Mechanism of beneficial effect of beta-adrenergic blockade on exercise-induced myocardial ischemia in conscious dogs.
Key result
Atenolol improved ischemic zone wall thickening during exercise from 27% to 50% of resting values (p<0.01), but this benefit was eliminated when heart rate reduction was prevented by atrial pacing.
Why the study?
Does atenolol improve exercise-induced myocardial ischemia and contractile dysfunction in dogs with coronary stenosis, and is this effect dependent on heart rate reduction?
Population
Conscious dogs with single vessel coronary stenosis (ameroid constrictor), n=9
Comparison
Atenolol administered before treadmill exercise… vs Control treadmill exercise without atenolol
Design
Preclinical
Authors
Discussion
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Implication
Hypothesis-generating in canine models; leaves open whether heart rate reduction drives beta-blocker benefits in patients.
Key Points
- This research investigates how reducing heart rate contributes to the benefits of beta-adrenergic blockade on exercise-induced myocardial ischemia in dogs.
- Conducted treadmill exercise tests on conscious dogs with coronary stenosis to induce myocardial ischemia.
- Administered atenolol intravenously, then measured heart rate and regional wall thickening before and after treatments.
- Used atrial pacing to manipulate heart rate during exercise to determine its effect on wall motion and blood flow.
- Atenolol reduced heart rate from 217 to 166 beats per minute and improved wall thickening from 27% to 50% of resting value (p < 0.01).
- When heart rate increased back to 217 beats per minute, wall thickening declined to 15% of resting value, indicating loss of benefit from atenolol.
- Regional blood flow during atrial pacing with atenolol was slightly reduced compared to the control, showing no remaining benefit when heart rate was normal.
Structured PICO
Does atenolol improve exercise-induced myocardial ischemia and contractile dysfunction in dogs with coronary stenosis, and is this effect dependent on heart rate reduction?
P
Population
Conscious dogs with single vessel coronary stenosis (ameroid constrictor), n=9
I
Intervention
Atenolol (0.3-1.0 mg/kg i.v.) administered before treadmill exercise, with subsequent atrial pacing to prevent heart rate reduction
C
Comparator
Control treadmill exercise without atenolol
O
Outcome
Regional myocardial ischemia (subendocardial blood flow) and contractile dysfunction (ischemic zone wall thickening during systole)surrogate
Main Result
Absolute Event Rate: 50% vs 27%
p-value: p=<0.01
The beneficial effect of atenolol on exercise-induced myocardial ischemia and wall motion abnormalities is primarily driven by the reduction in exercise heart rate.
Cite This Study
Guth et al. (1987) studied Exercise-induced regional myocardial ischemia (n=9). Atenolol vs. Control treadmill exercise was evaluated on Ischemic zone wall thickening during systole (% of resting value) (p=<0.01). Atenolol improved ischemic zone wall thickening during exercise from 27% to 50% of resting values (p<0.01), but this benefit was eliminated when heart rate reduction was prevented by atrial pacing.