Three dimensional geometry of acutely ischemic myocardium

Area of Science:

• Cardiovascular Physiology
• Myocardial Perfusion Dynamics
• Ischemic Heart Disease Pathophysiology

Background:

• Understanding coronary flow distribution is crucial for diagnosing and treating myocardial ischemia.
• Previous studies suggested relatively even blood flow across large ventricular regions.
• The heterogeneity of flow at the microvascular level within the left ventricle remains incompletely understood.

Purpose of the Study:

• To quantify the heterogeneity of coronary blood flow distribution to small myocardial segments in the canine left ventricle.
• To differentiate between inherent heterogeneity and extraneous factors influencing flow distribution.
• To analyze the impact of acute coronary occlusion on regional myocardial flow distribution and the geometry of ischemic zones.

Main Methods:

• Utilized radiolabeled microspheres (7-10 μm) to measure coronary flow distribution in 96 segments per left ventricle in 28 open-chested dogs.
• Acute mid-circumflex coronary artery occlusion was performed in 10 dogs to induce regional ischemia.
• Analyzed the three-dimensional geometry and flow distribution of ischemic and adjacent myocardial segments.

Main Results:

• Significant heterogeneity of coronary flow was observed in small adjacent myocardial segments (average SD = 17.3 ± 3.2% of mean flow).
• Approximately 50% of this heterogeneity was attributed to inherent variability, with the other 50% due to extraneous factors.
• Following occlusion, subendocardial segments were more severely affected than mid-wall or epicardial segments.
• No hyperperfused zone surrounding ischemic areas was detected; adjacent segment flows remained heterogeneous.

Conclusions:

• Inherent heterogeneity of coronary blood flow exists in the left ventricular myocardium at the segment level.
• The concept of a distinct, geometrically defined "buffer zone" of moderately ischemic myocardium surrounding severely ischemic areas is not supported by these findings.
• Myocardial ischemia following coronary occlusion exhibits complex, heterogeneous patterns, particularly affecting subendocardial regions.