Vagal reflexes and survival during acute myocardial ischemia in conscious dogs with healed myocardial infarction

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Abstract

The role of vagal tone and reflexes in the genesis of life-threatening arrhythmias was investigated in a clinically relevant animal model for sudden cardiac death. Forty-five dogs with a healed anterior myocardial infarction in which transient myocardial ischemia during exercise did not induce malignant arrhythmias were utilized for the study. They underwent a further exercise and ischemia test in which atropine (75 μg/kg) was injected before coronary artery occlusion. Novel occurrence of ventricular arrhythmia, or worsening of the type of arrhythmia present in the control test, occurred in 23 of 45 dogs (51%) and ventricular fibrillation occurred in 11 of 45 (24%, P = 0.001). Analysis of heart rate response to acute ischemia in the control test indicates that these 11 animals had powerful vagal reflexes during coronary artery occlusion, compared with the 34 survivors (-32 ± 35 vs. +2 ± 27 beats/min, P = 0.003). This study indicates that ~75% of animals resistant to ventricular fibrillation are characterized by weak sympathetic reflexes in response to acute myocardial ischemia. In the remaining 25% powerful vagal reflexes counteract concomitant reflex sympathetic hyperactivity, decrease heart rate, and are essential for survival.

Original languageEnglish
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume261
Issue number1 30-1
Publication statusPublished - 1991

Keywords

  • Atropine
  • Sudden death
  • Sympathetic reflexes

ASJC Scopus subject areas

  • Physiology

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