By Susan Green ~
Aortic dissection is a life-threatening catastrophic event. Essentially, the inner layer of the aorta splits and creates a false channel for blood flow. Without treatment, many persons experiencing this event will die within 48 hours. Before the 1950s, much like repair of aortic aneurysm, it was long thought impossible to correct aortic dissection surgically.
Within a decade of arriving at Baylor College of Medicine, Michael E. DeBakey built a thriving surgical department. In 1955, DeBakey described his emerging experience in surgical repair of aortic dissection to the American Surgical Association and presented the results of repair in 6 patients, which were published soon thereafter as the first successful repairs of aortic dissection. DeBakey and colleagues described techniques to redirect blood back into the true channel. Notably, regardless of the anatomical location and extent of dissection, all repairs were performed on the descending thoracic aorta—repair of the ascending aorta was more complicated and not yet possible. The article included a diagram classifying most of the 300 autopsy cases described in Shennan’s 1934 review into 9 types of aortic dissection.
Within the next 5 years, DeBakey and his team promoted this work through worldwide academic lectures and published more than a half dozen works on aortic dissection. By 1959, their surgical experience had grown to 45 repairs. In an article for the American Heart Association’s journal, Modern Concepts of Cardiovascular Disease, DeBakey described two basic forms of aortic dissection, distinguished by whether the dissection is limited to the descending thoracic aorta or if it involves the ascending aorta. Because of DeBakey’s many advancements in aortic surgery, repair of the ascending aorta was now possible, although it had not yet been attempted in the setting of aortic dissection. In DeBakey’s hands, the majority of repairs involved dissection of the descending thoracic aorta, and he speculated that aortic dissection involving the ascending aorta is rapidly fatal, such that affected patients are unlikely to survive long enough to present for repair. For those patients with descending thoracic aortic dissection, repair is fairly straightforward; on a working tour of Europe, DeBakey participated in one such repair in which a portion of the descending thoracic aorta was replaced with a section of Dacron graft. DeBakey sketched this repair in a travel journal and noted that the patient recovered.
By 1960, DeBakey had developed an early 5-type classification schema that was based on more than 50 repairs—only a handful of these cases involved ascending aortic dissection. DeBakey described type II aortic dissection as being limited to the ascending aorta, whereas type I aortic dissection typically extends from the ascending aorta to the descending thoracic aorta, often continuing distally. His classification schema is from a surgeon’s perspective, rather than a pathologist’s. Type II aortic dissection could now be repaired by replacing the entire affected section of the ascending aorta; in contrast, repair of the far more extensive type I aortic dissection was largely to redirect blood flow into the true channel. Type III aortic dissection involved the distal aortic arch and descending thoracic aorta. Types IV and V aortic dissection involved the descending thoracic aorta, which was strictly limited in type V and extended distally to the abdominal aorta in type IV. In this era, nearly all patients with aortic dissection involving the ascending aorta would die before they could be referred for surgical repair. As a result, this early classification schema was heavily skewed toward aortic dissection involving the descending thoracic aorta, which DeBakey indicated to be roughly 90% of all dissections repaired.
In late 1961, DeBakey and colleagues published data from 72 aortic dissection repairs, which represented a small portion (6%) of his team’s aortic operations. Here, DeBakey discussed his early thoughts on an evolving classification model, now with 4 types, to be used to guide repair. Types I and II were as described previously, but the distinction of aortic dissection involving the distal arch and descending thoracic aorta was abandoned, causing the previously described types IV and V to move up. The classification schema pulled heavily from Shennan’s 300 autopsy cases and from a review by Hirst and coauthors published in 1958, based on 505 cases from the literature (mostly autopsy cases) published from 1933 to 1954. Although only 6% of DeBakey and team’s 72 repairs were for type II aortic dissection, this type of dissection constituted 29% of 723 combined cases reported by Shennan and Hirst. Likewise, DeBakey and team had only attempted repair in 9 patients with type I aortic dissection (6 of whom did not survive), but nearly 50% of the combined cases of Shennan and Hirst involved this form of extensive dissection. The lethality of types I and II aortic dissection limited DeBakey’s surgical exposure to them. For those patients that survived the acute phase of a type II aortic dissection, repair was promoted in a widely available teaching film, Surgical Correction of Dissecting Aneurysm of Ascending Aorta with Aortic Valvular Insufficiency. Notably in 1963, DeBakey and his trainees would report the first successful repair of an acute DeBakey type I aortic dissection—repair of the ascending aorta was performed within 7 hours of onset and no doubt saved the young patient’s life.
Warning: The film contains explicit images of live surgery. Viewer discretion advised.
In 1965, DeBakey and his colleagues in Houston present his further refined and final 3-type model to classify aortic dissection by location and extent, which was based on the surgical treatment of 179 patients. Here, the dissection type signals the method of repair to surgically correct it. DeBakey’s classification of aortic dissection includes three distinct types: DeBakey type I dissection arises in the ascending aorta and extends into the descending thoracic aorta and beyond; repair is performed via a median sternotomy and involves transecting the ascending aorta and reapproximating the true and false channels. DeBakey type II dissection originates in and is confined to the ascending aorta; repair is performed via a median sternotomy and involves resecting the entire dissection and replacing it with a Dacron graft. DeBakey type III dissection arises in the descending thoracic aorta; repair is typically performed via a thoracotomy involves replacing the entire dissection with a Dacron graft (type IIIa) or extending repair further into the abdominal aorta (type IIIb).
DeBakey continued to publish his experience with aortic dissection and guiding repair by the 3 DeBakey types, adjusting specific operative approaches as the overall experience with aortic repair evolved. In 1982, DeBakey and his team at Baylor published his landmark 20-year experience regarding 527 patients undergoing repair to treat aortic dissection. In this publication, he defends his classification system against a competing system from Stanford that combined aortic dissection types I and II. DeBakey felt strongly that type II aortic dissection was worth distinguishing from type I because of their differing surgical approaches and prognosis; notably, at the age of 97, DeBakey himself survived a type II aortic dissection.
More than 50 years after a classification system for aortic dissection was developed by Michael E. DeBakey, it continues to provide clinicians with valuable information. In contemporary practice, appropriate classification of aortic dissection is essential to determining treatment and prognosis.
Susan Y. Green, MPH, is a Manager of Clinical Research within the Division of Cardiothoracic Surgery, Michael E. DeBakey Department of Surgery at Baylor College of Medicine in Houston, Texas. Ms. Green was an NLM Michael E. DeBakey Fellow in the History of Medicine in 2019. She can be found online @green_mph