Novel cardiovascular magnetic resonance imaging techniques to predict exercise capacity and prognosis in non-ischaemic dilated cardiomyopathy.

Introduction

Non-ischaemic dilated cardiomyopathy (DCM) is defined as dilatation and systolic impairment of the left ventricle in the absence of significant epicardial coronary artery disease or abnormal loading conditions. DCM is common condition with a prevalence of 1 in 250 and has substantial mortality through sudden cardiac death and pump failure. Current risk prediction models are suboptimal, and further work is required to find predictors of adverse outcome. Global longitudinal strain (GLS) has had conflicting results as to whether it determines prognosis in DCM and further work is needed to clarify this. Myocardial blood flow (MBF) has been found to be abnormal in DCM in a previous study using cardiovascular magnetic resonance (CMR), but has not been established with the novel Kellman quantitative perfusion technique. Furthermore, the determinants of impaired MBF in DCM are not well described. Although exercise capacity is reduced in DCM, the determinants of this are unclear. MBF has been found to be an important predictor of exercise capacity in other cardiac conditions.

Methods

Firstly, a systematic review was undertaken of several established databases of medical literature to determine whether GLS was predictive of prognosis in DCM. Subsequently, 37 patients with DCM were prospectively recruited into the main study. These patients underwent cardiopulmonary exercise testing and comprehensive CMR imaging with GLS assessment and quantitative myocardial perfusion.

Results

Our systematic review yielded 8 studies: 4 studies had an association between GLS and clinical outcomes in DCM and 4 studies did not. The larger higher quality studies tended to favour an association between abnormal GLS and clinical outcomes. In the prospective study, DCM patients had reduced myocardial perfusion reserve (MPR) compared to healthy controls (1.97±0.65 vs 3.08±0.79, respectively; p<0.001). MPR was a significantly correlated with % predicted peak VO2 (r=0.385; p=0.019). This remained significant when assessed in all multivariable models. MPR did not correlate with CMR markers of fibrosis.

Conclusions

The systematic review provides evidence to support GLS as a predictor of prognosis in DCM. However further larger prospective studies are required. MPR is reduced in patients with DCM when compared to controls. MPR is a significant predictor of percentage predicted peak VO2 in patients with DCM. CMR markers of fibrosis do not appear to contribute to reduced MPR in patients with DCM.