Type B acute aortic dissection (TBAAD) is a severe condition that requires urgent intervention to minimize complications and improve outcomes. Endovascular treatment has emerged as an effective approach for managing this challenging condition in acute complicated type B dissections or in case of high-risk features for later adverse event. This involves placing stent grafts to seal the tear, redirect blood flow, and promote clot formation. Endovascular treatment reduces mortality and complication rates, allowing for a faster recovery.
The benefits of endovascular repair in complicated TBAAD have been extensively demonstrated, showing lower morbidity and in-hospital mortality (5%-8% vs 15%-30%) rates compared to traditional open surgery. This technique offers better control over the extent of the dissection, leading to improved patient outcomes and shorter hospital stays.
It is essential to optimize antihypertensive therapy and provide proper patient education. Regular angio-CT scans should be done to monitor disease progression and ensure long-term success.
Endovascular treatment has revolutionized the management of TBAAD by providing a less invasive, more effective approach, enhancing patient care and prognosis.
Acute type B aortic dissection is a potentially life-threatening condition presented in this issue. Here, we discuss our endovascular approach for the treatment of complicated type B dissections.
Introduction
Acute aortic type B dissections (TBAAD) are vascular emergencies. These dissections occur in the downstream thoracic aorta, downstream of the left subclavian artery. They are challenging for physicians due to their rapid progression and potential complications. Their main cause is believed to be the weakened aortic wall experiencing sheer force and hemodynamic stresses. The damaged aortic wall, along with abnormal blood flow, causes the dissection to spread along the descending thoracic aorta.
According to the new SVS/STS classification of aortic dissection introduced by Lombardi et al. type B dissections presents the primary entry tear at zone 1 or beyond and their proximal and distal extension can be described by 2 subscripts that indicate the zone of the aorta involved (between 0 in case of retrograde dissection to 11). This classification could help clinicians in managing the precise treatment of the pathology, selecting the appropriate landing zone in order to prevent endoleak formation or stent graft migration.
Endovascular techniques have greatly improved the management of these dissections, leading to better patient outcomes and lower morbidity and mortality rates. ,
Epidemiology and Supposed Risk Factors
TBAAD dissections are less common than type A but still require urgent assessment. Their exact prevalence is difficult to determine. Studies have shown a direct relationship between hypertension and the risk of developing aortic dissections, highlighting the importance of blood pressure control in patients with high risk.
Connective tissue disorders are associated with an increased risk of aortic dissections. The genetic mutations involving extracellular matrix proteins genes, play a pivotal role in the pathogenesis of aortic pathologies. History of previous aortic surgery, aortic aneurysms, pregnancy, trauma, severe atherosclerosis, smoking history and dyslipidemia, may also increase risk of aortic dissections.
Age and gender distribution among individuals with acute aortic type B dissections show a peak incidence between 40 and 70 years, with a slight male predominance. The risk increases with age, reflecting the cumulative effects of vascular aging.
Early recognition and management of these predisposing factors can potentially reduce the incidence and severity of aortic dissections.
According to the most recent guidelines, the first step in treating TBAAD is blood pressure control. In cases of complicated TBAAD, urgent thoracic endovascular aortic repair (TEVAR) is necessary. For uncomplicated TBAAD with high-risk characteristics, TEVAR should be carried out in the semi-urgent phase.
Patient Assessment
It is essential to perform an early assessment of the patient’s clinical and hemodynamic conditions and carefully analyze the Angio-CT scan and angiographic images.
The International Registry of Acute Aortic Dissection (IRAD) and international guidelines offers important data that play crucial roles in guiding decision-making for therapeutic approach. Specifically, in our center, in addressing complicated acute or subacute type B aortic dissection characterized by rupture and/or malperfusion, we perform a thoracic endovascular aortic repair (TEVAR) provided the anatomical conditions are conductive. Alternatively, if TEVAR is not feasible due to anatomical constraints, we perform open surgical repair. We usually managed uncomplicated acute type B aortic dissections with optimal medical therapy. However, TEVAR should be considered also in uncomplicated acute type B dissection in case of high-risk features, such as refractory pain/hypertension, bloody pleural effusion, aortic diameter>4 cm, false lumen diameter >22 mm, radiographic malperfusion, early readmission (as described by the last SVS/STS guidelines). Our approach over time progressively changed in favor of TEVAR procedures in patients with high-risk features, as reported in the study of Murana et al. In case of hemodynamic instability, organ ischemia, retrograde extension of dissection, risk factors of disease progression such as persistent pain or dynamic changes, young age of the patient, overall prognosis are all factors that compel us to proceed with TEVAR intervention in urgency.
It is crucial to characterize all the specific anatomical features of the individual patient as well as all potential criticalities that could complicate the procedure. In planning each procedure, it is essential to identify the primary entry tear, locating the proximal and distal landing zones, and assessing the anatomical characteristics of the aortic segment where the endovascular graft cuffs will be positioned. Ensuring adequate coverage of the aorta above the lesion is important to achieve proper sealing of the endovascular coverage.
In evaluating the proximal landing zone, it is fundamental to characterize the distance of the intimal lesion from the emergence of the left subclavian artery, ideally having at least 2 cm of healthy aorta ( Fig. 1 ). If this condition cannot be met, it is necessary to consider the feasibility of a carotid-subclavian bypass with overstenting of the subclavian artery and – eventually – its embolization.
