Quantitative myocardial blood flow and perfusion reserve with exercise cardiovascular magnetic resonance

Myocardial blood flow (MBF) and myocardial perfusion reserve (MPR) can be quantified using vasodilator stress cardiovascular magnetic resonance (CMR). Exercise stress CMR (Ex-CMR) offers a more physiological assessment of cardiac functional reserve. While visual interpretation of Ex-CMR perfusion has been successfully applied, the feasibility of quantitative Ex-CMR perfusion remains unproven. We aimed to assess the feasibility of quantitative Ex-CMR perfusion imaging for characterizing exercise-induced perfusion responses and to perform a pilot study comparing MBF and MPR among patients with hypertrophic cardiomyopathy (HCM), heart failure with preserved ejection fraction (HFpEF), and non-cardiac dyspnea (NCD).

In this prospective study, patients with HCM, HFpEF, or NCD underwent Ex-CMR at 3T using a supine ergometer. Exercise was performed outside the scanner bore, followed by stress perfusion imaging 45-60 s post-exercise and rest perfusion 5-7 min later. A dual-sequence protocol with inline pixel-wise quantification was used to calculate MBF and MPR. Image quality and feasibility were visually assessed. Group comparisons were performed using analysis of variance and t-tests; linear regression was used to explore clinical associations.

Of 108 patients enrolled, 9 were excluded due to obstructive coronary artery disease or reduced ejection fraction. Quantitative Ex-CMR was successful (at least one analyzable paired rest and post-exercise slice) in 90% (10/99) of cases. Most frequent quality issues were inadequate gating or arrhythmias and slice misalignment. The final cohort included 89 patients: 34 HCM, 34 HFpEF, and 21 NCD. Patients with HCM showed significantly lower MBF and MPR than HFpEF and NCD (MBF: 1.03 ± 0.27 vs 1.25 ± 0.40 and 1.13 ± 0.25 mL/min/g; MPR: 1.27 ± 0.21 vs 1.41 ± 0.29 and 1.44 ± 0.22; all p < 0.05). Peak exercise heart rate was the strongest independent predictor of MBF (β = 0.009, p < 0.001) and MPR (β = 0.004, p = 0.022).

Ex-CMR quantitative MBF and MPR assessment is feasible in most patients after image quality control. While the increase in MBF was limited during low-to-moderate exercise intensity in this pilot study, Ex-CMR revealed distinct perfusion response patterns among studied cohorts.