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Coronary autoregulation is abnormal in syndrome X: insights using myocardial contrast echocardiography
Diana Rinkevich1, Todd Belcik, Nandita C Gupta
1Knight Cardiovascular Institute, Oregon Health & Science University, Portland, Oregon 97239-3098, USA.
Insights
Syndrome X in women shows abnormal coronary autoregulation, with higher resting blood flow and lower reserve capacity. This indicates coronary resistance vessels are the site of microvascular dysfunction in these patients.
Area of Science:
- Cardiology
- Vascular Biology
- Diagnostic Imaging
Background:
- Syndrome X in women is linked to coronary microvascular dysfunction, but the precise location remains unclear.
- This study aimed to pinpoint the microvascular site of dysfunction in women with Syndrome X.
Purpose of the Study:
- To characterize the microvascular site of dysfunction in women diagnosed with Syndrome X.
- To investigate coronary microvascular function using myocardial contrast echocardiography.
Main Methods:
- Myocardial contrast echocardiography was performed on 18 women with Syndrome X and 17 controls at rest and during hyperemia.
- Key parameters measured included mean microbubble velocity (β), myocardial blood volume (A), and computed myocardial blood flow (A · β).
- Plasma levels of eicosanoids, sex hormones, and C-reactive protein were also analyzed.
Main Results:
- Women with Syndrome X exhibited higher resting microbubble velocity (β) and myocardial blood flow (A · β) compared to controls.
- Despite similar heart rates and blood pressures, the study group showed a significantly lower β reserve after dipyridamole administration.
- No significant differences were found in hematocrit, eicosanoids, sex hormones, glucose, or C-reactive protein between groups.
Conclusions:
- Coronary autoregulation is impaired in women with Syndrome X, evidenced by elevated resting flow and reduced β reserve.
- These findings strongly suggest that the coronary resistance vessels are the primary site of microvascular abnormality in Syndrome X.
- Myocardial contrast echocardiography is effective in identifying microvascular dysfunction in this patient population.
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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