Abstract
Perioperative spasm of the internal mammary artery (IMA) may result in early restriction of bypass flow. Therefore, pharmacological pretreatment is usually suggested. We present a technique of temporary distal occlusion of the transsected IMA using a metal clip. After 1 hour of storage in normal saline (SAL) there were significantly better flow rates compared with proximal application of a bull-dog clamp. No further increase in flow was noticed after submersion of the IMA pedicle in verapamil (VER). This technique easily provides sufficient IMA flow at the time of anastomosis, probably due to continuous endoluminal dilatation of the IMA by blood pressure, and thus avoids pharmacological pretreatment with vasodilators.
Introduction
The internal mammary artery (IMA) is the conduit of choice for bypass grafting to the left anterior descending artery (LAD), but vasospasm during preparation may cause insufficient graft flow [1],[4].
To maximize IMA flow, clinical studies have focused on intra- or extraluminally applied different vasodilating agents [1],[2]. Intraluminal hydrostatic dilatation, however, may cause severe endothelial damage [3],[4]. With extraluminal application, site of administration and local dose may vary significantly. We therefore investigated if IMA distension by temporary distal occlusion would also prevent IMA spasm.
Patients and methods
A total of 40 patients (31 men, 9 women, mean age 64.6±8.3 years) underwent coronary bypass grafting using the IMA to the LAD with additional vein grafts.
After preparation the IMA was dissected proximal to its bifurcation and the free flow was determined (time 1). In 20 patients, each, the IMA was stored in a plastic cylinder filled with either normal saline (SAL) or verapamil (VER, 5 mg/150 ml) during cardiopulmonary bypass (CPB). Half of these patients, each, received either temporary distal IMA occlusion by titan clips or proximal application of bull-dog clamps (Table 1 ). Before anastomosis, the occluder was removed and the free flow was remeasured (time 2). Statistical analysis comprised Student’s t-test and analysis of variance (ANOVA).
IMA flow rates in the four study groups
Results
After comparable time intervals, flow increase was significant in all groups with superior results using distal compared with proximal occlusion (VER, mean increase 49.2 ml/min (distal) versus 30.2 ml/min (proximal, P=0.011); SAL, 40.5 ml/min (distal) versus 20.5 ml/min (proximal, P=0.04)). Pedicle submersion in VER did not result in higher flow rates compared with SAL (P=0.11).
Discussion
Perioperative IMA spasm may diminish bypass flow, resulting in increased morbidity. Previous studies have focused mainly on graft submersion techniques to prevent IMA spasm [1],[2].
We found that within 1 hour following IMA transsection, constricted arteries spontaneously dilate after pedicle submersion in SAL which was similarly described by Sasson [2]. VER did not have any additional effect on IMA flow. These results are in contrast to the data obtained by Cooper [1] who found an insignificant flow increase after application of SAL. However, his measuring interval (14–24 min) was significantly shorter compared with our study (58–68 min). It can be assumed that a longer period may allow IMA spasm to resolve, thus obscuring the vasodilating effect of VER.
However, we observed a significant flow increase after distal application of a clip compared with proximal IMA occlusion, which might be due to continuous endoluminal arterial dilatation by the blood pressure.
Commonly applied intravascular dilatation techniques include mechanical hydrostatic dilatation up to 200 mmHg following intraluminal application of vasodilators with similar positive effects on early flow rates [5]. However, evidence exists that this method carries the potential for severe intimal damage which might alter the long-term superiority of IMA grafts over saphenous vein conduits [3],[4].
To optimize IMA flow we therefore recommend temporary distal rather than proximal IMA occlusion. We conclude that this simple method of IMA preconditioning can be applied as an effective mean for endoluminal dilatation of the IMA graft. No additional pharmacological pretreatment of the IMA pedicle seems to be necessary.
