Comments regarding “Simplified Bernoulli's method significantly underestimates pulmonary transvalvular pressure drop”

Abstract

I have read carefully the recent article by Falahatpisheh et al. 1 I am grateful to the authors for their comprehensive and very sensible research of recent studies on the simplified Bernoulli equation (SBE), significantly underestimates pulmonary transvalvular pressure drop, utilizing 3.0T magnetic resonance imaging (MRI) 4D velocity mapping in 3D and time, to quantify the velocity field in the vicinity behind of the pulmonary valve and estimate the pressure drop by the general Bernoulli equation (GBE). Accordingly, Falahatpisheh et al 1 first used 4D-flow MRI to track the pattern of the flow-dependent phase for normal subjects and patients with repaired congenital heart defects. The pixel values of the velocity images were converted to physical velocity. The pressure drop through the pulmonary valve was approximated based on GBE and SBE, known as 4V 2 . In the GBE, the unsteady term comprises the integral of the derivative of velocity with respect to time over a flow streamline between the upstream and downstream velocity points were added. The results of their study show that the SBE method significantly underestimated the pressure drop compared to the GBE method during the entire systolic phase, including the peak systole. This difference may result in confusing circumstances for grading the stenosis when the pressure drop is within a doubtful range. With regard to the issue of pulmonary valve stenosis (PS), my take is that, just as in the case of other heart lesions, it is all a matter of "convention" and "correlation": that is, it is not important (any more) how accurate we are in the estimation of a certain parameter as long as we all have a common understanding of what it means and we have a clear correlation with known outcomes. In other words, it is not important if a right ventricular pressure pulmonary arterial (RV-PA) gradient is 80 mmHg or 60 or 40 (as these differences may very well depend on the method of measurement and the status of the patient: sedated/agitated); what is important is that we all have the same understanding of what it means to the patient (clinically) in the long and short run.That On the other hand, in the setting of a child with aortic stenosis (AS) and coarctation of the aorta, both lesions "collude" to underestimate each other's severity by decreasing the gradient across the obstruction. Therefore, we do not know if we need to balloon the aortic valve or the coarctation or both. Here I am sure that there may be a role for the GBE in accurately estimating the severity.To conclude, there would be a huge clinical advantage to developing a noninvasive measure of stenosis.

Validation of pressure drop assessment using 4D flow MRI‐based turbulence production in various shapes of aortic stenoses

“…The discrepancy between the simplified Bernoulli estimation and the true pressure drop has frequently been reported . Therefore, it functions as a relative metric for clinical cut‐off rather than a true pressure prediction . Considering the significant amount of clinical data that have been obtained with the simplified Bernoulli method, further methods to make the various pressure estimations interchangeable would be an important issue to investigate in the future.…”