Application of the proximal isovelocity surface area method for estimation of the effective orifice area in aortic stenosis

Although the echocardiographic effective orifice area (EOA) calculated using the continuity equation is widely used for the assessment of severity in aortic stenosis (AS), the existence of high flow velocity at the left ventricular outflow tract (LVOT) potentially causes its overestimation. The proximal isovelocity surface area (PISA) method could be an alternative tool for the estimation of EOA that limits the influence of upstream flow velocity. EOA was calculated using the continuity equation (EOA_Cont) and PISA method (EOA_PISA), respectively, in 114 patients with at least moderate AS. The geometric orifice area (GOA) was also measured using the planimetry method in 51 patients who also underwent three-dimensional transesophageal echocardiography. Patients were divided into two groups according to the median LVOT flow velocity. EOA_PISA could be obtained in 108 of the 114 patients (95%). Although there was a strong correlation between EOA_Cont and EOA_PISA (r = 0.78, P < 0.001), EOA_Cont was statistically significantly larger than EOA_PISA (0.86 ± 0.33 vs 0.75 ± 0.29 cm², P < 0.001). Both EOA_Cont and EOA_PISA similarly correlated with GOA (r = 0.70, P < 0.001 and r = 0.77, P < 0.001, respectively). However, a fixed bias, which is hydrodynamically supposed to exist between EOA and GOA, was not observed between EOA_Cont and GOA. In contrast, there was a negative fixed bias between EOA_PISA and GOA with smaller EOA_PISA than GOA. The difference between EOA_Cont and GOA was significantly greater with a larger EOA_Cont relative to GOA in patients with high LVOT flow velocity than in those without (0.16 ± 0.25 vs − 0.07 ± 0.10 cm², P < 0.001). In contrast, the difference between EOA_PISA and GOA was consistent regardless of the LVOT flow velocity (− 0.07 ± 0.12 vs − 0.07 ± 0.15 cm², P = 0.936). The PISA method was applied to estimate EOA in patients with AS. EOA_PISA could be an alternative parameter for AS severity grading in patients with high LVOT flow velocity in whom EOA_Cont would potentially overestimate the orifice area.