publications by Robert A Malkin.
Papers Published
- Vigmond, E. J. and Trayanova, N. A. and Malkin, R. A., Excitation of a cardiac muscle fiber by extracellularly applied sinusoidal current.,
J Cardiovasc Electrophysiol, vol. 12 no. 10
(October, 2001),
pp. 1145--1153 [11699523] .
(last updated on 2010/05/26)Abstract:
INTRODUCTION: The goal of this study was to examine the effect of AC currents on a cardiac fiber. The study is the second in a series of two articles devoted to the subject. The initial study demonstrated that low-strength sinusoidal currents can cause hemodynamic collapse without inducing ventricular fibrillation. The present modeling study examines possible electrophysiologic mechanisms leading to such hemodynamic collapse. METHODS AND RESULTS: A strand of cardiac myocytes was subjected to an extracellular sinusoidal current stimulus. The stimulus was located 100 microm over one end. Membrane dynamics were described by the Luo-Rudy dynamic model. Examination of the interspike intervals (ISI) revealed that they were dependent on the phase of the stimulus and, as a result, tended to take on discrete values. The frequency dependency of the current threshold to induce an action potential in the cable had a minimum, as has been found experimentally. When a sinus beat was added to the cable, the sinus beat dominated at low-stimulus currents, whereas at high currents the time between action potentials corresponded to the rate observed in a cable without the sinus beat. In between there was a transition region with a wide dispersion of ISIs. CONCLUSION: The following phenomena observed in the initial study were reproduced and explained by the present simulation study: insignificant effect of temporal summation of subthreshold stimuli, frequency dependency of the extrasystole threshold, discrete nature of the ISI, and increase in regularity of the ISI with increasing stimulus strength.Keywords:
Action Potentials • Electric Stimulation • Electrodes • Electrophysiologic Techniques, Cardiac • Heart • Heart Conduction System • Humans • Models, Theoretical • Muscle Fibers, Skeletal • Myocardium • Patch-Clamp Techniques • Sensory Thresholds • Systole • Time Factors