Change of Cardiac Metabolism according to Atrial Pacing

Background：In aerometabolic process, the human heart mainly utilizes free fatty acid as fuel.During anaerobic process, lactate production by the myocardium is increased and accumulates in the myocardium.Thus it decreases the contractility of myocardium.Therefore in patients with ischemic heart disease, lactate production must be increased by the myocardium during myocardial ischemia.During paroxysmal supraventricular tachycardia, patients frequently experience chest pain and ST segment depression suggesting acute myocardial ischemia.However it occurs on a physiologic basis independent of ischemia.The purpose of this study was to assess whether tachycardia induced by atrial pacing produces myocardial ischemia in patients without evidence of ischemic heart disease.Methods：Between May 28, 1996 and August 13, 1996, at the University of Keimyung, Dong-San Medical center, 15 patients(male 9, female 6, mean age of 38 years) with palpitation underwent electrophysiologic testing and had radiofrequency catheter ablation.There were no evidence of ischemic heart disease.Right atrial pacing was done with lengths of 500msec, 400msec and 350msec in each 5 patients.A 12 lead electrocardiogram, left ventricular end-diastolic pressure, blood from femoral artery and coronary sinus for lactate determinations and blood gas analysis were obtained simultaneously.They were obtained at baseline, at 1, 5, 10 and 15 minute of atrial pacing and at 1, 5, 10 minute after cessation of pacing.Results：Significant changes were not observed in PO 2 , PCO 2 , concentration of HCO 3 -, pH and O 2 saturation.In all patients, mean percent lactate extraction was above 10% and not significantly changed during atrial pacing.However ST segment depression was significantly progressive during atrial pacing and according to decrease the cycle length(p<0.05),also left ventricular end-diastolic pressure was significantly decreased during atrial pacing(p<0.05).Conclusion：Therefore tachycardia induced by atrial pacing for 15 minutes did not produce myocardial ischemia in patients without evidence of ischemic heart disease.Depression of ST segment