Who Was Studied?
In this study, published in the Circulation: Arrhythmia and Electrophysiology, the researchers pooled data from 5 large quaternary referral centers. The patients were <21 years or any age with congenital heart disease, systemic ventricular ejection fraction (SVEF) <45%, symptomatic heart failure, and significant electrical dyssynchrony prior to CRT.
The primary outcome was an ordinal response in SVEF at 6 or 12 months, i.e., improved (≥5% absolute SVEF increase), 2) unchanged, or 3) worsened.
For the longer-term effect, CRT recipients were also compared with a propensity‑matched control cohort using the trajectory of SVEF over a median 5.1‑year follow‑up.
How Often Did CRT Help?
Of 167 CRT recipients, 150 had evaluable 6–12 month data. The data suggested that 96 patients (64%) showed improved SVEF, 26 (17%) had no change, and 28 (19%) had worsened SVEF. 
The mean SVEF increase among CRT recipients was 11%, with an interquartile range of 3%–21%, underscoring that for many children and CHD patients, CRT can deliver clinically meaningful reverse remodeling.
In the longer-term comparison with 324 matched controls, most subgroups demonstrated a more favorable SVEF trajectory with CRT over years of follow‑up, supporting CRT as a disease‑modifying strategy rather than a short‑term fix.
Who Responds Best? Key Predictors
Univariable ordinal regression identified several baseline features associated with better CRT response. These include lower baseline SVEF, biventricular circulation, systemic left ventricle (LV), and conduction delay to the lateral wall of the systemic ventricle 
In contrast, the response was less convincing in 2 groups. These were patients with a systemic right ventricle and patients without a prior single‑site pacemaker.
Clinical Takeaways for Pediatric & Congenital Cardiologists
For clinicians juggling complex pediatric and CHD heart failure cases, this study offers several practical messages:
CRT often works, but not universally: Roughly two‑thirds of eligible children/CHD patients gained ≥5% SVEF, with an average 11% absolute improvement, reinforcing CRT as a key option in advanced pediatric heart failure.
Patient selection matters: The best candidates appear to be those with lower baseline SVEF, biventricular circulation, a systemic LV, and documented conduction delay to the systemic ventricular lateral wall
Systemic RV patients remain a gray zone: Benefit in those with a systemic right ventricle was not clearly demonstrated, underlining the need for cautious expectations and individualized decision‑making in this subgroup.