Quantitation of collateral and ischemic flows with microspheres and diffusible indicator

Area of Science:

• Cardiovascular Physiology
• Coronary Circulation Research
• Myocardial Ischemia Studies

Background:

• Coronary occlusion significantly impacts myocardial blood flow.
• The origin of blood flow to ischemic myocardium is complex and not fully understood.
• Collateral circulation plays a role, but non-collateral sources may also contribute.

Purpose of the Study:

• To differentiate between true collateral flow and non-collateral flow to ischemic myocardium.
• To quantify the contribution of overlapping coronary arteries to myocardial perfusion post-occlusion.
• To assess the adequacy of collateral channel geometry for microsphere passage.

Main Methods:

• Utilized microsphere injection into the left anterior descending (LAD) artery before and after occlusion.
• Measured non-collateral overlap and total ischemic LAD (TIF) flows.
• Mathematically derived true collateral flow (TCF) and compared with TIF.
• Simultaneously injected 86RbCl with microspheres to correlate flow measurements.

Main Results:

• Total ischemic flow (TIF) averaged 0.25 ml/min/g, while true collateral flow (TCF) was 0.14 ml/min/g.
• True collateral flow constituted only 50.6% of the total ischemic flow.
• 86Rb and microsphere densities correlated closely in ischemic myocardium, indicating adequate collateral geometry for 15-micron particles.
• Absolute 86Rb flows were consistently lower than microsphere flows.

Conclusions:

• Myocardial flow following coronary occlusion is not exclusively from collateral channels.
• Overlapping coronary artery circulations contribute significantly to perfusion of ischemic territories.
• Undeveloped collateral channels are geometrically capable of accommodating 15-micron particles.