Direct measurement of aortic regurgitation with phase-contrast magnetic resonance is inaccurate: proposal of an alternative method of quantification.

BACKGROUND

Phase-contrast magnetic resonance (MR) has been widely used for quantification of aortic regurgitation. However there is significant practice variability regarding where and how the blood flow data are acquired.

OBJECTIVE

To compare the accuracy of flow quantification of aortic regurgitation at three levels: the ascending aorta at the level of the right pulmonary artery (level 1), the aortic valve hinge points at end-diastole (level 2) and the aortic valve hinge points at end-systole (level 3).

MATERIALS AND METHODS

We performed cardiovascular MR in 43 children with aortic regurgitation. By using phase-contrast MR, we measured the systolic forward, diastolic retrograde and net forward flow volume indices at three levels. At each level, the following comparisons were made: (1) systolic forward flow volume index (FFVI) versus left ventricular cardiac index (LVCI) measured by cine ventricular volumetry; (2) retrograde flow volume index (RFVI) versus estimated aortic regurgitation volume index (which equals LVCI minus pulmonary blood flow index [QPI]); (3) net forward flow volume index (NFVI) versus pulmonary blood flow index.

RESULTS

The forward flow volume index, retrograde flow volume index and net forward flow volume index measured at each of the three levels were significantly different except for the retrograde flow volume index measured at levels 1 and 3. There were good correlations between the forward flow volume index and the left ventricular cardiac index at all three levels, with measurement at level 2 showing the best correlation. Compared to the forward flow volume indices, the retrograde flow volume index had a lower correlation with the estimated aortic regurgitation volume indices and had widely dispersed data with larger prediction intervals.

CONCLUSION

Large variations in systolic forward, diastolic retrograde and net forward flow volumes were observed at different levels of the aortic valve and ascending aorta. Direct measurement of aortic regurgitation volume and fraction is inaccurate and should be abandoned. Instead, calculation of the aortic regurgitation volume from more reliable data is advised. We recommend subtracting pulmonary blood flow from systolic forward flow measured at the aortic valve hinge points at end-diastole as a more accurate and consistent method for calculating the volume of aortic regurgitation.