Center LVAD Volume and Outcomes After Implant
How does the surgical volume of a center impact outcomes in patients with a left ventricular assist device (LVAD)?
The study investigators evaluated 7,416 patients undergoing LVAD implants from centers that provide surgical volumes, enrolled into INTERMACS (Interagency Registry for Mechanically Assisted Circulatory Support). The total INTERMACS cohort was comprised of 14,014 patients including those who underwent primary continuous flow LVAD or biventricular assist device implant between 2009 and 2015. They categorized center LVAD volume as very low (≤10 implants/year, n = 617 patients), low (11-30 implants/year, n = 2,561), medium (31-50 implants/year, n = 2,458), and high volume (>50 implants/year, n = 1,750). The main outcome of interest was patient survival based on center volume, derived from Kaplan-Meier and multivariable Cox regression. Early mortality (defined as death within 90 days of mechanical circulatory support implant) was the secondary outcome. They chose the 90-day time frame for early mortality because prior INTERMACS analyses have shown this to be the postoperative time frame with the highest hazard for adverse outcomes following LVAD, after which the hazard declines.
The study authors found that overall survival was associated with center volume (p = 0.003): 71 ± 1.8% (very low volume), 81 ± 0.8% (low volume), 83 ± 0.8% (medium volume), and 79 ± 1.0% (high volume) at 1 year. Compared with medium volume centers, the 90-day mortality was higher in very low volume (odds ratio [OR], 1.35; p = 0.04) and high volume (OR, 1.28; p = 0.018) VAD centers. The adjusted hazard ratio (HR [95% CI]) for mortality was 1.32 [1.11-1.56], 1.07 [0.95-1.21], and 1.17 [1.03-1.30] for very low, low, and high volume centers, respectively. After controlling for known correlates of LVAD mortality, the authors found that adjusted mortality remained 32% higher at very low volume LVAD centers compared with medium volume centers. After adjusting for known LVAD mortality risk correlates, they found that overall mortality remained 17% higher in high volume centers compared with centers implanting 31-50 VADs a year. The investigators found that center volume did not predict mortality (p = 0.25) in INTERMACS profile 1-2 patients (n = 3,688).
The authors concluded that patients undergoing LVAD implant at very low (<10 implants per year) and high volume US centers (>50 implants per year) have inferior outcomes to patients having surgery at centers performing 31-50 VADs a year.
This is an important study because its findings suggest bimodal risk of adverse outcomes associated with center volume: very low and high volume centers have lower average survivals than centers that perform 30-50 VADs a year. The next step is to evaluate what factors affect adverse outcomes so that survival can be improved in both low and high volume centers.
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