Cardiology Teaching Package
A Beginners Guide to Normal Heart Function, Sinus Rhythm & Common Cardiac Arrhythmias
Atherosclerosis
In this process, fat sticks to the lining of the arteries. As it thickens and hardens into a plaque (this process takes decades to develop), it continues to absorb fat which eventually begins to retain its fluidity. (see above). As the soft lipid core grows, the fibrous cap that holds it in check begins to stretch and thin out, ultimately rupturing and releasing the soft lipid core which is "thrombogenic", causing platelet adhesion and aggregation.
Thrombogenic material is material which starts a chain of chemical reactions leading to the creation of a thrombus, or clot.
It is important to understand that atherosclerosis, or "furring up of the arteries", is not a uniform process where the arteries all become narrower over a period of time, like calcification in lead pipes. Atherosclerosis often resembles a mountain range with peaks and valleys.
Imagine a mountain rage where there is cloud cover. The mountains emanate from one wall of the artery and the clouds are the opposite wall of the artery. At the top of the mountain the clouds are very close to the peak, but in the valley between the mountain there is lots of space. Now imagine the weather worsening and the cloud cover falling until it touches the peak of one of the mountains leaving no space.
Atherosclerosis is an uneven development which leads to some areas becoming very narrow indeed, and other areas being seemingly unaffected. All tissues in the body require oxygen to function properly. As the process of atherosclerosis causes narrowing in certain areas of the coronary arteries, it reaches a point at which there is not enough space left in the artery at that point for an adequate amount of blood and oxygen to pass through. (This is where the mountain peak is very close to the clouds.)
If there is not enough oxygen reaching the heart muscle to fulfil it's needs, the heart muscle becomes "ischaemic", in other words it begins to starve, just like a person who does not receive an adequate amount of food every day. This is Angina.
And if the oxygen is completely cut off (this is where the cloud cover falls so low that it meets the mountain peak), the heart tissue begins to die, just like a person who received no food whatsoever. This is a myocardial infarction.
