Unfolding the transition ratio: insight into the diagnostic criteria for the diagnosis of the origin of outflow tract ventricular arrhythmias
Authors: Lazzari L , Donzelli S , Parise A , Marallo C , Pirozzi C , Tordini A , Pace V , Di Meo F , Marini C , Carreras G 
Published: May 2024

Abstract

Background
algorithms for the diagnosis of the site of origin of ventricular outflow tract arrhythmias (OTVA) share the rationale that more posterior structures (LVOT) produce a greater vector approaching the precordial leads than anterior structures (RVOT), i.e. R waves in V1-V3 of greater amplitude and duration, a transition generally earlier than the QRS in sinus rhythm (SR), and vice-versa.

Methods
in a retrospective cohort of 45 patients (53.3% LVOT, 46.7% RVOT) with OTVA (left bundle branch block morphology, transition in lead V3, absence of conduction aberrancy in SR, who underwent successful catheter ablation were retrospectively analyzed, comparing the diagnostic yield of the main literature criteria.
a) The V2 transition ratio, (TR) calculated with the formula [(R\R+S)PVC : (R\R+S)SR] (LVOT if &gt; 0.6) [1].
b) The V1-V2 S-Rd, calculated as [(V1S + V2S) – (V1R + V2R)] (LVOT if &lt; 1.625) [2].
c) The V2S\V3R amplitude ratio (LVOT if &lt; 1.5) [3].
d) The transition zone index (TZI), obtained by subtracting the transition zone of the PVC with that of the SR (LVOT if &lt; 0) [4].
We extended the use of these criteria to the precordial leads V1 to V3; for TR the equation was applied to amplitude as well as duration measurements.

Results
Comparison of PVC QRS morphology with that of SR.
1. The diagnostic accuracy of the TR showed incremental values moving from lead V1 to V3, both using amplitude and duration measurements; compared to the modest accuracy of the V2 TR (AUC 0.630, 0.727), the V3 TR (LVOT if &gt; 1) showed an accuracy of 85.3% (AUC 0.804, 0.855).
2. Simplifying the complex TR equation, comparing R or S waves of the PVC with those of the SR, we again found incremental values of accuracy moving from lead V1 to V3, with better results for the SVT\SSR compared to the RVT\RRS; the V3 SVT\SRS) (LVOT if &lt; 1) showed an accuracy of 86.6% (AUC 0.917).
3. The TZI showed in our series a lower diagnostic yield compared to that of the literature (AUC 0.748, accuracy 73.3%)
Comparison of PVC QRS morphology between two contiguous leads:
4. Compared to the V1-V2 S-Rd (AUC 0.830), the V2-V3 S-Rd (AUC 0.855), calculated as [(V2S + V3S) – (V2R + V3R)] showed greater accuracy (82.2%).
5. Similarly, compared to the V1S\V2R amplitude ratio (AUC 0.774), the V2S\V3R (AUC 0.930) showed the greatest accuracy (88.8%, with a more balanced sensitivity and specificity moving the cut-off for the diagnosis of origin from LVOT to &lt; 2), resulting the criterion with the highest diagnostic yield.

Conclusions
variables that compare the morphology of the QRS of the PVC of two contiguous leads have greater accuracy than those that compare the morphology of the QRS of the PVC with that of the SR, with greater diagnostic yield when applied from lead V1 to V3; the V2S\V3R ratio represents the best criterion, with high sensitivity, like the V3 transition ratio; the simple ratio (SVT\SSR) can virtually replace the more complex TR, with similar accuracy but high specificity.