Development of the chronic pressure overload model by surgical banding of the pulmonary artery of eight week old miniature swine has been the focus of the work performed during the current year. In the first group of six animals, the banding was performed to not produce constriction of the pulmonary artery. However, normal intracardiac pressures and cardiac morphometric data obtained from this group three months after the banding procedure did not support the development of hypertrophy. In the next group of seven animals,the banding procedure was changed to produce the greatest pressure gradient between the pulmonary artery (PA) and right ventricle (RV) that could be tolerated without cardiovascular compromise. Nonabsorbable suture was used to constrict the band in six of the seven animals; absorbable suture was used in one of the seven. Absorbable suture failed to constrict the band for the three months necessary to complete the protocol. However, echocardiographic and necroscopy data from three to six animals sacrificed to date suggest that the modified technique is successful. RV-PA pressure gradients obtained by Doppler analysis from animals one month post-banding ranged from 27-55 mm Hg, with five of six gradients between 41-55 mm Hg. One of the six animals died two months post-banding as a result of ventricular fibrillation induced during electrophysiology testing protocol. Three to three and one half months post-banding, the remaining five animals all had intact bands and four of the five had significantly higher gradients, ranging from 55-90 mm Hg. One animal had severe tricuspid insufficiency and an RV-PA gradient of 16 mm Hg. At necroscopy, the intact band was noted to be just below the bifurcation of the pulmonary artery and the size of the right ventricle was greater than that of the left ventricle; the right atrium was also enlarged. We surmise that the constriction of the pulmonary artery, in this particular animal, caused the right ventricle to fail, resulting in tricuspid insufficiency and a decrease in the gradient established during the initial banding procedure. Both animals that completed the protocol, as well as the animal which fibrillated, had morphometric evidence of right ventricular hypertrophy. Three of the six animals with significant gradients will be necroscopied in the next few weeks. We are confident that, like the other animal sin this group, they will exhibit right ventricular hypertrophy.
