Cardiac Magnetic Resonance Assessed Fractal Complexity and Global Longitudinal Strain Predict Survival in Patients Undergoing Lung Transplant Assessment

Abstract

Right ventricular (RV) function strongly influences prognosis, but key metrics are not clear, particularly in WHO classified Group 3 pulmonary hypertension (PH) associated with lung disease. We assessed a cardiac magnetic resonance (CMR) index of global longitudinal strain as well as right ventricular (RV) trabecular complexity by its fractal dimension (FD), correlating to imaging indices and prognosis, in patients with underlying lung disease. Patients underwent CMR to assess biventricular volumes, and function. RV FD was assessed on CMR using freely available custom-written code (FracAnalyse). Global longitudinal strain was analysed using Circle CVI42. RV functional adaptation to increased afterload was assessed with the RV-pulmonary arterial (PA) coupling index (left ventricular stroke volume(SV)/RV end-systolic volume(ESV) ratio). Survival was analysed using the Cox proportional hazard ratio with the primary outcome of time to death. 56 patients with underlying lung disease underwent lung transplant assessment between 2013-2018, with a median follow up of 24 (interquartile range IQR 21.3) months. 35 out of 43 patients had echo-detected pulmonary hypertension with an estimated RV systolic pressure of >35mmHg. RV fractal dimensions, global longitudinal strain, and indexed RV end-diastolic and end-systolic volumes, and DLCO were significantly different in patients who died. On multivariate analysis, survival was predicted by global longitudinal strain and an index of RV fractal dimension (Table 1). Fractal analysis of RV trabecular complexity and global longitudinal strain, both RV functional adaptations to afterload assessed by CMR, predict survival in patients referred for lung transplant assessment. Assessment in a larger cohort is required to determine the utility of these metrics.