What is the final event?
(The upside down*)
The final event in most heart attacks, and strokes, is the development of a large, and often fatal, blood clot. If this happens in an artery in the heart, a coronary artery, it cuts off blood supply to an area of heart muscle and can lead to a myocardial infarction (MI) [myocardium = heart muscle, infarction = death of tissue due to lack of oxygen].
There is a related, but different mechanism of action, in most, strokes. In this case a blood clot that has formed in an artery in the neck (carotid artery), breaks off and travels to the brain where it gets stuck, blocking an artery. This leads to a cerebral infarction. There are other forms of stroke, with other causes, but this is the most common.
These are generally accepted models, and for the sake of brevity, it is also the model I am using here. Although I accept that it is not that simple. For example, you can have an MI with no blood clot found. Here, from a paper entitled: ‘Acute myocardial infarction with no obstructive coronary atherosclerosis: mechanisms and management’:
‘Myocardial infarction (MI) with no obstructive coronary atherosclerosis (MINOCA) is a syndrome with different causes. Its prevalence ranges between 5 and 25% of all MIs.’1
A heart attack with no blood clot. In truth, I think this can be easily explained, within the ‘obstructive’ model, but it would take too long for this blog. I will cover it at some point.
Anyway, to get back on track. It is generally accepted that the final event in cardiovascular disease is the formation of a large blood clot. This is the thing that causes both fatal, and non-fatal, strokes and heart attacks. Which is why atherosclerosis, as a disease, is often referred to as atherothrombosis. The idea being that atherosclerotic plaques gradually build up, over decades. In the final stage, the plaque ‘ruptures’ triggering the formation of a large and deadly clot.
The suggestion here, never ever explicitly stated, is that we have two different processes in operation. Plaque formation, then the blood clot. Or maybe you could look at this as one process, in two parts. Plaque growth, then plaque rupture – causing thrombus formation.
However, it is perfectly possible for thrombi to form with no underlying plaque, so the two processes need not be associated with each other. People with Hughes’ syndrome, for example, can die of strokes and heart attacks quite suddenly, caused by blood clots, with no plaque to be seen. [Hughes syndrome causes the blood to be highly likely to clot – hypercoagulable].
Which leaves the question hanging somewhat. Do we have one process – or two? I believe that the main reason for using the term atherothrombosis, is because this allows mainstream thinking to draw everything together as different manifestations of the same underlying process. Raised cholesterol causes plaques, these rupture, then a clot develops (which would not have formed had the plaque not been there). This allows clear wiggle room, but at some point you must decide, one process or two. This is not quantum physics.
In my world, it is far simpler. There is only one process. Atherosclerotic plaque are simply blood clots, in various stages of growth and/or repair. Plaque growth represents the formation of a new blood clot, at the same point, which is not cleared away properly. The final ‘thrombotic’ event is just a big enough clot forming to do real damage.
The first time I started to think about this seriously, was when I was reading a paper called ‘A Definition of Advanced Types of Atherosclerotic Lesions and a Histological Classification of Atherosclerosis. A Report From the Committee on Vascular Lesions of the Council on Arteriosclerosis, American Heart Association.’ The things I do for fun … clearly, I am just a geek.
Anyway, this paper rambled on and on, and on. Until, whilst propping my eyelids open, my interest suddenly sharpened as I came across the section on the definition of Type V(a) atherosclerotic plaques – don’t ask. For those who enjoy a bit of scientific jargon, here it comes. If you don’t care for jargon, just look at the text I have put in bold at the end.
‘Sequential histological studies of the lesions of large populations indicate that reparative connective tissue forms in and around regions of the intima in which large accumulations of extracellular lipid (lipid cores) disarrange or obliterate the normal cell and intercellular matrix structure. Sometimes the new fibrous tissue accounts for more of the thickness of the lesion than does the underlying lipid accumulation.
The new tissue consists of substantial increases in collagen and smooth muscle cells rich in rough-surfaced endoplasmic reticulum. In cases in which this tissue is particularly thick, some or much of it may be the remnant of thrombi that were incorporated and organized. Capillaries at the margins of the lipid core may be larger and more numerous than in type IV lesions, and they may also be present in the newly formed tissue. Lymphocytes, monocyte-macrophages, and plasma cells are frequently associated with the capillaries, and microhemorrhages may be present around them.
