Re: Perivascular tissue of internal thoracic artery releases potent nitric oxide and prostacyclin-independent anticontractile factor

CABG, Perivascular tissue, Nitric oxide, Saphenous vein, Internal thoracic artery

We read with interest the recent article by Malinowski et al. [1] on the release of a soluble anticontractile factor from perivascular tissue (PVT) of the internal thoracic artery (ITA). In this study the authors show that the PVT surrounding the ITA, the ‘gold standard’ graft in coronary artery bypass surgery (CABG), releases a nitric oxide (NO) and prostacyclin-independent anticontractile factor. The authors suggest that the presence of an active PVT might explain the functional difference between skeletonised and non-skeletonised ITA and influence vascular function after graft implantation. Possible drawbacks of removing PVT should be taken into account since preservation of this tissue might be beneficial.

Malinowski et al. suggest that the influence of PVT removal on the function of other vessels used for CABG, such as the saphenous vein, the radial or the gastroepiploic arteries should be analysed. Although we have not performed functional studies, we have recently shown that the PVT surrounding saphenous veins used as grafts in patients undergoing CABG exhibits positive endothelial nitric oxide synthase (eNOS) immunoreactivity, contains eNOS mRNA and protein and possesses NOS activity [2]. This finding is of particular relevance to the improved early- and long-term patency rates shown in patients receiving saphenous vein grafts prepared using a ‘no-touch’ method of harvesting [3] where the vein is removed complete with its cushion of surrounding tissue, much of which is fat. Indeed, a long-term prospective follow-up study (mean time 8.5 years) showed the patency of ‘no-touch’ vein grafts comparable to the ITA [3].

While the PVT is likely to play an important role in the improved performance of ‘no-touch’ saphenous vein grafts its contribution to the superior patency of the ITA in CABG patients may be questionable. As mentioned by Malinowski et al., the ITA is traditionally harvested as a pedicle, complete with surrounding tissue. In some centres, ITA skeletonisation is performed that provides a longer graft with superior flow and reduced postoperative sternal wound infection. However, a review of the ITA graft points out that data from long-term angiographic studies comparing pedicled with skeletonised ITA is not currently available. Furthermore, in this review, Del Campo [4] suggests that skeletonisation of the ITA might adversely affect the long-term patency of this conduit since in this preparation the vasa vasorum, innervation and lymphatic drainage of the vessel might be compromised. Again, the preservation of PVT in ‘no-touch’ saphenous vein grafts is likely to have a protective role since the capillary network contained within the surrounding cushion of fat and the underlying vasa vasorum are not damaged. The identification of eNOS associated with perivascular fat and endothelial cells of the capillaries and vasa vasorum accompanied by the finding that it possesses NOS activity indicates its potential to release NO when used as a bypass conduit. We suggest that the PVT of ‘no-touch’-harvested saphenous vein plays an important role in its superior patency rate comparable to the ITA and agree with Malinowski et al. that skeletonisation of vessels used for CABG should be re-evaluated.