‘Weighing up the Load’ – A Comparison of Cardiac Magnetic Resonance Methods to Assess Valvulo-Arterial Load in Patients with Aortic Stenosis
Background and Aim: The left ventricle (LV) faces a dual afterload in patients with aortic stenosis (AS) – both from the valve and vasculature. Together they form the global LV load. Two cardiac magnetic resonance (CMR) techniques have been described to quantify global LV load: (1) valvulo-arterial impedance instantaneous (ZVA-INS) and (2) valvulo-arterial load (VAL). The purpose of this study was to evaluate concordance (if any) between ZVA-INS and VAL. Methods: Twenty AS patients were compared (80 ± 9 years; 12 males; 80% severe). Aortic flow velocity data was obtained during breath-hold using through-plane PC Qflow imaging. ZVA-INS was determined as the relationship of aortic pressure and maximum aortic valve (AV) gradient to ascending aorta flow velocity in the time domain. VAL was determined as the relationship of aortic pressure to ascending aorta flow velocity in the frequency domain. Values from both methods were compared against total arterial compliance (TAC). Results: Global LV load was significantly higher when assessed by ZVA-INS (3990±1795 dynes.s.cm³) than VAL (946±318 dynes.s.cm³) (R=0.941; R²=0.886; F=109.2; P<0.01) due to the addition of maximum AV gradient. VAL was linearly related to TAC with no significant difference (R=0.313; R²=0.098; F=1.413; P=0.256). Conclusion: This study presents the first direct comparison of CMR methods to assess global LV load in patients with AS. We conclude a significant difference between ZVA-INS and VAL, but not between VAL and TAC. This relationship is most likely due to the addition of maximum AV gradient.
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