Incomplete Relaxation between Beats after Myocardial Hypoxia and Ischemia
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Key result
Recovery from myocardial hypoxia resulted in significant incomplete relaxation between beats at rapid heart rates, increasing from 0.8 cm H2O before hypoxia to 12.6 cm H2O at 5 minutes of recovery.
Why the study?
Does recovery from hypoxia or ischemia cause incomplete relaxation between beats in isolated cardiac muscle and intact ventricles?
Population
8 isolated cat right ventricular papillary muscles and 19 canine isovolumic left ventricles
Comparison
Hypoxia and acute ischemia with pacing at… vs Baseline (before hypoxia or ischemia)
Design
Preclinical
Follow-up
5 minutes after hypoxia/ischemia
Authors
Discussion
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Implication
Post-hypoxic incomplete relaxation may impair diastolic filling at high rates; leaves open its role in clinical diastolic dysfunction.
Structured PICO
Does recovery from hypoxia or ischemia cause incomplete relaxation between beats in isolated cardiac muscle and intact ventricles?
P
Population
27 animal models (8 cat papillary muscles and 19 canine hearts) subjected to myocardial hypoxia or ischemia to evaluate incomplete relaxation between beats.
I
Intervention
Hypoxia and acute ischemia (1.5-3 min period of acute ischemia and fibrillation) with pacing at increasing rates
C
Comparator
Baseline (before hypoxia or ischemia)
O
Outcome
Extent of incomplete relaxation (difference between lowest diastolic tension or pressure during pacing and true resting tension or pressure)surrogate
Main Result
Absolute Event Rate: 12.6% vs 0.8%
p-value: p=<0.01
Recovery from myocardial hypoxia or ischemia leads to significant incomplete relaxation between beats, particularly at higher heart rates, which may impair diastolic hemodynamics.
Limitations
- Isometric and isovolumic conditions lack overall fiber shortening during contraction.
- Potential for inadequate oxygen availability to the inner core of the papillary muscle at rapid pacing rates.
Cite This Study
Weisfeldt et al. (1974) studied Myocardial hypoxia and ischemia (n=27). Myocardial hypoxia and ischemia vs. Pre-hypoxia/ischemia control period was evaluated on Incomplete relaxation at 180 beats/min (canine isovolumic left ventricle) (p=<0.01). Recovery from myocardial hypoxia resulted in significant incomplete relaxation between beats at rapid heart rates, increasing from 0.8 cm H2O before hypoxia to 12.6 cm H2O at 5 minutes of recovery.
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