Recovery of myocardial function following brief versus prolonged atrial pacing stress in the presence of coronary artery stenosis.
The ability of myocardium distal to a severe coronary artery stenosis to recover from brief (5 min) versus prolonged (30 min) atrial pacing stress was compared in this study. Eight closed chest pigs were prepared with a coronary artery stenosis (82% lumenal diameter reduction) in the left anterior descending artery and ultrasonic length sensors in left anterior descending endocardium. Extent of recovery of systolic function 5 min following a brief (5 min) period of ischaemia induced by rapid (175 to 190 min-1) atrial pacing (AP-1) was compared with that following a prolonged (30 min) period of ischaemia induced by rapid atrial pacing (AP-2). Regional myocardial blood flow (ml X min-1 X g-1) was measured at control, during, and following atrial pacing. Regional shortening (%) distal to the stenosis declined versus control at both 5 min of AP-1 (10.0 +/- 7.3 (mean +/- 1 SD) to 0.6 +/- 0.9, p less than 0.01) and 30 min of AP-2 (6.8 +/- 3.3 to 2.1, +/- 3.5, p less than 0.01). However, within 5 min of discontinuing both brief as well as prolonged pacing, regional segmental shortening (5.7 +/- 3.9 and 7.0 +/- 6.9, respectively) returned to 50 to 70% of initial control levels (10.0 +/- 7.3). Regional shortening was similar 5 min following brief and prolonged stress. Distal left anterior descending zone epicardial regional myocardial blood flow increased (p less than 0.01) versus control at AP-1 (1.05 +/- 0.24 to 1.39 +/- 0.24) and 30 min of AP-2 (0.99 +/- 0.21 to 1.40 +/- 0.23).(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D001794:Blood Pressure; D002304:Cardiac Pacing, Artificial; D003326:Coronary Circulation; D003327:Coronary Disease / Q000503:physiopathology*; D006321:Heart / Q000503:physiopathology*; D006325:Heart Atria; D006339:Heart Rate; D013552:Swine; D013599:Systole; D013997:Time Factors