Spontaneous variation of ventriculoatrial interval after tachycardia induction: determinants and usefulness in the diagnosis of supraventricular tachycardias with long ventriculoatrial interval

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: None. BACKGROUND: Determining the mechanism of supraventricular tachycardias with prolonged ventriculoatrial (VA) intervals is sometimes a challenge, because the usual diagnostic manoeuvers based on pacing during the ongoing tachycardia cannot be performed or do not offer diagnostic accuracy. PURPOSE: To analyse the determinants, time course and diagnostic accuracy (atypical atrioventricular nodal reentrant tachycardias [AVNRT] versus orthodromic reentrant tachycardias through an accessory pathway [ORT]) of spontaneous VA intervals variation in patients with narrow QRS tachycardias and prolonged VA. METHODS: A total of 156 induced tachycardias were studied (44 with atypical AVNRT and 112 with ORT). Two sets of 10 measurements were performed for each patient: after tachycardia induction and one minute later. VA and VV intervals were determined. RESULTS: Among patients with AVNRT, there was a marked variability in the VA intervals after induction (Mn-VA: mean beat-to-beat variation of VA; MX-VA: maximum of the beat-to-beat VA variation). Figure 1. No significant differences were found in the variability of the VA interval between slow-slow versus fast-slow atypical AVNRTs (p>0.5 in all comparisons). And, even though the variability of the VA interval at one minute continued to be considerable, it tended to decrease after induction. However, as shown in Figure 1, in subjects with ORT, no relevant beat-to-beat changes in the duration of the VA intervals were seen, neither after induction nor at one minute later. The values of VA interval variability in ORT with septal versus free-wall accessory pathways were similar. Additionally, in 9 (20%) patients with atypical AVNRT and in 11 (10%) with ORT the Dif-VA increased from induction to one minute, with the maximum increment being of 29 ms and 6 ms, respectively. The difference between the longest and the shortest VA interval (Dif-VA) correlates significantly with the diagnosis of atypical AVNRT (C coefficient=0.95 and 0.85 after induction and at one minute, respectively; p<0.001). A Dif-VA ≥15 ms presents a sensitivity and specificity for atypical AVNRT of 50% and 99%, respectively after induction, and of 27% and 100% one minute later. Figure 2. We found a robust and significant correlation between the fluctuations of VV and VA intervals in atypical AVNRTs (Coefficient Rho: 0.56 and 0.76, after induction and at one minute, respectively; p<0.001 for both) but not in ORTs. CONCLUSIONS: The analysis of VA interval variability after induction and at one minute later correctly discriminates atypical AVNRT from ORT in almost all cases. Such variability of VA intervals is related to the fluctuations of VV intervals in atypical AVRNTs but not in ORTs. [Figure: see text] [Figure: see text]