Abstract
It is well known that electrical pacing is used as a method for prevention and termination of arrhythmia such as ventricular tachycardia (VT) or fibrillation (VF). However, many clinical and experimental studies reported that external stimulation resulted in the termination of reentrant activity and also re-initiation of new reentry. The dynamics of interaction of cardiac excitation waves with waves initiated by external pacing are poorly understood. When point stimulation was applied at the cardiac myocardium, a complex depolarization and hyperpolarization pattern called “Virtual electrode polarization” was derived during stimulation. To understand cardiac excitation propagation at defibrillation, we developed a high resolution optical mapping measurement system of action potential propagation and a micro electrical stimulus system to observe a cardiac excitation pattern at the point of stimulation applied during VT. Isolated rabbit hearts, stained with the voltage-sensitive dye, di-4-ANEPPS, were illuminated by high luminance bluish-green LEDs. The emitted fluorescence was long-pass filtered at a wavelength of 600 nm and captured by a high-speed digital video recorder. The recorded image was transferred to a PC and the digital image processed. Our system achieved both spatial resolution (0.11 mm/pixel) and temporal resolution (0.89 msec/frame). The stimulus electrode was a micro platinum wire φ 0.1 mm implanted into a transparent acrylic board and φ 0.04 mm coated copper wiring, so it was able to be measured by an optical mapping system during stimulation. Using this mapping system, we measured the initiation process of virtual electrode induced polymorphous reentrant activity derived by point stimulation during VT with high temporal and spatial resolution.
