Can CT Measures of Thoracic Muscle Provide Prognostication among Heart Transplant Recipients?

Abstract

Purpose As the waitlist of heart transplant patients continues to rise, it is important to objectively identify patients who will have positive outcomes post-transplant surgery. Skeletal muscle characterization by computed tomography (CT) is prognostic in various disease states and may provide important information for selecting optimal transplant candidates. The purpose of this study was to determine the impact of CT measured muscle measures on hospital length of stay (LOS) and mortality following heart transplantation. Methods A single-center heart transplant database from 1999 to present (n=370) was used to find all patients having a pre-transplant chest CT scan and associated outcome measures of LOS and mortality (n=189). Subjects having CT scans within 6 months of transplant were analyzed separately (n=103). Pre-transplant axial CT scans were analyzed for muscle quantity (cm2) and muscle density (Hounsfield units; HU) at the 12th thoracic vertebrae (T12) and aortic arch (AA) (i.e. pectoralis muscles). Muscle quantity was further delineated by low density area (tissue with HU from 0 - 30; LDM) and normal density area (tissue with HU range from 31 - 100; NDM). Mean HU was additionally measured at a region of interest in the middle of the right pectoralis major muscle on the AA axial slice (ROI HU). Results In a multivariable Cox model, after adjusting for age and gender, patients with higher mean ROI HU had greater 1-year survival rates in both the total cohort, and in the subset of patients with CT within 6-months of transplant (HR = 0.967, p=0.032, and HR = 0.950, p=0.043, respectively). In both the total cohort and within the subset cohort, patients having increased LDM, normalized to body surface area, had lower LOS days (p=0.045 and p=0.053, respectively) and those having a higher AA ratio of NDM to LDM had higher LOS days (p=0.005 and p=0.008, respectively). No other muscle metrics at the T12 area were prognostic. Conclusion In heart transplant recipients, greater ROI HU measured by CT scan prior to transplant was associated with higher 1-year survival whereas greater LDM (indexed to body surface area) at the AA axial slice was associated with lower LOS post-transplant. Prospective trials are necessary to determine the significance of CT muscle measures at the AA to identify patients that will positively benefit from heart transplantation.