What is the complex known as when impulses from both the atria and ventricles meet simultaneously in the heart?

The scenario described, where impulses from both the atria and ventricles meet simultaneously in the heart, is referred to as a fusion beat. A fusion beat occurs when impulses from the atria and ventricles stimulate the myocardial cells at the same time, resulting in a contraction that combines characteristics of both atrial and ventricular activation. This situation typically arises in cases of abnormal conduction or in the presence of various arrhythmias.

In contrast, cardiac block refers to a failure of electrical impulses to conduct through the heart's conduction system, leading to a delay or complete blockage of signals. Ventricular flutter is a rapid and chaotic rhythm originating in the ventricles, and it does not involve simultaneous atrial input. Pacemaker rhythm denotes the regular heartbeat established by the heart's primary pacemaker, typically the sinoatrial node, which does not involve the simultaneous activation characteristic of a fusion beat. Understanding these distinctions is crucial in the context of cardiac physiology and arrhythmias.