title: Differential effects of adrenergic antagonists (Carvedilol vs Metoprolol) on parasympathetic and sympathetic activity: a comparison of clinical results.
abstract: BACKGROUND
  Cardiovascular autonomic neuropathy (CAN) is recognized as a significant health risk, correlating with risk of heart disease, silent myocardial ischemia or sudden cardiac death. Beta-blockers are often prescribed to minimize risk.
  
  
  OBJECTIVE
  In this second of two articles, the effects on parasympathetic and sympathetic activity of the alpha/beta-adrenergic blocker, Carvedilol, are compared with those of the selective beta-adrenergic blocker, Metoprolol.
  
  
  METHODS
  Retrospective, serial autonomic nervous system test data from 147 type 2 diabetes mellitus patients from eight ambulatory clinics were analyzed. Patients were grouped according to whether a beta-blocker was (1) introduced, (2) discontinued or (3) continued without adjustment. Group 3 served as the control.
  
  
  RESULTS
  Introducing Carvedilol or Metoprolol decreased heart rate and blood pressure, and discontinuing them had the opposite effect. Parasympathetic activity increased with introducing Carvedilol. Sympathetic activity increased more after discontinuing Carvedilol, suggesting better sympathetic suppression. With ongoing treatment, resting parasympathetic activity decreased with Metoprolol but increased with Carvedilol.
  
  
  CONCLUSIONS
  Carvedilol has a more profound effect on sympathovagal balance than Metoprolol. While both suppress sympathetic activity, only Carvedilol increases parasympathetic activity. Increased parasympathetic activity may underlie the lower mortality risk with Carvedilol.
authors.affiliation: Associate Professor of Medicine, Emory University School of Medicine; Director of Electrophysiology, Atlanta Veterans Affairs Medical Center, Decatur, GA - USA.
authors.forename: Heather L
authors.initials: HL
authors.lastname: Bloom
authors.affiliation: Professor of Medicine/Pathology/Neurobiology, Director of Research and Neuroendocrine Unit, Department of Medicine, Strelitz Diabetes Center, Norfolk, VA - USA.
authors.forename: Aaron I
authors.initials: AI
authors.lastname: Vinik
authors.affiliation: Research Director, Autonomic Laboratory, Department of Cardiology, Drexel University College of Medicine, Medical Director, ANSAR Medical Technologies, Inc., Philadelphia, PA - USA.
authors.forename: Joe
authors.initials: J
authors.lastname: Colombo
keywords: Beta-blocker; Cardiovascular autonomic neuropathy; Heart rate variability; Patient outcomes; Respiratory analysis; Sympathovagal imbalance