Extensive cryoablation of the left ventricular posterior papillary muscle and subjacent ventricular wall. Impact on mitral valve function and hemodynamics.

Ventricular tachycardias that originate from the inferior left ventricular wall may necessitate transmural ablation involving the posterior papillary muscle of the mitral valve. The effect on mitral valve function and hemodynamics of extensive cryoablation of the left ventricular posterior papillary muscle and subjacent ventricular wall was studied in 16 dogs. Two sham experiments were done. All dogs were studied preoperatively and postoperatively by pulsed Doppler and two-dimensional echocardiography. Left ventricular angiographic and hemodynamic studies were performed preoperatively in six treated dogs and two control dogs and in all dogs at the end of follow-up (1, 3, or 6 months). Postmortem studies were performed in all dogs. The cumulative probability of freedom from mitral regurgitation at 2 months was 0.43 +/- 0.14. Thereafter no new cases of mitral regurgitation could be demonstrated. The angiographic degree of mitral regurgitation was mild in five and moderate in two dogs and did not increase from 3 to 6 months. One dog with acute severe mitral regurgitation died early of heart failure. A significant increase in left ventricular end-diastolic and mean pulmonary capillary wedge pressure of 9.4 +/- 2.5 mm Hg and 6.4 +/- 2.6 mm Hg, respectively, was found in treated dogs at 3 months. These results suggest that extensive cryoablation of the left ventricular posterior papillary muscle and subjacent ventricular wall can be accomplished with an acceptable risk of mild to moderate mitral regurgitation, and without serious detrimental effect on left ventricular function. Retraction is probably the main mechanism of mitral regurgitation.