Abstract
BACKGROUND: This study aimed to define and explain a novel form of pacemaker-mediated arrhythmia which is initiated and sustained by atrial capture loss coinciding with ventriculoatrial (VA) conduction within the postventricular atrial refractory period (PVARP). Unlike repetitive nonreentrant VA synchrony (RNRVAS), in the pseudo-RNRVAS, the atrium is not stimulated due to pacing below the threshold level, rather than because of refractory atrial myocardium. OBJECTIVE: The objective was to elucidate the mechanisms of this pseudo-RNRVAS, identify predisposing factors, and propose preventive strategies. METHODS: Twenty-one patients with dual-chamber cardiac implantable electronic devices (CIEDs) exhibiting stable VA conduction within the PVARP were included. Pseudo-RNRVAS were induced by altering atrial amplitude and lower rate interval while keeping other CIED parameters constant. RESULTS: Pseudo-RNRVAS developed after atrial capture loss in 20 out of 21 patients. Notably, 11 patients experienced pseudo-RNRVAS at heart rates ≤ 70 bpm, and 7 patients at AV delay ≤ 150 ms. The condition initiated immediately following the first ventricular pace beat after atrial capture loss in 18 patients. In six cases, pseudo-RNRVAS terminated intermittently and then restarted; in 14 cases, it did not resolve. CONCLUSION: Pseudo-RNRVAS can occur even at low heart rates and without specific predisposing factors seen in RNRVAS. Conditions that increase atrial pacing probability and threshold raise the likelihood of pseudo-RNRVAS. Early postimplantation may pose a heightened risk, correlating with pacemaker syndrome and susceptibility to heart failure.