Learning by failing: conduction system pacing and decrease in left ventricular ejection fraction identified at implant

Introduction Conduction system pacing (CSP) accepts selective (S) as nonselective (NS) left bundle branch pacing (LBBP) and left ventricular (LV) septal pacing, as part of physiological pacing. Most of patients (pts) maintain or increase their left ventricular ejection fraction (LVEF) when CSP is achieved. We try to find predictors associated with a proven decrease in LVEF during follow up. Methods From CSP pts implanted since 2019, we extracted those with a follow-up LVEF measurement, and we focused in pts with >5% decrease in LVEF. Implant features were looked at to find a pattern that help predict LVEF decrease. CSP success was judged with interpeak V6-V1 measurement and ECG new criteria seen at V6 standard ECG lead (presence of an S wave, positive T wave polarity and isoelectric ST segment) highly correlated with accepted interpeak V6-V1values: <33ms (LV septal:0-1 new criterion), >33ms (NS-LBBP: 2 new criteria) >44ms (S-LBBP: all 3 new criteria). Results Total cohort included 1028 pts, 62% males, median age 77,8 years old (+/-8,7 years). His pacing was attempted in 4.3% and LBBP in 95,7% of pts. 394 pts had a pre (49,2% +/- 13,7%) and post (51,2% +/-11,9%) LVEF measurement (52 pts were dead and 32 other pts were deemed too comorbid/old for a follow-up LVEF measurement). Finally, 31 pts (7,9% of pts) had a >5% decrease in LVEF at follow-up. LVEF decreased from -6 to -35%. All but two pts had >20% of ventricular pacing (mean 73% +/- 35%). Neither QRS duration (125,5+/-33ms pre-implant; to 137,4+/-12,8ms post implant), LVAT (78+/-12,8ms), nor V6-V1interpeak (36,9+/-14,9ms) could predict a LVEF reduction at follow-up. However, 25 of 31 pts exhibit at implant just a LV septal pacing pattern (0 or only 1 of the new ECG criteria); three other pts had lead micro dislodgment (ECG lost all new criteria), 1 had progressive valvular disease, 1 had chemotherapy and only 1 pt kept a good LBBP and had no reason to explain the LVEF decrease from 65% to 55% at follow up. Conclusion CSP pts decreasing their LVEF at follow-up can be identified by either the complete absence, or the achievement of only 1 new criterion present at implant (presence of an S wave, positive T wave polarity and isoelectric ST segment in V6); LV septal pacing may be not longer accepted and only NS-LBBP or S-LBBP should be sought and accepted as successful CSP implant to prevent LVEF decrease at follow-up.