Characteristics of endocardial monophasic action potentials recorded from areas with fractionated bipolar electrograms in infarcted canine ventricular myocardium

STUDY OBJECTIVE: The aim was to characterise monophasic action potentials recorded from subacutely infarcted myocardial regions, where fractionated bipolar electrograms could be obtained. DESIGN: Dogs underwent ligation of the left anterior descending coronary artery. Before and 8-12 d after ligation, monophasic action potentials and local electrograms were recorded endocardially from the apex of the left ventricle. EXPERIMENTAL MATERIAL: 15 anaesthetised mongrel dogs (30 mg pentobarbitone.kg-1) were used. MEASUREMENTS AND MAIN RESULTS: Multiphasic fractionated bipolar electrograms could be recorded from infarcted sites of the left ventricle with a mean duration of 69(SD 10) ms and a mean amplitude of 3.7(1.6) mV, compared to control values of 42(7) ms (p less than 0.05) and 9.4(2.2) mV (p less than 0.05), respectively. Endocardial monophasic action potentials recorded from these areas were similar to action potentials obtained from non-infarcted sites before coronary ligation. The fractionated extracellular potentials were superimposed on the monophasic action potential upstroke. MAP90 was 189(31) ms, MAP30 138(12) ms, versus control values of 182(27) ms and 139(10) ms (NS). Monophasic action potential amplitude was significantly reduced at infarcted sites compared to control, at 26(7) mV v 38(6) mV. Histological specimens were taken to confirm that measurements were obtained from infarcted tissue. CONCLUSIONS: It is possible to record monophasic action potential in subacutely infarcted canine ventricular myocardium; this technique might help in further studies to characterise electrophysiological mechanisms of ventricular arrhythmias in chronic myocardial infarction in man.