We have used five Langendorr perfused isolated rabbit heart preparations to investigate the effects of monophasic (MP) anodal (hyperpolarrang), MP cathodal (depolarizing) and Diphasic (BP) pulses comprising of hyperpolarizing and depolarizing phases. The conduction velocities at various distances were measured on the epicardtum along and transverse to the fiber direction using bipolar electrode arrays. Cellular transmembranic voltages were obtained using floating micrcelectrodes Speed of conduction in the longitudinal direction between 6mm and 9mm from the pacing site with 5V, 2msec stimulation was 23.3±3.9 cm/sec for cathodal, 31.3±1.7 cm/sec for anodal, and 32.4±2.1 cm/sec forme Diphasic pulse. Speed of conduction along the fiber direction was 49.7±1.5 cm/sec for cathodal, 54.9±0.7 cm/sec for anodal and 55,2±1.7 cm/sec for biphasic stimulation. The difference in anodal versus cathodal conduction velocity was found to be significant (pO.OOl). Thresholds dropped from 3.85±1.5 V for anodal pulses of 2 msec and 2.03±1.3 V for similar cathodal pulses to 2.15±0.9 V for a 2 msec biphasic pulse. The maximum upstroke ((dV/dt) max) of the action potentials was found to correlate well with the changes in conduction velocity. For a 4 V pulse of 2 msec duration, (dV/dt)max was 75.5±5.6 V/sec for anodal and 63.5±2.4 V/sec for cathodal stimulation along the fiber direction. We speculate that the increased electrical conduction and rate of voltage upstroke achieved by the pacing pulses tested here are due to the augmented number of fast sodium and perhaps the slow calcium channel currents available under the hyperpolarization pre-conditioning of the myocardium. These properties of MP anodal and BP pulses may offer some benefits to future pacemaker design.
|Original language||English (US)|
|State||Published - Dec 1 1996|
ASJC Scopus subject areas
- Molecular Biology