A patient who did an exercise stress test

A 46 year old man with hypertension and elevated cholesterol levels presented to his doctor with chest discomfort on inspiration. He had no history of chest pain or breathlessness on exertion. He did not have diabetes and he was not a smoker. However there was a strong history of cardiovascular disease in his family.
His physical examination was normal. The resting ECG was also normal. The doctor diagnosed non-cardiac chest pain in him but recommended an exercise stress test.

An exercise stress test using the Bruce Protocol is done. His heart rate and blood pressure are 96/min and 148/86mm Hg respectively at the onset of the test. He progresses steadily from Stage 1 to Stage 4 without any symptoms of chest pain or breathlessness and without any ECG signs of inducible myocardial ischemia. At the beginning of Stage 5, his heart rate is 150/min and his blood pressure is 145/90mm Hg. The exercise stress test is stopped because he feels tired. His peak exercise is recorded as 13 METS.

During recovery, the ECG shows ST segment depression, beginning from 3 minutes of recovery and persisting till the recording was stopped at 6 minutes.

Question: If this patient undergoes a coronary angiogram, which of the following is likely?

1. No coronary artery disease
2. Mild coronary artery disease
3. Severe coronary artery disease

Discussion

An exercise stress test is done for the purpose of detecting inducible myocardial ischemia. Parameters suggestive of inducible myocardial ischemia are: Angina during the performance of the test, ST segment changes, occurrence of ventricular ectopic beats, inability to complete the test, and failure of blood pressure to increase appropriately during the exercise.

This patient showed ST segment depression in the ECG during recovery from the test. Changes in the ST segment during recovery are as significant as ST segment changes during exercise. Hence we can infer that he has coronary artery disease.

When ST segment depression persists more than 8 minutes after the test is stopped or if the blood pressure does not increase as expected during the test, there is a high probability of severe coronary artery disease. Here, the ECG continued to show ST depression at 6 minutes after the test was stopped. Since the ECG was not recorded after that, we do not know for sure how long the ST segment would have remained depressed. Also, his systolic blood pressure did not show an appropriate increase. These tell us that he is likely to have severe coronary artery disease.

References:
1. The significance of ST segment depression that occurs only during the recovery phase of an exercise stress test. (http://www.ncbi.nlm.nih.gov/pubmed?term=2293816)
2. Exercise testing in the evaluation of coronary artery disease. (http://www.ncbi.nlm.nih.gov/pubmed/6979501)
3. The prognostic value of the exercise stress test. (http://www.ncbi.nlm.nih.gov/pubmed/3056676)