title: Thermodilution-derived coronary microvascular resistance and flow reserve in patients with cardiac syndrome X.
abstract: BACKGROUND
  Although increased coronary microvascular resistance (CMR), resulting in coronary microvascular dysfunction, is speculated to be responsible for myocardial ischemia in patients with cardiac syndrome X (CSX), it has never been directly demonstrated, and the correlation between CMR and severity of myocardial ischemia has not been elucidated in this setting. This study aimed to ascertain the increased CMR directly and to explore the relationship between CMR and severity of ischemia in patients with CSX.
  
  
  RESULTS
  We studied 18 patients with CSX and 18 age- and sex-matched control subjects. Thermodilution-derived coronary flow reserve and index of microvascular resistance were measured using a pressure-temperature sensor-tipped coronary wire. Exercise treadmill test was performed by the Bruce protocol for calculating Duke treadmill score. Coronary flow reserve was significantly lower (2.37±0.81 versus 3.68±0.72; P<0.001) and index of microvascular resistance was higher (33.1±7.9 versus 18.8±5.6 U; P<0.001) in patients with CSX compared with those in control subjects. The Duke treadmill score was correlated positively to coronary flow reserve (r=0.539; P=0.021) and negatively to index of microvascular resistance (r=-0.742; P<0.001) in patients with CSX.
  
  
  CONCLUSIONS
  Using an intracoronary thermodilution method, we for the first time directly demonstrated an increased microvascular resistance in patients with CSX. Furthermore, severity of ischemia was found to be intimately associated with CMR in this setting.
authors.affiliation: From the Department of Cardiology, First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China.
authors.forename: Chufan
authors.initials: C
authors.lastname: Luo
authors.forename: Ming
authors.initials: M
authors.lastname: Long
authors.forename: Xun
authors.initials: X
authors.lastname: Hu
authors.forename: Zhibin
authors.initials: Z
authors.lastname: Huang
authors.forename: Chengheng
authors.initials: C
authors.lastname: Hu
authors.forename: Xiuren
authors.initials: X
authors.lastname: Gao
authors.forename: Zhimin
authors.initials: Z
authors.lastname: Du
mesh_terms: D000368:Aged; D003331:Coronary Vessels / Q000502:physiology; D018450:Disease Progression; D005080:Exercise Test; D005260:Female; D053805:Fractional Flow Reserve, Myocardial; D006801:Humans; D008297:Male; D008833:Microcirculation; D017566:Microvascular Angina / Q000150:complications / Q000175:diagnosis*; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000150:complications / Q000175:diagnosis*; D013815:Thermodilution / Q000379:methods*; D014655:Vascular Resistance
keywords: cardiac syndrome X; microvascular angina