Should beta-blockers be withdrawn in post-myocardial infarction patients before treadmill test?

In most patients of myocardial infarction, beta-blockers are used for secondary prophylaxis and a treadmill test is required for risk stratification. To study the effect of oral beta-blockers on interpretation of treadmill test, 54 consecutive patients were subjected to treadmill test four to six weeks after myocardial infarction. Fourteen patients with strongly positive treadmill test were referred for coronary angiography. Treadmill test was repeated in 37 patients 72 hours after withdrawal of beta-blockers. The peak exercise heart rate was significantly different while off and on beta-blockers (148 +/- 13 bpm vs 124 +/- 14 bpm, respectively; p < 0.01). The test was negative on both the occasions in 17 patients. On stopping beta-blockers, the negative test became mildly positive in five and strongly positive in six patients. The mildly positive test became strongly positive in four patients and remained almost unchanged in five. In 10 patients there was conversion of negative or mildly positive treadmill test into strongly positive result after withdrawal of beta-blockers. Thus the risk stratification changed significantly in 27 percent patients. It is suggested that beta-blockers can and should be withdrawn in post-MI patients before doing treadmill test.