Pacemaker repetitive nonreentrant ventriculoatrial synchronous rhythm. A review.

Ventriculoatrial (VA) synchrony during dual chamber pacing can occur in any patient who has the ability to sustain repeated retrograde conduction. If the retrograde P wave is sensed, the result will be an endless loop tachycardia or repetitive reentrant VA synchrony. VA synchrony can also occur when a dual chamber pacemaker does not sense a retrograde P wave within the postventricular atrial refractory period. In this situation if the normally suprathreshold atrial stimulus at the end of the atrial escape interval is continually delivered when the atrial myocardium is physiologically refractory, the result will be a repetitive nonreentrant VA synchronous rhythm. Repetitive nonreentrant VA synchrony may produce unfavorable hemodynamic consequences and the pacemaker syndrome. It represents an example of functional atrial undersensing combined with functional loss of atrial capture. Management requires modification of the programmed settings of the pacemaker and utilization of certain algorithms designed for other functions but nevertheless effective in this situation.