We thank Dr DeGroff for his thoughtful comments and appreciate his concerns regarding our study design. Although it is true that the results of our study are based on echocardiographic studies performed primarily by a single sonographer, we felt it best, to the extent possible, to limit image acquisition in our study to a single sonographer in order to minimize variability in image acquisition. We recognize that there are many potential sources of variability in echocardiographic studies. Technical variability such as differences in echocardiographic equipment, and intraobserver and interobserver variability in image acquisition and measurements, play as important a role as interpatient, interstudy, and intrastudy variability. To minimize such technical variability, particularly equipment and interobserver variability, in our study, image acquisition was performed using the same equipment and by a “primary” sonographer with extensive experience participating in single-center and multicenter echocardiographic studies. To assess for variability in data interpretation, we performed a quality assessment for each of the tricuspid regurgitation (TR) spectral envelopes, and good interobserver reliability was shown.

We further recognize that our study was limited by the fact that our data were collected at a single point in time, and we were not able to assess test-retest reliability of Doppler echocardiography longitudinally. We felt that this emphasized even more the necessity of using one primary sonographer, because intraobserver variability is significantly lower than interobserver variability and induces less variance in image acquisition at a single point in time.

With regard to Dr DeGroff’s concern about out-of-plane error, we recognize the difficulty of capturing the maximal TR spectral Doppler velocity and appreciate the suggestion to use a nonsupine position to rectify this problem. Although theoretically appropriate, using a nonsupine or decubitus position during a simultaneous catheterization could potentially disturb the sterile field of operation, threaten patient safety, and change patient hemodynamics. We therefore did not attempt to manipulate patient position in our study. We did ensure that images were acquired in the apical, parasternal long-axis, and parasternal short-axis planes from the supine position in an attempt to ensure all optimal imaging planes were achieved while still being able to acquire simultaneous catheterization pressure tracings.

In response to Dr DeGroff’s suggestion of using a nonimaging continuous-wave Doppler probe, we feel that visualization of the direction of the TR jet using color Doppler is important and allows proper alignment of the ultrasound beam. We believe that use of a PEDOF probe may introduce beam alignment error, as visualization of the direction of the TR jet would not be possible. Additionally, we feel that the use of the PEDOF probe to determine maximal TR jet velocity in patients with various congenital cardiac defects, such as a paramembranous ventricular septal defect, left ventricle–to–right atrial shunt, or multiple valvular abnormalities would introduce an unnecessary element of uncertainty as to whether the spectral Doppler envelope captured was truly the maximal TR jet or if it was in fact the jet from an adjacent abnormal lesion. Such an error in interpretation could lead to error in patient management.