LEFT-TO-RIGHT VENTRICULAR INTERACTION WITH A NONCONTRACTING RIGHT VENTRICLE

Left ventricular systole is known to contribute to generation of right ventricular pressure and stroke volume. To study the interactions in a dilated noncontractile right ventricle after cardiopulmonary bypass we created a variable volume, neo-right ventricle by excision and repl acement of the right ventricular free wall with a xenograft pericardia l patch. We investigated the interactions in eight dogs with neo-right ventricle, instrumented to measure cardiac pressures and cardiac outp ut in control conditions (n = 69) and during partial pulmonary artery occlusion (n = 50). Results: The size of the neo-right ventricle was i ncreased from original right ventricular volume V-0 to V-1 (V-1 = V-0 + 54 +/- 23 ml), V-2 (V-2 = V-0 + 124 +/- 85 ml), and V-3 (V-3 = V-0 223 +/- 162 ml). Cardiac output increased with increasing left ventri cular end-diastolic pressure, indicating that the Frank-Starling mecha nism was operating in the left ventricle. However, cardiac output decr eased with increasing neo-right ventricular size (p < 0.001) and durin g pulmonary artery occlusion (p < 0.001). Maximal neo-right ventricula r pressure was a linear function of the maximal left ventricular press ure at each neo-right ventricular size and decreased,vith the increase in neo-right ventricular size (p < 0.001), both in control conditions and during pulmonary artery occlusion (p < 0.004), Stroke work of the neo-right ventricle and left ventricle decreased with increasing neo- right ventricular size (p < 0.002). The relationship between neo-right ventricular stroke work and left ventricular stroke work at different neo-right ventricular sizes was linear both in control conditions and during pulmonary artery occlusion: in control Y = 0.24X (r = 0.968, n = 69); in pulmonary artery occlusion Y = 0.35X (r = 0.986, n = 50). I n both conditions the intercept of the Linear relationship was not sig nificantly different from zero (p < 0.974 in control; p < 0.614 in pul monary artery occlusion). The slope was significantly increased in pul monary artery occlusion (p < 0.001). Conclusion: Left ventricular cont raction contributes 24% of left ventricular stroke work to the generat ion of right ventricular stroke work via the septum in the absence of a contracting right ventricle; this increases to 35% in the face of in creased pulmonary afterload. This mechanism can maintain adequate glob al cardiac function in the case of a noncontracting right ventricle wh ile right ventricular volume is kept small and afterload is not increa sed. The interventricular interaction of the ventricles must be consid ered when patients with postbypass right ventricular failure are treat ed.