Endocardial monophasic action potential recordings for the detection of myocardial ischemia in man: a study using atrial pacing stress and myocardial perfusion scintigraphy.

In a study designed to appraise the use of monophasic action potentials (MAPs) to detect myocardial ischemia in endocardial recordings, changes in steady-state MAP duration were compared in recordings between normal and ischemic areas of myocardium identified by the use of a radionuclide tracer simultaneously with the MAP recording procedure. Single-site recordings were made from the left or right ventricular endocardium or both in 26 patients (32 recording sites) during atrial pacing up to angina threshold. Pacing was maintained for 2 minutes at each increment in heart rate and MAPs were recorded at the end of each 2-minute period. Perfusion defects produced by atrial pacing stress were detected using technetium-99m hexakis-2-methoxy-2-methylpropyl-isonitrile injected at peak pacing stress. In 18 recordings from normally perfused areas of endocardium, MAP duration at 70% and 90% repolarization shortened by a mean (+/- SD) of 20.9 (3.7) msec and 22.0 (4.8 msec, respectively, for every 100 msec change in cycle length. This is in keeping with the effect of cycle length changes on the action potential duration. The extent of shortening was significantly greater (p less than 0.01) for 14 recordings from ischemic areas, being 32.0 (8.6) and 33.8 (9.7) msec, respectively, indicating the additional effect of localized myocardial ischemia. These results validate the applicability of the endocardially recorded MAPs for the detection of ischemia. Such methodology may provide a means of assessing therapeutic interventions aimed at the early phase of ischemia.