Paradoxical low gradient aortic stenosis reclassified using hybrid continuity equation by multidectector CT: Insights into diastolic function and post TAVR outcomes

Background: Paradoxical low flow low gradient aortic stenosis (PLF-AS) is a complex clinical entity posing challenges in diagnosis and management. Left ventricular outflow tract (LVOT) diameter underestimation is a key reason for inaccuracies in quantitation. We investigated the utility of a hybrid modified continuity equation using multidetector computed tomography (MDCT) derived LVOT diameter/cross sectional area and Doppler echocardiography (DE) to study the impact of reclassifying patients with severe PLF-AS. We further analyzed differences in diastolic parameters and outcomes in reclassified patients post-transcatheter aortic valve replacement (TAVR). Methods: Patients being evaluated for TAVR between January 2015 to July 2017 with both DE and MDCT data available were retrospectively reviewed. PLF-AS defined as valve area (AVA) ≤ 1 cm2 by DE, left ventricular EF ≥ 50%, stroke volume index (SVI) ≤ 35 mL/m2, and mean aortic pressure gradient ≤ 40 mmHg by DE. AVA was recalculated substituting MDCT LVOT data into the equation. The cut offfor severe AS with the hybrid equation was set as ≤ 1.2 cm2 as previously reported. Diastolic Parameters and TAVR outcomes (NYHA class, mortality and hospital admissions for CHF) were analyzed. Results: 67 patients were included in the analysis (mean age 79.9 ± 8.6 years, 49% female). Twenty four percent (n=16) of patients were ultimately reclassified from severe to moderate AS by merging MDCT and DE data. There was a significantly higher number of patients with diastolic dysfunction (grade I or higher) (95% vs 75%; p=.03) and restrictive physiology (grade 3 diastolic dysfunction) (33% vs. 8%; p=.032) in those who remained in the severe AS group using the hybrid equation. NYHA class prior to valve replacement was worse in the patients in the severe category (3.05 vs. 2.6; p=0.013). At a mean f/u of 19 months 67% (n=45) underwent TAVR (11 reclassified as moderate AS and 34 as severe AS). Those who remained in the severe AS range had a greater improvement in their SVI (35.5 vs. 26.9 p≤.001) aft er TAVR, and average improvement in NYHA class was significantly better in the severe AS group (1.63 vs 1.11 p=0.042 ). There was no significant difference between the two groups with regards to CHF hospitalization or all-cause mortality. Conclusion: Merging MDCT with DE reclassifies nearly a quarter of patients with severe PLF-AS into the moderate category. Patients with severe AS per hybrid equation have more advanced DD and had a more significant improvement in NYHA class and SVI. Future studies will need to assess if proceeding or deferring interventions can be based on combining MDCT and DE