Relation between graded, subcritical impairments of coronary flow reserve and regional myocardial dysfunction induced by atrial pacing in dogs.

The detection of either impairment of coronary flow reserve at rest or abnormalities of regional myocardial function during an ischemic stress are both means of defining the physiologic significance of coronary stenoses. The relation between these two indexes has not been defined previously, particularly in the setting of mild subtotal impairment of coronary flow reserve. Therefore, this relation was investigated in nine open chest anesthetized dogs. Graded, subcritical coronary stenoses were produced that impaired postocclusion hyperemic flow, but not coronary blood flow at rest. Subendocardial ultrasonic crystals were used to measure segment length shortening at rest and after maximal atrial pacing. There was a curvilinear relation between pacing-induced deterioration of segment length shortening and impairment in reactive hyperemia at rest with the most substantial decrease in regional function occurring when less than 20 to 40% of control reactive hyperemia remained. This corresponded to a reactive hyperemic ratio between 1.7 and 2.3. This nonlinear relation was paralleled by the relation between deterioration of regional function and the percent of control blood flow recorded at the time of regional postpacing dysfunction in the presence of coronary stenosis. It is concluded that coronary flow reserve may be substantially reduced before regional dysfunction induced by atrial pacing becomes pronounced. The extent of regional dysfunction during atrial pacing is, in large part, due to the alterations in coronary blood flow occurring during this form of stress in the presence of coronary stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)