Reduced resistances of septal artery collateral channels after cardiac sympathectomy

Effects of selective cardiac denervation on collateral blood flow after coronary artery occlusion in conscious dogs

The extent to which cardiac nerves regulate responses to myocardial ischemia remains controversial. Our data in conscious dogs indicate that neither selective posterior left ventricular (LV) wall denervation nor selective ventricular denervation, leaving the atria intact, modifies the effects of coronary artery occlusion (for 24 h) on regional myocardial function and infarct size as compared to normally innervated dogs. Since hemodynamic changes were similar among the three groups after coronary artery occlusion, it is possible to speculate that responses of collateral blood flow to the ischemic zone were also not modified by chronic selective cardiac denervation. To address this, individual samples were selected and included in either the infarcted (TTC negative) or salvaged (TTC positive) group. The infarcted and salvaged samples were paired according to blood flow levels of 0.1-0.2, 0.2-0.3, or 0.3-0.4 ml/min/g at either 5 min, 1 h, 3 h, or 6 h after coronary artery occlusion. The results demonstrated similar patterns of myocardial blood flow in tissue samples within the area at risk after coronary artery occlusion in the animals, regardless of whether the ischemic zone was innervated or denervated. While blood flow rose in ischemic tissue that ultimately was salvaged, and tended not to rise over the 24 h monitoring period in tissue samples that became necrotic, no differences could be discerned on the basis of intact or absent innervation of the ischemic zone. Thus, chronic absence of cardiac nerves does not affect regulation of ischemic zone blood flow following coronary artery occlusion in conscious dogs.

Comparison of the effects of acute and chronic beta-blockade on infarct size in the dog after circumflex occlusion

In order to compare the effects of acute and chronic beta-blockade on infact size, the left circumflex coronary artery was occluded for 6 hours in 33 anesthetized dogs. The dogs (18 to 22 kg) were divided into three groups; group 1 (N = 10) served as controls, group 2 received intravenous nadolol (average dose 1.25 mg/kg) just prior to coronary occlusion, and group 3 received oral nadolol (80 mg) twice daily for 16 days prior to coronary occlusion. To ensure equivalent degrees of beta-blockade at the time of occlusion, group 2 and 3 dogs were given incremental doses of intravenous nadolol to abolish the chronotropic response to isoproterenol (2 mu/kg IV). Left ventricular pressure, its first derivative (dP/dt), and heart rate were monitored. The anatomic risk region was determined antemortem by Evan's blue staining while the infarct zone was delineated postmortem by tetrazolium staining. Compared to Group 1, heart rate was 22% lower in group 2 and 15% lower in group 3 dogs 6 hours after occlusion (p less than 0.05). There were no differences among groups in peak left ventricular systolic pressure or mean arterial pressure. Infarct size as a function of the area at risk was 68 +/- 3% in group 1, 52 +/- 7% in group 2, and 44 +/- 8% in group 3. A significant difference was found only between groups 3 and 1. The data suggest that chronic beta-blockade provides greater protection against ischemic-induced necrosis than does acute beta-blockade. The greater protective effect of chronic beta-blockade may be due to chronic adaptive changes in either blood flow or metabolism.

Adverse effects of chronic cardiac denervation in conscious dogs with myocardial ischemia

The extent to which total chronic cardiac denervation protects the ischemic myocardium was investigated in conscious dogs. The major hemodynamic difference after coronary artery occlusion was that left ventricular end-diastolic pressure rose significantly more, P less than 0.01, in the denervated group (12 +/- 1.5 mm Hg) than in the normal group (4.4 +/- 1.4 mm Hg). Blood flow (radioactive microspheres) in the ischemic endo- and epicardium fell to similar levels at 3-5 minutes after coronary occlusion, but was significantly less (P less than 0.01) in denervated dogs at 3 hours after occlusion in the endo- (0.05 +/- 0.01) and epicardium (0.30 +/- 0.02 ml/min per g), than in the endo- (0.13 +/- 0.03) and epicardium (0.42 +/- 0.05 ml/min per g) in the normal group. A subgroup of normal dogs was also studied, with left ventricular end-diastolic pressure increased by volume loading to levels similar to those observed in the denervated group after coronary occlusion; in these dogs, blood flow was similar to that in the other two groups 3-5 minutes after coronary artery occlusion, but, at 3 hours, was significantly more depressed (P less than 0.01) than that observed in normal dogs without volume loading in both endo- (0.03 +/- 0.01) and epicardial (0.25 +/- 0.03 ml/min per g) layers. Infarct size, as a fraction of the area at risk, was significantly greater (P less than 0.05) in the denervated group (60 +/- 4.3%) and in the subgroup of normal dogs with elevated left ventricular end-diastolic pressure (73 +/- 5.8%), compared with the normal group without volume loading (37 +/- 8.1%). Thus, in conscious dogs, total chronic cardiac denervation exerts an adverse effect on infarct size which may be related to the sustained elevation in left ventricular end-diastolic pressure and consequent impairment of collateral perfusion.