Type B aortic dissection has recently seen renewed interest in the literature, prompting updates to concepts, classifications, therapeutic management strategies, and outcomes. It is a severe and complex pathology as it affects the body’s main artery where repair options are limited. With advances in technology and medical team experience, the endovascular approach has become preferred over open approaches due to its less invasive nature and higher success rates.

In our country, this pathology affects over 2,000 patients annually (incidence 3.5-6/100,000/year) and continues to pose a therapeutic challenge with certain management uncertainties. Traditional classification by the Stanford criteria and those proposed by DeBakey, as well as its categorization as “complicated” and “uncomplicated,” have guided therapeutic attitudes for decades. However, recent times have brought numerous considerations regarding this pathology. Authors from the center named after the pioneer of this pathology’s study and treatment, Dr. Michael Ellis DeBakey, as well as one of its survivors, review and propose innovative concepts on classification, pathophysiology, and treatment of this disease. Here, we proceed to synthesize these concepts.

COMMENTARY:

Various novel aspects are detailed in the work, highly recommended for reading and reviewing later on:

Modification of classification criteria:

Anatomical classification: Anatomical classification holds particular importance in determining prognosis and therapeutic management of patients with aortic dissections, especially type B. These classifications have undergone modifications and adaptations to the current criteria:

• Stanford classification:This is a clinically oriented classification that has undergone significant modifications over time. Traditionally, it distinguished two types of acute aortic syndrome (AAS), type A (involving the ascending aorta with an entry tear at this level) and type B (not involving the ascending aorta nor presenting the entry tear at this level, typically appearing in the proximal portions of the descending aorta). Determining the involvement of the ascending aorta has a pronounced prognostic importance as the risk of developing heart failure, cardiac tamponade, and/or coronary malperfusion significantly worsens the prognosis compared to AAS type B. However, with the emergence of concepts like retrograde dissection, which could affect an aortic territory proximal to the entry tear, and those forms where the involvement is exclusive or starts at the aortic arch, left some patients outside the classification, which led to the description of AAS type non-A non-B. The authors propose a further evolution of this classification, combining it with the landing zones of endoprostheses in the 11 segments into which Ishimaru divided the aorto-iliac territory, likely indicating future endovascular therapeutic intentions. The classification would consider the entirety of the affected territory, both by dissection and adjacent intramural hematoma, naming it A or B depending on whether the entry tear is located at the ascending aorta (zone 0) or any of the remaining 11 segments (1-11), respectively. Thus, the typical dissection with an ascending aorta flap would be known as AAS type A, indicating with a subscript the most distal segment to which it extends (for example, up to the common iliac artery would be A10). Similarly, a descending aorta dissection reaching below the renal arteries and flap at 2 centimeters from the left subclavian artery would be described as AAS type B3-9. And a dissection, with a flap under the left carotid artery extending with an intramural hematoma to the brachiocephalic trunk and distally to the external iliac would be named B1-11). Retrograde extension affecting the ascending aorta would not change the designation to A, as the letter would be determined by the entry point, so it would be called B0-11 (one of the forms of the previous non-A non-B AAS). Finally, the letter I followed by two subscripts (for example, I3-5) would correspond to those cases of intramural hematoma where the entry tear is not evident (in the example, intramural hematoma extending from the segment within the 4 centimeters distal to the subclavian artery to the portion of the thoracic aorta below the sixth thoracic vertebra).
• DeBakey classification:This is another of the classic classifications that, paradoxically, the authors of the work chose not to adapt to our times as they did with the previous one. It comprises three types of aortic dissection: I (involving the ascending aorta to the descending); II (limited to zone 0); and type III, subdivided into IIIA and IIIB when the involvement extends from zone 3 to the distal 4 (IIIA) or from 5 onwards (IIIB). Although with a clear anatomical focus, like the first version of the Stanford one, it had gaps in describing certain forms of AAS, particularly those originating or exclusively involving the aortic arch.
• TEM classification:This is the most recently proposed and combines anatomical and clinical features. It includes three concepts: T for “type” according to the modified Stanford classification (A: affects the ascending aorta, B: only affects the descending aorta, non-A non-B: involvement of the arch with/without descending aorta, not affecting the ascending aorta), E for “entry” according to the location of the entry tear (0: indeterminate, intramural hematoma; 1: ascending aorta, zone 0; 2: aortic arch, zones 1 and 2; 3: descending aorta, zones 3-11) and M for malperfusion (0: absent, 1: coronary, 2: cerebral; 3: spinal, iliac and/or limbs; +: with the presence of clinical signs, -: without the presence of clinical signs). This constitutes the main competitor of the first, and it must be determined by scientific organizations which of them is considered more recommendable for clinical practice. Much of this decision will fall on whether to continue recognizing the form of AAS type non-A non-B.

