The Relative Atrial Index (RAI) is a numeric parameter used to assess for cardiac shunt defects.
[citation needed] Large validation studies[2] in patients with known atrial septal defects showed that the RAI > 1.0 in the majority of cases.
This simple numeric parameter has found a role in the diagnostic work-up for possible shunt defects on standard tranthorcaic echocardiograms.
[6] The RAI was conceptualized in response to observed clinical inadequacies of standard transthoracic echocardiography in some shunt conditions.
The same author[7] had developed several Doppler echocardiographic numeric parameters over the last two decades to assess cardiac diastolic function.