Why the Bidirectional Glenn is Called "Bidirectional"
The bidirectional Glenn procedure is called "bidirectional" because it directs superior vena cava blood flow to both the right AND left pulmonary arteries simultaneously, unlike the classic Glenn which only perfuses the right lung. 1
Anatomical Basis for the Name
The procedure involves an end-to-side anastomosis of the divided superior vena cava to the undivided right pulmonary artery, which creates a pathway where blood flows in two directions across the pulmonary arterial system. 1, 2
Superior vena cava blood is directed to both right and left pulmonary arteries through the intact pulmonary artery confluence, establishing bilateral pulmonary perfusion from a single venous source. 1, 2
This contrasts sharply with the classic Glenn shunt, where the superior vena cava connects to the distal end of the divided right pulmonary artery, resulting in superior vena cava blood reaching only the right lung. 1
Clinical Significance of the Bidirectional Flow Pattern
The bidirectional nature provides critical physiologic advantages:
Bilateral pulmonary perfusion prevents the development of pulmonary arteriovenous malformations, which commonly occur with the classic Glenn due to absence of hepatic factors to the right lung. 1
The procedure creates pulsatile pulmonary artery flow pattern contributed by the ventricle in systole (pulsatile) and the superior vena cava in diastole (laminar), establishing a more physiologic flow distribution. 3
Superior vena caval flow averages 36% of total cardiac output, distributing this volume bilaterally to both lungs rather than unilaterally. 3
Common Pitfall to Avoid
Do not confuse terminology: the bidirectional Glenn is also called bidirectional cavopulmonary anastomosis (BDCPA) or bidirectional cavopulmonary shunt, all referring to the same procedure with bilateral pulmonary perfusion. 1, 2 The key distinguishing feature remains the undivided pulmonary artery that allows bidirectional flow distribution. 1