Balloon induced right ventricular outflow obstruction. A new approach to control of acute interventricular shunting after myocardial infarction in canines and swine

Current management of ventricular septal defect (VSD) after myocardial infarction (MI) is aimed at improving left ventricular (LV) performance by afterload reduction as a means of hemodynamic stabilization or shunt control. The current investigation was undertaken to determine whether primary manipulation of right ventricular (RV) performance by afterload enhancement was an effective means of reducing MI-VSD shunting. In five open-chest dogs an external LV-RV shunt was created with pulmonary-systemic flow ratios (Q(p)/Q(s)) averaging 2.26:1. Inflation of a balloon-tipped catheter in the main pulmonary artery (PA) reduced average Q(p)/Q(s) to 1.28:1 and shunt flow from 783 to 343 ml/min. However, this increase in RV afterload caused further significant increases in RV systolic and end-diastolic pressure and suggested that deterioration of RV function might be limiting the usefulness of this technique. To investigate whether inotropic support for the RV would overcome this limitation, a similar shunt was created in 11 open-chest swine. We then investigated the effects of dopamine, infused at 24, 60, and 120 μg/min, on Q(p)/Q(s) and other hemodynamic variables both with and without PA balloon inflation. Optimal shunt control was obtained when effects of dopamine were added to those of PA balloon inflation. Shunt flow that had been 1,633 ml/min was reduced to 892 ml/min with the PA balloon and reduced further to 757 ml/min with dopamine, which also lowered RV and LV end-diastolic pressure and reduced total systemic vascular resistance. In four other swine with left anterior descending ligations, PA balloon inflation and dopamine infusion again favorably affected hemodynamics. Epicardial mapping in these swine showed an increase in S-T segment displacement, suggesting that the cumulative effect of these interventions allowed hemodynamic improvement at the expense of enhanced ischemic injury. These data indicate that acute RV outflow obstruction with a balloon catheter is an effective means of temporarily reducing acute ventricular shunting and that dopamine may be a useful pharmacological agent to use with RV afterload manipulation to stabilize a patient prior to transfer to a medical center for more definitive therapy.