The aim of this study was to analyze the influence of changes in ventricular preload and afterload, atrial and ventricular pacing on the coronary flow reserve (CFR).

Five open chest anesthetized dogs were studied in five sequential stages:baseline, saline solution volume loading (293.8±29.2 ml for 10 min), atrial and ventricular pacing (120, 140, and 160 bpm), and aortic clamp. Coronary blood flow (CBF) was measured with electro-magnetic flowmeter. CFR was defined as the ratio of hyperemic CBF (hCBF) to resting CBF (rCBF). Hyperemia was induced by IV adenosine infusion (1 mg/kg/min).

1)After volume loading wtih saline solution, CFR significantly decreased (p<0.05) because rCBF was increased while hCBF remained unchanged. 2)Atrial pacing produced increase in rCBF but did not change hCBF. Consequently CFR singificantly reduced when heart rate (HR) increased from sinus rhythm to 120, 140, and 160 bpm (p<0.01). 3)Ventricular pacing produced decrease in hCBF but did not change rCBF. Consequently CFR significantly reduced as HR increased from sinus rhythm to 120 (p<0.05) , 140 (p<0.01), and 160 (p<0.01) bpm. 4)After aortic clamp, CFR significantly decreased (p<0.01) because rCBF increased while hCBF remained unchanged.

We found that CFR is dependent on the changes in volume loading, HR, and ventricular afterload that may commonly occur in clinical situations.