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

Background: The accuracy of conventional 2-dimensional echocardiographic an d Doppler techniques for the quantification of valvular regurgitation remai ns controversial. In this study, we examined the ability of real-time 3-dim ensional (RT3D) echocardiography to quantify aortic regurgitation by comput ing aortic regurgitant volume as the difference between 3D echocardiographi c-determined left and right ventricular stroke volumes in a chronic animal model. Methods. Three to 6 months before the study, 6 sheep underwent surgical inc ision of one aortic valve cusp to create aortic regurgitation. During the s ubsequent open chest study session, a total of 25 different steady-state he modynamic conditions were examined. Electromagnetic (EM) flow probes were p laced around the main pulmonary artery and ascending aorta and balanced aga inst each other to provide reference right and left ventricular stroke volu me (RVSV and LVSV) data. RT3D imaging was performed by epicardial placement of a matrix array transducer on the volumetric ultrasound system, original ly developed at the Duke University Center for Emerging Cardiovascular Tech nology. During each hemodynamic steady state, the left and right ventricles were scanned in rapid succession and digitized image loops stored for subs equent measurement of end-diastolic and end-systolic volumes. Left and righ t ventricular stroke volumes and aortic regurgitant volumes were then calcu lated and compared with reference EM-derived values. Results. 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 m L 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 a n 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 diff erence -4.7 +/- 5.4 mL per beat, compared with -0.03 +/- 9.7 mL per beat fo r the left ventricle). There was therefore a small overestimation of aortic regurgitant volume (4.7 +/- 10.4 mL per beat). Conclusion: Quantification of aortic regurgitation through the computation of ventricular stroke volumes by RT3D is feasible and shows good correlatio n with reference flow data. This method should also be applicable to the qu antification of other valvular lesions or single site intracardiac shunts w here a difference between right and left ventricular cavity stroke volumes is produced.