Pharmacologic- vs. ischemia-induced coronary artery vasodilation

Area of Science:

• Cardiovascular Physiology
• Myocardial Perfusion Dynamics

Background:

• Understanding coronary vasodilator reserve is crucial for managing ischemic heart disease.
• Reactive hyperemia is a common model, but its limitations in assessing maximal flow are debated.

Purpose of the Study:

• To compare total coronary vasodilator reserve during maximal drug-induced vasodilation versus reactive hyperemia.
• To investigate the transmural distribution of myocardial blood flow under maximal vasodilation.

Main Methods:

• Open-chest anesthetized dogs were used to measure coronary blood flow.
• Coronary vasodilation was induced using chromonar, adenosine triphosphate (ATP), or adenosine.
• Regional myocardial blood flow was assessed during reactive hyperemia (90-s occlusion) and drug-induced vasodilation.

Main Results:

• Maximal coronary blood flow achieved with vasodilators exceeded peak reactive hyperemia flow.
• Reactive hyperemia preferentially supplied the subendocardium.
• Drug-induced vasodilation resulted in preferential subepicardial flow, indicating a transmural gradient.

Conclusions:

• Total coronary vasodilator reserve is greater than that achieved during reactive hyperemia.
• A transmural gradient in vasodilator reserve exists within the left ventricle, favoring the subepicardium under maximal vasodilation.