Biphasic relaxation-frequency relations in patients with effort angina pectoris: a new marker of myocardial demand ischemia

Abstract

Background Relaxation-frequency relations (RFR) during demand ischemia have not been fully examined in patients with effort angina pectoris (AP). We sought to clarify the effects of pacing and exercise on RFR in patients with AP. Methods We recorded left ventricular (LV) pressures during rapid atrial pacing and symptom-limited supine bicycle exercise. RFR were analyzed in 24 patients with AP and 10 controls. Results LV pressure half-time (T 1/2) in controls was gradually shortened with an increase in heart rate (HR) during pacing (−19% ± 6% at peak HR). The changes in T 1/2 during pacing were biphasic with initial shortening (−12% ± 5% at the critical HR) followed by prolongation (−3% ± 7% at peak HR) in all patients with AP. The critical HR, at which T 1/2 was minimum, preceded the HR at 0.1-mV ST-segment depression, and finally chest pain occurred. The critical HR was correlated negatively with the severity of ischemia as assessed by thallium-201 scintigraphy. T 1/2 was remarkably shortened during exercise in controls (−41% ± 10% at peak exercise). In patients with AP, 2 distinct patterns of RFR were observed during exercise. T 1/2 was shortened progressively (−37% ± 8% at peak exercise) in 15 patients, whereas RFR remained biphasic (−21% ± 10% at the critical HR and −11% ± 11% at peak exercise) in the other 9 patients. Coronary angiography and exercise scintigraphy suggested more severe ischemia in patients with biphasic RFR during exercise. Conclusions Impaired RFR might be the most sensitive parameter of pacing-induced ischemia. The critical HR was closely related with severity of ischemia. Adverse effects of ischemia on LV relaxation may be alleviated by exercise.