We thank the authors for their interest in our article.1 First, we agree with them and would emphasize the difficulty of making a differential diagnosis between dual ventricular response due to dual atrioventricular nodal physiology and hisian extrasystole in bigeminy. In an attempt to differentiate between ventricular and dual response hisian bigemyned extrasystoles, we referred to the article published by Massumi et al.,2 where it is stated that–in the case of junctional parasystole-the interval between the junctional extrasystoles tend to be quite fixed and 2 variables namely PR1 and PR2 are seen. We observed slighty variable PR2 intervals as shown in Figure 1; also, the R2R2 intervals were not fixed. However, this does not completely rule out the diagnosis of junctional parasystole, which concurs with the statements in Massumi et al.2 Other electrocardiographs of the patient (not published) showed a similar phenomenon of 2 QRS complexes following 1 P wave. The sinus rates on these electrocardiographs differed from 60 bpm to 73 bpm with an exact doubling of the ventricular rate. This makes junctional parasystole less likely, unless the extrasystoles are triggered by normal conduction. Another electrocardiograph showed a PR2 lengthening until a P wave was followed by only 1 QRS complex, suggesting a type 1 pattern, second degree, atrioventricular block in the slow pathway. This could not be confirmed during the electrophysiology study. Although we did not map the ‘his’ region in detail, we retrospectively reviewed the activation pattern of the ‘his’ bundle. The ‘his’ potential appeared slightly earlier at the proximal bipolar electrode as compared to the distal electrode, both for AH1 and AH2. As stated by the authors and as published by Eizmendi et al.,3 a reversal in the activation pattern would have been expected with junctional extrasystoles.
In conclusion, we agree with the authors that the differentiation between dual ventricular response and junctional parasystole is difficult and that the criteria published to date only increase or decrease this probability. In our case, most of the published criteria pointed in the direction of a dual ventricular response. However, the final diagnosis was based on the successful termination of the arrhythmia by ablating the posterior aspect of the Koch's triangle; in other words, by ablation of the slow pathway.
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