Reactivity of the human internal thoracic artery to vasodilators in coronary artery bypass grafting

The internal thoracic artery (ITA) is a useful conduit for coronary artery bypass grafting (CABG) and the patency rate is indispensable. Recently we have developed a method for increasing ITA blood flow during surgery by directly injecting phosphodiesterase III inhibitor (PDE III-I) into the left ITA (LITA) to prevent its contracture. In this study, we compared the reactivity of LITA blood flows before and after injection of four drugs: saline, papaverine hydrochloride, isosorbide dinitrate (ISDN), and PDE III-I.

80 patients who were undergoing the first primary CABG, were randomly separated into four groups. Each group consisted of 20 patients. LITA graft free flow (GFF) and systemic mean blood pressure (MBP) were measured before and 1 min after direct intra LITA drug administration and blood vessel resistance (R) was calculated.

The saline group showed no significant changes in GFF, R value, and MBP. Significant increase in GFF was observed in the PDE III-I and ISDN groups. Except the saline group, each group exhibited a significant decrease in both the R value and MBP. A comparison of the change rate of MBP showed no significant differences among the four groups. The PDE III-I significantly increased the change rate of GFF and decreased the change rate of R value, when compared to the saline and papaverine hydrochloride groups. The PDE III-I showed a tendency to increase the change rate of GFF and to decrease the change rate of the R value compared to the ISDN group.

The results of this study suggested that the PDE III-I is the most effective for increasing the blood flow of a LITA graft for CABG during surgery.