Real-time 3-dimensional echocardiography for quantification of the difference in left ventricular versus right ventricular stroke volume in a chronic animal model study: Improved results using C-scans for quantifying aortic regurgitation

Abstract

Objective The purpose of our study was to test the applicability of calculating the difference between left ventricular (LV) and right ventricular (RV) stroke volume (SV) for assessing the severity of aortic (Ao) regurgitation (AR) using a real-time 3-dimensional (3D) echocardiographic (RT3DE) imaging system. Methods The Ao valve was incised in 5 juvenile sheep, 6 to 10 weeks before the study, to produce AR (mean regurgitant fraction = 0.50). Simultaneous hemodynamic and RT3DE images were obtained on open-chest animals with Ao and pulmonary flows derived by Ao and pulmonary electromagnetic flowmeters balanced against each other. Four stages (baseline, volume loading, sodium nitroprusside, and angiotensin infusion) were used to produce a total of 16 different hemodynamic states. Epicardial scanning was done with a 2.5-MHz probe to sequentially record first the RV and then the LV cavities. Cavity volumes from the 3D echocardiography data were determined from angled sector planes (B-scans) and parallel cutting planes (C-scans, which are planes perpendicular to the direction of the volume interrogation). AR volumes were determined from 3D images by computing and then subtracting RV SVs from LV SVs and then these were compared with electromagnetic flowmeter-derived SV and regurgitant volumes. Results There was close correlation between RV and LV SVs of the RT3DE and electromagnetic methods (C-scans: LV, r = 0.98, standard error of the estimate [SEE] = 2.62 mL, P = .0001; RV, r = 0.89, SEE = 2.67 mL, P < .0001; and B-scans: LV, r = 0.95, SEE = 3.55 mL, P = .0001; RV, r = 0.77, SEE = 2.78 mL, P = .0003). Because of the small size of the RV in this model, the correlation was closer for C-scans than B-scans for RV SV. AR volume estimation also showed that C-scan ( r = 0.93, SEE = 4.23 mL, P < .0001) had closer correlation than B-scan ( r = 0.89, SEE = 4.87 mL, P < .0001). However, B-scan-derived AR fraction showed closer correlation than did C-scan ( r = 0.82 vs r = 0.85, respectively). Conclusion In this animal model, RT3DE imaging had the ability to reliably quantify both LV (B- and C-scans) and RV SVs and to assess the severity of AR.