Abstract 2450: New Criteria During Ventricular Overdrive Pacing to Differentiate ORT From AVNRT
Background: Ventricular overdrive pacing (VOP) may provide useful information for differentiating orthodromic reciprocating tachycardia (ORT) from atrioventricular nodal reentrant tachycardia (AVNRT), independent from entrainment success.
Methods: 62 patients (pts) with ORT and AVNRT and VOP trains from the right ventricle (RV) within 40 ms of the tachycardia cycle length were included to assess the response to fusion beats at the beginning of VOP trains and to measure the ventricular stimulus to earliest atrial electrogram interval (SAI) when the VOP train resulted in termination of ORT. The SAI was measured on the atrial beat following the first fully RV paced beat in the train and each subsequent retrograde atrial beat until pacing terminated. A fixed SAI was defined as varying by <10 ms.
Results: There were a total of 55 VOP trains in 32 pts in the ORT group. 26 (47%) resulted in successful entrainment. Ventricular fusion beats were seen with the first VOP train in 22/32 (69%) pts and resulted in atrial pre-excitation in 15/22 (68%) pts, atrial delay in 3/22 (14%) pts, and termination with no subsequent atrial activation in 2/22 (9%) pts. No effect on atrial activation timing was seen in 2/22 (9%) pts. There were a total of 61 VOP trains in 30 pts in the AVNRT group. 39 (64%) VOP trains resulted in successful entrainment. Fusion beats were seen with the first VOP train in 20/30 (66%) pts and had no effect on atrial activation timing. Fusion beats that advance or delay subsequent atrial activation or terminate SVT with no subsequent atrial activation were associated with ORT (sensitivity 62% and specificity 100%). A total of 38/62 (61%) pts had VOP trains leading to termination (22 and 16 pts in the ORT and AVNRT groups respectively). The stimulus to earliest atrial electrogram interval (SAI) was fixed in 20/22 pts (91%) with ORT and in 0/16 (0%) of patients with AVNRT. A fixed SAI during a VOP train that terminates SVT was associated with ORT (sensitivity 62%, specificity 100%).
Conclusion: ORT is the likely mechanism when a ventricular fusion beat during a VOP train affects atrial activation timing or terminates SVT and when a fixed SAI is observed during a VOP train that terminates tachycardia.