Quantifying Pulmonary (Pulmonic) Regurgitation
Pulmonary (pulmonic) regurgitation (PR) or pulmonary insufficiency (PI) is the inappropriate retrograde flow of blood originating from the pulmonary valve and projecting into the right ventricle. PR is quantified easily by cardiac magnetic resonance imaging. Jets may be visible on cine images, but often are better visualized on phase contrast, velocity-mapping images (Figs.1&2).
Several methods may be employed to quantify PI. The simplest (and preferred) method is to quantify the reversal of diastolic flow from a phase contrast image, which is acquired perpendicularly to the pulmonary artery (PA) and distally to its valve. A region of interest (ROI) may be placed around the PA on the magnitude image for each cardiac phase such that the PA is contained completely within the ROI (Fig.2).
Software may be used to calculate the flow (ml/s) vs. time (ms) curve. To determine the regurgitant volume, the area under the curve should be integrated during all of diastole (Fig. 3).
Several factors may confound regurgitant volume data. First, the ROI might not include the entire PA during diastole, resulting in an underestimated PI volume. Second, the phase contrast series might not have been acquired distally to the pulmonic valve. Third, the phase contrast image might not have been acquired perpendicularly to the PA. Aliasing in systole (e.g., which occurs in pulmonic stenosis), however, does not interfere with the accurate quantification of pulmonic regurgitant volume.
Other approaches may be used for quantification in cases of isolated regurgitation (i.e., when no other regurgitant or intracardiac shunts are present):
1. Difference between the right ventricular stroke volume (RVSV, ml) and forward flow (Qs or Qp, ml); and/or
2. Difference between RVSV (ml) and left ventricular stroke volume (LVSV, ml).
The severity of PR may be categorized as described below (Tb.).
|Tb. Regurgitation Severity|
|Degree of regurgitation||Regurgitant volume (ml)||Regurgitant fraction (%)|
|Regurgitant volumes are measured directly. Regurgitant fraction (%)= volume of PR (ml)/RVSV (ml)|