The volume-outcome relationship for pulmonary endarterectomy in chronic thromboembolic pulmonary hypertension

Abstract

Background: We conducted a volume-outcome meta-analysis of pulmonary endarterectomy procedures for chronic thromboembolic pulmonary hypertension to objectively determine the minimum required annual case load that can define a high-volume centre.

Methods: Three electronic databases were systematically queried up to 1 May 2024. Centres were divided in volume tertiles. The primary outcomes were early mortality and long-term survival. Restricted cubic splines were used to demonstrate the volume-outcome relationship and the elbow-method was applied to define high-volume centres. Long-term survival was assessed using Cox frailty models.

Results: We included 51 centres (52 consecutive cohorts) and divided them into tertiles (T1: <6 cases per year; T2: 6-15 cases per year, T3: >15 cases per year), comprising a total 11 345 patients (mean age 52.3 years). Overall early mortality was 6.0% (T1: 11.6%; T2: 7.2%; T3: 5.2%; p<0.001), for which a significant nonlinear volume-outcome relationship was observed (p=0.0437) with a statistically determined minimal required volume of 33 cases per year (95% CI 29-35 cases), and a modelled volume of 40 cases per year corresponding to a 5.0% mortality rate. Nevertheless, early mortality still progressively declined in higher volume centres (from 6.7% to 5.4% to 2.9% in centres performing 16-50, 51-100 and >100 procedures annually). In addition, a significant volume effect was observed for long-term survival (adjusted hazard ratio per tertile 0.75, 95% CI 0.63-0.89; p=0.001).

Conclusion: There is a significant association between procedural volume and early mortality in pulmonary endarterectomy. An annual procedural volume of >33-40 cases per year may be used to define a high‑volume centre, although higher volumes still lead to progressively lower mortality rates.

Summary of the findings of the current study, defining high-volume centres for pulmonary endarterectomy in chronic thromboembolic pulmonary hypertension.

FIGURE 1

Geographical distribution (a), annual case volumes (b) and total sample sizes (c) of the included centres. Additional reference details can be found in the supplementary material.

FIGURE 2

Unadjusted (a) and adjusted (b) volume–outcome (V-O) relationship for early mortality and estimation of the case load that can define a high-volume centre based on unadjusted (c) and adjusted (d) early mortality. a and b present the restricted cubic spline analysis to express the relationship between volume and (un)adjusted early mortality. The size of the dots corresponds to the variance of the data. In other words, if the variance is small (i.e. there is a high degree of certainty), dots are large and relatively more weight is assigned to these findings. c and d graphically present the application of the elbow method to these curves to determine the case load that can define a high-volume centre. The solid red line represents the mean and dashed red lines represent the 95% confidence intervals.

FIGURE 3

Long-term survival for the overall cohort (a) and divided into tertiles (b).