Abstract & Commentary
Synopsis: Mitral Doppler E/Ea correlates better with PCWP than BNP and is more specific for predicting PCWP > 15 mm Hg.
Source: Dokaimish H, et al. Circulation. 2004;109:2432-2439.
A simple non-invasive method of estimating left ventricular (LV) filling pressure in critically ill patients, would be desirable. Hence, Dokaimish and colleagues sought to compare echo Doppler methods to serum B-type natriuretic peptide (BNP) levels for estimating pulmonary capillary wedge pressure (PCWP). They screened 57 consecutive patients, admitted to the intensive care unit, who had pulmonary artery catheters placed for clinical reasons. Exclusion criteria included atrial fibrillation, severe mitral regurgitation, and acute myocardial infarction, which eliminated 7 patients. The principal echo Doppler method was the ratio of the peak early mitral inflow velocity (E) to the early diastolic tissue-Doppler (Ea) of the mitral annulus (average of septal and lateral velocities). The admitting diagnoses, in the 50 patients, include heart failure, respiratory failure, and hemodynamic instability post major surgery or trauma. The objective of the study was to determine ability of E/Ea and BNP levels to predict PCWP > 15 mm Hg.
Results: Log BNP was weakly correlated with PCWP (r = .32, P =.02) but E/Ea correlated more strongly (r = .69; P < .001). The optimal cut point for E/Ea to predict PCWP > 15 mm Hg was 15; sensitivity 86%, specificity 88%. The optimal BNP cut-off was 300 pg/mL; sensitivity 91%, specificity 56%. In the 36 patients with cardiac disease, E/Ea performed even better in predicting PCWP > 15 mm Hg; sensitivity 92%, specificity 91% vs sensitivity 92%, specificity 51%, for BNP. Whereas, in the patients without cardiac disease, BNP appeared stronger at predicting PCWP > 15 mm Hg; sensitivity 81%, specificity 83% vs sensitivity 74%, specificity 72% for E/Ea. In the 9 patients who had all 3 measures repeated after 48-hours of treatment, E/Ea correlated better with change in PCWP than BNP did (r = .87; P < .003 vs r = -.59; P = .39, respectively). Dokaimish and colleagues concluded that in patients admitted to an Intensive Care Unit, mitral Doppler E/Ea correlates better with PCWP than BNP and is more specific for predicting PCWP > 15 mm Hg. Also, E/Ea is most accurate in patients with cardiac disease, whereas, BNP was more accurate in patients without cardiac disease.
Comment by Michael H. Crawford, MD
Today, intensive care units are mainly filled with severely ill multisystems disease patients, end-stage heart failure patients, or post-surgical patients with hemodynamic instability. Most are intubated, at least initially, and many have rhythm disturbances. The use of indwelling pulmonary artery catheters has declined in such patients because their risk outweighs their benefit. Thus, an accurate non-invasive technique for determining who has a high LV filling pressure would be of value. BNP is very attractive because it is a simple blood test, and has performed well in the Emergency Department setting for determining who is in heart failure when it is not obvious clinically. The more complicated patient in today’s Intensive Care Units is a different challenge, and the results of this study show mixed results for BNP. In the absence of structural heart disease, it was pretty good at determining who had a PCWP > 15 mm Hg, but in those with structural heart disease, it had a low specificity, and hence, a low positive predictive value. This is undoubtedly because BNP is influenced by other factors besides filling pressure in patients with cardiac disease, such as left atrial size, ejection fraction, LV mass, etc. If one can be certain that the patient has no structural heart disease, then BNP is an easy way to predict who is fluid overloaded, and in such patients the cut point is 250 pg/mL. However, if cardiac status is uncertain, then an echocardiogram needs to be done. Thus, some have suggested that a high BNP should be used to screen for who needs the more expensive echocardiogram.
In this study, mitral Doppler E/Ea performed best overall for predicting PCWP and especially PCWP > 15 mm Hg, but this is partly because 70% of the patients had cardiac disease. Mitral E/Ea may not have performed as well in a population with less heart disease. The result is not surprising since mitral E/Ea directly measures early flow across the mitral valve in diastole, and normalizes it for annular motion. Early mitral flow is most related to the early pressure gradient, which is heavily dependent on left atrial pressure. Interestingly, other echo Doppler filling parameters did not perform as well as mitral E/Ea in this study. LV, EF, mitral E velocity deceleration time, pulmonary venous systolic filling fraction, and the difference between pulmonary venous velocity A-wave duration and mitral A-wave velocity duration, all had correlation coefficients between 0.5-0.6 compared to E/Ea at r = .69. However, in those patients with E/Ea in the gray zone (8-14), consideration of these other parameters help correctly classify the patients with regard to PCWP.
The use of BNP serially, to assess response to therapy, was evaluated in 9 patients in this study, who had repeat measurements at 48 hours. The results were similar to other reports that have shown little value for BNP. It is not surprising that mitral E/Ea would change immediately with PCWP, but BNP, which is influenced by so many other factors, may lag in response to positive hemodynamic changes.
Dr. Crawford, Professor of Medicine, Associate Chief of Cardiology for Clinical Programs University of California San Francisco, is Editor of Clinical Cardiology Alert.