Stress testing

Stress testing

Many patents with coronary heart disease may have apparently normal rest ECG. So if you’re ECG is normal it does not completely exclude the possibility of pressure of significant block in your coronary arteries. If you have symptoms like exertional chest pain or breathlessness on mild to moderate exercise or suffering from easy fatiguibility, you should go for stress test to exclude the possibility of coronary heart disease. Any type of exercise results in an increase in myocardial (heart muscle) oxygen supply. This increase in oxygen need can only be met by coronary artery dilation or expansion. If you have significant block in any of your three coronary artery, the exercise induced increase in heart muscle oxygen consumption cannot be met due to presence of fixed block in coronary arteries. So during rest your ECG can remain normal and can indicate the abnormalities only during exercise, but in rest.

There are different ways to perform this test. But the Bruce treadmill test is the most popular one. During this test the patient is asked to walk fast or run on a treadmill and continuous ECG is recorded in a computer monitor. The test is continued as long as the ECG does not reveal any ischaemic change suggestive of block or target heart rate is achieved or the patient becomes fatigued.

Stress test is an excellent investigation for the diagnosis of coronary heart disease. This test is reported to have specificity of 77% for the detection of significant steno sis or block in any of your coronary arteries. If you are male and your stress test is positive for block then you can take it as 90% guarantee that you are having coronary artery disease. But in case of female this test is some times misleading and gives false positive result. If your stress test is positive, then doctor will advise you to undergo coronary angiogram. Stress test can tell you that probably you are having block but it can not tell you where are the blocks, how severe are the blocks and how many blocks you have. So stress test is the initial screening test but coronary angiogram is the final test for decision making.

Stress test is a noninvasive test and painless. Risk involved in this test is very little with a fatality of 1 in 10,000 patients. Preparation of the patient for this test is also simple. The patient is only advised not to take heavy meals 4 hours before testing. Patients undergoing diagnostic testing ideally should have beta blockers (e.g tenormin, tenoren, cardipro, betasec, betanol, tenoloc, inderal, indevar, adloc, carditab, propranol etc.) at least 24 hours before the test if possible. This test is also done after heart attack for further coronary risk stratification. If after heart attack this test becomes positive then it is a strong indication for coronary angiogram.

Smoking and Heart Disease

Smoking and Heart Disease

Smoking is one of the important remediable risk factor of heart attack. Tobacco products produce IHD in many ways:

1.    Smoking produces platelet aggregation (blood cell clogging) and helps in the formation of block inside the coronary arteries. It also helps in the formation of blood clot (solidification of blood).

2.    Blood clotting factor, fibrinogen level is higher in the smokers. In Framingham study, fibrinogen value was found significantly higher in the smokers.

3.    Cigarette smoking has been found to have adverse effect on the blood fat level. Compared with nonsmokers heavy smokers have lower levels of HDL (good cholesterol) and higher levels of LDL (bad cholesterol) and triglycerides.

4.    Acute inhalation of smoke is associated with increase in blood pressure which may have detrimental effects in patients with IHD.

5.    Approximately 50 to 150 microgram of nicotine is absorbed through the lung mucosa with each puff of tobacco. Nicotine is potent agonist for the adrenergic nervous system and it causes contraction of coronary and prevents normal blood flow in heart.

Diabetes and Heart Disease

Diabetes and heart disease

Diabetes is an independent risk factor for the development of coronary artery disease. The overall prevalence of coronary artery disease (IHD) is as high as 55% among adult patients with diabetes compared with 2-4% for general population without diabetes. Coronary heart disease is not only more prevalent, it is also clearly more extensive in diabetic than no diabetic patients.

Epidemiological data derived from the Framingham Heart Study demonstrated the increased incidence of heart attack in patients with diabetes and their poor outcome. The death rate from heart attack is more than double in men and more than quadruple in women who have diabetes, compared with the rate in their no diabetic counterparts. The relative risk of myocardial infarction (heart attack) is 50% greater in diabetic men and 150% greater in diabetic women. Similarly diabetic men succumb to sudden death 50% more often and diabetic women 300% more often than do their age-matched no diabetic counterparts. Diabetic women have poorer prognosis than do diabetic men and the cause is unknown. Acute myocardial infarction (heart attack) is said to account for as many as 30% of all deaths in diabetic patients.

Diabetes can predispose you to increased risk of heart attack for few reasons:

1.    Patients with diabetes have higher levels of VLDL (bad cholesterol) and triglycerides (fatty substance) and lower level of HDL (good cholesterol) than do patients without diabetes. Elevated fat level in blood induces coronary artery damage and cause thrombosis at any time.

2.    Blood cells, platelets aggregate spontaneously in patients with diabetes and form colt/thrombus inside coronary artery and cause heart attack.

3.    The blood of patients with diabetes appear much thicker (high viscosity) than normal and solidify easily causing coronary block.

4.    Autonomic neuropathy (nerve destruction by longstanding diabetes) may increase heart muscle oxygen demand and may reduce blood flow to heart muscle by causing increased vascular tone (contraction of the coronary artery).

Diabetic patients are at increased risk of complication associated with heart attack. Patients may fail to recognize the chest pain due to nerve damage. Diabetic patient may have heart attack without any chest pain and presentation may be atypical. Atypical symptoms like confusion, breathlessness, fatigue, vomiting may be the initial symptoms of heart attack. Patients may think that they are having these symptoms for their poor diabetic control like hypoglycaemia (low blood sugar) or due to hyperglycaemia (high blood sugar),  which may cause delay in initiation of treatment of heart attack. For these false beliefs 35% of diabetic patients with heart attack were admitted in general wards rather than to the coronary care unit. Atypical symptoms may alter the patient’s perception of the nature of their illness and interfere with their decision to seek medical care and may cause unfortunate fatality.

Type 2 diabetes increases the risk of coronary heart disease by a factor of two to four. The relative increase in the rate of coronary heart disease among patients with diabetes in most studies is greater for women than men.

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.