Abstract Body (Do not enter title and authors here): Background
Reduced myocardial blood flow (MBF) and myocardial perfusion reserve (MPR) in the absence of epicardial coronary artery stenosis are commonly attributed to microvascular dysfunction, a key pathophysiological feature of hypertrophic cardiomyopathy (HCM) and heart failure with preserved ejection fraction (HFpEF). Conventional vasodilator stress may not adequately reflect exercise capacity or the hemodynamic responses characterizing these conditions. To better understand exercise-induced myocardial perfusion response, we performed quantitative myocardial perfusion in conjunction with exercise stress cardiovascular magnetic resonance imaging (Ex-CMR).
Methods
A total of 108 patients (59±13 years, 43 male) with HCM, HFpEF, or non-cardiac dyspnea (NCD) were prospectively recruited for Ex-CMR at 3T using a CMR-compatible supine ergometer. Diagnoses of HCM and HFpEF were made according to current guidelines. Dyspneic patients without cardiac abnormalities were classified as NCD. Patients with obstructive coronary artery disease were excluded. Ex-CMR was performed using a standardized protocol (Fig. 1A), hemodynamic responses and symptoms were recorded (Fig. 1B and C). Quantitative CMR perfusion was acquired at three short-axis slice positions at rest and after peak exercise (Fig. 2A).
Results
Acquisitions with impaired image quality and segments with late gadolinium enhancement were excluded. The final cohort comprised 97 patients (Table 1). No significant differences in MBF during exercise or MPR were observed between patients with and without subjective symptoms or perceived high exertion (Fig. 1D). MBF at rest did not differ among the three groups (p=0.266) (Fig. 2B). Post-exercise MBF was higher in HFpEF patients, compared to NCD and HCM patients, while MPR was similar between HFpEF and NCD patients (1.41 vs.1.44, p=0.686), but lower in HCM compared to NCD (1.27 vs.1.44, p=0.005) and HFpEF (1.27 vs.1.41, p=0.019). Using multivariable linear regression, a higher exercise-induced heart rate was independently associated with both higher post-exercise MBF and MPR.
Conclusion
Ex-CMR identified distinct responses of MBF and MPR among patients with HCM compared to HFpEF and NCD. Post-exercise MBF is lower and MPR substantially worse when compared to NCD, as well as patients with HFpEF. These data show promise in defining abnormalities in exercise performance and the mechanism for functional limitations in HCM.