BACKGROUND: The sequence of atrial and ventricular electrograms following termination of ventricular pacing during supraventricular tachycardia has been shown to reliably differentiate atrial tachycardia from atrioventricular nodal reentrant tachycardia (AVNRT) and atrioventricular reentrant tachycardia (AVRT). However in patients with long HV intervals, this may be misleading due to a pseudo "A-A-V" response. The aim of the present study is to see if inclusion of the timing of the His-bundle in the electrogram response (ER) following ventricular pacing would reliably identify the mechanism of tachycardia in patients with long HV intervals. METHODS: Eight patients (7 men) with AVNRT and underlying bundle branch block and long HV (>55 msec) intervals underwent ventricular pacing at 10-40 msec shorter than the tachycardia cycle length during SVT. The ER was classified as "A-A-H" or "A-H" depending on the number of atrial electrograms (A) prior to His deflection following VEP. RESULTS: The ER following ventricular pacing was classified as A-H in all 8 patients. However, using conventional classification the response was A-A-V in 5 of 8 patients due to delayed ventricular activation secondary to long HV intervals and would erroneously suggest atrial tachycardia. The ER was A-V in only 1 of 8 patients. In the remaining 2 patients the A and V electrograms were simultaneous. CONCLUSIONS: Incorporating the His-bundle in the ER following ventricular pacing would eliminate the pseudo "A-A-V" response in patients with AVNRT and long HV intervals. Labeling the response to ventricular pacing as "A-H" or "A-A-H" is simple and more accurate.
BACKGROUND: The sequence of atrial and ventricular electrograms following termination of ventricular pacing during supraventricular tachycardia has been shown to reliably differentiate atrial tachycardia from atrioventricular nodal reentrant tachycardia (AVNRT) and atrioventricular reentrant tachycardia (AVRT). However in patients with long HV intervals, this may be misleading due to a pseudo "A-A-V" response. The aim of the present study is to see if inclusion of the timing of the His-bundle in the electrogram response (ER) following ventricular pacing would reliably identify the mechanism of tachycardia in patients with long HV intervals. METHODS: Eight patients (7 men) with AVNRT and underlying bundle branch block and long HV (>55 msec) intervals underwent ventricular pacing at 10-40 msec shorter than the tachycardia cycle length during SVT. The ER was classified as "A-A-H" or "A-H" depending on the number of atrial electrograms (A) prior to His deflection following VEP. RESULTS: The ER following ventricular pacing was classified as A-H in all 8 patients. However, using conventional classification the response was A-A-V in 5 of 8 patients due to delayed ventricular activation secondary to long HV intervals and would erroneously suggest atrial tachycardia. The ER was A-V in only 1 of 8 patients. In the remaining 2 patients the A and V electrograms were simultaneous. CONCLUSIONS: Incorporating the His-bundle in the ER following ventricular pacing would eliminate the pseudo "A-A-V" response in patients with AVNRT and long HV intervals. Labeling the response to ventricular pacing as "A-H" or "A-A-H" is simple and more accurate.