A New Metabolic Mechanism for Absence of Pain in Patients with Silent Myocardial Ischemia

Abstract

We undertook this study to detect if there is a relationship between lactate production in the myocardium and the presence or absence of chest pain in patients with coronary artery disease (CAD). Forty six patients with significant CAD including left anterior descending artery underwent echocardiography study, coronary angiography and pacing-induced ischemia. Serum lactate levels were determined in four blood samples, from mid-LV cavity and from coronary sinus before and after pacing-induced ischemia. Twenty eight patients comprised angina group and 18 patients comprised silent myocardial ischemia (SMI) group during pacing-induced ischemia. Eighteen patients (64.3%) of angina group had lactate production during ischemia. Eighteen patients of SMI group (100%) had diminished lactate extraction, and none had lactate production. The novel finding of this study is that the major difference in metabolism during SMI and angina pectoris is in the state of lactate production, which is absent during SMI and present during angina. We assume that lactate is the stimulus of cardiac ischemic pain and when its level increases, it stimulates pain receptors leading to chest pain.