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. 2013 Mar;26(3):290-6.
doi: 10.1016/j.echo.2012.12.008. Epub 2013 Jan 11.

Coronary autoregulation is abnormal in syndrome X: insights using myocardial contrast echocardiography

Diana Rinkevich  1 , Todd Belcik, Nandita C Gupta, Elizabeth Cannard, Nabil J Alkayed, Sanjiv Kaul
Affiliations

Coronary autoregulation is abnormal in syndrome X: insights using myocardial contrast echocardiography

Diana Rinkevich et al. J Am Soc Echocardiogr. 2013 Mar.

Abstract

Background: Syndrome X in women is thought to be caused by coronary microvascular dysfunction, the exact site of which is unknown. The aim of this study was to characterize the microvascular site of dysfunction in these patients using myocardial contrast echocardiography.

Methods: Women with exertional angina, positive test results on stress imaging, but no coronary artery disease (the study group, n = 18) and age-matched control women also with no coronary artery disease (n = 17) were enrolled. Myocardial contrast echocardiography was performed at rest and during dipyridamole-induced hyperemia. Mean microbubble velocity (β) and myocardial blood volume (A) were measured, and myocardial blood flow (A · β) was computed. In addition, plasma concentrations of eicosanoids, female sex hormones, and C-reactive protein were measured.

Results: Rest β and myocardial blood flow (A · β) were higher in the study compared with the control women (1.61 ± 0.68 vs. 0.74 ± 0.44, P = .0001, and 157 ± 121 vs. 54 ± 54, P = 0.0001, respectively) despite similar heart rates and systolic blood pressures. After the administration of dipyridamole, whereas the changes in A and A · β were not significantly different between the two groups, β reserve (the ratio of stress β to rest β) was markedly lower in the study group (1.48 ± 0.62 vs. 2.78 ± 0.94, P = .0001). Blood hematocrit, eicosanoids, female sex hormones, glucose, and C-reactive protein were not different between the two groups.

Conclusions: Coronary autoregulation is abnormal in patients with syndrome X (higher resting β and myocardial blood flow and lower β reserve), which suggests that the coronary resistance vessels are the site of microvascular abnormality.

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Figures

Figure 1
Figure 1
MCE time versus acoustic intensity plots at rest (blue circles and dashed lines) and stress (red circles and solid lines) in a subject from the control group (A) and a patient from the study group (B). β is higher at rest in the study patient but does not increase after dipyridamole, while in the control subject β increases 4 fold. See text for details.
Figure 2
Figure 2
β values at rest and during Dipyridamole stress in individual patients along with mean ±1 standard error of the mean in the control group (A) and the study group (B). Resting β is higher in the study compared to control groups (marked by asterisk) and change in β during stress is less in the study compared to control group (not achieving statistical significance). See text for details.
Figure 3
Figure 3
β reserve in the control versus syndrome-X patients with mean±1 standard deviation. See text for details.
See this image and copyright information in PMC

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