Chronic Thoracic Aortic Dissection: Comparison
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Thoracic aortic dissection (AD) is associated with increased morbidity and mortality. Acute aortic syndrome is the first presentation of the disease in most cases. While acute AD management follows concrete guidelines because of its urgent and life-threatening nature, chronic AD is usually overlooked, although it concerns a wide spectrum of patients surviving an acute event. 

  • aortic dissection
  • chronic aortic dissection
  • thoracic aortic aneurysm

1. Introduction

Aortic dissection (AD) is a fatal disease [1]. The Global Burden Disease 2010 study showed that the overall global death rate from aortic dissection (AD) and aortic aneurysms increased from 2.49 per 100,000 to 2.78 per 100,000 inhabitants between 1990 and 2010 [2,3][2][3]. As in other arterial diseases, an aortic disease may have an acute presentation or it may be diagnosed after a long subclinical phase. There are two clinical patterns in patients with AD [1]: patients with initially acute AD entering the chronic phase of the disease, and patients in whom the first diagnosis of chronic AD is made. Patients with chronic thoracic AD (CTAD) also include those previously operated for type A AD, with persisting dissection of the descending aorta. Patients with newly diagnosed chronic AD are often asymptomatic, and the exact timing of dissection is often difficult to determine [1].
Acute aortic syndrome is the first presentation of the disease in most cases [1]. In fact, acute AD survivors ultimately enter a chronic aortic disease course. The management of patients with CTAD is challenging as far as determining the best medical therapy and deciding on intervention are concerned. Although thoracic AD is an important clinical entity with high morbidity and mortality, even in the chronic phase, the available data concerning the management of CTAD is sparse in the literature. The 2001 ESC Task Force on the diagnosis and management of AD was one of the first documents in the world relating to disease of the aorta [4]. However, the 2014 ESC Guidelines on the diagnosis and treatment of aortic diseases was the last ESC Task Force on AD [1]. Since that time, the diagnostic methods for the imaging of aortic diseases have been improved, while the data on new endovascular and surgical approaches has increased significantly. Until recently, there were no guidelines or recommendations for imaging surveillance in patients with chronic aortic dissection. In a recent scientific statement from the American Heart Association, imaging and measurement techniques for patients with chronic aortic dissection are presented, while the need for standardized measurements and reporting for lifelong surveillance are clarified [5].

