Impact of oxygen extraction fraction on long-term prognosis in patients with reduced blood flow and vasoreactivity because of occlusive carotid artery disease

Abstract

Background Reduced cerebral blood flow and cerebrovascular reactivity to acetazolamide (type 3 ischemia) is believed as an independent predictor for subsequent ischemic stroke in patients with occlusive carotid artery diseases. However, recent studies have shown that type 3 patients can be divided into 2 pathophysiologically different subgroups as follows: those with elevated OEF and those with normal OEF. This study was aimed to clarify whether there is a difference in the prognosis between patients with type 3 and elevated OEF and those with type 3 but normal OEF. Methods Twenty type 3 patients were enrolled in this prospective, longitudinal cohort study. Hemodynamic and metabolic parameters were quantitatively determined by 15O-gas PET. All of them were medically treated. Results Oxygen extraction fraction was elevated in 9 patients but was normal in other 11. During an average follow-up period of 45.6 months, 3 of 9 patients with type 3 and elevated OEF developed ipsilateral ischemic stroke. The annual risk was 10.6%. The location and shape of cerebral infarction strongly suggested a key role of hemodynamic compromise in their recurrence. On the other hand, no subsequent stroke occurred in none of 11 patients with type 3 but normal OEF. There was a statistically significant difference in the incidence of ipsilateral ischemic stroke between 2 groups ( P = .0303). Conclusion Type 3 patients may be categorized into 2 subgroups as follows: those with elevated OEF and higher stroke risk and those with normal OEF and lower stroke risk, although larger number of subjects should be analyzed.