Interfacility Transfer of Medicare Beneficiaries With Acute Type A Aortic Dissection and Regionalization of Care in the United States

Abstract

Background: The feasibility and effectiveness of delaying surgery to transfer patients with acute type A aortic dissection-a catastrophic disease that requires prompt intervention-to higher-volume aortic surgery hospitals is unknown. We investigated the hypothesis that regionalizing care at high-volume hospitals for acute type A aortic dissections will lower mortality. We further decomposed this hypothesis into subparts, investigating the isolated effect of transfer and the isolated effect of receiving care at a high-volume versus a low-volume facility.

Methods: We compared the operative mortality and long-term survival between 16 886 Medicare beneficiaries diagnosed with an acute type A aortic dissection between 1999 and 2014 who (1) were transferred versus not transferred, (2) underwent surgery at high-volume versus low-volume hospitals, and (3) were rerouted versus not rerouted to a high-volume hospital for treatment. We used a preference-based instrumental variable design to address unmeasured confounding and matching to separate the effect of transfer from volume.

Results: Between 1999 and 2014, 40.5% of patients with an acute type A aortic dissection were transferred, and 51.9% received surgery at a high-volume hospital. Interfacility transfer was not associated with a change in operative mortality (risk difference, -0.69%; 95% CI, -2.7% to 1.35%) or long-term mortality. Despite delaying surgery, a regionalization policy that transfers patients to high-volume hospitals was associated with a 7.2% (95% CI, 4.1%-10.3%) absolute risk reduction in operative mortality; this association persisted in the long term (hazard ratio, 0.81; 95% CI, 0.75-0.87). The median distance needed to reroute each patient to a high-volume hospital was 50.1 miles (interquartile range, 12.4-105.4 miles).

Conclusions: Operative and long-term mortality were substantially reduced in patients with acute type A aortic dissection who were rerouted to high-volume hospitals. Policy makers should evaluate the feasibility and benefits of regionalizing the surgical treatment of acute type A aortic dissection in the United States.

Keywords: aneurysm, dissecting; causality; confounding factors, epidemiology; epidemiology; patient transfer; surgery.

Figure 1.

Landscape of study population. The top row represents the presenting hospital type for each patient. Percentages are row percentages within initial group. Patients transferred from high-volume hospitals were excluded from analyses.

Figure 2.

Mortality after surgery for acute type A aortic dissection stratified by transfer status, volume status, and reroute status. All-cause mortality is plotted against time after surgery and stratified by whether patients (A) were transferred, (B) had surgery at a high-volume or low-volume hospital, and (C) were rerouted to a high-volume hospital. Numbers of patients at risk are included below each figure. Note that some numbers are not integers due to matched pairs with variable controls. CI, confidence interval; HR, hazard ratio

Figure 3.

Hospital volume-dependent hazard of operative mortality after repair of acute type A aortic dissection. The hazard ratio for operative mortality among patients undergoing repair of acute type A aortic dissection at a hospital of a given volume, compared with patients undergoing surgery at a hospital at the upper decile for volume, is plotted against hospital aortic surgery volume as a continuous variable (red solid line). Dashed red lines represent the 95% confidence interval. Hospital volume is based on the number of proximal aortic surgeries performed during the study period. The reference is set to 105 cases (upper decile of surgical volume and definition used for “high volume” in the present study. The horizontal gray line represents a relative hazard of 1. The histogram at the bottom of the figure depicts the number of hospitals with that particular volume.

Figure 4.

Location of United States hospitals categorized by aortic surgery volume and proportion of patients having surgery at high-volume hospitals by state. (A) The geographic location of each hospital in the study that treated a Medicare beneficiary with a type A aortic dissection stratified by proximal aortic and arch surgery volume. The hospital locations are plotted over a population density map of the counties within the continental United States (not shown: Alaska and Hawaii, 0 high-volume hospitals). (B) The proportion of patients that received surgical treatment for an acute type A aortic dissection at a high-volume hospital within each state of the continental United States (not shown: Alaska, 0%; Hawaii, 0%).