Conduction System Pacing correction of pacemaker induced cardiomyopathy made it simple despite T wave memory at implant

Introduction

Successful conduction system pacing (CSP) implants can be achieved using ECG qualitative criteria in lateral precordial leads (V5-V6): Presence of a S wave, of an isoelectric ST segment, and a positive T wave polarity. However, these criteria do not always work when a pacemaker induced cardiomyopathy dependent patient is upgraded to CSP, as T wave memory alters normal repolarization. A super response of resynchronisation is defined as >15% of left ventricular ejection fraction (LVEF) absolute increase at follow-up.

Methods

All patients receiving a CSP device, with a paced pre-implant ECG, were analyzed. Different ECG features were analyzed. Inter-peak V6-V1 values was used as gold standard and a 6-8 weeks post implant ECG was also obtained to ascertain resolution of T wave memory. A subset of patients had a LVEF assessment performed at follow-up.

Results

From a 5-year cohort of 697-consecutive patients (pts), 125 were CSP-upgrades due to pacemaker induced cardiomyopathy (17,9%). Mean-age was 77.4 y.o. (±0.2 years; range 22-94y.o.). Mean QRS was 178ms (range 114-248ms) before CSP attempt. Post implant mean-QRS was 140ms (range 90-202ms).The interpeak V6-V1 could not be measured in 50-pts (40%). A V6-V1 interpeak interval greater than 33ms was achieved in 38% of pts, and no association with any of the repolarization ECG markers to ascertain success was found. Most patients had a negative T wave post implant (81,5%); in those patients, T waves become positive (T wave memory) at 6-8 weeks post implant-ECG in 52% of cases, meaning negative T waves alone cannot indicate successful or failed CSP at implant. However, depolarization markers could help in these patients, as the presence of a S wave in precordial lateral leads had an accuracy of 80% to predict an inter-peak V6-V1 > 33ms; (sensitivity 75%, specificity 83%, PPV 69% and NPV 87%, p=0,0067). A subset of 15 of these pts presented a hyper response to CSP resynchronisation (LVEF >20% increase in absolute values), and 13 of these 15 pts presented with an S wave in V5-V6 at implant (see figure).

Conclusion

In CSP pacemaker upgrades, isoelectric ST segments and a positive T wave in lateral leads, even if rarely seen (19,5%), are associated with successful CSP implants (as in non paced patients); but negative T waves at implant turn positive in at least half or more of the cases, 6-8 weeks after (T wave memory carried from previous paced rhythm).

Ideally current of injury, interpeak V6-V1 and transition patterns while thresholds should guide these implants. Depolarization ECG markers could also be used to guide these CSP implants (as presence of a S wave in lateral leads and initial ‘r’ wave in V1); a presence of an S wave in V5-V6 at implant could be a marker of hyper response to CSP resynchronisation.CSP PICPM correction FAP