Abstract 1542: Value of High Output Pacing in Mapping of Post-Infarction Ventricular Tachycardia
Introduction: Identification of critical isthmus sites for post-infarction ventricular tachycardia (VT) ablation can be challenging. Unexcitable scar during pacing can identify one of the borders of the re-entry circuit. This area however is not thought to be critical to the circuit. Because of current-to-load mismatch, higher power might be required in order to obtain capture of individual surviving muscle bundles within scar tissue. The purpose of this study was to evaluate the value of high output capture of scar tissue in patients with post-infarction VT.
Methods: In a consecutive series of 18 patients (15 men, age 62 ± 9, EF 0.28 ± 0.15) with post-infarction VT, mapping was performed using an electroanatomic mapping system. A voltage map was obtained during sinus rhythm and bipolar pace-mapping was performed in areas with low voltage (< 1.5 mV) with an output of 10 mA at a pulse width (PW) of 2 ms. High output capture was defined when capture at these settings failed but capture could be achieved with increased output. If there was no capture at the initial settings, output was increased to 20 mA at a PW of 2 ms, eventually the PW was increased up to 10 ms as required to achieve capture. A critical isthmus was defined as a site with a matching pace-map, and/or matching stimulus-QRS to electrogram-QRS intervals in the presence of concealed entrainment, and/or mechanical termination of VT and failure to induce VT after radiofrequency ablation.
Results: Focal areas with high output capture could be observed in 10/18 (56%) patients. In 9/10 patients in whom high output capture was present (mean output: 20 mA; mean pulse width: 7.4 ms), this area was critical for the re-entry circuit of 10 VTs (cycle length 444 ± 72 ms). A total of 77 VTs (cycle length 390 ± 115 ms) was induced in these patients. Forty-three isthmus sites could be identified and effectively ablated for 56 of the VTs. During a follow-up of 4.9 ± 5.3 months 2 patients had VTs that were not targeted during the ablation.
Conclusions: High output pacing is helpful in identifying critical areas of post-infarction VT that otherwise might be missed.