Predisposing factors for ventricular arrhythmias.
The majority of ventricular arrhythmias that affect humans are reentrant. Three components are then of relevance: the substrate, trigger, and facilitatory factors. The substrate comprises an area of slow conduction and unidirectional block. The anisotropic conduction of ventricular muscle is a contributory factor but, on its own, is unlikely to support a pathological arrhythmia. Ischemia and infarction are important but are not the exclusive disease mechanisms for creating patchy electrical conditions that will support reentry. Trigger factors are not well understood, but the perturbing influence of ectopic beats is important. Ectopic beat frequency correlates with risk, but variable coupling may be a more effective trigger, operating by "scanning" the cardiac cycle. Facilitatory factors act when both substrate and trigger are present and include autonomic tone, electrolyte imbalance, and biochemical influences. In the future, they may be important therapeutic targets. Substrate, trigger, and facilitators--all are interdependent. Separating their individual contribution is difficult and may be inappropriate. Sometimes the substrate is created by the trigger or facilitator and the facilitator may be the actual trigger. These issues raise exciting prospects for arrhythmia control but should not overshadow the fact that minimizing or preventing disease of ventricular muscle is the optimal clinical goal.
Campbell
R W
RW
Freeman Hospital, Newcastle upon Tyne, England.
D000818:Animals; D001145:Arrhythmias, Cardiac / Q000175:diagnosis* / Q000503:physiopathology; D006352:Heart Ventricles / Q000503:physiopathology; D006801:Humans