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Hemodynamic and arrhythmogenic effects of aversive stress during myocardial ischemia
G E Billman1, D C Randall, D R Brown
1Department of Physiology, Ohio State University, Columbus.
Insights
Behavioral stress during heart attacks impacts cardiovascular responses differently based on timing and prior heart damage. Autonomic reflexes play a key role in these cardiac responses.
Area of Science:
- Cardiovascular Physiology
- Behavioral Neuroscience
- Cardiac Electrophysiology
Background:
- Pavlovian conditioning can elicit cardiovascular responses.
- Myocardial ischemia, or heart attack, can alter autonomic nervous system function.
- Understanding how behavioral stress affects the heart during ischemia is crucial for patient outcomes.
Purpose of the Study:
- To investigate the cardiovascular response to a conditioned stimulus (CS+) during acute coronary occlusion in dogs.
- To determine if a prior myocardial infarction influences the cardiovascular and arrhythmogenic response to behavioral stress.
- To examine the role of autonomic reflexes in modulating these responses.
Main Methods:
- Two groups of dogs underwent Pavlovian conditioning with a tone (CS+) paired with a shock.
- Group I dogs experienced CS+ during control and acute coronary occlusion.
- Group II dogs with induced myocardial infarction received CS+ during control and acute coronary occlusion, followed by arrhythmia susceptibility testing.
Main Results:
- The conditioned cardiovascular response (heart rate, blood pressure) persisted during acute coronary occlusion despite ischemia.
- Significant differences in heart rate and left ventricular pressure responses were observed during occlusion versus no occlusion in dogs with prior infarction.
- Susceptible dogs, unlike resistant dogs, showed increased arrhythmias during CS+ presentation after infarction.
Conclusions:
- The cardiovascular response to behavioral stress during myocardial ischemia is influenced by the timing of the stimulus, the presence of infarction, and autonomic reflex status.
- These findings highlight the complex interplay between behavioral stress, cardiac ischemia, and autonomic control.
- Individual differences in autonomic reflexes may predict susceptibility to arrhythmias during stressful cardiac events.
Abstract:
Pavlovian conditioning was accomplished in two groups of dogs by following a 30-s tone (the CS+) with a short (less than or equal to 1 s) electric shock). An inflatable occluder was implanted around the left circumflex coronary artery in all animals. The CS+ was presented to Group I dogs (n = 6) during control (i.e., no coronary occlusion) and at 30 s and 3 min after the onset of a 4-min left circumflex coronary occlusion. The CS+ evoked a robust increase in heart rate and blood pressure in the control state. A conditional cardiovascular response was still evoked during the acute coronary occlusion despite the evolving myocardial ischemia. No increase in ventricular ectopic beats occurred during the CS+. An anterior myocardial infarction (16.8 +/- 1.7% of left ventricular mass, mean +/- SEM) was created in Group II dogs (n = 8) at the time of surgery. A CS+ was presented, as above, both alone and 1 min after the beginning of a 2-min left circumflex coronary occlusion. There were significant differences in the conditional response in heart rate, left ventricular (systolic) pressure (LVP) and d(LVP)/dt for trials given during the coronary occlusion compared with no occlusion. These dogs were then classified as 'resistant' or 'susceptible' to ventricular arrhythmias approx. 4 weeks later using an exercise and coronary occlusion test. Three of five susceptible dogs, but none of three resistant dogs, evidenced increased severity of arrhythmias during the CS+. We conclude that the nature of the cardiovascular response to behavioral stress during myocardial ischemia depends in part upon the timing of the CS+, the presence or absence of a resident myocardial infarction and the status of the autonomic reflexes controlling the heart.