P136 - T WAVE MEMORY PRECLUDES ECG CRITERIA TO ASCERTAIN IF THE CONDUCTION SYSTEM PACING LEAD HAS REACHED THE LEFT BUNDLE AREA

Background: Conduction System Pacing (CSP) gains acceptance as an alternative to cardiac resynchronization in pacemaker induced cardiomyopathy patients. ECG lateral lead repolarization is a new marker of CSP success, as if the depolarization occurs through conduction system, repolarization should be normal (positive T waves in lateral leads). When an upgrade to CSP from a previous paced rhythm is performed, T wave memory could affect CSP repolarization patterns.

METHODS AND RESULTS: We extracted all patients with a paced pre-implant ECG, and analyzed repolarization pattern (positive or negative T waves) in lateral V5-V6 leads. We compared these pattern with the already validated inter-peak V6-V1 values and with a 6-8 later ECG when available.
From a 5 year cohort of 595 consecutive patients, 108 were CSP upgrades from previous paced patients (18,2%). Mean age was 77.4 y.o. (± 0.2 years; range 22-94 y.o.). Medtronic 3830 leads were used for most implants. A His pacing was targeted in 6,5% of patients. Mean QRS was 178ms (range 114-248ms) before CSP attempt. Post implant, mean QRS (from the pacing spike) was at 140ms (range 90-202ms)
The interpeak V6-V1 could not be measured 42 patients (39%), a sign of a sicker population.
A V6-V1 interpeak interval greater than 33ms was achieved in 38% of patients, and there was no association with any of the ECG markers to ascertain succes.
Most of the patients had a negative T wave at implant (81,5%) that turned positive (T wave memory) on the ECG at 6-8 weeks post implant in 52% of cases, precluding to use abnormal repolarization as a mark of failure to CSP implant. On the other side, on the 25 patients (23%) with interpeak values of less than 34ms (a clear sign of failure to achieve CSP), there were only 3 patients (13%) with a positive T wave, making a positive T wave a sign of sucessful CSP implant, but a negative T wave of no value to guide the implant.

Conclusion: In CSP pacemaker upgrades, a positive T wave in lateral leads, even if rarely seen, is associated with more succesful CSP implants (as in non paced patients); but, a negative T wave turns positive in at least half or more of the cases, 6-8 weeks after (T wave memory carried from previous paced ryhthm). Other criteria should be used to guide these CSP implants.