Importance of the Design of an Exercise Protocol in the Evaluation of Patients with Angina Pectoris

The severity of angina and the effects of therapeutic interventions in patients with coronary artery disease have been assessed by determining changes in both exercise performance and the triple product (TP) of heart rate, systolic pressure, and ejection time occurring at angina. However, the validity of conclusions based on such changes is uncertain since the effects of different exercise protocols on these variables have not been determined. Twelve patients with angina were studied during upright bicycle exercise; repeated bouts of exercise using a standard protocol of 20-w increments every three minutes produced no consistent changes in TP at angina. When exercise began 20 to 60 w above the work load of the standard protocol that produced angina, exercise capacity was reduced (average 1'40'' vs. 4'40'', P < 0.001), and triple product at angina exceeded control anginal values (average 4,840 vs. 4,150, P < 0.001). In the control studies nitroglycerin (TNG) and carotid sinus nerve stimulation (CSNS) enabled patients to exercise to a higher level, although the triple product at angina was unaltered. However, at the higher work load TNG and CSNS exerted only minimal effects on exercise capacity, indicating that if the work load is excessive, a reduction in myocardial oxygen consumption produced by a therapeutic intervention may be comparatively minor so that a potentially salutary effect would be masked. We conclude that work loads causing angina in less than three minutes cannot reliably be used for studying the effects of therapy. However, if progressive work loads are chosen which cause angina in the control studies in three to six minutes, exercise capacity and triple product at angina provide important information about the efficacy and mechanism of action of a therapeutic intervention.