Concept of Venous Steal: The Impact of Vascular Stenosis and Outflow Pressure Gradient on Blood Flow Diversion

The phenomenon of vascular steal is blood flow diversion between collateral vessels with common inflow restricted by arterial stenosis. Blood is diverted from the high-pressure to the low-pressure and/or low-resistance system. Historically, vascular steal has been associated with anatomical bypass or vasodilatation in the collateral network and is called “the arterial steal.” However, we have demonstrated that in a region with increased compartmental pressure, blood is shunted to the collateral network with a lower outflow pressure. Thus we extended the concept of arterial steal to the outflow pressure related diversion and - since this occurs due to the gradient between intracompartmental and systemic venous pressure - we named this phenomenon “the venous steal.” Both arterial steal, due to increased collateral network conductivity, and venous steal, due to lower collateral outflow pressure, reduce compartment perfusion—not directly, but through increased flow and pressure gradient across the arterial stenosis, what decrease the segmental compartmental perfusion pressure- difference between poststenotic (inflow) and compartmental (outflow) pressures. The phenomenon of venous steal in the compartment with fixed inflow stenosis arises due to the outflow pressure gradient between collateral regions and is widespread indeed. It occurs in intra- and extracranial compartments in the head, endo- and epicardial compartments in the heart, ischemic core-penumbra during evolving stroke; focal edema (due to inflammation, trauma, external compression) and peripheral regions in shock- contributing to the regional blood flow maldistribution due to the venous steal. Treatment of venous steal addresses inflow stenosis, increased compartmental pressure and systemic loading conditions (arterial and venous pressure) aiming to reverse malperfusion due to the venous steal redistribution in the ischemic regions.