Myocardial lactate metabolism during pacing induced angina pectoris

Myocardial lactate metabolism was studied in 20 patients with coronary heart disease during and immediately after slight angina pectoris induced by atrial pacing. Myocardial lactate extraction ratio (MLE) decreased from 0.27 +/- 0.03 (SEM) before angina to 0.01 +/- 0.06 during angina, and further to -0.32 +/- 0.11 at 15 sec after pacing. Lactate production was found to occur in eight patients during pacing and 13 patients after pacing. Cardiac venous flow was measured by thermodilution in eight of these patients. 'Net ischaemic lactate efflux' increased by 23 +/- 4 mumol/min 15 sec after pacing, whereas 'lactate uptake in non-ischaemic regions' diminished by 11 +/- 2 mumol/min. Lactate production 15 min after pacing was revealed in all patients with subtotal stenosis of the left anterior descending coronary artery (LAD), whereas it was less frequently observed in patients with occluded LAD and collaterals to the post-stenotic area. Increased washout of metabolites from the ischaemic myocardium during the early recovery period is the main reason for the rather high sensitivity of ischaemia detection by this procedure. This permits shorter pacing periods and less pain than in earlier studies. Both MLE and electrocardiographic changes were equally reproducible after 20 and 45 min recovery period.