For the past few weeks, I’ve made Wednesday “Article Review” day. I’ll still post reviews that I deem pertinent on other days, but the goal is to post one each Wednesday at a minimum.
The Hubmed page for today’s article is here: Unpinning of a Rotating Wave in Cardiac Muscle by an Electric Field by Alain Pumir and Valentin Krinsky
Tachycardia (fast heart beat) is commonly caused by a rotating wave of activation in the heart. The study of rotating waves of this type has years of legacy in theoretical and chemical dynamics studies. Today’s article covers rotating waves pinned to anatomical obstacles such as valve openings in the heart. Rotating waves circle a core, which can be functional (a property of the wave shape and dynamics) or anatomical (an obstacle). In the case of an anatomical obstacle, the wave can be eliminated by ablation, which is commonly used in the atria, electrical defibrillation, or possibly unpinning / antitachycardia pacing (ATP). Ablation is typically invasive, requiring catheterization, and defibrillation requires an external shock, or surgery to implant an ICD. Defibrillation, either externally or internally, damages the heart, is painful, and often causes loss of consciousness. Antitachycardia pacing and electrical unpininning open the possibility of elimination of tachycardia with small shocks.
The principle of electrical unpinning, proposed by Huyet et al. (1998) and Krinsky et al. (1995), is that when a localized stimulus is applied in a certain part of the wave tail, it may move the core of the rotating wave. It’s difficult to place a stimulus in a particular place at a particular time in a patient’s heart, but it turns out that when an electrical field is applied over an obstacle, areas of depolarization (positive change) and hyperpolarization (negative change) manifest on the borders of the obstacle.
The paper by Pumir and Krinsky details how a small electrical field may be applied at a specific timing relative to wave rotation in order to create such a depolarization on an obstacle that will unpin a wave attached to that same obstacle. They used simplified models of cardiac action potentials, including the Beeler-Reuter and Fitzhugh models. Since the method deals with the dynamics of a spiral wave, and not with particulars of ionic currents, it’s a safe bet that the methods will apply in more complex models and cardiac tissue.
I won’t repeat the article’s simple and logical explanation of how it works — go read it. It’s only 9 pages, the figures are clear, and the math is mercifully simplified in a way that (ostensibly) doesn’t undermine the results.