Detection of myocardial ischemia by regional dysfunction during and after rapid pacing in conscious dogs.

Publisher Website
Google Scholar
Abstract
The effects of increased heart rate (HR) on regional myocardial function and circumflex coronary artery blood flow (CBF) were examined in the conscious dog before and during coronary artery stenosis. Regional myocardial function (ultrasonic crystals) was determined during graded elevations of HR and after pacing. Before coronary stenosis (implanted hydraulic cuff), both control segment and a segment to be rendered ischemic showed similar responses to increased HR, with increases in CBF and no significant change of coronary flow pattern. During coronary stenosis, which reduced resting CBF to 75% of control, percent shortening (%.DELTA.L) in the control segment did not change significantly, end-diastolic length in the ischemic segment increased and %.DELTA.L decreased in proportion to the increase in HR; holosystolic elongation occurred at 180 beats/min, accompanied by a slight decrease of CBF, and the flow pattern changed to an elevated systolic/diastolic ratio. After the cessation of pacing without coronary stenosis, potentiation of %.DELTA.L and peak segment velocity were observed for several beats. Upon stopping pacing with coronary stenosis, there was early potentiation of %.DELTA.L and velocity, but the ischemic segment then became very depressed at 5 s post pacing, gradually returning to 90% of control %.DELTA.L after only 5 min. Regional depression of myocardial function during and after stress testing by pacing-induced increases in HR is a sensitive indicator of coronary artery narrowing, even in the absence of dysfunction at rest.