Type Va lesions may be multilayered: several lipid cores, separated by thick layers of fibrous connective tissue, are stacked irregularly one above the other. The term multilayered fibroatheroma can be applied to this morphology. The lipid core that is deepest and closest to the media may have formed first. Mechanical forces may play a role in the modeling of such lesions.
Additional lipid cores in locations and planes different from the first could be induced as asymmetric vascular narrowing and changes in lumen configuration modify hemodynamic and tensile forces, creating a redistribution of the regions of predisposition for lesion formation.
The architecture of some multilayered fibroatheromas could also be explained by repeated disruptions of the lesion surface, hematomas, and thrombotic deposits. Organization (fibrosis) of hematomas and thrombi could be followed by renewed accumulation of macrophage foam cells and extracellular lipid between the newly formed fibrotic layer and the endothelial surface.’ 2
In layman’s terms what does it mean? It means that a number of plaques look exactly as if they were created by the repeated formation of blood clots, one on top of another. A concept further reinforced, when the paper looked again at thrombosis.
‘It has been reported that advanced atherosclerotic lesions containing thrombi or the remnants of thrombi are frequent from the fourth decade of life on. In 1975 Chandler and Pope compiled and reviewed studies that reported the frequency and nature of lesions with incorporated thrombi.
In a recent study of a population aged 30 to 59 years, 38% of persons with advanced lesions in the aorta had thrombi on the surface of a lesion. These thrombi ranged in size from minimal (microscopic) to grossly visible deposits, and some consisted of stratified layers of different ages. Immunohistochemistry revealed wavy bandlike deposits related to fibrin within the advanced lesions of an additional 29% of persons. Because of their structure, these were thought to represent the remnants of old thrombi. Similar data were reported by other authors.
The fissures and hematomas that underlie thrombotic deposits in many cases may recur, and small thrombi may reform many times. Repeated incorporation of small recurrent hematomas and thrombi into a lesion over months or years contributes to gradual narrowing of the arterial lumen. Some thrombi continue to enlarge and occlude the lumen of a medium-sized artery within hours or days.’
Perhaps the key sentence here, from my point of view, is the following:
‘Repeated incorporation of small recurrent hematomas and thrombi into a lesion over months or years contributes to gradual narrowing of the arterial lumen.’
Here, right here, is proof of the concept that plaques definitely do grow through repeated thrombus formation at the same point on the artery. Do all plaques do this? My own belief is that they do, but in many cases the repair mechanisms and other factors disrupt a clear picture of layered plaque growth. Essentially, the core of the plaque turns into mush (known as a lipid core) which obliterates evidence of how the plaque actually grew.
What else supports the idea that plaques are, in reality, blood clots? Well, very early on in their development, rather than in the third or fourth decades of life, you can find high levels of fibrin and fibrinogen, which are key components of blood clots. Here from a paper ‘Lipids and plasma fibrinogen: early and late composition of the atherosclerotic plaque.’
‘The precursor of large fibrous plaques appears to be the gelatinous lesion, which is characterized by oedema, accumulation of large amounts of low density lipoproteins and fibrinogen in the expanded interstitial fluid space, deposition of fibrin, and smooth muscle cell proliferation. It is postulated that deposition of fibrin may be a key event, stimulating smooth muscle cell proliferation by providing a scaffold for migration, a source of fibrin degradation products which are mitogenic, and binding thrombin. Fibrin may also be a factor in lipid accumulation because it binds lipoprotein (a) with high affinity, and may also bind low density lipoprotein.’3
In short, early plaques contain a lot of fibrin (key component of a blood clot), also lipoprotein (a), which is LDL with a different protein attached. Fibrin binds to Lp(a) forming very stable, and difficult to remove, blood clots. So, it is not just in type V(a) plaques that we find evidence of blood clotting. We find it very early on as well.
Sorry, If I am getting a bit jargonified at this point – if that is indeed a word. But I am aware that some highly trained scientific people do cast their eyes over this blog, and I do not want to make this too broad brush. Also, here, I am discussing the very core of my ideas about CVD, and I want to be as accurate as I can be. Equally, I do not want to put people off by delving too deep.
