Cardioacceleration by Atrial Pacing and Transmural Metabolite Levels in the Canine Left Ventricle

Creatine phosphate, adenosine triphosphate, and lactate levels were determined for the outer, middle, and inner layers of the canine left ventricle in animals paced at 100, 150 or 200 beats/min. A slightly lower creatine phosphate level was noted for the inner layer compared to the outer and middle layers of the ventricle at all three heart rates. No evidence of a heart rate effect on metabolite levels in any of the ventricular layers was found. The results indicate that the coronary circulation autoregulates the transmural distribution of myocardial blood flow sufficiently well to maintain an adequate oxygen delivery to all layers of the ventricle under these conditions despite previous reports of a reduced subendocardial to subepicardial blood flow ratio and a lower subendocardial oxygen tension.