Vorhofkardiomyoplastik in einer experimentellen "Fontan-zirkulation"

Introduction: The Fontan circulation is a direct connection between the systemic veins and the pulmonary artery. Consequently the pulmonary flow is passive due to the gradient between right and left atrial pressure. In patients with increased pulmonary resistance, the surgical procedure of atrio-pulmonary connection is prone to fail. The goal of this experiment was to increase the atrial pulmonary flow after the Fontan operation by performing a right atrial cardiomyoplasty (ACMP). Material and methods: In 19 Foxhounds the left m. latissimus dorsi (LD) was mobilized and transferred as a pedicle into the chest. After sternotomy a "Fontan circulation" was created under cardiopulmonary bypass (CPB) by connecting the right atrium (RA) with the pulmonary artery (PA) by a valveless conduit. The tricuspid valve was closed with a patch. In 11 dogs (group 1), a valve was implanted in the inferior vena cava (IVC) and pulmonary hypertension was simulating by partial occlusion of the conduit resulting in a gradient of 10 mmHg between RA and PA. In the other 8 dogs (group 2), no valve was implanted, but flowmeters were placed in the IVC and the superior cava (SVC). In all dogs the RA was enlarged by a fascia lata patch before the LD was wrapped over the RA and stimulated synchronously with burst impulses. Results: After coming off CPB, high central venous pressures (22.5 ± 5.8 mmHg) were necessary to maintain hemodynamic stability. With LD-stimulation in a 1: 3 mode in group 1, RA pressure (P) increased from 23.1 ± 7.7 to 45 ± 10.5 mmHg (p<0.001), PAP from 15.5 ± 4.3 to 25.5 ± 7.6 mmHg (p < 0.001) and CVP increased to 33.1 ± 11.3 mmHg (p < 0.05). Stroke volume increased from 11.4 ± 4.7 to 17.2 ± 4.3 ml and peak conduit-flow from 1286.3 ± 880.3 to 2329 ± 1173 ml/min (all p < 0.001). In group 2 a strong backflow into IVC and SVC was observed with LD-stimulation, resulting in a less pronounced pressure/flow increase in the pulmonary artery. Conclusion: Our experimental model demonstrates the feasibility of a "ventricularization" of the RA by using the force of the LD. However, the hemodynamic benefit of ACMP was achieved only when a valve was implanted in the ICV.