Determination of atrial shunt size needed to balance an electrohydraulic total artificial heart

An interatrial shunt (IAS) was developed and tested to balance a volumetrically coupled electrohydraulic total artificial heart (EHTAH). The IAS diameter was determined theoretically with the equation: [formula: see text] where D = orifice diameter, delta P = pressure drop across the orifice, rho = fluid density, Q = volume flow through the orifice, and C = empiric constant. The calculated orifice diameter was 2.9-5.3 mm to keep a 3-5 mmHg pressure difference between left and right atria, with 0.42-1.05 L/min of expected flow through the IAS. Three different sizes (3.4, 5.4, and 5.5 mm) of IAS were implanted and tested in four calves. The in vivo left-right pressure difference ranged from 3 to 8 mmHg, with 0.57-1.38 L/min of theoretically calculated flow through the IAS. At autopsy, none of the IAS showed macroscopic thrombus formation.