Critical mass hypothesis revisited: role of dynamical wave stability in spontaneous termination of cardiac fibrillation

Abstract

The tendency of atrial or ventricular fibrillation to terminate spontaneously in finite-sized tissue is known as the critical mass hypothesis. Previous studies have shown that dynamical instabilities play an important role in creating new wave breaks that maintain cardiac fibrillation, but its role in self-termination, in relation to tissue size and geometry, is not well understood. This study used computer simulations of two-and three-dimensional tissue models to investigate qualitatively how, in relation to tissue size and geometry, dynamical instability affects the spontaneous termination of cardiac fibrillation. The major findings are as follows: 1) Dynamical instability promotes wave breaks, maintaining fibrillation, but it also causes the waves to extinguish, facilitating spontaneous termination of fibrillation. The latter effect predominates as dynamical instability increases, so that fibrillation is more likely to self-terminate in a finite-sized tissue. 2) In two-dimensional tissue, the average duration of fibrillation increases exponentially as tissue area increases. In three-dimensional tissue, the average duration of fibrillation decreases initially as tissue thickness increases as a result of thickness-induced instability but then increases after a critical thickness is reached. Therefore, in addition to tissue mass and geometry, dynamical instability is an important factor influencing the maintenance of cardiac fibrillation.

Modifying L-Type Calcium Current Kinetics: Consequences for Cardiac Excitation and Arrhythmia Dynamics

“…The space step was 0.015 cm and the time step varied from 0.1 to 0.01 ms. Spiral waves were initiated using a standard S1S2 cross-field protocol. Spiral tip was defined by the intersection of two iso-voltage lines (at -30 mV) in 1-ms interval and tracked as described previously (19).…”

Pharmacological Blockade of <I>I</I><SUB>Ks</SUB> Destabilizes Spiral-Wave Reentry Under <I>&beta;</I>-Adrenergic Stimulation in Favor of Its Early Termination

“…In contrast, a A B shortening of APD by an L-type Ca 2+ -channel blocker (verapamil) was shown to stabilize SWs and to increase the sustainability of VTs (19). It has also been demonstrated in theoretical studies on a 2-dimensional myocardial tissue model of finite size that APD prolongation by blockade of potassium currents destabilizes SW reentry and facilitates its early termination, indicating that maintenance of the reentrant arrhythmia critically depends on the ratio between tissue mass and wavelength (35). Our 2-dimensional mathematical model analysis is in line with this interpretation, since APD shortening by ISP and its reversal by 293B were associated with stabilization/ destabilization of rotors in favor of their persistence and termination, respectively.…”

Innovations in Clinical Cardiac Electrophysiology: Challenges and Upcoming Solutions in 2018 and Beyond

“…86 This theory requires a certain critical mass of myocardium to be available for the sustaining of fibrillation, and it is difficult to explain fibrillation in smaller animal using this theory alone. 87,88 The existence of drivers of AF may also explain reports of persistent AF terminating with point ablation. 89 Drivers of AF can exist as rapidly discharging foci or, more commonly, in the form of spiral waves or rotors.…”