Persistence of coronary vasodilator reserve despite functionally significant flow reduction

Area of Science:

• Cardiovascular Physiology
• Myocardial Perfusion
• Coronary Vasodilator Reserve

Background:

• Understanding coronary vasodilator reserve is crucial for managing myocardial ischemia.
• Low-pressure perfusion can significantly impact coronary blood flow and cardiac function.
• The response of coronary vasodilation to reduced flow under low pressure requires further investigation.

Purpose of the Study:

• To determine if coronary vasodilator reserve is maintained during reduced coronary flow and abnormal regional function under low-pressure perfusion.
• To assess the impact of adenosine on coronary flow and regional function at low perfusion pressures.

Main Methods:

• Utilized an open-chest anesthetized dog model.
• Cannulated the left circumflex coronary artery (LC) for controlled perfusion.
• Measured regional segment lengths using sonomicrometer crystals and regional flow with radiolabeled microspheres.
• Administered adenosine to assess vasodilator response at varying LC pressures (80, 50, and 35 mmHg).

Main Results:

• Coronary flow decreased transmurally at LC pressures of 50 and 35 mmHg.
• LC segmental shortening decreased significantly (30% of control) at 35 mmHg, indicating impaired function.
• Adenosine administration increased endocardial and epicardial LC flow significantly at 35 mmHg.
• LC segmental shortening improved to 50% of control after adenosine at 35 mmHg.

Conclusions:

• Transmural coronary vasodilator reserve is preserved even with significant reductions in coronary flow and impaired regional function at low perfusion pressures.
• Adenosine-induced increases in coronary flow are associated with a modest improvement in regional cardiac function under these conditions.