• When there is transient pause in pacemaking activity of sinus, atrial, and junctional automaticity foci for at least 1 cycle, a ventricular escape beat arises from the ventricular automaticity focus and is conducted directly to neighboring ventricular cells.
• The resulting beat has a no P wave, but only widened QRS (due to inefficient conduction) .
• As soon as the sinus node resumes its packmaking activity, the original sinus rhythm also returns to baseline.
• This is seen in parasympathetic stimulation (which only affects SA, AV, and atria, not the ventricles).
• A ventricular escape rhythm arises when there is there is conduction block from AV to the ventricles or failed pacemaking activity of all automaticity foci above, the ventricular automaticity focus takes over for a longer period of time and sends its own impulses to the neighboring ventricular cells.
• The resulting rhythm runs at a new rate (inherent ventricular rate at 20-40 bpm) and consists of no P waves and widened QRS complexes.
• Occasionally, P waves might be present (originated from any one automaticity focus above the ventricles) but they are uncoordinated with QRS complexes.
