeks later.
This does not really fit with the current model of heart disease, which is very simple, and it goes something like this:
- The coronary arteries gradually narrow and thicken.
- At some point, a thrombus forms on top of one of the narrowest bits (the plaque),
- This blocks the artery completely.
- The heart muscle then rapidly runs out of oxygen and infarcts (dies).
- In around 50% of cases you die as the heart stops beating, or goes into fibrillation – or suchlike
I call this the plumbing model of heart disease. Pump, pipes, blockage to the pipe in the pump …death. However, you can have final stage 100% occlusive atherosclerotic plaques without an MI. It is also perfectly possible have an MI without atherosclerosis. In addition, the formation of a thrombus does not necessarily correlate in any way, in timescale, with the MI – at all.
Because of all these problems with the current model, it would be perfectly possible to argue that we have the entire process of ‘heart disease’ the wrong way round. Indeed, I regularly communicate with a Brazilian called Carlos Monteiro, a researcher who proposes the myogenic theory of heart disease. He believes that the MI starts within the heart muscle itself, and the clot in the arteries comes afterwards.
His reasoning – following on from the work of his father in Law, the cardiologist Dr Mesquita is, as follows:
- Clinical observations showing the absolute lack of efficacy of anticoagulants in the treatment of unstable angina pectoris. Unstable angina is considered to be a stage leading to myocardial infarction
- The strong correlation of myocardial infarction with stress or unusual physical activity
- Frequent coronary angiographies showing no obstructions in the presence of myocardial infarction
- Many anatomic-pathological studies have demonstrated no relationship between thrombus and infarction, which led many authors since the 1940s to consider coronary thrombosis—the clot in the arteries—as a consequence of acute myocardial infarction, not its cause
- The development of coronary thrombus after a heart attack, demonstrated experimentally4
True or false, right or wrong? Can the myogenic theory explain more of what we actually see? Yes, no, maybe. Personally, I don’t think his theory is correct in totality, although it has many correct bits in it. Causality is always a bugger, which way round do things go? This before that, or that before this? Are things actually related at all?
Sorry to say that I provide no further explanations. Or this blog would end up three hundred pages long, and I will not impose such a thing on anyone. What I hope to have made clear is that we have models and definitions of heart disease/IHD/MI that cannot be considered even remotely adequate. Whatever is going on, it is a far more complex and interesting thing than the plumbing model.
Which boils down to one simple thing. Namely that to ask the question, what causes heart disease, is easy. But in order to try and answer it we have to establish, as clearly as is possible, what the bloody hell is this disease? If find that you cannot find the answer to anything whilst sinking into a bog, or staring into the fog. Both of which seem the activities of choice of my cardiology colleagues.