TMT / Tread Mill Test / Stress Test

Tread mill test plays an important role in the diagnosis of ischaemic heart disease in cardiology.

Ischaemic heart disease (or coronary artery disease) broadly means blockages in the vessels of the heart. (Heart also needs supply of blood for its muscles which is obtained from arteries to the heart). These blockages can lead to angina (chest discomfort) or even heart attacks. 

ECG in a patient with coronary artery disease may be normal. This does not mean that the patient is risk free.

In TMT, electrodes are applied to the patient (like we do when taking an ecg) and he/she has to walk on a tread mill belt. ECG is recorded throughout the test and can be seen on the monitor.

The basic fundamental behind the test is to increase the workload on the heart by graded exercise and see the response on the ECG, blood pressure, symptomatic status, etc.

An ECG which may be normal at rest may show an abnormality when the patient exercises. Or a pre existing abnormality may become more intense or show additional abnormalities. 

Thus TMT is a useful for :

1) Assessing the possibility of Ischaemic Heart Disease.

2) Assessing the exercise capacity.

3) Assessing the BP response to exercise.

SENSITIVITY & SPECIFICITY

We must also be aware that the sensitivity & specificity of stress test is not 100%.

This means that it may miss out certain cases of significant coronary artery disease. On the other hand, there may be cases where the test suggests disease but the coronary angiography comes out to be normal (This may especially happen in the cases of young ladies) with the TMT being false positive. 

RESULTS

The result of a TMT may be labelled broadly as Positive or Negative.

A negative result here is in fact a good result. It means that there is no significant blockage in the arteries.

A positive result on the other hand means that there is a significant blockage in the arteries and the patient needs further investigations eg coronary angiography.