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

ABSTRACT

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 (EOACont) and PISA method (EOAPISA), 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. EOAPISA could be obtained in 108 of the 114 patients (95%). Although there was a strong correlation between EOACont and EOAPISA (r = 0.78, P < 0.001), EOACont was statistically significantly larger than EOAPISA (0.86 ± 0.33 vs 0.75 ± 0.29 cm2, P < 0.001). Both EOACont and EOAPISA 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 EOACont and GOA. In contrast, there was a negative fixed bias between EOAPISA and GOA with smaller EOAPISA than GOA. The difference between EOACont and GOA was significantly greater with a larger EOACont 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 EOAPISA 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. EOAPISA could be an alternative parameter for AS severity grading in patients with high LVOT flow velocity in whom EOACont would potentially overestimate the orifice area.