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

Transmural recording of monophasic action potentials

To investigate the possibility of transmural recording of repolarization through the ventricular wall, KCl monophasic action potential (MAP) electrodes positioned along plunge needles were developed and tested. The MAP electrode consists of a silver wire surrounded by agarose gel containing KCl, which slowly eluted into the adjacent tissue to depolarize it. In six dogs, a plunge needle containing three KCl MAP electrodes was inserted into the left ventricle to simultaneously record from the subepicardium, midwall, and subendocardium. In six pigs, eight plunge needles containing three KCl MAP electrodes and two plunge needles containing similar electrodes except for the absence of KCl were inserted into the ventricles. In three guinea pig papillary muscles, a KCl electrode was used to record MAPs along with two microelectrodes for recording transmembrane potentials. Transmural MAP recordings could be made for >1 h in dogs and >2 h in pigs with a significant decrease in MAP amplitude over time but without a significant change in MAP duration. With the electrodes without KCl in pigs, the injury potentials subsided in <30 min. When the pacing rate was changed to alter the action potential duration and refractory period in dogs, the MAP duration correlated with the local effective refractory period (r = 0.94). The time course of the MAP duration recorded with a KCl MAP electrode in guinea pig papillary muscles corresponded well with that of the transmembrane potential recorded with an adjacent microelectrode. It is possible to record transmural repolarization of the ventricles with KCl MAP electrodes on plunge needles. The MAP is caused by the KCl rather than being a nonspecific injury potential.

The rise time of the monophasic action potential--a new index of local use-dependent conductivity by sodium channel blockers in human myocardium

The kinetics of global use-dependent conduction slowing produced by sodium channel blockers in the human heart, estimated as a change in the QRS width, are known to be similar to those of use-dependent block of the maximum rate of depolarization in in vitro studies. However, the kinetics of the regional use-dependent decrease in conductivity have not been investigated. We examined whether the rise time of the monophasic action potential would be clinically useful as a marker of the local use-dependent decrease in conductivity by sodium channel blockers. In 12 patients without organic heart disease, monophasic action potentials (MAPs) were recorded at the right ventricular endocardium using a contact electrode before and after the administration of disopyramide (n = 6, 2 mg/kg, i.v.) or pilsicainide (class Ic agents, n = 4, 1 mg/kg, i.v., and n = 2, 150 mg, po) while the stimulus frequency was abruptly increased from 100/min to 150/min. The rise time, defined as the interval from the pacing pulse to the first peak deflection of the monophasic action potential, and the ORS width were measured simultaneously. In the absence of the sodium channel blockers, the abrupt increase in heart rate did not alter the QRS width or the rise time. In the presence of the agents, both variables were lengthened exponentially. The rate constants of onset changes in the QRS width and the rise time were 2.1 +/- 0.5 beats and 2.1 +/- 0.4 beats after the administration of disopyramide, and 7.5 +/- 3.0 beats and 8.2 +/- 4.0 beats after pilsicainide, respectively. The rate constant of the rise time was closely correlated with that of the QRS width. The present results are very closely comparable with the onset rate constants of use-dependent block of the maximum rate of depolarization in in vitro studies. These results suggest that (1) the rise time is a good indicator of local use-dependent decrease in conductivity by sodium channel blockers in human hearts and (2) the local use-dependent decrease in conductivity has kinetics similar to those of use-dependent sodium channel blocks.

Recording of transmembrane action potentials in chronic ischemic heart disease and dilated cardiomyopathy and the effects of the new class III antiarrhythmic agents D-sotalol and dofetilide

We recorded intracellular endocardial action potentials (AP) in left ventricular specimens obtained from 10 patients with dilated cardiomyopathy (dil CMP) and 7 patients with chronic ischemic heart disease (CAD) in whom orthotopic heart transplantation had been performed. The concentration-dependent electrophysiological effects of the new class III antiarrhythmic agents dofetilide (Dof) (3 x 10(-8)-10(-6) M) and D-sotalol (D-Sot) 10(-5)-5 x 10(-4) M) were determined. The following parameters were recorded: action potential amplitude (APA), resting membrane potential (RMP), AP duration at 95 and 50% of repolarization (APD95, APD50), maximal upstroke velocity (V(max)), and effective refractory period (ERP) at a cycle length of 1 Hz. The measured AP parameters did not differ in dil CMP and CAD. APD50, APD95, and ERP were significantly prolonged at Dof concentration > or = 10(-7) M and at D-Sot concentrations > or = 10(-4) M. No effects were observed on RMP, APA, or V(max). The AP characteristics of dil CMP and CAD did not differ. The data demonstrate class III effects of Dof and D-Sot on endocardial AP of diseased human ventricular myocardium. As compared with those of D-Sot, the effects of Dof on APD and ERP were similar but were obtained with lower concentrations.