title: Coronary autoregulation is abnormal in syndrome X: insights using myocardial contrast echocardiography.
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.
authors: Knight Cardiovascular Institute, Oregon Health & Science University, Portland, Oregon 97239-3098, USA.
authors: Diana
authors: D
authors: Rinkevich
authors: Todd
authors: T
authors: Belcik
authors: Nandita C
authors: NC
authors: Gupta
authors: Elizabeth
authors: E
authors: Cannard
authors: Nabil J
authors: NJ
authors: Alkayed
authors: Sanjiv
authors: S
authors: Kaul
mesh_terms: D000368:Aged; D015415:Biomarkers / Q000097:blood; D001783:Blood Flow Velocity / Q000502:physiology; D001810:Blood Volume / Q000502:physiology; D002097:C-Reactive Protein / Q000378:metabolism; D016022:Case-Control Studies; D003287:Contrast Media; D004452:Echocardiography / Q000379:methods*; D015777:Eicosanoids / Q000097:blood; D005260:Female; D012739:Gonadal Steroid Hormones / Q000097:blood; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D008833:Microcirculation / Q000502:physiology; D017566:Microvascular Angina / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D008875:Middle Aged; D014655:Vascular Resistance
chemical_list: D015415:Biomarkers; D003287:Contrast Media; D015777:Eicosanoids; D012739:Gonadal Steroid Hormones; D002097:C-Reactive Protein