So, at this point, I shall only look at one more highly scientific study, which I think is important. One of the things I always tend to do, is to look at extremes. By which I mean populations with the highest rates of CVD, or medical conditions that accelerate CVD, and suchlike.
I believe answers are to be found at the extremes. To that end I became very interested in people who received heart transplants. For they, unfortunately, develop atherosclerosis at a very high rate. It tends to be called vasculopathy, as it is not exactly the same as atherosclerosis, but that may simply be a result of how fast it develops.
‘Cardiac allograft vasculopathy (CAV) is the major cause of long-term mortality after heart transplant (HTx). Cardiac allograft vasculopathy has heterogeneous pathologic features characterized by vascular wall inflammation, fibrous intimal thickening, and atherosclerosis.’
I believe that, because it is developing quickly, it is possible to see ‘plaques’ forming and growing in a way that is very difficult in the rest of the population. Or, to put it another way, we have an accelerated model of CVD, where things are revealed that may normally be hidden.
Here is the key section from the paper: ‘Repeated episodes of thrombosis as a potential mechanism of plaque progression in cardiac allograft vasculopathy.’
In conclusion, our observations demonstrate that a finding of ML (multi-layered) appearance, which may be indicative of repeated episodes of mural thrombosis, is not infrequent in asymptomatic cardiac transplant recipients. These findings may contribute to progression of cardiac allograft vascolopathy (CAV). The current study gives new insight into the potential role of coronary thrombosis in plaque progression in CAV.’4
Once again, repeated thrombus formation and plaque growth, causing multi-layered plaque progression.
I shall finish here by quoting myself in a previous blog:
‘Interestingly, at one point Pfizer also started to promote atherothrombosis as the cause of heart disease. For sentimental reasons I have kept hold of an educational booklet produced by Pfizer in 1992. On page four it states:
‘Several features of mature plaques, such as their multi-layered pattern, suggest that the platelet aggregation and thrombus formation are key elements in the progression of atherosclerosis. Platelets are also known to provide a rich source of growth factors, which can stimulate plaque development.
Given the insidious nature of atherosclerosis, it is vital to consider the role of platelets and thrombosis in this process.’ [Well, quite]
There is little point in referencing this document, as I probably have the only copy left in existence. It is called ‘Pathologic triggers. New insights into cardiovascular risk.’ Produced by Medi Cine Inc. For Pfizer Inc Copyright 1992, All rights reserved etc. etc.
It is interesting that when Pfizer did not have a statin, they were looking away from cholesterol as a cause of cardiovascular disease. It will come as no surprise to you that this was not through some altruistic attempt to discover the truth about the true cause of heart disease. It was to help market their drug doxazosin (a BP lowering drug) which had some additional anticoagulant properties.’
Of course, I have not answered all questions here. But I wanted to give you some insight as to my core thinking on CVD. Having jumped around for years I decided to start at the end, the final blood clot, and then worked backwards.
Was it possible, I asked myself, that blood clotting was not just responsible for the final clot, but also for the entire process of atherosclerosis? I believe that the evidence is out there, and clearly supportive, if you choose to look at it this way round.
I suppose you could say that I do not believe in atherothrombosis. I believe in thromboatherosis (you’re right, I just made that word up). In thromboatherosis, plaques start, and grow, through repeated thrombus formation at the same spot in an artery. In the end, a clot gets big enough to cause a stroke or heart attack. Sometimes the clot can be big enough to kill, without any underlying plaque, but normally it will form over an already existing plaque – where plaque rupture can be the trigger.
In short, there is only one process in CVD. It is the development of atherosclerotic plaques through repeated thrombus formation, followed by the final thrombus formation. As you can see this is actually very close to mainstream thinking. The only difference is that you have to flip your thinking through one hundred and eighty degrees, to see it upside down.
*for those who enjoyed Stranger Things
P.S. Pop quiz. Why do plaques never develop in the heart itself? Here the pressure is highest, damage to endothelium must be greatest and yet, and yet, no plaques – ever.