Lack of effect of prior training on subsequent ischaemic and infarcting myocardium and collateral development in dogs with normal hearts.
Academic Article
Overview
abstract
To determine whether exercise training in animals with normal coronary arteries has a salutary effect on ischaemic myocardium, 24 dogs were randomly assigned to be either trained or confined to cages for three months. All dogs then underwent left thoracotomy for placement of indwelling right and left atrial and aortic catheters and a loose snare ligature around the proximal left circumflex coronary artery. Three days after operation control scintigrams were recorded after injection of thallous chloride-201 in animals running on a treadmill to achieve exercise heart rates of 220 beats.min-1. Four days later the snares were pulled to occlude the left circumflex artery and infarct size determined by measuring venous activity of creatine phosphokinase. Three days after infarction the first post-ligation scintigram was performed after thallium-201 injection in exercising animals. Exercise scans were repeated at 10 days and 2, 4, and 6 weeks after coronary ligation. During the final exercise study collateral blood flow was measured with radioactive microspheres. There was no difference in mean creatine phosphokinase appearance time, peak creatine phosphokinase activity, or measured infarct size between the trained and sedentary dogs. The ratio of thallium-201 activity in left circumflex artery or ischaemic area to left anterior descending artery or normally perfused myocardium fell from 100% before occlusion to 86.6% in the sedentary animals and 80.6% in the trained dogs three days after coronary ligation. Although these falls were significant (p less than 0.025 and p less than 0.005 respectively), there was no difference between groups. Over the next five and a half weeks the scintigraphic defect shrank as the thallium-201 ratio gradually increased, but changes were again similar in both groups. At six weeks there was little difference in exercise collateral flow to left circumflex artery myocardium and flow to normal myocardial tissue in cage confined and trained dogs. Therefore, no beneficial effect of exercise training in dogs with normal hearts could be seen on ischaemic or infarcting myocardium or coronary collateral development after coronary ligation.
