Valentin Krinski

Scanning and resetting the phase of a pinned spiral wave using periodic far field pulses.

Spiral waves in cardiac tissue can pin to tissue heterogeneities and form stable pinned waves. These waves can be unpinned by electric stimuli applied close to the pinning center during the vulnerable window of the spiral. Using a phase transition curve (PTC), we quantify the response of a pinned wave in a cardiac monolayer to secondary excitations generated electric field pulses. The PTC can be used to construct a one-dimensional map that faithfully predicts the pinned waves response to periodic field stimuli. Based on this 1D map, we predict that pacing at a frequency greater than the spiral frequency, over drive pacing, leads to phase locking of the spiral to the stimulus, which hinders unpinning. In contrast, under drive pacing can lead to scanning of the phase window of the spiral, which facilitates unpinning. The predicted mechanisms of phase scanning and phase locking are experimentally tested and confirmed in the same monolayers that were used to obtain the PTC. Our results have the potential to help choose optimal parameters for low energy antifibrillation pacing schemes.

Eliminating pinned spiral waves in cardiac monolayer by far field pacing

Fibrillation in the heart often consists of multiple spiral waves of electrical activation in cardiac tissue. To terminate these multiple waves, recently proposed Low Energy Antifibrillation Pacing (LEAP) uses a series of low energy pulses. This achieves an energy reduction of about 80% in animal experiments. To understand the mechanism of LEAP we study the interaction of electric pulses with pinned spiral waves in monolayers of cardiac cells. Optical mapping and controlled placing of heterogeneities allow us to observe the activation dynamics in these monolayers during field pulsing. We show that a pinned wave can be terminated by a series of pulses when one of the pulses falls in the vulnerable window of the pinned spiral.

A new far-field cardiac defibrillation mechanism

Introduction. Experimental research activity has recently focused on a promising new method for low-energy defibrillation. Called far-field defibrillation, the method imposes electric field pulses that engage the bulk of the heart tissue, in contrast to other methods that deliver electrical energy locally through implanted electrodes. The effectiveness of this method can potentially depend on the timing of the delivery of the pulses. Here we describe a new mechanism by which these electric field pulses might terminate reentrant waves that operates independently of shock timing. Methods. A three-dimensional finite-difference monodomain computer simulation, which includes a full ion channel model and resistive gap junction coupling, is run in rectangular domains of different widths, designed to represent heart walls of varying thicknesses. Once a reentrant action potential scroll wave is established in the system, an electric field stimulus is delivered with varying field vector orientations through the imposition of its effect on the domain boundary conditions. Results. We find that, once the surface perpendicular to the scroll wave filament is depolarized by the electric field, termination of the scroll wave always results. Termination is nearly immediate in the case of thin walls (0.5 cm). In thicker walls (e.g., 2.0 cm), interaction of the induced wave with the scroll wave results in an L-shaped filament, which then shrinks and disappears by the same mechanism by which scroll wave rings terminate. Termination thus occurs independently of wall thickness, timing, and electric field orientation, as long as the latter has a normal component sufficient (about 1 V/cm) to elicit a wave. This new mechanism will likely operate alongside other mechanisms, and thus has the potential to lower the defibrillation threshold.