2. Definitions and Classification

AD is a condition caused by an intimal tear that propagates antegradely or retrogradely and separates the aortic layers (intima from media), creating a false lumen that expands at the expense of the true lumen, thereby jeopardizing the integrity of the aorta and its branches. It can be the result of a vasa vasorum rupture with subsequent hemorrhage within the aortic wall. AD is the catastrophic result of an aneurysmal disease. The most common risk factors associated with aortic dissection are older age, uncontrolled hypertension, smoking, cocaine abuse, genetic aortic syndromes (Marfan, Ehlers-Danlos, Loeys-Dietz), congenital diseases like bicuspid aortic valve, coarctation of the aorta, Turner syndrome, chest trauma, prior cardiac surgery and procedural instrumentation, and inflammation-vasculitides (giant cell arteritis, syphilis, Takayasu’s arteritis) [6,7][6][7]. Pregnancy is also strongly associated with aortic dissection [6].
The DeBakey classification, focusing on ascending or descending involvement in the dissection process and at the initial entry tear, divides AD into three categories: I-involving ascending, descending aorta and aortic arch, II-confined to the ascending aorta, III-confined to the descending aorta [8,9][8][9]. The Stanford classification, taking into account only the extent of the dissection process irrespective of the initial entry point, divides AD into two groups: A: Any ascending aortic dissection; B: Any dissection that does not involve the ascending aorta [8]. However, in neither of the above classifications dissections limited to the aortic arch or dissections arising distal to the left subclavian artery but not involving the ascending aorta are adequately represented (10% of all dissections) [2]. Lansman et al. [10] suggested a classification that takes into account the origin and the propagation of the dissection. Von Segerssen et al. [11] introduced the term non-A-non-B for dissections. The ESC 2014 aortic guidelines make no comment regarding arch dissection, whereas the 2010 AHA guidelines suggest managing dissections of the descending aorta with entry tear within the arch as proximal type B dissections. Dissections involving the arch are associated with a greater need for urgent or late open aortic surgery or aortic interventions and aortic events after a mean follow-up.
The development of modern imaging techniques, able to detect subtle pathological signs, and of various treatment strategies, gave the chance to further refine the anatomic classification scheme of AD [12]. The new classification system, TEM, takes into account the dissection’s extension (T-Type of dissection: A, B, non A-non B), the primary entry location (E-0: no entry tear visible, 1: entry tear within the aortic root or ascending aorta, 2: entry tear within the aortic arch, 3: entry tear distal to the aortic arch), and end-organ malperfusion (M-0: no malperfusion present, 1: coronary malperfusion, 2: malperfusion of the supra-aortic branches, and 3: malperfusion of the spinal cord, viscerals, renals, lower extremities, or a combination of these). (+) is added when a combination of radiographic and clinical malperfusion is present [13,14][13][14]. Another classification system is the SVS/STS scheme. Based on the place of entry tear, the dissection is classified as A or B. Then, the aorta is divided into 12 aliquot zones (0–11) from the proximal to the distal part, so that the distal extent of the dissection is designated by zone. For type A dissection, the entry tear is located in zone 0. In type B dissections, the entry tear originates in zone 1 or beyond. Two subscripts further characterize type B dissections, letter P describes the proximal zone, and letter D the distal zone of the involved aorta. For instance, B1,9 dissection describes a proximal involvement in zone 1, distal extension in zone 9 and the entry tear anywhere between 1–9. If the entry point is not identified, the dissection is characterized as I. The vast majority of chronic dissections are patients with a history of dissection with or without repair [15]. This group is at risk of subsequent aortic events (acute on chronic dissection) and the way they can be classified can be really complicated as it is necessary to report previous pathology, type of repair and current residual anatomy [15]. The new classifications supply specialists with important information predictive of outcome (entry tear location, malperfusion) and can further guide the therapeutic approach. In daily practice, however, the Stanford classification supplemented with the term non-A-non-B suffices for other healthcare professionals [1,6][1][6]. The aforementioned classifications were developed to assist clinicians in the management of AD.
As regards timing, AD can be described as acute, subacute, and chronic (<14 days, 15–90 days, >90 days from symptoms onset, respectively) [1].
While acute AD management follows concrete guidelines because of its urgent and life-threatening nature, chronic AD is usually overlooked, although it concerns a wide spectrum of patients surviving an acute event. Patients with chronic AD do not share uniform features, as their profile is shaped based on the initial nature of AD, the different survival rates among the subtypes (type A vs. type B), and the clinical course (complicated vs. uncomplicated for type B) which dictates different optimal treatment method (conservative, endovascular, or surgical treatment).

