A recent article1 revisited the existence, nature, and imaging of so-called Thebesian veins, a phantomlike entity that has been mentioned in the medical literature since the early 1700s. In that article, Potu and colleagues1 describe the incidental cannulation of a left ventricular (LV) Thebesian vein during LV angiography. The flow rate in the mechanical contrast injector was set at 10 mL/s, which may have produced a jet pressure at the tip of the catheter (a right coronary 5F JR4) that was high enough to cause the catheter to whip around and penetrate a newly developed subendocardial space. As the cineangiogram shows,1 the compression of this intramural vesicle (or tear) during systole did not result in chronic, persistent drainage into the LV cavity, but only slow drainage into preexisting, connected small posterior cardiac veins and ultimately into the coronary sinus. The injected contrast dye cleared in approximately 30 seconds. Chest pain and electrocardiographic changes during such a generally benign event are rare.
Thebesian Veins: A Brief History
Descriptions of Thebesian vessels have surfaced intermittently over the centuries, generating both illusion and confusion. These channels, cavities, or veins are frequently described as structures embedded in the walls of the heart.2–6 They supposedly include arteriosinusoidal, venosinusoidal, arterioluminal, and venoluminal vessels that drain into cardiac chambers through openings in the endocardial surface; they have been called foramina venarum minimarum or sinusoidal channels when they drain blood from the coronary arteries.6 Thebesian veins are typically said to have a luminal diameter of 0.5 to 5 mm (Fig. 1).6,7
Over the centuries, various authors have posited that 30% to 90% of coronary blood drains through the cardiac venous system, which would include Thebesian veins.5,6 Thus, Thebesian veins reputedly provide myocardial perfusion and drainage.5,6 Despite a few claims that Thebesian veins increase morbidity and mortality, a study of more than 50,000 patients who underwent coronary angiography revealed that only 0.06% had prominent Thebesian veins; when compared with a matched control group of almost 600 patients without such Thebesian veins, the study group was not at greater risk of death.8
Similar statements about the anatomy and function of Thebesian veins have been published, despite trivial (if any) supporting evidence, particularly from histologic imaging. Current cardiac anatomy and physiology textbooks generally do not mention such structures in the normal heart.9 Is it time then to critically and conclusively lay to rest the concept of Thebesian veins? In hindsight, reviewing the historical evidence may enable us to recognize an epochal opera buffa (comic opera) in medicine. Let us summarize the facts.
First, in 1708, Adam Christian Thebesius, a Silesian medical student in Leiden, Holland, presented his doctoral dissertation,4,10 in which he claimed to have discovered a new anatomic entity in the heart's coronary circulation that eventually became known as Thebesian veins. However, the only visual evidence presented was a drawing, by the author himself, of the inner LV wall from a specimen of an autopsied heart (Fig. 2).10 Depicted were dark holes that Thebesius hypothesized drained blood from the coronary arteries or the heart muscle itself into the LV cavity.
Second, over the next 300 years, intermittent publications and academic lectures mentioned the persistently popular subject of Thebesian veins. In 1928, a well-respected cardiovascular professor at Harvard Medical School, J.T. Wearn, published a report on a complex series of experiments in both human cadavers and live animal hearts.5 Wearn presumed that as much as 90% of the coronary blood flow ends up in the Thebesian veins, an astonishing conclusion that has never been confirmed. In addition, he claimed that the Thebesian veins are most likely postcapillary and originate in coronary veins, but empty into various cardiac cavities.4,7,10
Third, in the more recent clinical literature, the main mentions of Thebesian veins are related to accidental penetration of the subendocardium by inappropriate catheters during LV angiography1,11 or in the context of rare accompanying defects.3,12,13
Fourth, another modern experimental study on sheep hearts suggested that Thebesian foramina could be seen in both ventricular chambers.2 By injecting India ink into each coronary artery in autopsied hearts, the investigator identified communications between the coronary arteries and cardiac chambers (arterioluminal vessels) and between the coronary veins and cardiac chambers (venoluminal vessels) in 16 of 36 hearts. However, no arteriograms were provided to depict the actual physiology of coronary arteries and veins in the sheep.
Fifth, in structurally normal human hearts, most of what are called pseudo-Thebesian veins occur in the presence of multiple coronary artery-to-LV microfistulae (Fig. 3).3,12 In these cases, angiograms show runoff from mildly dilated coronary arteries that is most often limited to patchy areas in the LV free wall and diastolic flow into what is probably an anomalous layer of noncompaction with inner trabeculations and intertrabecular spaces in the LV. Figure 3 shows that the contrast is almost totally expelled from the noncompaction layer into the main LV cavity during systole.3 This is the most compelling example in humans of direct, albeit abnormal, communication between the epicardial coronary arteries and the LV.3 However, such findings are rare, occurring in approximately 1 per 2,000 cases among a general population undergoing angiography.9 Moreover, the clinical relevance of these malformations is trivial in the framework of the entire coronary circulation. The occasionally mentioned coronary steal attributed to preferential flow into cardiac cavities from nutrient branches3,12,13 is probably an erroneous description, because it is usually based on a clinical hypothesis, not on objective evidence. A trivial amount of fistulous flow on angiograms has been taken as evidence of clinically relevant coronary steal; however, such flows are often not substantial enough to cause ischemia or angina at rest, making coronary steal unlikely. These conditions seem related not to Thebesian veins but to various associated anomalies. Of note, blood flow in these microfistulae appears to account for <2% of total coronary flow, although this is difficult to quantify.
An exception to our arguments against the existence of Thebesian veins in normal hearts can be found in patients with complex congenital heart disease. In a series of infant cases from Boston Children's Hospital,13 noncompaction cardiomyopathy appeared to be part of various complex and associated myocardial malformations. However, the observed arteriovenous communications were probably multiple coronary artery-to-LV microfistulae of benign importance. Unfortunately, selective coronary angiograms were not available for most of the infants studied.
For the reasons outlined above, the term Thebesian veins should be used only in relation to the history of medical investigations, which centuries ago were limited by inadequate imaging technology and pathophysiologic knowledge. Claims regarding the existence of important, numerous, or clinically relevant drainage channels from the coronary vessels should be abandoned. Most assuredly, 99% of the coronary circulation drains into the coronary venous sinus or directly into the right ventricular inlet. By themselves, holes visible in the inner LV wall do not originate from coronary arteries; instead, they are a sign of blind cavities that are likely related to intertrabecular spaces. Multiple arterioventricular microfistulae are rare and constitute the most definite, direct communications between coronary arteries and the LV in the human heart.9 Finally, accidental intramyocardial injection of angiographic contrast leads to tattooing or a subintimal hematoma, but not to visualization of preexisting functional Thebesian channels.
In closing, however, we offer some consolation to the Silesian community (now in modern Poland), where native son Thebesius was celebrated for centuries as a medical genius: although he may forfeit claim to his eponymous but essentially mischaracterized Thebesian veins, his name and influence will live on in the Thebesian valve of the coronary sinus.