Is Dispersion of Refractoriness the Key to Reentry Vulnerability in Myocardial Ischemia? Insights From Simulations

It is commonly known that reentrant arrhythmias, such as certain types of tachycardias and – most importantly fibrillation, are life-threatening if they occur in the ventricles, and can become chronic (increasing mortality and morbidity) if they take place in the atria. Reentrant-type arrhythmias in heart tissue are normally initiated by the unidirectional block of the electrical wavefront traveling through the myocardium. Well-known experimental observations have shown that different myocardial zones with different degrees of electrical excitability must co-exist adjacent to each other in order for a reentry to occur. According to the classical theory, spatial dispersion of refractoriness (i.e. different values of effective refractory period [ERP] in neighboring zones) is the key to unidirectional block, because a wavefront can be blocked when entering a region with large ERP, surround it via short-ERP tissue, and retrogradely invade the large-ERP zone when its ERP has finished, giving rise to a reentrant pattern.