Quantification of mitral regurgitation by Doppler echocardiography

Aliasing-tolerant color Doppler quantification of regurgitant jets

Conservation of momentum transfer in regurgitant cardiac jets can be used to calculate the flow rate from color Doppler velocities. In this study, turbulent jets were simulated by finite elements; pseudocolor Doppler images were interpolated from the computations, with aliasing introduced artificially. Jets were also imaged by color Doppler in an in vitro flow system. To suppress aliasing errors, jet velocities were fitted iteratively to a fluid mechanical model constrained to match the orifice velocity (measured without aliasing by continuous-wave Doppler). At each iteration, the model was used to detect aliased velocities, which were excluded during the next iteration. Iteration continued until the flow rate calculated by the model and number of calculated nonaliased pixels were unchanged. The good correlations between measured and calculated flow rates in the experimental (R2 = 0.933) and computational studies (R2 = 0.990) suggest that this may be a clinically useful approach even in aliased images. Published by Elsevier Science Inc.

Grading of mitral regurgitation by quantitative Doppler echocardiography: calibration by left ventricular angiography in routine clinical practice

BACKGROUND

Quantitative Doppler echocardiography and proximal flow convergence methods are validated techniques for quantifying mitral regurgitation. However, the clinical interpretation of the values calculated is hindered by the absence of calibration of ranges of severity in large numbers of patients.

METHODS AND RESULTS

In 180 consecutive patients (men, 62%; mean age+/-SD, 66+/-11 years), the results of Doppler quantification of isolated mitral regurgitation were calibrated by use of left ventricular angiographic grading performed within 3 months in routine practice and without intervening events. The thresholds of the quantitative variables corresponding to the angiographic grades were identified by maximizing the sum of sensitivity and specificity and minimizing their difference. The mitral regurgitation grade by angiography was 2.7+/-1.3. The mean value and correlation with angiographic grades for effective regurgitant orifice were 43+/-37 mm and r=.79 (P<.0001); for regurgitant volume, 62+/-45 mL and r=.80 (P<.0001); and for regurgitant fraction, 45+/-17% and r=.78 (P<.0001). Despite some overlap, differences between mitral regurgitation grades were all significant (all P<.05). The thresholds for severe mitral regurgitation (grade 4) were 60 mL, 50%, and 40 mm2 for regurgitant volume, regurgitant fraction, and orifice, respectively.

CONCLUSIONS

In routine practice in large numbers of patients in a clinical laboratory, Doppler echocardiographic quantification of mitral regurgitation shows highly significant correlation with qualitative angiographic grades. Despite an expected overlap between classes, the calibration by angiography of grading ranges for the quantitative variables provides a framework for their interpretation and allows the definition in clinical practice of thresholds for severe mitral regurgitation.

Quantification of asymmetric valvular regurgitant jets by color Doppler ultrasound in vitro

Accurate quantification of regurgitant jets in natural and prosthetic heart valves has been a goal of health care workers and researchers for many years. One promising new method applies the law of conservation of momentum transfer to velocities measured by color Doppler ultrasound to calculate the flow rate in the jet. One complicating factor is that regurgitant jets from real heart valves may be highly asymmetric. The purpose of this investigation was to determine whether the accurate calculation of the flow rate in asymmetric jets imaged by color Doppler requires an asymmetric formulation of the conservation of momentum transfer, combined with a method for imaging the jet in three dimensions. Asymmetric jets issuing from narrow slits were imaged in an in vitro, steady flow system. The ultrasound transducer was rotated around the jet axis to image the jet in three dimensions. The three-dimensional imaging confirmed that jets from slits are indeed asymmetric, but become relatively axisymmetric far from the orifice. Images were analyzed by computer and the calculated flows compared to measured flows. The accuracy of an asymmetric formulation of the conservation of momentum transfer method was compared to a simpler, axisymmetric formulation. If axisymmetry was assumed in asymmetric jets, significant errors in the calculated flow rates occurred. In these cases, the calculated flow also varied widely with distance from the orifice. When asymmetry was taken into account, the errors were considerably reduced. The results suggest that, in asymmetric jets, the momentum transfer is convected around the jet axis.

Factors reducing left and right ventricular output during simultaneous atrioventricular activation in the pig heart

Forward stroke volume fell by 26% (23-30%) (median and 95% confidence interval) when simultaneous atrioventricular (AV) pacing was induced at constant heart rate in 10 anaesthetized open-chest pigs. To assess the relative importance of factors which could cause this reduction in right and left ventricular (RV and LV) output, we compared cardiac dynamics when either ventricular filling or forward stroke volume was equally reduced by caval constriction and simultaneous AV pacing. We estimated the degree of ventricular filling by recording segment lengths (SL) in the free walls of both ventricles. Our analysis revealed that abolished active LV filling by the left atrium reduced forward stroke volume by 11% (8-14%). The remaining fall in output could be attributed to mitral regurgitation. In the right side of the heart the response was different. The drop in RV filling during simultaneous AV pacing accounted for approximately one-half of the fall in forward RV stroke volume. Estimates based on SL recordings demonstrated that forward RV stroke volume fell by 7% (2-25%) because of tricuspidal regurgitation. Pulmonary artery pressure was 4.5 (3.4-5.7) mmHg higher during simultaneous AV pacing than during caval constriction, representing a relative rise in afterload that reduced the RV stroke volume by 6-8%. Thus, reduced ventricular filling during simultaneous AV pacing accounted for approximately one-half of the drop in forward output from both ventricles. Slightly more than one-half of the reduction in forward LV stroke volume could be attributed to mitral regurgitation. In the right side of the heart tricuspidal regurgitation and a relative rise in pulmonary artery pressure each accounted for about one-quarter of the fall in forward RV output.