CARDIAC INDEX QUANTIFICATION BY DOPPLER ULTRASOUND IN PATIENTS WITHOUT LEFT-VENTRICULAR OUTFLOW TRACT ABNORMALITIES

Objectives. We attempted to ascertain whether cardiac index can be dir ectly estimated from Doppler mean velocity. Background. Although diver se Doppler echocardiographic methods have been described for cardiac o utput quantification, they are not widely used in clinical practice. C ross-sectional area measurement has been identified as the main source of error in flow volume quantification. Methods. A three-phase study by Doppler echocardiography was conducted in 306 patients. In phase I, the normal mean velocity ratio of the left and right ventricular outf low tracts was established in 170 normal subjects. In phase II, cardia c index, calculated as the product of aortic annular area index by mea n velocity (conventional method), and mean velocity determined in the left ventricular outflow tract and ascending aorta by pulsed and conti nuous wave Doppler, respectively, were correlated with thermodilution cardiac index in 66 patients. In phase III, the accuracy of the regres sion equations obtained was prospectively assessed in an additional 70 patients. Results. The normal left/right ventricular outflow tract me an velocity ratio by pulsed wave Doppler was 1.1 +/- 0.1. Cardiac inde x (CI) calculated by the conventional method and thermodilution (TD) s howed acceptable correlation (r = 0.90, CITD = 1.20 CIPWD + 357; r = 0 .86, CITD = 0.90 CICWD + 262) for pulsed (PWD) and continuous wave (CW D) Doppler, respectively, but with systematic underestimation (- 28 +/ - 13%, p < 0.01) by pulsed wave Doppler. Mean velocity (MV showed exce llent correlation with the thermodilution cardiac index (r = 0.97, CIT D = 172 MV(PWD) - 172; r = 0.93, CITD = 129 MV(CWD) - 255). When these regression equations were prospectively applied, better agreement wit h the thermodilution cardiac index was obtained by pulsed wave Doppler directly from mean velocity (SD 240 ml/min per m(2)) than when aortic annular area was considered in the calculation (SD 428 ml/min per m(2 )). Similar results were obtained by continuous wave Doppler (SD 433 v s. 599 ml/min per m(2)) but with less accuracy. Conclusions. Left vent ricular outflow tract mean velocity determined by pulsed wave Doppler permits easy, accurate cardiac index quantification in the absence of left ventricular outflow abnormalities. The simplicity of this method enhances its clinical applicability in noninvasive monitoring of cardi ac index.