Hybrid continuity equation using multidetector CT and echocardiography aids reclassifying severity in patients with paradoxical low flow low gradient severe aortic stenosis
Kupsky D, Al-Darzi W, Jacobsen G, Ananthasubramaniam K. Hybrid continuity equation using multidetector CT and echocardiography aids reclassifying severity in patients with paradoxical low flow low gradient severe aortic stenosis. J Am Coll Cardiol. 2018;71(11)
Background: Paradoxical low fow low gradient aorticstenosis (PLFLGAS) is a complex clinical entity withchallenges in accurate diagnosis. Doppler echocardiography (DE) may understate the left ventricular outfow tract (LVOT) area and may introduce inaccuracies incalculation of the valve area. Multidetector computed tomography (MDCT) has been shown to more accurately characterize the LVOT and annulus. We thus hypothesized that utilizing a hybrid modifed continuity equation by substituting LVOT diameter and derived cross sectional area from MDCT, patients with severe PLFLGAS would be reclassifed to a lesser severity. Methods: Patients being evaluated for transcatheter aortic valve replacement (TAVR) between January 2015 to July 2017 who had both echo and MDCT data available were retrospectively reviewed. Inclusion criteria consisted of aortic valve area (AVA) < 1 cm2by DE, left ventricular ejection fraction ≥ 50%, stroke volume index (SVI) < 35 mL/m2, and mean aortic pressure gradient ≤ 40 MMHG by DE. AVA was then recalculated substituting MDCT LVOT data into the equation. The cut off for severe AS with the modifed continuity equation was set as < 1.2 cm2as previously reported. Results: 67 patients were ultimately included in the analysis (mean age 79.9 ± 8.6 years, 49% female). Mean LVOT area was signifcantly larger by MDCT compared with DE (4.8 ± 1.0 vs. 3.3 ± 0.6 cm2; p < 0.001). Modifed continuity equation yielded a signifcantly larger AVA (1.04 ± 0.24 vs. 0.72 ± 0.17 cm2; p < 0.001). Twenty four percent (n=16) of patients were ultimately reclassifed from severe to moderate AS by merging MDCT and Doppler data. The 16 patients reclassifed into the moderate category had larger DE AVA (0.86 ± 0.08 vs. 0.67 ± 0.16 cm2; p<0.001) and higher SVI (30.9 ± 2.8 vs. 26.9 ± 5.4; p<0.001) compared to those who remained in the severe range. Conclusion: Merging MDCT with DE reclassifes nearly a quarter of patients with severe PLFLGAS into the moderate category. Considering patients are currently referred for aortic valve interventions (surgical or TAVR) based on DE data, future studies will need to assess if proceeding or deferring interventions can be based on combining MDCT and DE.