Left-ventricular-only cardiac resynchronization therapy with electrocardiographic optimization: 100-day follow-up
Authors: Thong T , Nguyen-Huu D , Truong V K N , Nguyen-Lien N , Nguyen-Thi-Cam T , Vuong-Dinh C , Vu-Manh T , Hoang-Phuong N 
Published: May 2024

Abstract

Background
LV-only (LVo) cardiac resynchronization therapy (CRT) was recognized in 2013 as a non-inferior alternative to bi-ventricular (biV) CRT [1]. In a triple-chamber device it can extend service life, reduce atrial fibrillation risk. A number of LVo systems have been proposed but have not been shown to be superior to biV [2] due to a lack of individualized optimization of the LV atrio-ventricular delay.

Purpose
An LVo algorithm with an electrocardiographic optimization for each patient along general principles was developed and successfully implanted in a dozen patients with triple-chamber devices. The algorithm has been reported earlier. Since the RV lead is redundant, a dual chamber CRT (dcCRT) version was developed, with just the RA and LV leads. A preliminary series of 8 dcCRT implants were performed with good results.

Methods
A 2-week training class on LV lead implantation was held in July 2023. Fourteen dcCRT’s were implanted. Inclusion criteria: CRT indications, Left-bundle-branch block, good A-RV conduction, mostly sinus rhythm. 100-day follow-ups were performed on 15 patients (including 2 earlier patients) and reported here.

Results
In Fig.1
Implant LVEFs (Simpson): 16% to 38%. At the 100-day follow-ups, the LVEFs range from 24% to 62%.
6 (40%) remained below LVEF 35%, 9 (60%) exceeded the 35% threshold, 3 (20%) exceeded 45%, including 2 (13%) with 56% and 62%.
Only 3 patients with small 2-3% LVEF improvements. All others were &gt;5%, up to 29%.
Since the devices can measure thoracic impedance, Z, 1024 times/hour, with the hourly average combined for a daily average, the 100-day daily Z trends were analyzed. The implant and 100-day Z’s are plotted in Fig.2. Except for the 2 patients whose Z measurements were left off, the universal upward Z trend is an indication of improved LV blood flow in all patients, helping reduced excessive lung fluid. Z changes range from 14 to 34 Ohms. Of the 2 patients in Fig.1 with only 2% LVEF improvements, their Z improvements were meaningful 23 Ohms increases!
The Z and LVEF trends indicate that the therapy had a 100% success.

Conclusions
The 100-day follow-ups of the ECG optimized LVo CRT of 15 patients with dcCRTs show results superior to what have been reported in previous biV studies, thanks to the ECG optimization. This indicates that this may be a superior alternative to biV CRT. While the study was done with dcCRT, it should be applicable to all triple chamber CRT (-P/-D) devices which can support LVo pacing.
Unlike other CRT algorithms, if the device supports LVo, it can be applied. It is safe since the programming can be reverted to biV at any time! This opens the possibility for improving the health of current CRT patients and extending the service lives of their devices, in addition to improved de novo results.
The dcCRT is no longer viable since bipolar LV leads have been discontinued in favor of quadripolar leads, but the results apply to all CRT systems.Fig 1. LVEF @ implant & 100 dayFig 2. Thoracic Z @implant & 100 day