Effect of exercise on perfusion of collateral-dependent myocardium in dogs with chronic coronary artery occlusion.

Abstract

A B S T R A C T Since the ability of mature intercoronary collateral channels to increase myocardial blood flow in response to drug-induced coronary vasodilation has been questioned, the present study was undertaken to evaluate the response of coronary collateral circulation to the stress of exercise. Studies were performed at rest and during two levels of treadmill exercise in six dogs a minimum of 6 mo after placement of an Ameroid constrictor on the left circumflex coronary artery. Regional myocardial blood flow was estimated in normally perfused anterior and predominantly collateral-dependent posterior left ventricular wall with left atrial injections of radionuclide-labeled microspheres 7-10 lOtm in diameter. At rest, heart rate was 87+7 beats/min and mean myocardial blood flow was comparable in control and collateral-dependent regions (0.96+0.13 and 0.97 +0.14 ml/min g, respectively). During exercise, heart rates increased to 180+13 and 228+14 beats/min and myocardial blood flow (MBF) in the anterior control region increased linearly with heart rate (HR), (MBF = 0.133 HR -0.202, r = 0.88). MBF to the posterior collateral-dependent region was similarly augmented during exercise (MBF = 0.140 HR -0.252, r = 0.89), so that the linear correlation between HR and MBF was similar for the control and collateral-

Differential electrocardiographic effects of myocardial ischemia induced by atrial pacing in dogs with various locations of coronary stenosis.

“…This is consistent with data of Cox et al,3 Heaton et al, 35 and Tomoike et al,20 who demonstrated the functional inadequacy of coronary collaterals to protect against exercise-and catecholamine-induced ischemia. These data are not in accord with those of Lambert et al 36 who reported maintenance of normal transmural distributions of coronary flow during exercise. That the latter study was performed 6 months after ameroid constrictor placement rather than after shorter time periods as in the other and current studies, as well as other methodologic differences, may be responsible for the differences.…”

Coronary collateral function during exercise.

“…In addition, four of the six group 2 NIECDMRs were associated with fatigue rather than chest pain as the exercise-limiting symptom. Thus, although the presence of ischemia during exercise in group 2 NIECDMRs was unclear, the distinctly higher level of exercise achieved in this group suggests that uniform global malperfusion and inappropriate timing of thallium injection as causes of false-negative exercise MPI are less likely.24 Experimental studies of fully developed chronic collaterals in dogs have shown that protection from ischemia during exercise ranges from minimal to complete.25 26 Regional Nature of Collateral Protection…”

Exercise Training Enhances Vasodilation Responses to Vascular Endothelial Growth Factor in Porcine Coronary Arterioles Exposed to Chronic Coronary Occlusion

“…[1][2][3][4] CCO creates a proangiogenic environment that is dependent on the presence of growth factors and appropriate receptors. 1,5 Indeed, increased myocardial release of vascular endothelial growth factor (VEGF) has been demonstrated after coronary artery occlusion.…”