Pulmonary Venous Flow Reversal in MR
April 1, 1999 3 minutes read
Pulmonary Venous Flow Reversal in MR
ABSTRACT & COMMENTARY
Synopsis: Pulmonary venous flow reversal is a useful sign of severe mitral regurgitation, but its sensitivity is low.
Source: Enriquez-Sarano M, et al. Am J Cardiol 1999;83:535-541.
The accurate, noninvasive determination of mitral regurgitation (MR) severity is challenging, yet of critical importance clinically. Systolic flow reversal in the pulmonary veins is part of the angiographic diagnosis of 4+MR (severe) and can be detected by pulsed Doppler trans-thoracic echocardiography. Thus, Enriquez-Sarano and colleagues evaluated the physiologic determinants of pulmonary venous flow (PVF) and the diagnostic accuracy of PVF reversal for severe MR in 128 patients with at least mild MR. The quantitation of MR was done by two methods: a quantitative Doppler determination of mitral and aortic stroke volumes and quantitative, two-dimensional echocardiography of the left ventricular and aortic stroke volumes. From these measurements, regurgitant volumes, fraction, and flow orifice were calculated. In the 128 patients, regurgitant fraction varied from 4% to 81% and PVF reversal in systole was observed in 39 patients. In a multivariate analysis, decreased PVF independently correlated with a larger regurgitant orifice, eccentric MR jets, longer jets, larger left atria, and lower MR velocity. In the patients with organic MR (not due to left ventricular dysfunction), increased filling pressures were associated with PVF reversal. For severe MR, defined as regurgitant orifice greater than 35 mm2 and regurgitant fraction more than 50%, PVF reversal showed a sensitivity of 60% and a specificity of about 90%. Enriquez-Sarano et al conclude that in patients with MR, PVF reversal is complex and determined by MR severity, left ventricular filling pressure, jet characteristics, and left atrial volume. Thus, PVF reversal is a useful sign of severe MR, but its sensitivity is low.
Comment by Michael H. Crawford, MD
Most echocardiography laboratories now routinely measure pulmonary venous flow (PVF). One major reason for this is to help with the determination of MR severity. Thus, this report on the value of PVF for determining MR severity is of interest. Systolic PVF was lower in MR patients vs. normals (4 vs 59 cm/sec) and the ratio of systolic to diastolic flow was lower (0.25 vs 1.6). However, there was considerable variability and the predictive value of PVF for determining MR severity is low. PVF reversal was useful if present, but sensitivity was low for severe MR. The explanation for these disappointing results was that PVF has multiple determinants in patients with MR, including jet characteristics and left atrial volume. It seems obvious that whether an MR jet impinges on a pulmonary vein orifice would affect PVF, but the exact relationship is unclear even in this study. Also, it is well known that increased left atrial size can blunt the hemodynamic effects of MR upstream, keeping left atrial and pulmonary pressures low despite severe MR. Thus, it is not surprising that some patients with severe MR will have normal PVF.
This study exhibits different results than other studies that have shown a high correlation between PVF and MR severity, especially with PVF reversal. Some of the latter studies suffered from being small, select studies and others used an angiographic gold standard for severe MR, which included visualization of reversed flow of the angiographic dye in the pulmonary veins during systole. Not surprisingly, such studies showed a better correlation with Doppler PVF findings. This study used two Doppler echo gold standards that estimated regurgitant volume or the regurgitant fraction of total stroke volume. These techniques are imprecise and subject to error, but they do not suffer the tautologic problem of using an angiographic standard. Also, by using two measurement techniques, the precision of this study was enhanced. In addition, both techniques gave similar results, so the veracity of the conclusions is strengthened. Unfortunately, most echocardiographic laboratories do not attempt quantitation of MR severity because of the time required and the perceived imperfections in the techniques, relying instead on multiple criteria for MR severity, including color jet characteristics, chamber sizes, various velocities, estimated pulmonary pressure, and mitral apparatus deformities. This study and others suggest that quantitation of regurgitation should be used more frequently in those with at least moderate MR or more.
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