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BOSTON -- Early cardiac resynchronization therapy (CRT) benefited patients with moderately reduced ejection fraction (EF) and left bundle branch block (LBBB) but no indication for pacing, according to trial findings that suggested potential prevention of disease progression.

In the crossover design trial of patients with a CRT-capable pacemaker implanted, mean left ventricular ejection fraction (LVEF) increased 5.3% during the CRT-on phase, with 42% recovering to above 50%. Average LV end-systolic volume (LVESV) improved 21% with CRT on, and 65% had a reduction of at least 15%.

Those randomized to have the CRT feature off and only receive VVI right ventricular pacing at 40 bpm for the first 6 months saw further significant improvement in both measures after switching to the CRT-on phase with DDDR biventricular pacing at 60-150 bpm for another 6 months.

And those for whom the CRT-on phase came first had rebound in both measures after switching it off, although not to as high a level as seen in those who waited longer to get CRT, Yong-Mei Cha, MD, of the Mayo Clinic in Rochester, Minnesota, reported at the . LVESV remained lower than baseline even after the 12-month trial period.

"Despite the CRT being turned off, the effects of CRT may persist beyond 6 months," she told attendees at the late-breaking clinical trial session. "Further studies are needed to investigate the CRT long-term outcomes of heart failure progression and survival in this patient population."

Another possibility is that there was a spillover effect from CRT that should have been accounted for by a washout period between treatment phases, suggested HRS session study discussant Bharat K. Kantharia, MD, of New York-Presbyterian Hospitals in New York City.

It was important to study, though, he acknowledged, because guidelines barely touch this relatively recent category of moderately-reduced ejection fraction, with LVEF in the 36-50% range. What they do say is that New York Heart Association (NYHA) stage II-IV heart failure with moderately-reduced LVEF patients without pacemaker indications who have LBBB can be considered for CRT with biventricular pacing, albeit with a class 2b recommendation due to a low level of evidence.

CRT has been proven to reduce LVEF, reduce heart failure admissions, and improve survival in patients with low LVEF of 35% or less, but it hasn't been as well established for the approximately 4% of the population who has heart failure with mild to moderately reduced EF, Cha noted.

"We confirmed early CRT improves cardiac systolic function in these patients, which supports HRS guidelines," she said in a press release from the HRS.

Her group's trial included 76 adults (mean age 68, 71% male, 68.9% NYHA class II) getting a CRT device implanted and an LVEF in the 36-50% range, LBBB, and a QRS duration of at least 130 ms who had been on optimal medical therapy for at least 6 months and whose LVEF had been stable over that period as proven by echocardiograms.

Those with advanced comorbid conditions, a short life expectancy, a preexisting CRT device, or a second- or third-degree atrioventricular block that required ventricular pacing were excluded.

Average LVESV declined from 116.1 mL at baseline to 109.4 mL with CRT-off first (P=0.11) then to 87.6 mL once it was turned on (P<0.001 vs both). It went from 109.8 mL at baseline to 91.7 mL in the CRT-on first group (P<0.001) and then rose to 99.3 mL after CRT was turned off (P=0.03 vs on and 0.01 vs baseline).

Average LVEF rose from baseline 41.3% to 42.7% in the CRT-off first group (P=0.19) to 46.0% once it was turned on (P=0.008 vs off and 0.002 vs baseline). It went from 42.7% to 48.5% (P<0.001) in the CRT-on first group then down to 45.9% once turned off (P=0.11 vs on and 0.03 vs baseline).

NT pro-BNP also declined with CRT on (P=0.018).

No significant improvement was seen in NYHA class or 6-minute walk distance between CRT-on and CRT-off by paired analyses, although the study appeared underpowered for those clinical endpoints.

In terms of adverse events, no deaths were deemed related to the procedure or LV failure. Two patients needed a lead revision, and two had right ventricular lead perforation requiring pericardiocentesis. No pneumothorax, pocket hematoma, or infection occurred.

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