Lateral wall repolarization in standard ECG as a criterion to democratize conduction system pacing

Conduction System Pacing (CSP) is gaining acceptance when high ventricular pacing burden is expected, and as an alterative to cardiac resynchronization. Criteria to ascertain CSP proper lead placement requires an EP system, not widely available. We hypothesized that when the conduction system is reached and depolarization occurs through normal, fast conducting tissue, repolarization (ST segment and T waves normalization) should be also normal in lateral leads.

We extracted all CSP attempted implants form our initial experience. Various accepted criteria for CSP capture were evaluated for each patient, along with two ECG only criteria: any r’/R’ in V1 and T wave polarity in lateral leads, as visual only criteria to CSP capture

A cohort of 368 consecutive pts was evaluated, 38% were women. Only Medtronic 3830 leads were implanted. Mean age was 77,4 (+/- 9,2 years; range 22-98 y.o.). Implant indication was: Sick sinus 26%, AV block 42%, Abnormal conduction induced cardiomyopathy 26%, AV node ablation 6%. A His was targeted in 7% of pts, and 30% had pre-implant narrow QRS. Leads were directed anterior 25%, posterior 21% and mid-septal in 54% of cases (based on inferior lead polarities). A QRS from the pacing spike of 140ms or narrower was achieved in 79% of implants, a LVAT narrower than 80ms in 73% (narrower than 90ms in 81% of pts and impossible to evaluate in 6% of pts: due to Q-S in V6), and a V6-V1 inter-peak higher than 40ms was achieved in 33% of pts (the criterion was impossible to measure in 35% of pts). An r’/R’ was visible in V1 in 57% of pts, and lateral wall normal repolarization was achieved in 37% at implant. All pts with lateral wall normal repolarization and V6-V1 inter-peak measurable, had values greater than 33ms; and no pts with V6-V1 inter-peak less than 33ms had a normal repolarization in lateral wall.

CSP implants are feasible using only ECG parameters. Lateral wall repolarization (normalization of ST segment and T waves when the lead arrives at the conduction system) is helpful to differentiate septal capture versus conduction system capture, is easy to evaluate in all patients, and provides another tool to ascertain CSP capture when r’/R’ are not seen (mostly in anterior oriented positions) or V6-V1 inter-peak is impossible to measure (lack of either positive V5-V6 or visible r’/R’ in V1). In our early experience it validates the fact that despite narrow QRS and visible r’/R’ in V1, most of our pts ended up with only with septal capture, and using lateral wall repolarization as an extra tool, would have prompted extra turns to arrive to the conduction system.