Quantification of Mitral Regurgitation by the Automated Cardiac Output Method: An In Vitro and In Vivo Study

Background: Recently, the automated cardiac output method (ACM) was introduced for the calculation of blood flow at the left ventricular outflow tract (LVOT). This study was performed to examine the possibility of using ACM for flow calculation at the level of the mitral valve and for the quantification of mitral regurgitation (MR) in vitro and in vivo. Methods and Results: In a computer-controlled in vitro model of the human heart, aortic and mitral normal bioprosthetic valves were inserted. ACM and electromagnetic probe flow measurements correlated well at the LVOT and at the mitral level ( r 2 = 0.79 and 0.77, respectively). For stroke volumes ranging from 30 to 100 ml/beat, there was no statistically significant bias between ACM and electromagnetic flow probe (-1.5 and 1.3 ml for LVOT and mitral level, respectively). Limits of agreement were [-14; +11] ml and [-18; +16] ml, respectively. We evaluated 68 patients in our in vivo study. They were divided into three groups according to the results of “standard” echocardiographic Doppler methods for the semiquantification of MR: echocardiographic color Doppler cartography, intensity of the continuous wave Doppler spectra, and in some patients, pulmonary venous flow, conventional Doppler, and proximal isovelocity surface area quantitative data. Group 1 consisted of 35 patients without MR or a physiologic one; the 17 patients in group 2 had a mild MR (1-2/4) and in group 3, 16 patients with MR 3-4/4 were included. Regurgitant volume (RV) was calculated as the difference between ACM mitral flow and ACM aortic flow, and regurgitant fraction (RF) was defined as the ratio between RV and ACM mitral flow. When mitral flow was measured only from the four-chamber view, we found in group 1, RV = -0.57 (0.67) L/min and RF = -16% (19%); in group 2, RV = -0.31 (1.06) L/min and RF = -8% (19%); and in group 3, RV = 1.53 (0.94) L/min and RF = 23% (13%). RV and RF were statistically higher in group 3 compared with group 2 or group 1 ( p < 0.0005), but no significant difference was found between groups 1 and 2. When mitral flow was measured by the mean value of ACM four-chamber and two-chamber views, this resulted in group 1, RV = –0.26 (0.63) L/min and RF = –8% (15%); in group 2, RV = 0.01 (1.04) L/min and RF = -2% (18%); and in group 3, RV = 2.07 (1.21) L/min and RF = 34% (19%). RV and RF were again significantly higher in group 3 ( p < 0.0001). There was no significant difference between group 1 and group 2, but in group 1