The process of circulation in which the blood circulates in the blood vessels of the heart. These vessels through which the oxygenated blood is delivered to the heart muscles (myocardium) are called coronary arteries.The deoxygenated blood is removed from the heart by the cardiac veins.
The blood is supplied by the coronary arteries to the heart. It cannot utilize the blood inside it. The anatomy of the coronary arteries is of use only to cardiac physicians who perform angiograms and cardiac surgeons who perform the coronary by-pass operation.
Unlike other arteries, the coronary arteries have very little collateral circulation, i.e. the coronary arteries are end arteries. When a major coronary artery is blocked, the heart muscle supplied by it dies ( myocardial infarction syn. heart attack). When the blood supply to the heart is reduced, the term used is ischemia. During ischemia, there may be a pain in the chest—angina pectoris.
Myocardial ischaemia is treated with drugs. However, in recent years 2 new techniques have emerged, namely:
1. Coronary by-pass operation. The blocked artery is bypassed by a graft of a vein.
2. Coronary angioplasty. A balloon is passed into the narrowed coronary artery and dilated to stretch the narrowed coronary artery.
Coronary Heart Disease
1. When circulation is blocked in the coronary arteries the particular part of the heart muscle which receives its blood supply from the blocked coronary artery dies because of lack of oxygen. The patient suffers from myocardial infarction or heart attack.
2. Because of death of heart muscle tissue, the rhythm of the heart may become irregular and the patient may die because of fatal arrhythmias. Majority of patients die duri ng the first few hours because of arrhythmias.
3. If the patient survives, the dead heart muscle becomes scar tissue.
4. If the damage is extensive, the heart goes into failure and the patient dies.
5. Usual cause of block is atherosclerosis or deposit of fats in the coronary arteries. After the first heart attack the patient may get a second heart attack and if he survives this, a third heart attack. The mortality rate is approx. 20% in the first attack and higher in subsequent attacks.
6. If the block is not severe and only a reduced quantity of blood reaches the heart, heart muscle may not die, but the patient suffers from pain called angina pectoris.
7. Angina may be precipitated by effort (angina of effort) or it may come on at rest (angina at rest).
8. There are now drugs for the treatment of angina. These drugs reduce the work load of the heart.
9. Drugs have become available which if given during the first 6 hours of a heart attack, dissolve the obstructing clot and reduce mortality. These are enzymes. Heart failure may be treated with specific drugs.
10. There are drugs which give some protection against heart attacks. One of these, is Aspirin which reduces the clotting tendency. Other drugs may also reduce the incidence of heart attacks, but definite supporting proof is not available.
Cardiac failure is the failure of the heart as a pump.
1. The chamber which usually fails is that which has toperform the maximum work, i.e. the left ventricle.
The usual causes are:
(a) High blood pressure
(b) Myocardial damage caused by coronary artery disease.
(c) Valvular damage which compromises the efficiency of the heart.
(d) Certain diseases with unknown causes, e.g. cardiomyopathy.
(e) Disturbances of rhythm of the heart, e.g. auricular fibrillation.
2. When the heart fails, the cardiac output falls. Most of the blood in the left ventricle is not pumped out (low ejection fraction).
3. The bad effects are 2-fold:
(a) Blood flow to the tissues is reduced. Of particular importance is fall in kidney blood flow which results in diminished urine output. Salt and water are retained. Blood volume may increase.
(b) Blood accumulates behind the left ventricle resulting in lungs (pulmonary blood vessels) getting overfilled with blood. The lung air space is reduced and the patient’s breathing becomes heavy and laborious. The patient gets out of breath—dyspnoea.
4. When heart failure becomes severe, the patient dies. once heart failur sets in. the usual duration of survival is not more than 5 years. However modern therapy may reverse early heart failur.