We determined flow reserve in otherwise healthy patients as a measure of myocardial microvascular responsiveness.1 The vasodilator response of the myocardium to infusion of adenosine is largely mediated by vascular smooth muscle relaxation and partly by endothelial release of nitric oxide.2,3 As Crystal4 points out, a decreased flow reserve may become clinically relevant for our population in situations where hypoxemia and tachycardia are combined with low perfusion pressures, and he suggests that a reduced mean arterial blood pressure is a likely explanation for a lower flow reserve during sevoflurane anesthesia. Also, he expects that an intracoronary infusion of a vasodilatory drug, such as papaverine, or a reactive hyperemic response could disentangle the interaction between system hemodynamics and myocardial microvascular perfusion. Although both interventions are indeed interesting suggestions, our specific goal for the current study was to gain insight into myocardial microcirculatory changes during general anesthesia in a clinically relevant scenario in which hemodynamic variables were not controlled for.
Two important features of myocardial contrast echocardiography used in this study make it a suitable imaging modality. First, the noninvasive and bedside character allows measurements in cardiovascularly healthy patients, both with and without anesthesia. Second, and perhaps most importantly, contrast echocardiography allows a unique glance into the behavior of the myocardial microvasculature in the perioperative setting, which is not feasible with other imaging techniques like positron emission tomography.5 During continuous infusion of an ultrasound contrast agent consisting of microbubbles, a steady-state concentration is reached after a few minutes. At that moment, tissue signal intensity reflects myocardial blood volume.6 Subsequently, measuring the rate at which microbubbles replenish myocardial tissue after their destruction provides an estimate of the exchange rate. The product of myocardial blood volume and exchange rate reflects myocardial blood flow.
To evaluate the potential value of myocardial contrast echocardiography for clinical and research purposes, we first investigated the myocardial microvascular behavior in cardiovascularly healthy patients with and without anesthesia. After this necessary first step, we are currently focusing on patients with preexisting reduced myocardial flow reserves using the same technique. As such, we hope to gain more insight into the complex interaction of general anesthesia, perioperative hemodynamics, and preexisting myocardial perfusion abnormalities.
Carolien S. E. Bulte, MD
Christa Boer, PhD
Stephan A. Loer, MD, PhD
R. Arthur Bouwman, MD, PhD
Department of Anesthesiology
VU Medical Center
Amsterdam, The Netherlands
1. Bulte CS, Slikkerveer J, Kamp O, Heymans MW, Loer SA, de Marchi SF, Vogel R, Boer C, Bouwman RA. General anesthesia with sevoflurane decreases myocardial blood volume and hyperemic blood flow in healthy humans. Anesth Analg. 2013;116:767–74
2. Camici PG, Crea F. Coronary microvascular dysfunction. N Engl J Med. 2007;356:830–40
3. Smits P, Williams SB, Lipson DE, Banitt P, Rongen GA, Creager MA. Endothelial release of nitric oxide contributes to the vasodilator effect of adenosine in humans. Circulation. 1995;92:2135–41
4. Crystal GJ. The effect of sevoflurane on coronary flow reserve. Anesth Analg. 2013;117:745
5. Vogel R, Indermühle A, Reinhardt J, Meier P, Siegrist PT, Namdar M, Kaufmann PA, Seiler C. The quantification of absolute myocardial perfusion in humans by contrast echocardiography: algorithm and validation. J Am Coll Cardiol. 2005;45:754–62
6. Bulte CS, Slikkerveer J, Meijer RI, Gort D, Kamp O, Loer SA, de Marchi SF, Vogel R, Boer C, Bouwman RA. Contrast-enhanced ultrasound for myocardial perfusion imaging. Anesth Analg. 2012;114:938–45