Branch-to-Total Pulmonary Artery Area Ratio as a Predictor of Flow Limitation in Tetralogy of Fallot: MRA and Phase Contrast MRI Study

Objective: The severity of branch pulmonary artery stenosis and associated flow restriction can be assessed using catheter angiography and lung perfusion scintigraphy. However, these techniques are time-consuming and have various limitations. This study aims to establish a ratio of the narrowed-to-total pulmonary artery area to assess flow restriction. Methods: A net flow of the right and left pulmonary arteries was calculated by phase-contrast magnetic resonance imaging (MRI), and the cross-sectional area was calculated at the narrowest point of the branch pulmonary artery using multiplanar reconstruction images from magnetic resonance angiography. A right-to-left pulmonary artery flow ratio between 61/39 and 43/57 was considered normal. The narrowed-to-total pulmonary artery area ratio was calculated to establish a threshold for physiologically significant branch pulmonary artery stenosis. Results: A total of 272 patients were included in the study. About 136 patients diagnosed with branch pulmonary artery stenosis were compared with 136 patients exhibiting normal branch pulmonary artery flow. The patients with branch pulmonary artery stenosis exhibited a significantly reduced narrowed-to-total pulmonary artery area ratio, with values of 0.46 and 0.38, respectively, showing a statistically significant difference (P < .00001). A branch-to-total pulmonary artery area ratio of ≤0.40 exhibited a sensitivity of 67.65% and a specificity of 91.91% in detecting branch pulmonary artery stenosis, as confirmed by the calculated area under the curve of 0.86 with a 95% CI ranging from 0.813 to 0.899 (P < .0001). The positive predictive value was 84.79%, and the negative predictive value was 80.99%. Conclusion: A narrowed-to-total pulmonary artery area ratio of ≤0.40, measured by cross-sectional imaging, can help identify patients who may need catheter angiography, especially when cardiac MRI is unavailable or flow measurement is not possible.