Does systolic subepicardial perfusion come from retrograde subendocardial flow?

Area of Science:

• Cardiovascular Physiology
• Myocardial Blood Flow Dynamics
• Coronary Circulation Research

Background:

• Understanding coronary blood flow regulation is crucial for diagnosing and treating cardiac conditions.
• Cardiac contraction's influence on myocardial perfusion remains a complex area of study.
• Transmural distribution of blood flow is vital for maintaining cardiac function.

Purpose of the Study:

• To investigate the effect of cardiac contraction on systolic coronary flow.
• To analyze the transmural distribution of myocardial blood flow during cardiac cycles.
• To determine the mechanisms behind altered blood flow during systole and diastole.

Main Methods:

• Phasic blood flow velocity in extramural coronary arteries was measured using Doppler velocimetry in 12 dogs.
• Regional myocardial blood flow was quantified using radiolabeled microspheres.
• Coronary perfusion was controlled using a servo-controlled circuit during beating and diastolic states.

Main Results:

• Systolic flow in epicardial arteries was negligible or reversed.
• Subepicardial blood flow was 24.2% higher during beating than asystole.
• Subendocardial flow was 49.8% lower during beating compared to asystole.
• Increased heart rate reduced subendocardial flow, while superficial flow remained unaffected.
• Reduced coronary artery pressure exacerbated systolic reverse flow and altered transmural flow ratios.

Conclusions:

• Cardiac contraction is the primary driver of altered regional blood flow between beating and diastolic conditions.
• Little myocardial blood flow enters from extramural arteries during systole.
• Retrograde blood flow from the subendocardium to the subepicardium during systole explains observed flow changes.
• This systolic retrograde flow may offer protection against subepicardial ischemia.