Significant importance is held by the origin of visceral vessels and intercostal arteries from the native aorta, potential predictors of organ ischemia and spinal cord injury. The most vulnerable area for spinal cord ischemia due aortic dissection is the middle thoracic region, between the territories of the artery of Adamkiewicz and the thoracic radicular arteries. Usually, in our center we do not place cerebrospinal fluid drainage in emergency cases. However, in patients with high risk of spinal cord ischemia, spinal cord drainage is placed preoperatively the day before surgery or in operating theatre just before the beginning of the intervention by our anesthesiologists, usually for elective cases. These high-risk patients include those requiring more than one endograft implantation on the descending aorta or coverage of the distal thoracic aorta extending within 3 cm of the celiac trunk origin, presenting perioperative hypotension, requiring coverage of the left subclavian artery with the graft, having a history of previous thoracic or abdominal aortic repair, presenting occlusion of hypogastric artery. ,
A highly relevant aspect is the assessment of potential re-entry sites along the course of the aorta. The extent of pathology involving the abdominal tract and the possible need for relining of visceral vessels or the use of uncovered stents, following techniques such as PETTICOAT or STABILISE must be evaluated.
These techniques entail placing a stent in the aorta to restore its integrity, facilitating reattachment of torn aortic layers. These techniques aim to stabilize the aorta, improve blood flow, and reduce the risk of complications like false lumen expansion and rupture.
Eventually, the careful evaluation of peripheral vascular access must be performed to assess potential calcifications and tortuosity that could complicate the transit of sheaths for device delivery Up to 30% of patients may have iliac artery conditions that make transfemoral access challenging. Traditionally, groin surgical cutdown was used to access the vessel, but a growing number of experts advocate for a percutaneous approach, avoiding the need for a surgical incision and vessel exposure.
Potential Complications
Despite advances in technique over the years endovascular stenting of type B dissection presents some potential complications such as spinal cord ischemia, endoleaks, stent induced new entry tears (SINE), access site complications, guidewire injuries, retrograde dissections, renal injury, unintentional great vessel coverage, aortoesophageal and aortobronchial fistulas and device failure. The rate of these complications depends mainly on the patient anatomy and the center expertise. The most frequent acute complications are represented by SINE and retrograde dissection (5% and 2-3%, respectively). , Stent oversizing and reduced stent length are the main risk factors for the development of these complications. Furthermore, big intimal tears, dilatated ascending aortas and short space of healthy nondissected aorta for the proximal landing zone are other risk factors for the development of retrograde dissection. We reported an example of retrograde dissection after TEVAR, where it is possible to see how the intimal tear is so close to the left subclavian emergency ( Fig. 2 ).
Surgical Technique
Graft Selection and Sizing Method
The graft selection is based on the anatomical characteristics of the dissection and on the clinical presentation of the patients. In emergency we usually conduct TEVAR procedures utilizing prosthesis in order to cover the intimal tear primarily at the thoracic level with an oversizing range of 0-9%, above the origin of the celiac trunk. However, if visceral malperfusion occurs or persist at the level of the abdominal vessels due to lack of expansion of the true lumen, we employ the petticoat technique. At proximal landing zone, in acute approach, we prefer to use nonbare stent prosthesis. Furthermore, in acute cases we do not use branched or fenestrated prosthesis, because these procedures need a precise planning of the patient’s anatomy and a customized prosthesis. We are planning to introduce in the future the possibility of developing off-the-shelf branched stents to treat complicated type B dissections in emergency situations.
An element of essential importance is the selection of the appropriate size of the graft.
The thoracic descending aorta undergoes evaluation using multiplanar reconstruction, encompassing tri-dimensional, sagittal, axial, and coronal planes. The aortic central axis and outer boundary are then pinpointed. Various axial projections, perpendicular to the aortic central axis, are scrutinized along the entire downstream aorta, taking <3 mm “slices”. All diameters of the dissected aorta are reported according to the cross-sectional area. Particular attention is given to the proximal and distal landing zones, where planimetric assessments are performed, measuring luminal area, as well as maximum and minimum diameters, using either semi-automated polygonal border tracing or linear measurements.
Current recommendations suggest measuring aortic diameter for stent sizing at predetermined planes within the aortic arch in zone 3 or in zone 2 when subclavian artery coverage is necessary, descending aorta (first quartile), and distal landing zone.
To assess proximal landing zone dimensions, outer-to-outer wall measurements are obtained in axial, sagittal, and frontal planes within “normal aortic segments” with minimal or no thrombus, calcification or debris. The minimum length of proximal and distal sealing should be at least 2.5 cm. To prevent complications, proximal graft oversizing should not exceed 10% of the maximum diameter calculated across the 3 planes in the nondissected aorta. Rylski et al. , proposed a method involving the subtraction of 3 mm from the outer-to-outer wall diameter at the aortic arch zone 2 in a dissected aorta.
We incorporate Figure 3 and Figure 4 for illustrative purposes with a sample graft sizing plan implemented at our center for a patient with a type B aortic dissection.
The procedure in emergency setting is entirely performed under deep general anesthesia, with the patient intubated and with monitoring of electrocardiography, blood pressure, invasive pressure, and transesophageal echocardiography. The comprehensive picture of the devices needed is provided in Figure 5 .
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