Importance of myocardial ischaemia for recruitment of coronary collateral circulation in dogs

Study objective – The aim of the study was to investigate collateral coronary flow and regional myocardial function following different coronary occlusion protocols. Design – Effects of brief left anterior descending artery (LAD) occlusions in dogs (using a pneumatic occluder around the proximal artery) on collateral circulation were evaluated using three different protocols, each producing the same period of pressure gradient across the collateral network: (1) 10 s occlusion × 30 at 1 min intervals; (2) 1 min occlusion × 5 at 1 min intervals; (3) 5 min occlusion × 1. Each protocol was followed by a 10 s occlusion after a further 1 min period. Subjects – 14 mongrel dogs of either sex were used, weight 10-21 kg. Measurements and main results – Left ventricular pressure, left circumflex coronary artery (LCCA) flow, and subendocardial segment shortening (%ΔL) in the area perfused by the LAD were monitored. Collateral blood flow from LCCA to LAD territory was measured as a stepwise decrease in LCCA flow on release of LAD occlusion. During the first 10 s of occlusion, %ΔL decreased from 23.6(SEM 2.2)% to 14.2(2.9)%. After protocol (1), %ΔL decreased from 23.1(2.2)% to 14.8(3.0)%. By contrast, after protocol (2) and (3) %ΔL decreased only slightly, from 22.7(2.6)% to 20.5(2.8)%, and from 22.4(2.4)% to 19.8(2.4)%, respectively. Although collateral blood flow remained unchanged after protocol (1), it increased from 1.6(0.4) ml·min−1during the first LAD occlusion to 3.0(0.7) ml·min−1(p