The comments by Drs. Woehlck, Cinquegrani, and Connolly are appreciated. The authors have highlighted an important issue with regard to any diagnostic test, i.e.
, the correlation between a positive result and a specific disease. In the case of the interpretation of ST segment on an electrocardiogram, it is the correlation of ST segment changes with structural coronary artery disease, not myocardial ischemia, that has been used in the stress test literature to define a positive test. Therefore, I agree with the authors of the letter that the presence of myocardial ischemia cannot be ruled out in surgical and obstetric patients without structural disease. In fact, short-term ST segment changes after induction of general anesthesia in patients with normal coronary arteries has led to a myocardial infarction, most likely the result of coronary spasm. 1
However, ST segment depression is not pathognomonic for myocardial ischemia. It is conceivable that ST segment depression changes observed during elective caesarean section or general surgery in low-risk patients reflect supply–demand mismatches in patients without known structural coronary disease, but many of these changes did not correlate with the hemodynamic effects or the medication usage outlined by the authors. 2–4
Additionally, regional wall motion abnormalities, a more sensitive marker of myocardial ischemia, were not correlated with the electrocardiographic changes. 2,3
Ideally, coronary sinus lactate measurements would be required to determine the etiology, but they have not been studied in these cases. Therefore, I agree with the authors and appreciate their comments that ST segment depression perioperatively in these patients may reflect myocardial ischemia from supply–demand mismatches, and treatment of hemodynamic derangements should be implemented. However, further evaluation or treatment beyond control of heart rate and blood pressure is warranted rarely in the absence of other signs or symptoms.
Lee A. Fleisher M.D.