Retrograde internal mammary to coronary artery anastomoses

In an effort to expand the utilization of the internal mammary artery (IMA) for revascularization of the distal coronary artery branches, distally pedicled retrograde internal mammary arteries (retro-IMA) were evaluated in 10 mongrel dogs with a mean weight of 38 +/- 13 kg. One IMA was transected at it's origin (retro-IMA) and compared to the contralateral IMA which was transected at the level of the 5th intercostal space. At a mean systemic pressure of 68 +/- 15 mmHg the mean pressure measured at the tip of the IMAs with antegrade flow was 63 +/- 14 mmHg in the retro-IMAs with retrograde flow (p less than 0.05; pressure ratio 0.8). With the same mean systemic pressure, mean antegrade free flow of the IMAs was assessed 97 +/- 43 ml/min versus 48 +/- 13 ml/min in the retro-IMAs with retrograde flow (p less than 0.005; flow ratio 0.5). Left retro-IMA to coronary artery anastomosis was performed in 6 animals to the distal left anterior descending (LAD) coronary artery and in 2 animals to the distal left obtuse marginal branch. Right retro-IMA to coronary artery anastomosis to the right posterior descending coronary artery was performed in 2 animals. The LAD coronary artery was ligated proximally to the retro-IMA to coronary artery anastomosis while the retro-IMA remained crossclamped. After documentation of significant ischemia (EKG, left atrial pressure), the crossclamp of the retro-IMA graft was removed. Subsequent normalisation of EKG and left atrial pressure occurred in all animals. We conclude that the canine retro-IMA delivers significant retrograde flow and discuss a possible use in humans.