Analysis of aortic valve gradients by transseptal technique: Implications for noninvasive evaluation

The peak instantaneous aortic valve gradient derived from Doppler echocardiography is commonly used to predict the severity of aortic stenosis. Peak instantaneous gradient should not be equated with the mean gradient or “peak to peak” gradient measured at cardiac catheterization. The primary purpose of this study is to assess the relationship between the aortic valve gradients, using a two‐catheter transseptal technique in 102 patients with aortic stenosis, mixed aortic stenosis and regurgitation, and following aortic valve replacement. These cases were drawn from a series of 111 consecutive transseptal procedures for patients with isolated aortic valve disease. No major complications occurred, and the most common reason for technical failure was inability to engage the atrial septum in postoperative patients. Although the peak instantaneous gradient correlates well with the mean gradient in aortic stenosis (r = .94, P < .001), mixed stenosis and regurgitation (r = .95, P < .001), and after aortic valve replacement (r = .86, P < .001), it systematically overestimates both the mean gradient and the peak to peak gradient. Neither the peak instantaneous nor the mean gradient correlates highly with aortic valve area in aortic stenosis (r = −.48, P < .01 peak; r = −.58, P < .001 mean gradient), mixed aortic stenosis and regurgitation (r = −.39, P NS peak; r = −.42, P NS mean gradient) or following aortic valve replacement (r = −.26, P NS peak; r = −.53, P < .01 mean gradient). Systolic time intervals also were analyzed from the simultaneous left ventricular and ascending aortic pressure tracings. The systolic ejection period, time to peak gradient, time to peak left ventricular pressure, and time to peak aortic pressure correlated poorly with aortic valve area. This study indicates that the mean gradient, which is consistently smaller than the peak instantaneous gradient, can be estimated by a simple regression formula: mean gradient = 0.70 peak instantaneous gradient. The mean gradient, which is usually less than the peak to peak gradient over 58 mm Hg and greater than the peak to peak gradient under 58 mm Hg, can be estimated by: mean gradient = 0.71 peak to peak gradient + 17 mm Hg. The limitations of isolated gradients in predicting aortic valve area indicate the importance of accurate flow measurements for optimal determination of the severity of aortic valve obstruction.