Regurgitant volume and regurgitant fraction
The regurgitant volume refers to the volume of blood flowing backwards or in the reverse direction through the valvular plane within a beat or cardiac cycle.
The regurgitant fraction is referred to the backflowing blood volume divided by the forward flow volume and is expressed in percent [%].
Terminology
The regurgitant volume is also known as ‘retrograde flow volume’ or ‘backward flow volume’.
Usage
Regurgitant volume (RVol) and a regurgitant fraction (RF) are parameters used in the quantification and grading of valvular insufficiency.
Measurement
MRI
Retrograde volumes of the semilunar valves can be directly measured with velocity-encoded phase-contrast imaging at the valvular tips approximately 5mm distal to the valve or halfway between the annulus and the sinotubular junction (proximal to the coronary ostia) .
Regurgitant volumes of the atrioventricular valves can be calculated by subtracting the antegrade flow volume across the respective semilunar valve from either the volumetric measured ventricular stroke volume or the diastolic inflow across the atrioventricular valve or the difference between left and right ventricular stroke volume obtained from volumetric cine images .
The regurgitant fraction can be calculated from retrograde and antegrade flow volumes :
Regurgitant fraction [%] = retrograde flow volume [ml] / anterograde flow volume [ml] x 100
Alternative calculations
An alternative calculation for the aortic regurgitant volume in case of a dilated aortic root where the direct measurement might be inaccurate is to subtract main pulmonary artery net flow volume from aortic forward flow volume possibly accounting for bronchial flow (ca. 5%) .
Caveats
Accuracies might be limited in the following situations:
- velocities greater 3.5 m/s are limited because of dephasing due to turbulent flow
- dilated aortic root or main pulmonary artery
Interpretation
Aortic regurgitation
Suggested thresholds for grading the severity of chronic aortic regurgitation with regurgitant volume and regurgitant fraction as per 2014 ACC/AHA valvular heart disease guidelines :
- mild RVol < 30 mL/beat RF <30%
- moderate RVol 30-59 mL/beat RF 30-49%
- severe RVol ≥ 60 mL/beat RF ≥ 50%
The following threshold for cardiac MRI was suggested as a risk for progression to aortic valve replacement :
- regurgitant volume > 42 mL/beat
- regurgitant fraction > 33%
Mitral regurgitation
Recommended thresholds for grading chronic mitral regurgitation with echocardiography are found below. There are no specific thresholds in respect to cardiac MRI and guidelines suggest the use of those approved for echocardiography :
- mild RVol < 30 mL RF <30%
- moderate RVol 30-59 mL RF 30-49%
- severe RVol ≥ 60 mL RF ≥ 50%
One study suggested the following threshold for cardiac MRI as a risk for progression to symptomatic mitral regurgitation and other indications for mitral valve replacement:
- regurgitant volume > 55 mL/beat
- regurgitant fraction > 40%
Pulmonic regurgitation
Recommended thresholds for grading the severity of pulmonic regurgitation by echocardiography :
- mild RF <20%
- moderate RF 20-40%
- severe RF > 40%
Cardiac MRI has some advantages over echocardiography and is used in patients with pulmonic regurgitation after surgery for tetralogy of Fallot.
A regurgitant fraction > 40% is considered as severe .
Tricuspid regurgitation
Recommended thresholds for grading the severity of tricuspid regurgitation by echocardiography (2D PISA) :
- mild RVol < 30 mL
- moderate RVol 30-44 mL
- severe RVol ≥ 45 mL
See also