3. Presentation, Diagnosis and Follow-Up

The largest group of patients with chronic AD (~60%) are those who survived the acute phase of type A AD and were treated surgically, but there is a residual false lumen distal to the surgical repair [5]. A smaller proportion of patients is considered totally cured when the dissected segment is totally resected without the persistence of false lumen [5]. An even more scarce group of patients, considering the life-threatening nature of the disease, are those with type A AD not diagnosed in the acute phase due to absent or atypical symptoms, who survived and entered a chronic phase [5]. The second highest frequency group of patients with chronic AD is represented by those initially diagnosed with type B AD who followed an uncomplicated course and were treated conservatively (~25%) [5]. The third fraction of patients with chronic AD (~15%) consists of patients with complicated type B AD who underwent endovascular or surgical treatment and survived [5]. The term complicated is used to describe recurrence of pain and failure to control blood pressure, early aortic expansion, malperfusion, and signs of rupture like haemothorax, increasing mediastinal and periaortic haematoma, and dictates a more aggressive approach (endovascular or surgical) compared to the uncomplicated type B AD, which can be managed conservatively [5]. Additional features associated with a worse prognosis are the false lumen diameter, the site of intimal tear, and retrograde dissection into the aortic arch. Finally, acute aortic syndromes apart from AD include intramural haematoma and penetrating aortic ulcer, which could also progress into a chronic phase requiring similar management to chronic AD [5].
Consequently, patients with chronic AD can be divided into two categories [1]. The first consists of patients who have received medical, endovascular, or surgical treatment for an acute AD, survived 90 days after the initial event entering a chronic phase, while the second consists of patients with a diagnosis of chronic AD for the first time [8]. These patients require lifelong surveillance with imaging. Imaging studies should evaluate the entire aorta, as the dissected part may remain stable, progress, become aneurysmal, or heal. The report should refer to the result of the initial treatment approach, to any difference from baseline or subsequent scans, and to any new pathologies (presence of aneurysms, malperfusion, or entry flow relative to andografts). The follow-up intervals should be individualized. After the predischarge baseline scan, surgically repaired AD should be followed up at 6 months, 12 months, and annually, thereafter. For patients that remain stable over time, longer follow-up intervals are recommended. Medically managed type B AD should be scanned 1–3 months after the initial event, followed by 6-month, 12-month and annual follow-up. Endovascular treatment requires scanning 30 days after the procedure (early complications) and subsequent monitoring at 6 and 12 months. Annual follow-up is necessary, even in stable patients. Follow-up intervals should be individualized in the case of abnormal findings requiring closer monitoring [5]. Due to the chronic nature of the disease and the need for many serial measurements, a standardized protocol on how to perform, measure, compare, and report is very important [5]. Patients with a diagnosis of CTAD for the first time are quite rare, usually totally asymptomatic, and only incidentally detected while undergoing scanning for other purposes.
When symptoms appear, they are usually associated with aortic expansion and subsequent aneurysm formation or with urgent late complications [1,5][1][5]. Aneurysms are detected in 34–38% of patients with chronic type B AD and in up to 49% of patients operated for type A AD with residual chronic AD in the distal aorta [5]. Possible symptoms are chest, abdominal or back pain, shortness of breath, cough, hoarseness, and dysphagia [1,16][1][16].
Malperfusion can manifest as lower limb ischaemia or mesenteric ischaemia, causing claudication or abdominal pain, or as deteriorating renal function [1,5][1][5]. Patients with chronic AD remain at risk of new intimal tears in the remaining aorta [5]. Retrograde type A AD is present in 6.9% of patients with chronic type B AD treated with TEVAR, in 4.3% treated with surgery, and in 3.6% treated medically [5]. It is more common in patients with Marfan syndrome [5]. The most detrimental expression of chronic AD is late aortic rupture, seen in approximately 3–18% of patients [5]. Aortic dissection and rupture both cause acute chest pain [1,5][1][5]. Obtaining a careful medical history directed to symptom onset is necessary in patients with an incidental finding of AD in an attempt to reveal the exact timing of dissection. The clinical examination focuses mainly on the cardiovascular and neurologic status. Blood pressure, murmurs, and peripheral pulses must be assessed. Electrocardiography may show ischaemic changes or hypertrophy, while a chest x-ray may reveal a widened mediastinum or a prominent aortic knob [1,17][1][17]. Non- invasive imaging techniques continue to be the gold standard for diagnosing both acute and chronic AD [1,6][1][6]. In chronic AD, aortic dimensions, intimal flap motion and thickness, false lumen patency, and aneurysm formation should be evaluated [5]. In symptomatic patients, findings compatible with rupture (pleural effusions, mediastinal haematoma) may be found [1].
The follow-up of patients with chronic AD is mainly based on symptoms and on the findings of the imaging modalities. Aortic expansion > 60 mm, annual aortic growth rate > 10 mm/year, persistent patency of the false lumen (thrombosed lumen has a beneficial impact on aortic enlargement and long-term survival), recurrent pain, and signs of end organ ischaemia are indicative of instability, so TEVAR or surgery is recommended [1,5,18][1][5][18]. In uncomplicated chronic AD, annual clinical and imaging evaluation is recommended, irrespective of the treatment method previously applied [1]. Computed tomography angiography is the imaging method of choice for the follow up of patients with chronic AD.

References

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