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Heart Disease

Let us now discuss how coronary artery obstructions affects the heart.

What is ischaemic heart disease (IHD)?
Angina and heart attacks are both manifestations of coronary artery obstruction due to fatty ( cholesterol) deposits in the wall of the artery, thereby reducing its lumen ( cavity) and, consequently, the flow of blood to the corresponding portion of the heart muscle. This reduction in blood supply is called ‘ischaemia’, and the disease of the heart caused by this condition is called ‘ischaemic heart disease’ or IHD for short. It is also called coronary artery disease ( CAD). Various types of angina and heart attacks ( myocardial infarction) are manifestations of IHD.
Figure 5 illustrates a normal unobstructed artery (a), a partially obstructed artery ( b), and an almost completely blocked artery ( c).

How Does a partially obstructed coronary artery affect the heart?
The amount of blood flowing through a partially blocked coronary artery will naturally be less than normal, the reduction being proportional to the degree of obstruction. This reduced blood supply may be perfectly adequate for normal functioning of the heart when at rest, but, during exertion, the heart rate and the work load of the heart go up, increasing its oxygen requirement. This requirement has to be met by increased blood supply. Due to the obstruction, the blood supply cannot be augmented beyond a certain limit. This causes lack of oxygen in the heart. The heart muscles cries with pain, which we call angina pectoris or, for short, angina. The pain is relived if the patient stops exertion bringing down the heart rate and, consequently, its oxygen requirement. When the blood supply matches the oxygen demand of the heart, the pain resulting from angina stops.

Do the attacks of angina cause damage to the heart ?
An episode of angina is a temporary imbalance between the supply and demand of oxygen to the heart muscle. The pain lasts for a few minutes, up to a maximum of 20 minutes. It does not cause permanent damage to the heart muscle.

How does complete obstruction developing in a coronary artery affect the heart?
If the obstruction becomes complete, little blood or no blood can flow across the obstruction. The corresponding segment of the heart muscle is acutely and severely deprived of blood and, consequently, of oxygen. This severe ischaemia cannot last long without necrosis and the death of the affected tissue. This is called myocardial infarction or simply heart attack.

What causes the complete obstruction in the coronary artery?
This may be caused by thrombosis ( clotting of blood) occurring on the cholesterol deposit, or by spasm of the artery, or both.

Is it correct to say that both angina and heart attack are basically the two sides of the same coin?
Yes, absolutely. As you have seen, the basic cause of both angina and infarction is coronary artery obstruction. It is the same process which causes various manifestations of ischaemic heart disease in varying degrees of severity, depending upon the degree of coronary artery obstruction. There is a wide spectrum of variations, and, therefore, no two cases are exactly alike in severity and seriousness.

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