{'fraction_non_alphanumeric': 0.023016517736257784, 'fraction_numerical': 0.0027078256160303275, 'mean_word_length': 5.643884892086331, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Right ventricular pacing maneuvers for the differential diagnosis of supraventricular tachycardia

Dear Editor We read the article “Anterograde His bundle activation during right ventricular overdrive pacing in supraventricular tachycardia” by Elbatran et al with interest.1 We believe that their study is likely to form a valuable addition to the literature. They reported that anterograde His bundle activation, atrial acceleration, and extranodal response to parahisian pacing generally exclude atrioventricular nodal reentrant tachycardia (AVNRT) and favor the diagnosis of atrioventricular reentrant tachycardia (AVRT). Narrow complex tachycardias are usually of supraventricular origin and have many different types and mechanisms. However in clinical practice, the term supraventricular tachycardia (SVT) is usually referred to three main types of tachycardia: (a) AVNRT, (b) AVRT, and (c) atrial tachycardia. Differential diagnosis of these three tachycardias is critically important because successful ablation of SVT is dependent on an accurate diagnosis of the tachycardia. We know that entrainment of tachycardia cycle by right ventricular (RV) pacing provides useful information for the differential diagnosis of SVT. To date, several diagnostic maneuvers during RV pacing have been defined such as postpacing interval minus tachycardia cycle length (PPI-TCL), ventricular extra stimulation during tachycardia atrial response upon cessation of pacing, anterograde His activation during entrainment, stimulus-atrial, ventriculoatrial intervals, and parahisian pacing.2–4 These maneuvers are useful for the differential diagnosis of AVNRT, AVRT, and AT. Besides, PPI-TCL is useful to differentiate the left-sided accessory pathways from right-sided accessory pathways. However, none of these maneuvers are highly specific or sensitive for the differential diagnosis of SVT. Therefore, a combination of more than one maneuver helps in differentiation. As mentioned by authors, none of the patients in AVNRT group show anterograde His bundle activation. However, authors determined anterograde His bundle activation in 20 of 32 patients in the AVRT group. Although limited by the small number of the study sample, it is clear that anterograde His bundle activation during RV pacing is highly specific (100%) for the diagnosis of AVRT. But it still had moderate sensitivity. We believe that the main problem is to increase the diagnostic specificity of anterograde His bundle activation. In left-sided accessory pathways, anterograde His bundle activation generally does not occur due to the mechanism and location of accessory pathway. Similarly, in rare cases, stable fusion may occur above His bundle and in those patients we cannot determine anterograde His bundle activation. However, for the rest of AVRT patients, we can speculate that several factors may improve the detection of anterogradeHis bundle activation.Wehave a few questions and would like to hear the opinion of the authors about these issues. First, can we improve the detection of anterograde His bundle activation by changing the pacing cycle length?Does increasing or decreasing the pacing cycle length prevent the overlapping of the signals determined fromHis bundle catheter? Second, should changing the RV pacing sides or pacing near the coronary sinus be helpful? Third, did the authors use pharmacologic agents such as beta-agonists or adenosine during electrophysiologic study? Do they think that it may affect the sensitivity of anterograde His bundle activation? Finally, are there any other mechanisms or factors be helpful for the improvement of the determination of anterograde His bundle activation.