The first and foremost is that an ECG of the patient concerned must be recorded. Characteristic ECG changes may occur as a result of damage to the heart muscle. However, ECG may not show any change for the first few hours, or even for a day in a case of heart attack.

In case the ECG is normal, and the patient is clinically a suspected case of heart attack, a Troponin T (TnT) strip test of blood must be carried out as it is a bedside test and the results are available at the spot say in just 15 minutes. In this way no time is lost in starting the treatment of the patient. In case the test is positive, two vertical lines appear on the strip. One vertical line always appears, which means that the test is negative. Even if second vertical line is faint, it should be considered weakly positive i.e. the severity of the attack is less.

Besides the above, raised levels of certain enzymes in the blood also aid in diagnosis, since damaged cells of the heart muscle release certain enzymes, and the creatinine phosphokinase - CPK (MB) is elevated, say usually within 2-4 hours. Therefore, its levels in the blood should also be measured. Likewise, rising activity of serum glutamic oxaloacetic transaminase (SGOT), lactic dehydrogenase (LDH) may also be determined.

Other tests that are usually required are X-rays of the chest, both for heart size and lung fields. A fasting lipidogram, blood uric acid, blood sugar help to know any associated risk factors contributing to CAD. In addition, colour Doppler echocardiography and Holter monitoring may also be required.

Still more tests are required to be carried out which are given below:

Treadmill stress test (TMT) or exercise ECG test:

It is a very important test, and is carried out in almost all cases of CAD. This test reveals the response of the heart to the stress of exercise. The patient is connected to the ECG machine, and is asked to walk on a treadmill. The recordings of ECG indicate the response of the heart during exercise. If the muscle of the heart is getting less supply of blood during exercise, the same will be evident in the ECG.

Since a normal resting ECG does not rule out CAD, the stress test may prove valuable in the detection of occult/asymptomatic cases of CAD. This test is especially indicated when the person is suffering from one or more risk factors responsible for CAD like high blood pressure, high blood sugar/cholesterol/uric acid, etc. and/or when there is a strong family history of CAD.

Besides detection of hidden cases, a stress test is also indicated following a heart attack, in all cases. It tells about the extent of lesion, prognosis, including efficacy of treatment. In some cases, after a heart attack, only a modified treadmill stress test may be possible in which only a specific heart rate is achieved as the patient starts exerting.

In addition to the above, TMT must be carried out in all cases of angina pectoris. If it is negative, it may again be repeated after 1-2 months. If it is positive, it means there is a blockage in the coronary arteries/its branches, and the patient may need further tests like the thallium stress test or coronary angiography. In such cases all investigations, as in the case of heart attack, should be carried out for proper treatment.

Thallium stress test:

In this test, thallium is injected intravenously while the patient is at peak exercise. Thallium goes through coronary arteries/ branches and collects in the heart muscle. If the collection of thallium in the heart muscle is normal, it means that coronary arteries are functioning normally. Thus, it gives an indirect evidence of the functioning of coronary arteries. It is a non-invasive test and some prefer to carry it out before coronary angiography.

Coronary angiography:

Besides thallium study, coronary angiography may also be required. In some cases even direct coronary angiography may be carried out without taking the help of the thallium study. It is a highly reliable diagnostic test.

In this test, a dye is pushed into the coronary arteries through a very thin plastic tube (catheter), inserted into an artery (femoral artery), located in the middle of the fold of the groin, and series of X-rays are taken. This study, as well as the extent of lesion in the coronary arteries, gives the correct picture of a particular patient. After carefully studying the report of angiography, a suitable treatment can be planned.
Stress echocardiography

Instead of the thallium stress test, stress echo cardiography may be done to assess the viability of the heart muscle. It is a non-invasive test and can be done in remote areas as well.