Global myocardial ischaemia in severe aortic stenosis reverses early after aortic valve replacement
Authors: Thornton G D , Bennett J , Gama F , Nitsche C , Mravljak R , Abiodun A T , Aziminia N , Xue H , Pierce I , Lloyd G , Davies R , Manisty C , Moon J C , Kellman P , Treibel T A 
Published: June 2023

Abstract

Funding Acknowledgements
Type of funding sources: Foundation. Main funding source(s): British Heart Foundation

Background
Myocardial ischaemia is common in aortic stenosis (AS) and is associated with exercise capacity, onset of symptoms and adverse myocardial remodelling. Positron emission tomography and invasive coronary studies have evaluated myocardial blood flow before and after aortic valve replacement (AVR), but these have been limited by imaging resolution, or by assessment of flow in a single coronary territory rather than the extent of the myocardium. Cardiovascular magnetic resonance (CMR) can determine myocardial function, remodelling and scar burden, and can also quantify pixel-wise stress myocardial blood flow (MBF). Using AI-based segmentation, global and regional stress and rest MBF can be determined inline with high precision and reproducibility.

Purpose
We aimed to evaluate the early effects of AVR on myocardial ischaemia in patients with severe symptomatic AS without flow limiting coronary disease.

Methods
Patients with severe symptomatic AS, without flow limiting coronary stenosis (by CT or invasive angiography), undergoing either surgical or transcatheter AVR were prospectively recruited. Patients underwent baseline echocardiography, paired cardiovascular magnetic resonance (CMR) with adenosine stress (140mcg/kg/min for 4 minutes) pre-operatively and a median[IQR] of 62 [40–83] days post-operatively.

Results
26 patients (median [IQR] age 71 [66–75], 73% male) were included (3 patients only had rest perfusion due to safety concerns). The median [IQR] peak aortic velocity by echocardiography (Vmax) was 4.3 [4.1–4.5]m/s and AVA 0.8 [0.6–0.9]cm2. At a median 62 days post-AVR [IQR 40–83 days], the Vmax improved to median [IQR] 2.5 [2.0–2.9]m/s and the LV mass by CMR regressed from median [IQR] 83 [76–92]g/m2 to 72 [66–88]g/m2 (13% reduction), p = 0.001. Stress myocardial blood flow (MBF) increased 21% from median [IQR] 1.63 [1.38–2.21]ml/g/min to 1.97 [1.68–2.52]ml/g/min, p&lt;0.001. Resting MBF did not change (0.88 vs 0.84, p = 0.32).
Both epicardial and endocardial stress MBF improved after AVR, but the improvement in global stress MBF was mostly driven by a 40% improvement in endocardial MBF from median [IQR] 1.26 [1.18–1.78] to 1.77 [1.62–2.32]ml/g/min. Likewise there was an improvement in the endocardial to epicardial ratio from median [IQR] 0.73 [0.67–0.81] to 0.85 [0.80–0.97], p&lt;0.001.

Conclusions
Severe AS results in marked subendocardial ischaemia which may be a substrate for myocardial fibrosis and adverse cardiac events, but is highly and rapidly reversible by valve intervention. The improvement in myocardial blood flow is driven by 40% increase in subendocardial blood flow. This effect is seen despite only modest early LV mass regression. Larger studies with histological correlation are required to determine the relative contributions of afterload and structural capillary rarefaction to ischaemia in these patients.