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Systole has little effect on diastolic coronary artery blood flow
Insights
Systolic contraction does not limit diastolic coronary flow at heart rates below 160 beats/min. This study found no significant attenuation of coronary blood flow during diastole due to myocardial contraction.
Area of Science:
- Cardiovascular Physiology
- Cardiac Electrophysiology
Background:
- Myocardial systolic contraction is a critical determinant of cardiac function.
- Understanding its effect on coronary blood flow is essential for diagnosing and treating cardiac conditions.
Purpose of the Study:
- To investigate whether myocardial systolic contraction attenuates diastolic coronary flow.
- To compare coronary blood flow during diastole with flow during induced asystole.
Main Methods:
- The study utilized a canine model with cannulated circumflex coronary arteries perfused at constant pressure.
- Heart rates were manipulated (80-200 bpm) using pacing after inducing atrioventricular block.
- Flow during diastole was compared to flow during prolonged asystole under various treatment conditions.
Main Results:
- Asystolic coronary flow initially matched diastolic flow at heart rates up to 160 bpm across all treatment groups.
- At 200 bpm, asystolic flow was slightly higher than diastolic flow, potentially due to artifact.
- No significant limitation of diastolic coronary flow by systolic contraction was observed.
Conclusions:
- Myocardial systolic contraction does not limit diastolic coronary flow at heart rates below 160 bpm.
- This effect is unlikely to be significant even at higher heart rates.
- Findings challenge the hypothesis that systolic compression significantly impedes coronary perfusion.
Abstract:
The hypothesis that myocardial systolic contraction attenuates diastolic coronary flow was tested by comparing flow during diastole to flow during a prolonged asystole. The circumflex coronary artery was cannulated and perfused at constant pressure in closed-chest, morphine- and alpha-chloralose-anesthetized dogs. The heart was paced at 80, 120, 160, or 200 beats/min after atrioventricular heart block under control, intracoronary adenosine, and intravenous norepinephrine treatment conditions. Cessation of pacing while holding coronary pressure constant at the previous diastolic pressure resulted in asystolic circumflex flow that initially equaled the previous diastolic flow during heart rates of 80, 120, and 160 in all treatment groups. Initial asystolic circumflex flow was approximately 5% higher than the previous diastolic flow at a heart rate of 200 beats/min, but this was probably due to an artifact. It is concluded that systolic contraction does not limit diastolic coronary flow at heart rates less than 160 beats/min and probably does not at higher heart rates.