Effects of heart rate on hemodynamic severity of coronary artery stenosis in the dog

Summary In 14 open-chest mongrel dogs, the effects of heart rate on hemodynamic severity of proximal coronary artery stenosis were studied. Stenosis was produced by a circumferential wire snare on left cirucmflex coronary artery. An intermediate stenosis was defined by reduction of peak reactive hyperemia response to 200% of control flow, a critical stenosis by prevention of any reactive hyperemia flow to a 15-s occlusion. Heart rate was increased stepwise from control to 160 and 200 beats/min by left atrial pacing. In intermediate stenosis, increased pacing rate reduced peripheral coronary pressure distal to the stenosis from 77±3 to 73±4 to 65±3 mm Hg (p<0.05) and increased stenosis resistance from 0.30±0.05 to 0.34±0.05 to 0.35±0.05 resistance units (p<0.05). In critical stenosis, increased heart rate changed peripheral coronary pressure from 45±5 to 49±5 to 48±5 mm Hg (p<0.01) and reduced stenotic resistance from 1.24±0.19 to 1.08±0.18 to 1.15±0.19 resistance units (p<0.005). A significant correlation between changes in stenotic resistance and peripheral coronary pressure was obtained (r=−0.71, p<0.001). In maximally dilated coronary arteries, a circumferential stenosis decreased circumflex artery flow to 50%. Increased pacing rate up to nearly 200 beats/min raised peripheral coronary pressure distal to the stenosis from 51±4 to 56±4 mm Hg (p<0.005) and changed stenotic resistance from 0.41±0.13 to 0.30±0.06 to 0.33±0.10 resistance units (p<0.05).