Role of Cardiac Magnetic Resonance Imaging measured Myocardial Perfusion Reserve in asymptomatic patients with Aortic Stenosis: a comparison with Exercise Testing

Background: The management of asymptomatic patients with severe aortic stenosis (AS) is controversial. Cardiovascular Magnetic Resonance (CMR) imaging has been proposed as a potential prognostic marker that may help select patients for aortic valve replacement (AVR). Aims: To establish: the reproducibility of novel CMR techniques; determinants of peak VO2 and MPR; effect of Ranolazine; and predictors of outcome in asymptomatic moderate-severe AS, and compare MPR to exercise testing as predictors of outcome. Methods: The PRIMID-AS study was a multi-centre, prospective, observational study, with blinded analysis of imaging data. AS patients and controls underwent: trans-thoracic echocardiogram (TTE), symptom-limited cardiopulmonary exercise test (CPET), adenosine stress CMR at 3T and a CT calcium score, and were followed up for a minimum of 12 months, or until a primary endpoint occurred (symptom-driven AVR, MACE or cardiovascular death). Additionally a pilot study on the short-term effect of Ranolazine in asymptomatic patients with moderate-severe AS was carried out in 19 patients. Results: 174 patients (age 66.2±13.34 years, 76% male, aortic valve area index 0.57±0.14 cm2/m2) were recruited as part of PRIMID-AS study, in addition to 23 age- and comorbidity-matched controls. Patients showed evidence of LV remodeling and impaired MPR, but preserved exercise capacity compared to controls, suggesting a state of ‘compensation’. MPR and longitudinal strain were independently associated with age- and sex-corrected peak VO2, whilst extra-cellular volume (ECV) and AS severity were independently associated with MPR. A primary outcome occurred in 39 (22.4%) patients. MPR showed moderate association with outcome (area under curve (AUC)=0.62 (0.52-0.71, p=0.019), as did exercise testing (AUC=0.58 (0.49-0.67, p=0.071), with no significant difference between the two. Ranolazine did not improve diastolic function or MPR significantly. Conclusions: MPR was associated with exercise capacity and symptom-onset in initially asymptomatic patients with AS, but with moderate accuracy and was not superior to symptom-limited exercise testing.