Quantification of aortic regurgitation by real-time 3-dimensional echocardiography in a chronic animal model: Computation of aortic regurgitant volume as the difference between left and right ventricular stroke volumes

The accuracy of conventional 2-dimensional echocardiographic and Doppler techniques for the quantification of valvular regurgitation remains controversial. In this study, we examined the ability of real-time 3-dimensional (RT3D) echocardiography to quantify aortic regurgitation by computing aortic regurgitant volume as the difference between 3D echocardiographic-determined left and right ventricular stroke volumes in a chronic animal model. Three to 6 months before the study, 6 sheep underwent surgical incision of one aortic valve cusp to create aortic regurgitation. During the subsequent open chest study session, a total of 25 different steady-state hemodynamic conditions were examined. Electromagnetic (EM) flow probes were placed around the main pulmonary artery and ascending aorta and balanced against each other to provide reference right and left ventricular stroke volume (RVSV and LVSV) data. RT3D imaging was performed by epicardial placement of a matrix array transducer on the volumetric ultrasound system, originally developed at the Duke University Center for Emerging Cardiovascular Technology. During each hemodynamic steady state, the left and right ventricles were scanned in rapid succession and digitized image loops stored for subsequent measurement of end-diastolic and end-systolic volumes. Left and right ventricular stroke volumes and aortic regurgitant volumes were then calculated and compared with reference EM-derived values. There was good correlation between RT3D left and right ventricular stroke volumes and reference data ( r = 0.83, y = 0.94x + 2.6, SEE = 9.86 ml. and r = 0.63, y = 0.8x - 1.0, SEE = 5.37 ml., respectively). The resulting correlation between 3D- and EM-derived aortic regurgitant volumes was at an intermediate level between that for LVSV and that for RVSV ( r = 0.80, y = 0.88x + 7.9, SEE = 10.48 ml.). RT3D tended to underestimate RVSV (mean difference −4.7 ± 5.4 ml. per beat, compared with −0.03 ± 9.7 ml. per beat for the left ventricle). There was therefore a small overestimation of aortic regurgitant volume (4.7 ± 10.4 ml. per beat). Quantification of aortic regurgitation through the computation of ventricular stroke volumes by RT3D is feasible and shows good correlation with reference flow data. This method should also be applicable to the quantification of other valvular lesions or single site intracardiac shunts where a difference between right and left ventricular cavity stroke volumes is produced.