Impact of Center Left Ventricular Assist Device Volume on Outcomes After Implantation: An INTERMACS Analysis

Abstract

Objectives: This study examined patient outcomes after left ventricular assist device (LVAD) implantation across a range of center surgical volumes.

Background: In order for a center to qualify for reimbursement, Centers for Medicare and Medicaid Services (CMS) requires it to implant ≥10 LVADs or total artificial hearts over a 3-year period. The impact of center LVAD surgical volumes on patient outcomes has not been thoroughly scrutinized.

Methods: Center volumes were provided for 7,416 patients undergoing LVAD implantation who were enrolled in INTERMACS (Interagency Registry for Mechanically Assisted Circulatory Support). Center LVAD volume was categorized as either very low (≤10 implants/year, n = 617), low (11 to 30 implants/year, n = 2,561), medium (31 to 50 implants/year, n = 2,458), or high (>50 implants/year, n = 1,750). The main outcome of interest was patient survival based on center volume derived from Kaplan-Meier and multivariate Cox regression.

Results: Overall survival was associated with center volume (p = 0.003), as follows: 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 ratios (HRs) for mortality were 1.32 (95% confidence interval [CI]: 1.11 to 1.56), 1.07 (95% CI: 0.95 to 1.21), and 1.17 (95% CI: 1.03 to 1.30) for very low, low, and high volume centers, respectively. Center volume did not predict mortality (p = 0.25; n = 3,688) in INTERMACS profile 1 patients (patients who had sustained cardiogenic shock) and profile 2 patients (patients with progressive hemodynamic decline despite inotropes).

Conclusions: Center volume correlates with post-VAD survival, with worse survival noted at very-low volume centers. These findings suggest that current U.S. VAD center standards warrant reconsideration.

Keywords: LVAD; mortality; risks; volume.

Figure 1. Survival in INTERMACS patients (years 2012–2014) by Center VAD Volume

Significant differences were noted on pairwise comparison between medium volume (31–50 VADs/yr) and high volume (>50 VADs/yr) and medium volume and very low volume (<10 VADs/yr) centers.

Figure 2. Survival in Profile 1–2 Patients Based on Center Volume

Survival was examined in Profile 1–2 patients. The Breslow p value favors the early period of the curve (operative interval). Significant differences in survival were noted in pairwise comparisons between high volume (>50 VADs/yr) centers and both medium (31–50 VADs/yr) and low volume (11–30 VADs/yr) centers. No differences were noted between very low volume (<10 VADs/yr) and medium volume centers.