It is common to find heart patients who have normal ECG. One must remember that the ECGs are taken at rest when the heart is beating at its lowest rate. Even with 90% blocks the patients can have a normal ECG. In such cases the patient would also agree that at rest there is no pain in the chest, the angina symptoms would only come when they increase the heart rate, while doing some physical exertion like walking.
This is the condition where we need a TMT test. The patients are to gradually increase their heart rate, thus increasing the blood requirement of the heart muscles. Simultaneously ECG records are taken. If there is a blockage of approximately more than 70% ECG shows changes, suggestive of Angina.
Patients have to physically exert for this test which uses a computerised machine. The level of the exercise is gradually increased according to a standard protocol called the Bruce’s Protocol. The continuous ECG monitoring during the exercise would reflect any blood and oxygen deficit in the muscles of the heart during exercise. The patient is asked to stop exercising as soon as ECG changes appear or any symptoms of chest pain or discomfort or breathlessness are felt.
TMT test is also called Exercise Stress Test, Computerised Stress Test or simply Stress test. This is the most easy, popular and common test performed on heart patients to determine the severity of the heart disease. Taken at an interval, this test can also show the improvement or deterioration of patient's angina.
A negative TMT or Stress Test is declared when the patient can reach a certain heart rate without showing any ECG changes. This rate is called a target heart rate and is calculated by a formula (Target Heart Rate = 220 – age of patient). If this rate is reached by the patient without producing any ECG changes, though the TMT can be called negative, but it would not mean that the blockage is zero. It will only mean that the person performing the test probably has a blockage less than 70%.