Vagal reflexes and survival during acute myocardial ischemia in conscious dogs with healed myocardial infarction.
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 micrograms/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 approximately 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.
De Ferrari
G M
GM
Department of Physiology and Biophysics, University of Oklahoma, Oklahoma City 73190.
Vanoli
E
E
Stramba-Badiale
M
M
Hull
S S
SS
Foreman
R D
RD
Schwartz
P J
PJ
D000208:Acute Disease; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000503:physiopathology; D001285:Atropine / Q000494:pharmacology; D002304:Cardiac Pacing, Artificial; D003327:Coronary Disease / Q000378:metabolism / Q000503:physiopathology*; D004285:Dogs; D006339:Heart Rate; D009203:Myocardial Infarction / Q000503:physiopathology*; D012018:Reflex / Q000502:physiology*; D014630:Vagus Nerve / Q000502:physiology*; D014693:Ventricular Fibrillation / Q000139:chemically induced
D001285:Atropine