Define ventricular escape rhythm.

Ventricular escape rhythm is best defined as a protective mechanism where the ventricles generate a heartbeat when higher pacemakers, such as the sinoatrial (SA) node or atrioventricular (AV) node, fail to initiate or maintain an adequate heart rate. This rhythm typically occurs when there is a significant disruption in the normal conduction pathways, leading to bradycardia or even asystole. In the absence of impulses from the SA node, the Purkinje fibers in the ventricles can take over pacing, resulting in a lower heart rate, usually between 20-40 beats per minute.

This intrinsic pacing from the ventricles is critical for maintaining some level of cardiac output and perfusion when higher pacemakers are dysfunctional. While ventricular escape rhythms are essential in the short term, they are not sustainable for long periods and could lead to further complications if not addressed. In this context, classifications such as normal rhythms originating from the SA node or those being always irregular do not apply to ventricular escape rhythm, as those focus on different mechanisms of heart rhythm generation. Similarly, while a myocardial infarction can lead to various arrhythmias, it is not inherently the definition of ventricular escape rhythm itself.