Quantifying Aortic Regurgitation
Aortic regurgitation (AR) or aortic insufficiency (AI) is quantified easily by cardiac magnetic resonance imaging. AR may appear as one or more flow jets originating from the aortic valve and projecting into the left ventricular outflow tract. Typically, the jets are holodiastolic, readily apparent on the 3-chamber long-axis view, and are best visualized on imaging sequences with longer echo times (TE) (F1).
Several methods may be employed to quantify AR. The simplest (and preferred) technique is to quantify the reversal of diastolic flow from a phase contrast image, which is acquired perpendicularly to the aorta and distally to the aortic valve. A region of interest (ROI) may be placed around the aorta on the magnitude image for each cardiac phase such that the aorta is contained completely within the ROI (F2).
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 (F3).
Importantly, several pitfalls may confound regurgitant volume data. First, the ROI might not include the entire aorta in diastole, resulting in an underestimated AI volume. Second, the phase contrast image might not have been acquired distally to the aortic valve. Third, the phase contrast image might not have been acquired perpendicularly to the aorta. Aliasing in systole (e.g., which occurs frequently in aortic stenosis), however, does not interfere with the accurate quantification of aortic regurgitant volume.
Other approaches may quantify regurgitant volume in cases of isolated regurgitation (i.e., when no other regurgitant lesions or intracardiac shunts are present):
- Difference between left ventricular stroke volume (LVSV, ml) and forward flow (Qs or Qp, ml)
- Difference between LVSV (ml) and right ventricular stroke volume (RVSV, ml)
The severity of aortic regurgitation may be determined as categorized below (Tb.).
|Tb. Regurgitation Severity|
|Degree of regurgitation||Regurgitant volume (ml)||Regurgitant fraction (%)|
|Regurgitant volumes are measured directly. Regurgitant fraction (%)= volume of AR (ml)/LVSV (ml)|