Cycle length criteria for His-bundle capture are capable of determining pacing types misclassified by output criteria

Background: His-bundle pacing is currently defined according to the output criteria. However, potential nonselective His-bundle pacing (NSHBP) might be misclassified as right ventricular pacing by the output criteria. Objective: The purpose of this study was to use the novel cycle length (CL) criteria by decremental CL pacing to determine the type of pacing and to differentiate NSHBP from right ventricular pacing in particular. Methods: His-bundle pacing was performed in 212 patients with normal His-Purkinje conduction (group 1) and 39 patients with His-Purkinje conduction disease for correction of the condition (group 2). The CL criteria state that if decreasing the CL to a certain level results in QRS morphology changes, then NSHBP is ascertained. Results: NSHBP was obtained in 170 patients in group 1 and 22 patients in group 2. In group 1, NSHBP was validated in 160 patients by both output criteria and CL criteria. NSHBP was misclassified as right ventricular pacing by the output criteria but was correctly classified by CL criteria in the remaining 10 patients (6%). In group 2, NSHBP was all validated by both criteria. Among the 192 patients with NSHBP, the shortest CL (318 ± 29 ms; range 270–470 ms) with which a stimulus can be conducted along the His bundle was at least 20 ms longer than that of surrounding myocardium (264 ± 16 ms; range 250–330 ms) for each patient, suggesting potentially high sensitivity of the CL criteria. Conclusion: CL criteria can determine the types of cardiac pacing independently and can avoid misclassification by output criteria.