Exploring the association between cardiac magnetic resonance parameters of cardiac function and exercise capacity in patients with coronary artery disease

Abstract Background Coronary artery disease (CAD) is the biggest cause of heart failure worldwide (1). Repeated or sustained ischaemic insult can result in impaired cardiac function that contributes to impaired exercise capacity. Clinically, this is typically detected as a decline in ejection fraction (EF) on echocardiography. However, data suggest diastolic impairment and other sub-clinical markers of reduced contractility can be detected long before a reduction in EF is reported (2). 4D flow cardiac magnetic resonance (CMR) imaging allows detailed assessment of intra-cardiac flow patterns and quantification of left ventricular (LV) kinetic energy (KE) and may offer incremental value in the detection of early cardiac impairment in patients with CAD (3). We sought to determine the relationship between 4D flow derived parameters of LV function and exercise capacity in patients with CAD. Methods Patients with stable CAD underwent CMR imaging on a 1.5T GE system. The CMR protocol included cine imaging and whole-heart 4D flow acquisition. LV relative flow components (Figure 1) and multiple phasic KE were assessed. All analyses were performed using dedicated advanced imaging analysis software. Exercise capacity was evaluated using the six-minute walk test (6MWT), and a stepwise backward multiple regression model was used to assess the predictive value of clinical and CMR parameters for the six-minute walk distance (6MWD). Results A total of 30 patients were included (mean age 66±9.0 years, 76.7% male). The average 6MWD was 431.6±75.1 metres. On univariate analysis, percentage of residual flow on 4D flow component analysis (R=-0.504, p=0.047) and average diastolic KE (R=-0.543, p=0.036) were significantly associated with the 6MWD. On multivariate analysis, independent predictors of 6MWD were presence of fractional flow reserve (FFR) positive disease (β=-60.0, p=0.035), LV mass (β=1.42, p=0.013), and percentage of residual flow (β=-3.66, p=0.007) (Model R2=0.66, p=0.0038, Figure 2). In contrast, neither EF nor LV volumes were associated with 6MWD. Conclusion In this study, percentage of residual flow derived from 4D flow component analysis was independently predictive of 6MWD alongside LV mass and FFR positive disease. Residual flow refers to blood that remains in the LV for two cycles or more and is therefore an indicator of reduced flow efficiency associated with early cardiac impairment. Our study therefore suggests that 4D flow CMR assessment of intra-cardiac flow components may provide additional insight into functional limitation in patients with CAD beyond conventionally applied measures.Flow components on 4D flow CMR Actual vs. predicted plot of 6MWD