Chronological classification: Comprises hyperacute forms (<24 hours), acute (from 24 hours to 14 days), subacute (from 2 weeks to 3 months), and chronic (>3 months). These cut-off points are marked by pathophysiological aspects of maturation of both the medio-intimal membrane and the free wall of the false lumen. Both aspects have therapeutic value in terms of the possibility of remodeling the true lumen and the pertinent circulatory adaptations (irrigation through the true or false lumen, situations of subclinical malperfusion); and prognostic value in terms of the development of serious or fatal complications.

Therapeutic decision:

The clinical classification must consider type B aortic dissection as “complicated” and “uncomplicated”. The former is described as that form with the development of rupture or clinical threat of the same and/or malperfusion (clinical or not) and corresponds to a therapeutic emergency. On the other hand, an intermediate concept of “high-risk” dissection has been described, applicable to the acute phase, where a therapeutic attitude also urgently applies, analogous to the complicated situation. Otherwise, although “uncomplicated” dissection has traditionally been considered for conservative treatment, multiple works highlighted by the authors (INTEAD, INSTEAD-XL, ADSORB) describe poor outcomes in almost half of these patients. Selecting candidates is crucial, with the subacute phase being the choice for carrying out endovascular treatment that allows correcting aortic remodeling and preventing both future complications and the aneurysm process, which would limit subsequent therapeutic action, impacting survival. Some of these predictors have been described in previous entries of this blog, to which we refer you (Uncomplicated type B aortic dissection: TEVAR or not TEVAR… and when to TEVAR) [Not addressing these predictors, leaving patients with potential poor evolution to the only alternative of medical treatment, entails an accumulation of adverse events in the follow-up and aortic dilation that, reaching the 55-60 mm proposed as an indication in clinical guidelines, frequently makes complete percutaneous treatment difficult. As recognized by Mani et al., it often requires adopting a thoracoabdominal approach with FEVAR (fenestrated-EVAR) and BEVAR (branched-EVAR), where in less than 50% of cases a reduction in aortic diameter is achieved. Other authors have reported low success rates of the procedure and complications during follow-up (endoleaks, migration). In addition to the aforementioned predictors, the authors expose different odds ratios from the analysis of the IRAD (International Registry of Aortic Dissection) of the main prognostic factors in patients with type B aortic dissection that would be clinical markers to cement the decision of a surgical/interventional/hybrid treatment instead of the conservative one in the acute/subacute phase. Among them, limb ischemia (OR = 3), periaortic hematoma (OR = 3), aortic diameter >5.5 cm (OR = 3), acute renal failure (OR = 3.6) stand out.

Technical aspects:

Positioning regarding cerebrospinal fluid (CSF) drainage: the authors indicate that CSF drainage is recommended as a therapeutic option (in the presence of spinal neurological symptoms) rather than prophylactic (application prior to procedures). It is considered the best risk-benefit balance of the procedure, as a rate of spinal neurological events <5% has been described, which balances with an equivalent rate of adverse events (epidural hematoma, subarachnoid hemorrhage, infection, malfunction of the drainage system due to obstruction, malposition, migration, etc.) if applied systematically prophylactically. In fact, they consider that, in the presence of spinal neurological symptoms, permissive arterial hypertension may have a greater therapeutic benefit than drainage.

Treatment of complicated aortic dissection: the reasons why complicated aortic dissection requires emergency treatment are rupture or the threat of the same and the presence of malperfusion (clinical or subclinical).

