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CORONARY  ARTERY DISEASE  (CAD)
 

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Apart from organ transplantation procedures, coronary artery bypass (CAB) surgery is without doubt the most invasive surgery that is performed on the human body. It is so ironical that a surgery of such magnitude is necessitated if the subject is not able to effectively undertake lifestyle modification and effective treatment for maladies like hypertension, diabetes and obesity. CAB is usually performed as an ultimate recourse when all other measures like drug therapy and angioplasty/stenting etc are not able to ensure better conditioning for a diseased heart. CAB can be performed before or after an actual heart attack (myocardial infarction). CAB literally provides a new lease of life to those who undergo it. "Lease' yes, do not this term. CAB is just a temporary lease, and if the patient is still reticent about his diet, drug regimen, hypertension, diabetes and weight control, he/she is sure heading towards another CAB surgery. There are innumerable people who have undergone 2-3 CAB surgeries.

Coronary artery disease (CAD) is also referred to as as ischemic heart disease (IHD). This circulatory malaise starts taking shape with the gradual aging and narrowing of coronary arteries by cholesterol deposits (plaques). The diseased coronary arteries do not only fail to properly irrigate particular segment(s) of the myocardial muscle with blood & oxygen, eliciting a painful ischaemic (blood-deprived) response from that part of the heart. For sometime the heart tissue may survive with low oxygen supply (hypoxic state), but sooner or later the lining of the coronary artery becomes so diseased and damaged (structurally irregular) that blood clot (thrombus) may begin forming there (thrombosis). Soon, the clot may almost totally block blood supply to the affected part of the heart (coronary thrombosis) and the thus-targeted heart muscle instantly exhibits signs of damage (infarction) consequent to sudden oxygen-deprivation. This situation is called a full-blown heart attack or a myocardial infarction.

Reduced supply of oxygen to heart may result in a condition called angina (stable or unstable unstable), a full-blown heart attack (myocardial infarction), and also sudden cardiac arrest/death (especially at the time of sudden emotional or physical stress). In most CAD scenarios, the most common symptom is chest pain or discomfort which may (or may not) travel to (usually the left) shoulder, arm, back, neck, or jaw. People often tend to confuse such discomfort with gastric issues like heartburn of gas episode. Such episodes of chest region pain/discomfort may last just a few minutes or less, and may even get better with rest. During this period of distress there may be shortness of breath as well, accompanied by mild or profuse sweating may also occur. One may feel somewhat giddy, and unsteady as well ... there may be a tendency to lapse into short spells of drowsiness. It is indeed strange that sometimes no such symptoms may be present (silent episodes in diabetic or hypothyroidism patients). All these symptoms indicate the onset of a heart attack, though almost similar symptoms may be present with some other complications like heart failure or an irregular heartbeats (cardiac arrhythmias). At times, merely coronary artery spasms (pseudo heart attacks) may also trigger the same set of symptoms

The major risk factors towards developing CAD include smoking, hypertension, chronic diabetes, sedentary lifestyle, moderate to acute obesity, high blood cholesterol, and overindulgence in rich food and alcoholic drinks. Organically, the underlying mechanism for deteriorating oxygen supply to heart involves atherosclerosis and/or arteriosclerosis (thickening & narrowing of arteries). Quite a few diagnostic tests like electrocardiogram (also ambulatory electrocardiogram, cardiac stress testing, coronary computerized tomographic angiography, and coronary angiogram/angiography etc.

Prevention or delaying the production of these degenerative change in the body requires (i) healthy diet, (ii) regular light exercise, (iii) optimal weight management, (iv) not smoking, and (v) going easy on diet including saturated animal fats and alcohol. Regular and effective medication for diabetes, high cholesterol, or hypertension must always be continued. Treatment of CAG involves, besides the preventive measures just mentioned, therapy with anti-platelet drugs (aspirin or others), beta blockers, or nitroglycerin. Procedures such as percutaneous coronary intervention (PCI) or coronary artery bypass surgery (CAB) may be used in severe disease.


We do not tend to describe here the detailed procedure of coronary bypass surgery, which is resorted to, if at all necessary, and only following confirmation of the patient's clinical assessment upon a preliminary coronary angiographic investigation. If the state of the health of the coronary arteries doesn't warrant a CAG (coronary artery graft) the coronary blockage is treated more conservatively (though the technique is still quite invasive) by what is referred to as balloon angioplasty and/or stenting. The purpose of such procedure is to mechanically dilate (with medicated or non-medicated stents) the narrowed coronary arteries. The procedure may have to be repeated over a few years, just as CAG may need to be repeated if there is a clinical recurrence of the original ischemic or thrombogenic problem.

Angioplasty is an invasive procedure designed to alleviate CAD or angina pectoris (see below)  by physically opening up narrowed blood vessels. It is similar to cardiac catheterization (see below in angina prectoris), except that a a catheter with a balloon tip is inserted into the coronary arteries while the process is being followed on a fluoroscope monitor, a special type of mobile X-ray. As the catheter reaches the targeted narrowed segment, the balloon is then inflated to flatten the plaque. In a new variation, a rotating blade similar to a tiny roto-rooter shaves the plaque into tiny particles, rather than simply flattening it out. In another variation, a laser beam is used to vaporize the plaque.

