Recovery of myocardial function following brief versus prolonged atrial pacing stress in the presence of coronary artery stenosis

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Abstract
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·min−1·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±lSD) to 0.6±0.9, pinitial 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<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). Regional myocardial blood flow in endocardium distal to the stenosis decreased (p<0.01) versus control at AP-1 (1.01±0.33 to 0.77±0.28) but not significantly at 30 min of AP-2 (0.95±0.25 to 0.87±0.40, p=NS). Thus recovery of regional systolic function although incomplete was similar 5 min following discontinuation of both brief as well as prolonged atrial pacing stress.