# Diabetes Differentially Affects Vascular Reactivity in Isolated Human Arterial and Venous Bypass Grafts

## TL;DR

This study shows that diabetes increases spasm risk in venous bypass grafts, which could help improve surgical outcomes for heart bypass patients.

## Contribution

The study is the first to show that diabetes worsens potassium chloride-induced contractions in human saphenous vein grafts.

## Key findings

- Diabetic patients' saphenous veins showed increased contractions to potassium chloride and phenylephrine.
- Endothelium-dependent relaxation was not impaired in diabetic patients' grafts.
- Diabetes does not affect internal mammary artery spasm responses but increases saphenous vein spasm risk.

## Abstract

Arterial and venous graft spasm can occur during harvesting or immediately after coronary artery bypass grafting (CABG), leading to increased perioperative morbidity and affecting graft patency rates. Bypass grafts harvested from diabetic patients are particularly prone to spasm. This study aimed to elucidate the functional characteristics of human bypass grafts for the internal mammary artery (IMA) and saphenous vein (SV), from both diabetic and non-diabetic patients, and to determine how diabetes affected their responses to spasmogenic and relaxant agents. SV and IMA graft rings isolated from diabetic and non-diabetic patients during CABG were placed in an isolated organ bath system. Contractions to potassium chloride (10–100 mM) and phenylephrine (10−8–10−4 M) were evaluated, and relaxation responses to acetylcholine (10−9–10−4 M) and sodium nitroprusside (10−8–10−4 M) were assessed to evaluate endothelial and smooth muscle function, respectively. We observed increased responses to phenylephrine, an alpha-1 adrenoceptor agonist, in both IMAs and SVs, as well as an increased responses to potassium chloride, a non-receptor agonist, in SVs in diabetic patients compared to non-diabetic patients. We did not observe any deterioration in endothelium-dependent relaxations in either SV or IMA grafts under diabetic conditions. This study is the first to demonstrate that diabetes exacerbates potassium chloride-induced contractions in human SV grafts. Understanding the differences in potassium chloride-induced contraction profiles between arterial and venous grafts is essential in optimizing graft spasm management and improving the patency rates of bypass grafts.