Abstract 15919: Cardiac Sympathetic Blockade Increases Hyperemic Myocardial Blood Flow Assessed by Contrast-Enhanced Ultrasound
Introduction Perfusion of the myocardium is primarily regulated by local metabolic and endothelial factors. Cardiac sympathetic fibers play an additional modulatory role. With this study, using high thoracic epidural anesthesia for acute and reversible sympathetic blockade, we aimed to investigate how cardiac sympathetic innervation influences myocardial vasoreactivity.
Methods Ten cardiovascular healthy patients (4 women, 6 men; age 48±13 years) scheduled for high thoracic epidural anesthesia were included. Sympathetic blockade of at least Th1 to Th6 was induced by injection of lidocaine 2% via a catheter in the epidural space. Myocardial contrast echocardiography was used for quantification of myocardial blood volume and blood flow by analysis of replenishment curves obtained during continuous microbubble infusion. Contrast echocardiography was performed with and without thoracic epidural anesthesia and included measurements at rest, during adenosine-induced hyperemia (endothelium-independent vasodilation) and after sympathetic stimulation by the cold pressor test (endothelium-dependent vasodilation). Data are mean±SD.
Results Resting myocardial blood flow was comparable with and without epidural anesthesia (1.0±0.3 versus 0.8±0.2 ml min-1 g-1), despite decreased systolic and diastolic blood pressure with epidural anesthesia. Adenosine infusion increased blood flow to 4.3±1.1 ml min-1 g-1 with epidural anesthesia, which was significantly higher than without epidural (2.8±1.0 ml min-1 g-1; P=0.0008). This difference was the result of a further increase in myocardial blood volume during epidural anesthesia. The cold pressor test increased myocardial blood flow to 1.5±0.4 ml min-1 g-1 in the absence of an epidural, whereas no difference in flow was observed during epidural anesthesia (also 1.0±0.3 ml min-1 g-1).
Discussion These results suggest that cardiac sympathetic blockade augments the endothelium-independent vasodilator capacity of the myocardium, while the stress-induced vasodilator response is blunted. Extrinsic alterations in sympathetic regulation may therefore be of consequence in patients at risk for disturbed myocardial perfusion under demanding conditions like surgery.
- © 2012 by American Heart Association, Inc.