Treadmill Stress ECG

Treadmill Exercise ECG is usually done with a computerized treadmill unit which controls the motor speed of the treadmill as well as monitors the ECG. ECG is recorded periodically during the test in addition to documenting any specific events like arrhythmias. Ideally treadmill test is done in a basal state so that the process of digestion of food and consequent increase in cardiac output does not interfere with the assessment. If it is a diagnostic test, the individual should be off medications. But if it is for assessment of effort tolerance while on treatment, it may be done on medications.

Though various protocols like Naughton and ramp protocol are in vogue, the popular one is Bruce protocol. There is also a Modified Bruce protocol for those with lower functional capacity or for early post infarction evaluation. Standard Bruce protocol has seven 3 minute stages. In stage I the gradient is 10% and it rises 2% per stage. The starting speed is 1.7 mph and increases in increments of 0.8 to 0.9 mph per stage.

In Modified Bruce protocol, stage I has a gradient of zero and stage II a gradient of 5%. Speed is the same in the first 3 stages of Modified Bruce protocol (1.7 mph). Stage 3 of Modified Bruce protocol is equivalent to Stage I of standard Bruce protocol. Further stages are similar to Bruce protocol, though the number of the stage will be higher by a magnitude of 2.

Treadmill exercise test ECG series starts with the pretest ECG and recordings in every stage of exercise and recovery phase. Sometimes an ECG during hyperventilation is also recorded before the start of exercise. This pretest ECG of a treadmill exercise test series shows a bit of artifacts, especially in leads II and III. The pretest heart rate is about 100/minute, possibly due to apprehension.

ECG recording in stage 1 of Bruce protocol of treadmill exercise test. The heart rate has increased and there are now many artifacts and no significant ST segment shift is evident.

Recording at the peak exercise shows significant horizontal ST segment depression in inferior and lateral leads at a fast heart rate. But the significant level of artifacts in the raw rhythm strip make us suspect whether the ST segment depression could be artefactual due computerized averaging in the computer synthesised rhythm.

The recording in early phase of recovery at 1 minute, shows very little ST segment depression, making us suspect further whether the earlier recording was really due to myocardial ischemia. But the ST segment is down sloping in inferior leads.

ECG at 3 minutes of recovery, shows further worsening of ST segment depression, in inferior and lateral leads, establishing the presence of significant myocardial ischemia.

TMT recovery phase ECG at 6 minutes showing the persistence of down sloping ST segment depression. This calls for further evaluation including coronary angiography and revascularization if feasible. Moreover, ECG recording has to be continued till ST segment shift resolves.