Can the MAP technique be applied to study triggered activities of the heart? Intracellular evidence in vivo.

Monophasic action potential (MAP) recording with contact electrode has been applied to study triggered activities of the heart. Intracellular evidence in vivo, however, of the MAP technique is lacking. In the present study, transmembrane action potential (TAP) recorded with floating glass microelectrode was compared with MAP in 18 cat hearts in vivo. The results were as follows. 1) In control conditions, the MAP duration at 50 and 90% repolarization was similar to that of TAP without any significant difference. 2) 10 sec after CsCl (0.5 mM/kg, i.v.), early afterdepolarization (EAD) appeared in the middle-late period of phase 3 both in the MAP and TAP; 30 sec after CsCl, the amplitude of MAP-EAD was 3.4 +/- 1.3 mV and that of TAP-EAD was 25.6 +/- 9.3 mV. Delayed afterdepolarization (DAD) was also induced by CsCl in phase 4 of the MAP and TAP simultaneously. The amplitude of MAP-DAD was 3.3 +/- 0.6 mV and that of TAP-DAD was 13.0 +/- 5.3 mV. 3) Triggered arrhythmias, including premature ventricular beat and tachycardia, induced by CsCl repeated injection were observed in the MAP and TAP recording synchronously. The present study not only provides an intracellular and direct evidence in vivo but also suggests that the contact electrode MAP technique could be applied to study triggered activities of the heart in vivo.