COMPARISON OF ISCHEMIC AND PHYSIOLOGICAL-RESPONSES DURING EXERCISE TESTS IN MEN USING THE STANDARD AND MODIFIED BRUCE PROTOCOLS

The importance of low-level (warm-up) exercise for reducing exercise-induced myocardial ischemic symptoms in patients with coronary artery disease is well-recognized by clinicians. Whether altering the abruptness of exercise, such as that which occurs during different frequently used testing protocols, affects myocardial ischemic variables and maximal exercise capacity has not been resolved. This study seeks to determine the effects of altering the increment of work-rate change per exercise stage on both the ischemic threshold and maximal exercise capacity using 2 frequently used exercise testing protocols. Thirty-two patients with documented coronary artery disease and previously positive exercise tests (ischemic ST depression greater-than-or-equal-to 1.0 mm) performed symptom-limited exercise tests using both the standard and modified Bruce protocols in random order, 1 hour apart. Exercise electrocardiograms were analyzed to determine the ischemic threshold, defined as heart rate at onset of greater-than-or-equal-to 1.0 mm ischemic ST depression. Patients achieved a higher peak heart rate (124 +/- 19 vs 117 +/- 21 beats/min; p < 0.0001), rate-pressure product (21.4 +/- 3.9 vs 19.8 +/- 4.1 beats/min x mm Hg x 10(3); p less-than-or-equal-to 0.0001) and oxygen consumption (VO2) (18.5 +/- 3.7 vs 16.5 +/- 4.4 ml/kg/min; p less-than-or-equal-to 0.001) with the standard than with the modified Bruce protocol. At matched submaximal exercise stages there were no differences in VO2, heart rate or oxygen pulse between protocols. Time to ischemic threshold was significantly reduced with the standard compared with the modified Bruce protocol (312 +/- 107 vs 607 +/- 221 seconds; p < 0.0001). All other variables at the ischemic threshold were not significantly different between protocols, including heart rate, rate-pressure product, diastolic blood pressure and VO2. These data indicate that: (1) Myocardial ischemic threshold is the same with these 2 frequently used exercise testing protocols and is not altered by varying the work-rate increment between protocols. (2) Exercise capacity is greater with the standard than with the modified Bruce protocol, as patients achieved a higher peak heart rate, rate-pressure product and VO2. (3) The physiologic responses at matched submaximal work rates are similar. Accordingly, ischemic and hemodynamic data obtained using these 2 protocols can be equivalently compared.