Thallium Heart Test

Thallium scan of Heart

The concept of introducing a radioactive substance into the body for diagnostic purposes has been in practice for more than three decades. Radioactive iodine is being used for diagnosis and treatment of various thyroid gland diseases. The isotope scan is also used for assessing kidney function and for diagnosis of spread of different cancers in body. The isotope emits radioactive energy scintillates (lights up) in a gamma camera. Radioactive particles like thallium and MIBI (methyl isonitryl butyl isonitryl) scan are frequently used for the diagnosis of coronary artery disease. Thallium scan and MIBI scan are almost like a conventional stress test. The test is also carried out like a conventional exercise test. The patient is exercised (walking fast or running of a treadmill) until near fatigue or development of chest pain. The isotope is then injected through intravenous route in one hand vein. Then the test is terminated. The patient then lies down while a gamma camera is focused on the heart. This camera then takes multiples picture of the heart at different angles. Thallium and MIBI is preferentially taken up by viable myocardial (heart muscle) cells in the presence of normal coronary flow with out any block. Areas of the heart which are supplied by stenos ed or blocked coronary artery can not take thallium or MIBI normally and shows impaired uptake of the isotope. This defect documented by gamma camera is called perfusion defect. In this test perfusion at rest and at peak exercise are also compared to document reversibility of blood flow. Thallium scan is superior to exercise ECG test in the diagnosis of coronary artery disease. The accuracy of isotope scan has been shown to be around 95% in the detection of significant blockage in coronary artery as opposed to 75-85% in the case of the conventional exercise ECG test. Exercise ECG can detect coronary artery block but can not accurately detect the territory of muscle involved and how much muscle is in threat. The added advantage of isotope scan over a conventional exercise ECG test is the ability to localize the blocked coronary arteries. The pump function of the heart can also be assessed by isotope scanning. This heart function test is called MUGA scan. Coronary angiogram is a invasive test which carries definite risk so difficult to perform repeatedly for the evaluation of continued patency of coronary arteries after balloon angioplasty and by-pass operation. But isotope scan can be done repeatedly on the same patient in evaluating continued patency of coronary arteries after balloon angioplasty and by-pass surgery. That’s why nuclear cardiology has established itself as a most useful non-invasive diagnostic modality. These procedures do not require any special preparation on the part of the patient. It is a safe procedure and the isotopes used exhibit very low radioactivity.

High cholesterol and Heart Attack

High blood cholesterol and heart attack

Cholesterol is a complex fatty substance produced by liver for various functions in the body. The amount of cholesterol in our food also contributes to the cholesterol level in blood. If we take excess amount of cholesterol rich food it well predisposes us to increased risk of heart attack. Any excess of cholesterol results in the deposition of cholesterol in the arteries resulting in narrowing and hardening of the arteries (atherosclerosis). When the narrowing of the artery becomes severe enough to result in insufficient blood supply to the heart, chest pain (angina) occurs. The chest pain usually occurs on exertion and is usually relieved by rest. When the artery is completely blocked, the portion of the heart muscle supplied by the artery will be damaged, resulting in heart attack.

Basic research and evidence from observational studies and clinical trials have shown a consistent positive relation between the blood cholesterol level and the risk of heart attack. Recent overviews have indicated that a I percent reduction in a person’s total blood cholesterol level yields a 2 to 3 percent reduction in the risk of coronary heart disease. The seven countries study found that coronary artery disease was less common in Japan and Mediterranean countries (where the average diet is low in cholesterol and saturated fat) than in the United States. Finland and Netherlands (where the cholesterol and saturated fat content of average diet is higher). In the United States, the Framingham Heart Study and more recently the Multiple Risk Factor Intervention Trial (MRFIT) have shown that the incidence of coronary artery disease is positively associated with blood cholesterol levels in a continuous, graded and progressive manner. By reducing the blood cholesterol level to normal the risk of heart attack can be decreased by 23%. In the Oslo study the smoking cessation and cholesterol lowering resulted in 47% reduction of heart attack and sudden death compared to control.
Cholesterol in blood is carried in two main forms, low density lipoprotein (LDL) and high density Lipoprotein (HDL). LDL is called bad cholesterol and HDL is called good cholesterol. High LDL cholesterol is associated with atherosclerosis (blockage of coronary artery). HDL cholesterol or good cholesterol removes excess bad cholesterol from the arteries. It is good for the HDL cholesterol to be high and the LDL cholesterol to be low. The role of another blood lipid, triglyceride in producing heart disease independently is questionable. But a recently published study, Helsinki Heart Study documented an inverse relation between elevated triglycerides and low level of HDL that may be reversed with treatment by Gemfibrozil.
The public health effect of the National Cholesterol Education Program’s guidelines is great. Their aim is to lower mean blood cholesterol levels to less than 200 mg% (5.2 mmol per liter), primarily by decreasing the total fat content of the diet to below 30% of total calories and saturated fat to below 10%. The HDL level is to be kept above 55 mg%. A mean 11% increase in the level of HDL cholesterol (good cholesterol) corresponded to a 34% decrease in the incidence of coronary heart disease.

Aspirin for Heart attack

Can low dose aspirin prevent heart attack?

Attention has recently focused on the possible role of prophylactic low-dose aspirin in reducing the risk of heart disease. The hypothesis that platelet inhibition with low-dose aspirin reduces the risk of heart attack n apparently people have been tested in two trials of primary prevention in men. The U.S physicians Health Study of 22,071 men 40 to 84 years of age observed a statistically significant 44% reduction in the risk of first heart attack whereas the British Doctor’s Trial of 5139 men 50 to 79 years of age observed no significant reduction. However an overview of both trials of primary prevention demonstrated a 33% reduction in the risk of fatal heart attack. Although no randomized trial has been completed specifically in women, the Nurses Health Study recently reported that women who took one to six aspirin weekly were 32% less likely to have an acute myocardial infarction.

At present the data on the role of aspirin in the primary prevention of stroke and heart attack are inconclusive. But some authorities recommend routine use of aspirin in asymptomatic men and women older than 50 years to prevent first myocardial infarction. It is important to view the clear benefits of aspirin in the primary prevention of heart attack in the context of what is already known about the modification of other coronary risk factors. It would be unfortunate if a middle aged smoker took aspirin instead of quitting smoking, because the benefits from quitting far exceed any protective defect of aspirin of heart attack. Any decision to use aspirin prophylaxis should be made on an individual basis, and in general, should be considered only for those whose absolute risk of a first heart attack is sufficiently high to warrant accepting the potential adverse effects of long-term aspirin use.

Antioxidants

Antioxidants with coronary artery disease

Epidemiological studies have suggested that high intake of antioxidants may modify coronary artery disease risk. The relative impact of vitamin E, vitamin C, beta carotene and flavonoids still remains unclear. Nurses Health Study and the Health Professional’s Follow-up Study showed 34% and 36% reduction in coronary events, respectively among women and men who take vitamin E supplement regularly. Oxidized LDL (bad cholesterol particles are believed to play a key role in the atherogenesis (blockage formation). So, theoretically any oxidant is likely to prevent coronary artery narrowing by preventing oxidation of LDL. In the European Community Multicenter Study on Antioxidants, Myocardial Infarction and breast cancer trial high beta carotene intake was protective only among smokers; vitamin C intake showed no relationship with coronary artery disease.

Results from most of the observational and experimental studies consistently support an effect of vitamin E supplemental on reducing the risk of heart attack. It is suggested that supplemental intake of vitamin E at or above 100 IU/day will reduce incidence of coronary artery disease. Long-term intake of vitamin E may reduce the progression of blockage in coronary arteries.