Prevalence of Extracardiac Coronary Collateral Supply Via the Internal Mammary Arteries

Background

Surgical bypass creates an artificial anastomosis between a diseased coronary artery and an extracardiac vessel. Often one of the internal mammary arteries (IMA) is used for this procedure. These connections have been very rarely described to occur naturally, representing extracardiac coronary collaterals.

In contrast to the extensively studied coronary collateral circulation within the heart, clinical attention has been paid only anecdotally to extracardiac-to-coronary anastomoses. Usually this has been in the form of case reports giving account of angiographically visible anastomoses between the coronary circulation and the internal mammary artery (IMA), typically in the presence of a chronic occlusion of a coronary artery. In the anatomical literature,the most common types of extracardiac anastomoses include bronchial-to-coronary-artery and IMA-to-coronary-artery connections. Anastomoses between the IMA and the coronary circulation have been documented to occur in 12% of post-mortem patients with CAD.

Importantly, hitherto existing observations typically have relied on visual methods insensitive for the adequate detection especially of structurally present but poorly functional anastomoses. On a diagnostic coronary angiogram, collaterals are visible only if the recipient vessel is subtotally stenotic or fully occluded, or can be rendered visible during coronary spasm or by temporary balloon occlusion of the recipient artery and simultaneous injection of contrast medium into the other arteries, respectively. Similarly, the macroscopic pathologic postmortem examination is likely to underestimate the true number of extracardiac coronary collaterals.

When present, pre-existing connections between the IMA and the coronary circulation could be promoted to serve as natural bypasses to diseased coronary arteries. Promotion of extracardiac blood flow to the coronary circulation has very rarely already been attempted in the past. In a minimally invasive intervention, bilateral surgical ligation of both IMA was performed in a few patients, resulting in clinical improvement and disappearance of angina. However, with the advent of coronary surgery, efforts aimed at promotion of naturally existing bypasses have been abandoned for the placing of artificially created extracardiac anastomoses to the coronary circulation.