BACKGROUND: The distal insertion of right atriofascicular pathways remains a source of debate. Moreover, there are various morphologies of preexcited QRS complexes involving atriofascicular pathways that have been poorly characterized. OBJECTIVE: To characterize the distal insertion of atriofascicular accessory pathways and to provide a mechanism for the change in QRS morphology observed between short and long ventriculo-His (V-H) antidromic atrioventricular reentrant tachycardias (AVRTs) in the same patient. METHODS: Thirteen patients with atriofascicular pathways and preexcited AVRT with short V-H and long V-H intervals were studied. For each patient, the tachycardia cycle length, V-H interval, QRS width, and axis were compared. A baseline His-ventricular interval was also recorded. RESULTS: The baseline His-ventricular interval was significantly longer than the V-H interval during antidromic AVRT (median 50 ms vs. 10 ms; P < .0001). Retrograde right bundle branch block increased the V-H interval (median 10 ms vs. 85 ms; P < .0001), the tachycardia cycle length (median of 302.5 ms vs. 350 ms; P < .0001), and the QRS width (median 120 ms vs. 140 ms; P < .0002). At least subtle changes in QRS morphology, axis, or QRS width were seen in all patients. CONCLUSIONS: The distal insertion of right atriofascicular pathways fuses with the right bundle branch. The various QRS morphologies seen during the change from short V-H to long V-H antidromic AVRT can be explained by fusion, particularly over the left anterior fascicle.
BACKGROUND: The distal insertion of right atriofascicular pathways remains a source of debate. Moreover, there are various morphologies of preexcited QRS complexes involving atriofascicular pathways that have been poorly characterized. OBJECTIVE: To characterize the distal insertion of atriofascicular accessory pathways and to provide a mechanism for the change in QRS morphology observed between short and long ventriculo-His (V-H) antidromic atrioventricular reentrant tachycardias (AVRTs) in the same patient. METHODS: Thirteen patients with atriofascicular pathways and preexcited AVRT with short V-H and long V-H intervals were studied. For each patient, the tachycardia cycle length, V-H interval, QRS width, and axis were compared. A baseline His-ventricular interval was also recorded. RESULTS: The baseline His-ventricular interval was significantly longer than the V-H interval during antidromic AVRT (median 50 ms vs. 10 ms; P < .0001). Retrograde right bundle branch block increased the V-H interval (median 10 ms vs. 85 ms; P < .0001), the tachycardia cycle length (median of 302.5 ms vs. 350 ms; P < .0001), and the QRS width (median 120 ms vs. 140 ms; P < .0002). At least subtle changes in QRS morphology, axis, or QRS width were seen in all patients. CONCLUSIONS: The distal insertion of right atriofascicular pathways fuses with the right bundle branch. The various QRS morphologies seen during the change from short V-H to long V-H antidromic AVRT can be explained by fusion, particularly over the left anterior fascicle.