Repetitive reentrant and non-reentrant ventriculoatrial synchrony in dual chamber pacing.

Repetitive retrograde ventriculoatrial (VA) conduction in patients with dual chamber pacemakers may cause two forms of VA synchrony. (1) Endless loop tachycardia (pacemaker-mediated tachycardia) or repetitive reentrant VA synchrony occurs when the pacemaker senses retrograde P waves. Appropriate programming can prevent pacemaker reentrant tachycardia in almost all cases. However, the measures used to control tachycardia may themselves create new problems. (2) AV desynchronization arrhythmia or repetitive non-reentrant AV synchrony occurs when the pacemaker does not sense retrograde P waves. In this form of VA synchrony, the atrial stimulus is ineffectual because it falls in the atrial myocardial refractory period generated by the preceding unsensed retrograde P wave. A long atrioventricular interval and a relatively fast lower rate (or sensor-driven rate with DDDR pacing) favor the development of AV desynchronization arrhythmia and its unfavorable hemodynamic consequences.