• Rupture: In the presence of hemothorax, decompression with thoracic drainage is not recommended until complete control of the leak has been achieved, due to the risk that it may progress. In fact, it is recommended to maintain a shock situation with permissive hypotension without excessive use of crystalloids in resuscitation in order to limit hemodilution and related hemostatic alterations. Coverage of the leak site by deploying an endoprosthesis in the true lumen that obliterates the false lumen should be the objective and treatment of choice, in accordance with current clinical guidelines. Although the criteria for considering technical success in aortic dissection require the presence of good proximal sealing (absence of type IA endoleak) and between endoprosthesis modules (absence of type III endoleak), the presence of collateral branches or distal re-entries (type II and IB endoleaks, respectively), could maintain the patency of the false lumen and perpetuate the bleeding in this context. Mere expansion and pressurization of the true lumen may be sufficient to redirect aortic remodeling in other contexts, but not in the case of rupture. Strategies such as the “candy-plug” (endoprosthesis in napkin ring parallel to the previous one but housed in the false lumen with obliteration within the narrow area with an Amplatzer® device), the “Knickerbocker” (which will be described later) or embolization with coils (of the false lumen and/or collateral branches) will pursue achieving thrombosis of the portion of false lumen isolated between the proximal sealing and the distal level of the endoprosthesis housed in the true lumen.
• Malperfusion: can affect different levels (cerebrovascular, visceral, and/or limbs) and can be classified as static (when there is a permanent obstruction of distal flow due to obliteration of the true lumen by the pressurized false lumen and/or thrombosis) or dynamic (when the compromise of flow depends on hemodynamic aspects such as coverage of the ostium of the vessel by the medio-intimal membrane or exists a variable compression of the true lumen by the false lumen dependent on its pressurization). The first therapeutic option consists of expanding the true lumen by deploying an endoprosthesis with coverage of the entry tear and redirection of flow inside it, without type IA or III endoleaks, since in 4 out of 5 cases the dynamic mechanism predominates over the static one. If the malperfusion situation persists (which is recommended to be checked by IVUS), treatment with direct stenting channeling the true lumen of the tributary vessel may be considered. The authors do not contemplate fenestration percutaneous treatment strategies or creation of new re-entries in the medio-intimal membrane, suggesting surgical alternatives such as open fenestration or extra-anatomic bypasses.

Treatments to prevent aneurysmal degeneration: one of the main reasons for aneurysmal degeneration is because adequate treatment has not been applied in earlier stages that would have favorably conducted aortic remodeling. However, even when applying it, due to the possibility that distal re-entries to the treated dissection at the thoracic level remain and perpetuate the patency of the false lumen, different techniques have been proposed to potentiate favorable aortic remodeling. Among them, the authors highlight:

• “Knickerbocker”: consists of a specific oversized point with a compliant balloon at the mid-distal level of the endoprosthesis module, until it obliterates the false lumen at that level. This alternative emerged as a rescue from an acute rupture situation where hemorrhage was perpetuated from distal re-entries to the false lumen. However, it may be applied in the prevention of aneurysm of the residual false lumen at the treated segment level and could even lead to the loss of proximal sealing. It was proposed the development of a prosthesis with a bulboid zone prepared to be expanded in case it is necessary to perform this procedure, but it did not have diffusion in practice. PETTICOAT (Provisional ExTension To Induce COmplete ATtachment): emerged as an evolution of the initial idea of an open-cell stent Djumbodis expanded by a compliant balloon. This system intends to expand the true lumen until obliterating the false one. The implants were carried out in open surgery (precursor of the “frozen elephant trunk”) and endovascular in the aortic arch, descending aorta or visceral trunks, these latter in the era prior to the development of BEVAR and FEVAR. The discrete results and cases of stent fracture led to the development of new systems, such as the Cook® Zenith® (stent composed of a portion of covered endoprosthesis followed by an open-cell stent distally) or the Jotec® E-XL® (independent open-cell stent) that replaced it. The STABLE trial showed a success rate in thrombosis of the thoracic false lumen in 70% of the patients, but only in 10% of the abdominal one, using the composite stent Cook® Zenith®, which is why a third of the patients required reintervention at 5 years. The discouraging results of the STABLE trial were improved by repeated non-randomized studies, including one that used the Jotec® prosthesis that achieved a 54% successful remodeling rate compared to 18%, by extending the treatment with an open-cell endoprosthesis with stent. Finally, and despite the benefit demonstrated in aortic remodeling, since it did not translate into a survival benefit, a review of the Cochrane collaboration and a meta-analysis by Qui et al. limited the generalization of PETTICOAT therapy.
• STABILISE (STent-Assisted Ballon-Induced intimaL dISruption and rElamination): consists of a more aggressive variation of PETTICOAT, where following a scheme of a consecutive and/or overlapped endoprosthesis and open-cell stent, the false lumen is obliterated by direct balloon dilatation, instead of depending on the spontaneous expansion of the open stent due to its radial force and material properties (nitinol). This action may even condition the rupture of the medio-intimal membrane, especially from the chronic phase. The technique has demonstrated good results, with complete aortic remodeling at the thoracic level in 100% of the cases and 83% at the abdominal level. However, the experience remains very limited.
• Embolization of the false lumen: which includes direct embolization, collateral branches or techniques such as the previously described “candy plug”.

In short, aortic dissection is a dynamic entity, both in its pathophysiology and in the scientific evidence around its knowledge. The efforts of the reference groups will continue to deepen the treatment alternatives. The legacy of pioneers like Michael DeBakey who initiated the principles of its study and approach, is assured.

REFERENCE:

Eidt JF, Vasquez J. Changing management of type B aortic dissections. Methodist DeBakey Cardiovasc J. 2023 Mar 7;19(2):59-69. doi: 10.14797/mdcvj.1171.