Training in dogs with normal coronary arteries: lack of effect on collateral development

STUDY OBJECTIVE - The aim of the study was to investigate the effect of exercise training on coronary collateral development in a normal heart animal model. DESIGN - Dogs with normal hearts were fitted with balloon occluders around the left circumflex coronary artery. Haemodynamic variables and myocardial blood flow (using radioactive microspheres) were measured during 1 min circumflex occlusions at rest and during exercise, before and after a 12 week exercise programme. Resting measurements were also made after 4 weeks. SUBJECTS - Trained subjects were 10 one year old beagles; eight beagles served as sedentary controls. Although measurements were made in all dogs at 4 weeks, four trained and three control animals died during the experiment because of complications, so the data reported at 12 weeks are derived from six trained and five sedentary animals. Except during the few occasions when the left circumflex artery was transiently occluded to allow measurement of collateral flow, all coronary arteries were patent and without impediment to normal flow. MEASUREMENTS and RESULTS - Measurements of haemodynamic variables and coronary blood flow were made at the start and repeated at 4 weeks (resting measurements only) and 12 weeks of exercise training. Initial resting circumflex collateral flow was 0.26(SEM 0.05) cm3.g-1.min-1 in the training group and 0.23(0.03) in the control group (NS). The ratio of ischaemic to normal blood flow was 0.16(0.02) in both groups. At 4 weeks there were no changes in either group. At 12 weeks the ischaemic to normal blood flow ratio had increased in both trained and sedentary dogs to 0.24(0.05) and 0.26(0.06) respectively, but the trend over the 12 week period was not significant. The decline in cardiac output and dramatic increase in left atrial pressure during combined coronary occlusion and exercise were comparable in both groups at weeks 1 and 12. CONCLUSIONS - Exercise does not accelerate the development of coronary collaterals in dogs with normal coronary arteries.