Copyright © 2004, European Society of Cardiology
Exercise unmasks autonomic dysfunction in swine with a recent myocardial infarction
Experimental Cardiology, Thoraxcenter, Erasmus MC, University Medical Center Rotterdam, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands
* Corresponding author. Tel.: +31 10 4638066; fax: +31 10 4089494. Email address: d.duncker{at}erasmusmc.nl
Objective: Severe congestive heart failure is associated with autonomic imbalance consisting of an increased sympathetic and decreased parasympathetic activity. In the present study, we investigated the influence of alterations in autonomic balance on cardiovascular function in 11 swine with left ventricular (LV) dysfunction produced by a 2- to 3-week-old myocardial infarction (MI).
Methods: Swine underwent permanent occlusion of the left circumflex coronary artery resulting in MI of the lateral LV wall. Autonomic activity was studied 2–3 weeks later using blockers of muscarinic (atropine), 
-adrenergic (phentolamine) and β-adrenergic (propranolol) receptors.
Results: Under resting conditions, parasympathetic and sympathetic control of the heart and coronary circulation were similar in MI and normal swine. In contrast, during exercise of MI compared to normal swine, (i) there was a more pronounced gradual inhibition of parasympathetic control of heart rate with increasing exercise intensity; (ii) circulating catecholamines increased excessively, resulting in an increased β-adrenergic influence on heart rate, while (iii) the β-adrenergic influence on global left ventricular contractility was decreased, reflecting a blunted left ventricular β-adrenergic responsiveness. Furthermore, (iv) an -adrenergic vasoconstrictor influence was absent in the anterior LV wall of both MI and normal swine, while (v) the β-adrenergic vasodilator influence in the coronary circulation was not different between normal and MI swine, which, in conjunction with the elevated catecholamine levels during exercise, suggests a diminished β-adrenergic responsiveness of coronary resistance vessels within remote non-infarcted myocardium in MI swine.
Conclusions: Swine with a recent MI display autonomic dysfunction, which is characterized by a more pronounced inhibition of parasympathetic influence and an exaggerated increase in sympathetic drive during exercise, as well as reduced myocardial and coronary vascular β-adrenergic responsiveness.
KEYWORDS Autonomic nervous system; Coronary circulation; Remodeling; Heart failure; Ventricular function
Time for primary review 21 days
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