Kugel's Artery

The cardiological literature on coronary arterial anatomy consistently neglects the atrial portion of it. There are several reasons for this, most notably that the ventricular portion of the coronary articulation is larger and much more important to the clinician than is the atrial, and that the atrial arteries are extremely variable. In general, the basic organizing framework for the distribution of the major coronary arteries on the ventricular side (namely the interventricular septum and the atrioventricular grooves) is missing on the atrial side. Since large coronary arteries are related to the large myocardial masses that are ventricular, they do not appear in the atrial territory. Only 2 coronary atrial arteries are generally recognized with a term more specific than “atrial branch”: the sinus node and the atrioventricular node arteries. Of the other, multiple branches, only one is frequently (but inconsistently) recognized in the literature with a specific name, and no real definition: the Kugel's artery.

In the preceding article (see page 267), Nerantzis and colleagues¹ set out to answer the question, Does Kugel's artery exist and where does it course? They performed a prospective, gross anatomic study of 100 consecutive necropsy specimens. To this aim, they devised a new method, consisting of the injection of a radiopaque semisolid medium (barium sulfate) into the coronary arteries, at high pressure, and of the acquisition of 1.5-cm-thick sections of the heart, encompassing the lower 1 cm of the atria and the upper 0.5 cm of the ventricles. The authors do not provide an exact definition of Kugel's artery, and clearly they could comment only on arteries coursing at the bottom (caudal) part of the inter-atrial septum. Indeed, Kugel's original article² mentions 3 different atrial branches, each of which he named “arteria anastomotica auricularis magna,” or large atrial anastomotic branch, and none of which he identified as “Kugel's artery” (see his Table I). The generally understood attribute of any so-called Kugel's artery (the 3rd variation described in Kugel's article¹) is that it connects an anterior coronary artery located around the aortic root (the left main, the circumflex, or the right coronary arteries) to a posterior arterial branch (the right coronary or circumflex arteries) in the atrioventricular groove. The minimal cross-sectional dimension that qualifies such an atrial branch to be called Kugel's artery is given neither by Kugel's own article nor by any other report in the literature.

Nerantzis and colleagues conclude that homologous small branches (an anastomotic network or indirect communications) existed in all 100 of their normal hearts, but in only 6 hearts do they call such an anastomotic channel a Kugel's artery, apparently because it has a larger channel. Various authors have carried out similar studies, but none in such a systematic, comprehensive manner. However, we must realize that the methods used by Nerantzis could not reveal other anastomotic branches located at other levels in the atrial septum or free wall of the atria.

Coronary arteries are usually described as terminal, which means that the vessels provide blood to specific myocardial territories and do not anastomose with other arteries. At the current time, millions of clinical angiographic studies have demonstrated quite well that atrial branches generally feature a richly interconnected network of smaller (<1 mm in diameter) arteries, with quite variable anatomic locations. We must ask if the recognition and specific naming of the larger atrial arteries in this network is worthwhile and whether the larger branches have clinical and functional relevance.

In my judgment, the assignment of specific nomenclature is not warranted if an atrial artery is not capable of causing myocardial infarction (upon spontaneous occlusion or surgical ligation), is not operable (bypassable), or is not usable as a bypass channel.

Larger atrial branches (the ones that attracted the curiosity of Kugel) can be present in a normal heart without the implication that they serve a function in baseline collateral circulation; for this reason, they can be occluded without ill effect. Their function might become apparent only in the event of a sudden occlusion of either of the 2 arteries that they connect, at which time their presence might decrease the ischemic consequence. Smaller, poorly organized atrial vessels might also develop into much larger vessels (“acquired Kugel's”?), during the days or months following such an acute occlusive event. In that (frequent) scenario, the protective value of the network would be quite limited (too late in development, too small). Some question remains regarding the possibility that truly anastomotic, larger atrial branches can undergo spasm and lead to spontaneous, resting ischemia in the territory supplied by the dependent occluded artery. A few anecdotal cases have been encountered in clinical practice. The likelihood that such branches will develop atherosclerotic changes and become a potential cause of effort-related angina or myocardial infarction at the time of their occlusion is quite low. Atrial collateral-dependent coronary arteries are more likely to lead to ischemic consequences if disease develops at a proximal site, in the artery that provides collateral flow.

In conclusion, atrial branches have a highly variable anatomic pattern, and specific features do not require recognition on clinical grounds, with the exception of the atrioventricular and sinus node arteries. The importance of atrial branches relates mainly to their potential as a source of collateral circulation, in the event of acquired obstruction of the vessels with which they connect.