Ectopic foci and rotational activity as keys to atrial fibrillation

Atrial fibrillation (AF) is the most common sustained arrhythmia, but it is also mechanistically mysterious. Its onset is typically triggered by ectopic foci with short cycle length causing premature depolarization. These point sources are borne from a failure in the intracellular calcium handling system within individual cardiomyocytes. In contrast, AF drivers that perpetuate activity are often caused by rotational features (micro-reentrant circuits), thereby providing a continual source of substrate electrical activation. Newer techniques have created a window of opportunity to investigate the effect of both triggers and drivers in the onset and maintenance of AF. Newly developed Tau20-RETROmapping, a rule-based system using electrogram energy and percentage of sites exhibiting an increased energy level as metrics, identifies individual AF wavefronts and driver-like activation patterns with high sensitivity and specificity. Another novel technology, electrographic flow (EGF), discerns active point sources generating divergent, centrifugal flow from passive rotational patterns where wavefronts converge centripetally. It maps likely sources initiating and perpetuating AF, identifying both ectopic foci and rotational activity. Refractory gradients have been shown to be of importance in the onset of rotational activity in AF. An early prospective clinical study has demonstrated that strong refractory period gradients (SRG) are readily mapped during sinus rhythm, and that ablation there increases success rate for terminating AF. Minimal or no correlation was found between the hotspots versus low voltage or likely fibrotic areas. Understanding the mechanics of AF onset via these new techniques and technologies will likely lead to improved treatment efficacy.