• Dual Chamber Pacing Tied to Better Outcomes, QOL LOCK HF analysis adds to advantages over RV-only pacing

    Improved clinical outcomes and quality of life can be added to the list of advantages biventricular pacing holds over right ventricular (RV) pacing in cardiac resynchronization therapy (CRT), a BLOCK HF study analysis suggested.

    Biventricular pacing was associated with better outcomes as early 6 months, with 53% versus 39% of RV-only pacing patients improved on the clinical composite of death, heart failure-related urgent care, and adverse left ventricular remodeling. Another 24% versus 33% had those composite scores unchanged, and 24% versus 28% worsened, respectively (posterior probability [PP]=0.998, where ≥0.95 was considered significant for benefit).

    The biventricular pacing advantage held at 2 years, Anne B. Curtis, MD, of New York’s University at Buffalo, and colleagues reported in the prespecified secondary analysis in the Journal of the American College of Cardiology.

    Improvement in New York Heart Association (NYHA) functional classification did not differ significantly between groups at 6 months or 2 years, although analysis adjusted for crossovers showed more patients improved by 1 class or maintained their status with biventricular pacing at 2 years (PP=0.952).

    Patients with biventricular pacing improved on self-reported quality of life at first (6 months: +5 points on the Minnesota Living With Heart Failure Questionnaire versus +0.3 for RV pacing, PP=0.998), but that effect diminished by 2 years (+2.6 versus +1.5, PP=0.727).

    “For patients with atrioventricular block and systolic dysfunction, biventricular pacing not only reduces the risk of mortality/morbidity, but also leads to better clinical outcomes, including improved quality of life and heart failure status, compared with RV pacing,” the authors wrote, which they chalked up to “preventing future dyssynchrony and heart failure as much as treating currently existing dyssynchrony.”

    The same trial had previously shown that “biventricular-paced patients had a reduced incidence of a composite endpoint of death, heart failure-related urgent care, and adverse left ventricular [LV] remodeling,” they noted.

    It has become clear that “chronic delivery of RV stimulation >40% of the time may induce intraventricular dyssynchrony and thereby deteriorate cardiac function and prognosis, particularly in patients with pre-existing ventricular dysfunction and heart failure,” Frieder Braunschweig, MD, PhD, and Cecilia Linde, MD, PhD, both of Karolinska University Hospital in Stockholm, wrote in an accompanying editorial.

    “One could speculate that the protective effect of biventricular pacing against adverse ventricular remodeling by RV pacing would further increase with time,” they wrote, though it appears “that the main benefit of biventricular pacing is likely observed within the first year after implantation.”

    The BLOCK HF substudy included 691 patients with atrioventricular (AV) block and heart failure who were randomized to biventricular or RV pacing with their pacemaker or defibrillator. The majority (73%) were in NYHA functional class I or II at baseline.

    Curtis and colleagues acknowledged that their primary limitation was “missing data due to either missed visits or study closure.” Additionally, “there was an imbalance in crossovers between the arms, and sensitivity analyses showed that results at later time points may have been affected by discontinuation of randomized therapy,” they noted.

    “Although the present paper provides further important support for biventricular pacing as a first line alternative in patients with high-degree AV block, uncertainties remain,” Braunschweig and Linde agreed, citing the number of patients who had unsuccessful device implantation (6.3%) or were otherwise excluded (8.3%) from the trial for various reasons.

    “In a clinical setting without the option of a run-in, most of these patients would have been counted as a treatment failure, thus diminishing the advantages of biventricular pacing described in the study. By the same token, an a priori decision for RV pacing would preclude the complication risk associated with LV lead implantation, an advantage not reflected by the results of the present study,” they commented.

    The pair also raised concerns over unintentional unblinding, a real possibility if phrenic nerve stimulation occurred.

    The editorialists concluded that “discussions about the optimal use of biventricular pacing in patients with high-degree AV block is expected to continue.”


    The BLOCK HF study was sponsored by Medtronic.

    Curtis declared serving on the advisory boards of St. Jude Medical, Sanofi, Pfizer, Janssen Pharmaceuticals, and Daiichi-Sankyo; and receving royalties from Pressure Products and Merit Medical; as well as consulting income from St. Jude Medical and Medtronic.

    Braunschweig reported relationships with Biotronik, Boston Scientific, Medtronic, and St. Jude Medical.

    Linde reported relationships with AstraZeneca, Biotronik, Cardio3, Medtronic, Novartis, St. Jude Medical, and Vifor.


    Journal of the American College of Cardiology


    Curtis AB, et al “Improvement in clinical outcomes with biventricular versus right ventricular pacing” J Am Coll Cardiol 2016; DOI: 10.1016/j.jacc.2016.02.051.


    Journal of the American College of Cardiology


    Braunschweig F, et al “Biventricular stimulation: a BLOCKbuster in cardiac pacing?” J Am Coll Cardiol 2016; DOI: 10.1016/j.jacc.2016.01.088.

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