Fractional flow reserve of pedicled left and right internal thoracic arteries Free

Glineur et al. [1] provide important functional data on fractional flow reserve in bypass grafts. Debate about single or bilateral mammary artery (BIMA) utilisation continues, and is usually centred around sternal wound complications.

However, Glineur et al. reveal an important point in their data which I feel is not adequately explained in their manuscript, or the accompanying editorial [2]. Why should the right internal mammary artery (RIMA) grafts have a lower resistance to flow than the left internal mammary artery (LIMA) grafts? In their manuscript, the authors speculate that LIMA has better long-term results secondary to interactions between flow and LIMA wall, frictional forces, release of endothelial factors, and superior endothelial cell function.

Superior endothelial cell function has to be questioned due to the same endothelium being present in the LIMA and the RIMA. Endothelium is known to secrete nitric oxide (NO), an important vasodilator. Statin therapy, which was not commented on in the paper, needs to be consistent across the patient group as statins both upregulate endothelial nitric oxide synthase (eNOS) and inhibit inducible nitric oxide synthase (iNOS) [3].

Technique of harvest also remains an important factor, which was not mentioned in the manuscript. Skeletonisation removes surrounding periadventitial connective tissue, however this is known to affect vascular reactivity [4]. Patients having RIMAs are more likely to be skeletonised secondary to the perceived risk of reduced sternal ischaemia and dehiscence.

An additional point not mentioned by Glineur or Pijls in the editorial comment is that the RIMA tends to be a larger diameter vessel, particularly in right-handed manual workers, compared with the LIMA. This point probably explains the lower resistance of the RIMA compared to that of LIMA.

References