ePLAR: Echocardiographic Pulmonary to Left Atrial Ratio
ePLAR is a simple echocardiographic estimation useful in differentiating pre-capillary from post capillary pulmonary hypertension .
ePLAR = TR Vmax/(Mitral E/e’)
ePLAR: Echocardiographic pulmonary to left atrial ratio
TR Vmax: Maximum velocity of tricuspid regurgitation jet by Doppler echocardiography in m/s
E: E wave in the mitral flow Doppler
e’: Septal mitral annular tissue Doppler velocity
ePLAR values are lower in post-capillary pulmonary hypertension. E/e’ reflects left ventricular filling pressure which is left atrial pressure. TR Vmax reflects the pulmonary artery systolic pressure. That is how TR Vmax divided by E/e’ is a pulmonary to left atrial ratio.
ePLAR can be used to triage patients for pulmonary vasodilator therapy non-invasively. It may be noted that right heart catheterization is the gold standard for differentiating pre-capillary from post capillary pulmonary hypertension. Pulmonary capillary wedge pressure is elevated in post-capillary pulmonary hypertension.
In a study of 16,356 echocardiograms, normal reference value of ePLAR was 0.30±0.09m/s .
Elevated ePLAR in acute submassive pulmonary embolism suggests increased transpulmonary gradients even in the absence of acute elevation of pulmonary arterial pressure . Estimation of ePLAR increases the sensitivity of echocardiography in submassive pulmonary embolism. An ePLAR of ≥ 0.3 m/s had a sensitivity of 70%. This is in comparison with 29% sensitivity of TRVmax ≥ 2.9 m/s and 32% for reduced TAPSE (Tricuspid Annular Plane Systolic Excursion).
Comparison of changes in ePLAR with exercise between iron man athletes and age matched controls showed a two fold increase in ePLAR . This corresponded to a four fold increase in pulmonary pressures compared to systemic pressure in ironman athletes. It is known that though both systemic and pulmonary vascular resistance decreases with exercise, the reduction is more in systemic vascular resistance. As mentioned earlier, ePLAR is a marker of transpulmonary gradient. Authors of the study mentioned that previous studies have suggested that this can lead to right ventricular dysfunction , right ventricular arrhythmias and even sudden cardiac death in endurance athletes.