Exercise-induced myocardial ischemia in a cold environment. Effect of antianginal medications.
The influence of cold on the threshold for myocardial ischemia and the efficacy of antianginal drugs in a cold environment were assessed in 24 patients with stable angina and exercise-induced ST depression. Treadmill exercise tests were done according to a randomized double-blind protocol 90 minutes after administration of placebo, 80 mg propranolol, or 120 mg diltiazem, each at both -8 degrees and 20 degrees C. Eight of the patients were classified by history as cold-sensitive before the study. For the entire group, none of the exercise end points differed significantly between cold and normal temperatures with placebo. However, cold-sensitive patients developed 1 mm ST depression 30% sooner (169 +/- 41 versus 244 +/- 38 seconds, p less than 0.01) at -8 degrees C compared with 20 degrees C. At the onset of ischemia, rate-pressure product was lower in the cold (19.8 +/- 1.0 versus 22.0 +/- 1.6 x 10(-3), p less than 0.05). Both propranolol and diltiazem prolonged time to onset of 1 mm ST depression at both temperatures. The magnitude of improvement at -8 degrees C was equal to that at 20 degrees C, and differences between the two drugs were not statistically significant. Only diltiazem prolonged total exercise duration. Thus, as assessed by exercise testing, cold does not worsen ischemic threshold in most stable angina patients. However, in a subgroup identifiable by history, ischemic threshold is lower in the cold. Propranolol and diltiazem are as effective for exercise-induced ischemia in a cold environment as at normal temperatures.