Internal mammary artery use. Sternal revascularization and experimental infection patterns

We have described previously the acute sternal devascularization produced by mobilization of one or both internal mammary arteries (IMAs). The present experiments were conducted to examine the time course of sternal revascularization and infection patterns after IMA use. Twenty-four 8-week-old domestic pigs were obtained from a herd in which active Streptococcus faecalis had been detected in recent litters. After control blood flow procedures (microspheres) were completed, each pig underwent a median sternotomy; one or both IMAs were mobilized as a pedicle, and the sternotomy was repaired. Repeat blood flow determinations were made in half the pigs at 1 week and in the remainder after 2 weeks. The pigs were killed, the wound was examined, cultures were taken as indicated, and tissue was harvested for blood flow analysis. Despite the retention of an intact IMA on the contralateral side, persistent, significant sternal ischemia existed 2 weeks after repair. However, when both IMAs were used, the extent of devascularization was exaggerated, and revascularization was impaired further. Revascularization of intercostal muscle occurred more rapidly and was essentially returned to normal 2 weeks after sternotomy and IMA harvest. Active mediastinitis with erosion of the sternum was found in one (17%) of six pigs at 1 week and in four (67%) of six pigs at 2 weeks when the IMAs had been rotated bilaterally. No wound infections were detected in the single IMA resection group. These data suggest that bilateral IMA mobilization may delay an already slow revascularization process and predispose to infectious complications.