Myocardial Degeneration and Cardiac Arrest in Squirrel Monkey: Physiological and Psychological Correlates

Behavioral factors and cardiovascular changes associated with myocardial degeneration and cardiac arrest induced by shock avoidance stress were studied. Pairs of avoidance and yoked squirrel monkeys were exposed to a 24‐hr session. Myocardial degeneration and cardiac arrest were more readily induced in avoidance than yoked monkeys. The cardiac lesions were not related to body weight, aggressive behavior, or number of shocks received during stress, but an increased heart rate without hypertension during the first stress hour was more evident in avoidance than yoked monkeys. These cardiac changes were attributed to an autonomic disturbance associated with the response contingencies of the avoidance situation. An autonomic effect also appeared to be involved with stress‐induced death. These deaths were characterized by a sudden, severe bradycardia without initial hypotension and cardiac arrest which was attributed to either parasympathetic activation or sympathetic inhibition. While heart rate decreased in all monkeys, stress‐induced death followed only in monkeys which gave up and stopped contending with the stress. Thus, stress‐induced myocardial changes and death were related to autonomic disturbances precipitated by psychological stress.