LAUSR

Editorial for “Diverse Right Ventricular Remodelling Evaluated by Cardiac Magnetic Resonance Imaging and Prognosis in Eisenmenger Syndrome with Different Shunt Locations” Eisenmenger syndrome (ES) represents a severe phenotype of pulmonary arterial hypertension (PAH) associated with congenital heart disease. The end stage is characterized by cyanosis, secondary erythrocytosis, and multiorgan complications, which result from paradoxical right-to-left shunting. Resting oxygen saturation, sinus rhythm, shunt location, and biventricular function have previously been identified as predictors of death in patients with ES. However, the pathophysiological process of maladaptive right ventricular (RV) remodeling is complex, and its prognostic implications are less well understood. In ES patients, RV remodeling is commonly attributed to the development of PAH. However, adults with ES have a survival advantage over those with idiopathic PAH, signaling complexities of RV function that are not well understood. PAH represents the most direct method of RV remodeling from increased RV afterload. In congestive cardiac failure patients, where the prognostic impact of RV remodeling is well studied, RV dysfunction occurs as a result of intrinsic myocardial dysfunction, maladaptive left ventricular (LV) remodeling, impaired ventricular septal motion, and pericardial constraints improved by progressive LV volume overload. RV dysfunction may be further exacerbated by tricuspid regurgitation, which results from RV and tricuspid annular dilatation. In this issue of JMRI, magnetic resonance (MR) imaging was used to prospectively investigate RV remodeling and its relationship with prognosis in ES subgroups classified by shunt location (prevs. post-tricuspid valve). Patients with atrial septal defect and/or anomalous pulmonary venous drainage were classified in the pre-tricuspid group, whilst those with a ventricular septal defect and/or patent ductus arteriosus were classified into the post-tricuspid group. A total of 54 patients were analyzed (16 pre-tricuspid shunt and 38 post-tricuspid shunt). MR evaluation included RV morphology, systolic function, RV–pulmonary artery (PA) coupling, and myocardial fibrosis. Invasive hemodynamic indices were measured by right heart catheterization (RHC). Prognosis was compared between ES subgroups. The endpoint was all-cause mortality or readmission for heart failure. Although there was a significant difference in patient age (43 vs. 34 years; P = 0.02), which is a limitation of the study, the demographic data were otherwise well balanced. Patients with pre-tricuspid shunt had lower mean pulmonary artery systolic pressure (mPAP) and pulmonary vascular resistance index (PVRi) by RHC but higher pulmonary to systemic flow ratio. Patients with post-tricuspid shunt were characterized by higher mPAP and PVRi but smaller pulmonary to systemic flow ratios. However, interpreting invasive hemodynamics in ES is complex, as PAH may be confounded by elevated left atrial filling pressures, pulmonary venous obstruction, and because PVRi calculation is flow dependent. MR is an indispensable addition to RHC in ES patients as it is able to characterize shunt location and anatomy, biventricular function, and RV–PA decoupling—all of which give a more complete understanding of PAH than pulmonary pressures alone. In this study, patients with a pre-tricuspid shunt were found to have larger RV dimensions, increased RV volume indices and RV/LV volume ratio, worse RV ejection fraction, evidence of RV–PAC decoupling as defined by ratio of RV stroke volume to end-systolic volume, and poorer clinical outcomes. These findings highlight the importance of RV dysfunction as a prognostic tool in patients with PAH, irrespective of etiology. Utilization of MR also allows for myocardial tissue characterization, an area in which conventional echocardiographic techniques are limited. Patients in the pre-tricuspid group had higher native T1 values and extracellular volumes, as well as a higher burden of myocardial fibrosis. These are important markers of poor prognosis in LV