Page 144 - Coronary hemodynamics in acute myocardial infarction - Matthijs Bax
P. 144

Chapter 8
vascular function.19 It has been demonstrated to increase myocardial blood flow, acting as a slow vasodilator inducing vasodilation in a time and dose dependent manner.20-22 In patients with coronary artery disease, intracoronary insulin infusion increases coronary blood flow in the absence of an increase in myocardial oxygen demand.20 The most important physiological mechanism that contributes to insulin-induced vasodilation is the L-arginine to nitric oxide pathway in the vascular endothelium.23 Despite the effects of insulin resistance on glucose uptake and resulting hyperglycaemia, it has been shown that the insulin-induced coronary vasodilation still occurs in obese patients with insulin resistance.24 Therefore, the association observed between myocardial microvascular function and admission glucose levels might reflect the effect of elevated plasma levels of insulin, secondary to acute relative insulin resistance, on myocardial vascular function. Unfortunately, plasma insulin levels were not measured in the present study and the proposed mechanism of action should be considered hypothesis-generating.
Concomitant causes of increased baseline flow velocity in STEMI
In addition to the influence of alterations in glucose homeostasis on microvascular function, and in particular bAPV and BMR, other factors may have had a concomitant effect on bAPV. Due to regional myocardial dysfunction, hyperkinesia of remote non-ischaemic myocardium may occur, leading to a predominant increase in bAPV due to an increase in local myocardial oxygen demand.25.26 In addition, an increase in left ventricular end-diastolic pressure or stiffening of the myocardium because of hypoxic perfusion, may result in a restriction in myocardial capacitance, leading to an isolated increase in reference vessel bAPV.27,28 Nonetheless, the association between admission glucose levels and the bAPV retained significance after adjusting for the identified confounders, including infarct size WMSI which can be considered important predictors for the magnitude of hyperkinesia, left ventricular end- diastolic pressure and hypoxic perfusion.
Implications for the present study
The present study implies that admission glucose levels are associated with reference vessel microvascular function in the acute setting of STEMI, influencing resting coronary vascular tone and increasing resting flow. Importantly, increased bAPV has previously been documented to be associated
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