Coronary bypass surgery is reserved for for severe coronary disease that cannot be adequately controlled with drugs and is not amenable to angioplasty either. Segments of healthy blood vessels from either an artery in the chest or a vein in the leg, are used to bypass severely narrowed/blocked parts of the coronary arteries. Up to seven or eight bypass grafts may be done in a single operation, thus greatly enhancing blood irrigation to the myocardium and consequently reducing the incidence of angina and the risk of a heart attack. The surgery usually takes 3-4 hours, although some complicated cases require as many as 8-10 hours. The patient spends 2-3 days in an intensive care unit (ICU) or coronary care unit (CCU), and another 5-7 days in the hospital. Even though the operation is usually considered safe, it is not entirely risk-free, and the potential dangers must be weighed against the benefits that are expected.

One of the very common manifestation of CAD is the disease called angina pectoris (hurtful pectoral or breast muscles). Angina is a recurrent and troublesome chest pain under the breastbone (sternum). often spreading to the neck, jaw, arms, and upper back, but it is usually described as a sensation of pressure, tightness, heaviness, or even choking, and is often accompanied by shortness of breath. Severe angina or an episode of sudden coronary vasospasm may feel like an actual heart attack itself, but is a temporary condition that doesn't cause any permanent damage. It does, however, signal the risk of a possible impending heart attack. Angina occurs when the myocardium (heart muscles) is not getting enough oxygen. The most common cause is atherosclerosis, a narrowing of the coronary arteries due to deposits of fatty plaques of cholesterol. These narrowed arteries may be able to deliver enough oxygen-rich blood to the heart muscle to carry on normal activities. But when the heart is made to work harder such as during unaccustomed physical exertion or periods of stress, the heart muscle becomes starved of oxygen (ischemic hypoxia) and elicits pain response. Simple activities like a rather heavy meal or exposure to cold weather may also precipitate angina as the blood flow is diverted from the already poorly irrigated coronary arteries to other parts of the body for temporarily enhanced blood-supply requirements of those regions. Some people experience angina even while resting or actually sleeping. Such unprovoked, or variant angina, is at times caused by a spasm in the coronary arteries, usually at the site of localized fatty deposit. More often, it is classifies as unstable angina, and is a sure warning sign of an impending heart attack.

There is no specific test for diagnosing angina as such, but the cardiologist can invariably draw a conclusive opinion after talking to the patients about the details of his angina episodes. Routine tests include an electrocardiogram (ECG or EKG), BP measurement, some blood & urine tests, and a chest X-ray. If at all the doctor suspects angina, additional tests may be ordered to be able to correctly assess any underlying heart ailment. An exercise stress test  can usually confirm that physical stress brings on ischemia (and elicits pain). This may at times be accompanied by echocardiography (an examination using high frequency sound waves, or even nuclear scanning, in which thallium or some other radioactive substance is injected into the blood stream and then tracked by special gamma cameras. These last two tests can often pinpoint the areas of the heart muscle that are deprived of blood/oxygen. A more invasive procedure, cardiac catheterization, is needed to make a precise diagnosis of the actual state & progression of 'coronary artery disease'. In this examination, a thin, flexible tube is inserted into an artery in the leg (or less commonly, the arm) and worked all the way up to the heart. A dye is then injected into the coronary arteries to make them visible on X-rays.

There are numerous effective medical treatments available for angina, ranging from exercise-conditioning and medication to surgery. Depending upon the severity of symptoms and degree of coronary disease, lifestyle changes and drugs are usually tried first, with surgery reserved only for the cases that cannot be effectively controlled by more moderate and less invasive approaches. After an exercise stress test, z doctor prescribes a regimen of physical activity designed to increase endurance without provoking angina. Patients are taught to monitor their heart rate, and to increase their exercise (intensity or duration, or both) gradually. Such conditioning prompts the coronary arteries to grow collateral circulation (natural, pre-emptive bypass) over a period of time, thus increasing blood flow to the affected segments of the myocardium receiving inadequate blood/oxygen.

There are numerous drugs that can control or prevent angina. The choice depends on the circumstances and whether or not there are other contributing factors like hypertension. Two classes of drugs - nitrates and calcium channel blockers - open or dilate the coronary arteries, allowing more blood to flow through them in partial compensation of what would have otherwise been possible in the diseased artery. This actions also lowers blood pressure in a dose-dependent way, reduces heart's workload, and increases blood flow to the myocardium. A third class of drugs, beta-blockers, alleviates angina by reducing the action of norepinephrine, a neurotransmitter that carries signals that carries signals from the sympathetic nervous system. Blocking these signals also reduces the heart's workload by allowing it to beat slower and less forcefully than usual.

Calcium-channel blockers  and beta-blockers are taken daily to prevent angina, nitroglycerin - the most commonly prescribed nitrate - is used both to stop and prevent angina. During an attack, a nitroglycerin pill placed under the tongue or in the cheek pocket is absorbed rapidly into the bloodstream, usually providing relief within 5 minutes or so. The effect wears of quickly, however, for more sustained or preventive action, nitroglycerin is also available as a skin patch or ointment. In these forms, the drug is slowly absorbed through the skin, thus providing protection from attacks.

ANTI-PLATELET DRUGS & CLOT-BUSTERS IN CAD