Decreased coronary flow reserve after transient myocardial ischemia in dogs

The effect of a transient (15 min) period of regional ischemia on coronary flow reserve in the postischemic myocardium was studied in 24 open chest dogs. Coronary flow was measured with electromagnetic flow probes, and flow reserve was determined during reactive hyperemia after 30 s coronary occlusions and during intracoronary infusions of adenosine. Measures of flow reserve after 15 min of ischemia were made after coronary flow returned to basal levels and flow reserve was then monitored for 1 h. All measures of coronary flow reserve were significantly reduced after transient ischemia: peak flows during reactive hyperemia and intracoronary adenosine infusions decreased by 20 and 24%, respectively, the peak/basal flow ratio by 16% and the repayment/debt ratio by 54%; minimal coronary vascular resistance during reactive hyperemia and intracoronary adenosine increased by 29 and 33%, respectively. Abnormal flow reserve was present for at least 1 h. No changes in flow reserve were detected in control animals over the same time period. Thus, a transient period of myocardial ischemia significantly decreases coronary flow reserve for a prolonged period of time. This "vascular stunning" must be considered when flow reserve is used to assess the functional significance of a coronary stenosis and could be the cause of variable exercise tolerance in patients with angina pectoris.