The mechanism of RNRVAS and predisposing factors
RNRVAS was first described by Serge Barold in 19911. Several studies showed that in two chamber devices, long AV delay, long PVARP, short lower rate interval, presence of VA conduction and long VA conduction periods were predisposing factors of RNRVAS1,2,11. A few studies described ventricular ectopic beats and retrograde atrial conduction after ventricular pacing as a trigger mechanism for RNRVAS1,8. Andric et aldescribed a patient with DDD Pacemaker implanted for AV block after mitral valve replacement 12. The patient was admitted for decompensated heart failure caused by ELT and RNRVAS with increased atrial threshold. In this case report, the induction of RNRVAS due to increased atrial threshold was not demonstrated, but was suggested as the possible cause. There are no other cases in literature with evidence showing the relationship between increased atrial threshold and RNRVAS.
In this study, we show that the absence of VA conduction accompanied by presence of AV block decreases the risk of RNRVAS development in both univariate and multivariate analyses.
VA conduction is mandatory for development of RNRVAS and AV block is frequently accompanied by VA block. We showed that only 21.2% of the patients with AV block had VA conduction. This number is consistent with the findings of Richter et al 13.
The absence of VA conduction in the remaining 78.8% explains why patients with AV block experience RNRVAS less. Av block results in increased ventricular pacing ratio which was an independent predictor of absence of RNRVAS development in univariate and multivariate analyses in this study.