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Introduction

Both chronic and acute diseases of the aorta, including trauma, are attracting increasing attention both in the light of an ageing Western population and with the advent of modern diagnostic modalities and therapeutic options to manage aortic pathology. In the case of aortic ectasia the individual rate of expansion and the risk of rupture may be assessed from co-morbidities, hypertensive state, or connective tissue disease, and should be quantified regardless of anatomic location for timely selection and treatment. Acute aortic syndrome, a term comprising acute dissection, intramural haematoma, and penetrating aortic ulcers, may share common ground by the observation of microapoplexy of the aortic wall, eventually leading to higher wall stress, facilitating progressive dilatation, intramural haemorrhage, dissection, and eventually rupture; chronic hypertension and connective tissue disorders are likely to promote this mechanism.

Definition

Acute aortic syndrome (AAS) consists of different emergency conditions with similar clinical characteristics and challenges. These conditions include aortic dissection, intramural haematoma (IMH), transection following trauma and penetrating atherosclerotic ulcer (PAU). The common denominator of AAS is disruption of the media layer of the aorta with bleeding with IMH along the wall of the aorta, resulting in separation of the layers of the aorta, or transmurally through the vessel wall in case of ruptured PAU or trauma. In the majority of patients (90 %), an intimal disruption is present that results in tracking of blood between the layers of the media potentially rupturing through the adventitia or back through the intima into the aortic lumen [1]. With regards to the time domain, acute dissection is defined as occurring within 2 weeks of onset of initial pain; subacute, between 2 and 8 weeks from the onset of pain; and chronic, more than 8 weeks from the onset of pain. Anatomically, acute thoracic aortic dissection can be classified according to either the origin of the intimal tear or whether the dissection involves the ascending aorta [2]. The two most commonly used classification schemes are the DeBakey and the Stanford systems (Fig. 5.1).

Figure 5.1
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Aortic dissection classification: DeBakey and Stanford classification as the currently most frequently used classification systems for aortic dissection

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Prevalence of Risk Factors

Aortic dissection and its variants are rare diseases, with an estimated incidence of approximately 2.6-3.5 cases per 100,000 person/year [3]. Around 0.5 % of patients presenting to an emergency department with chest of back pain suffer from aortic dissection [4]; two-thirds of them are male, with an average age at presentation of approximately 65 years. A history of systemic hypertension found in up to 72 % of patients is by far the most common risk factor (Table 5.1). Atherosclerosis, a history of prior cardiac surgery, and known aortic aneurysm are other major risk factors [5]. The epidemiology of aortic dissection is substantially different in young patients (<40 years of age) where risk factors such as Marfan syndrome and other connective tissue disorders take precedence. In general 60 % of aortic dissections are classified as proximal (type A) and 40 % as distal (type B) according to the Stanford classification. The PAU seems to affect mostly the descending thoracic aorta and abdominal aorta in 80 % of cases [6]. Data from previous studies suggest an incidence of PAU ranging from 2.3 to 11 % in patients presenting with AAS [7]. Conversely, acute IMH accounts for 5–20 % of all AAS; both of them have a clear relation to old age, arterial hypertension, and atherosclerosis [8].

Table 5.1 Risk conditions for aortic dissection
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Presentation and Diagnosis

The symptoms of an IMH with or without PAU are similar to those of acute aortic dissection. Although they are distinct pathologies, differentiation between such aortic conditions can be difficult or even impossible solely by clinical means. Patients are typically around 60 years of age with comorbidities ranging from hypertension and Marfan’s syndrome to prior surgery or vascular interventions (Table 5.2). Pain is the most commonly presenting symptom of acute aortic dissection, independent of age, sex, or other associated clinical complaints [3]; pooled data from over 1,000 cases showed that acute dissection is perceived as abrupt pain in 84 % with severe intensity in 90 %. Although classically described as tearing or ripping, patients are more likely to describe the pain of acute dissection as sharp or stabbing, and fluctuating [4]. Pain location and associated symptoms reflect the site of initial intimal disruption and may change as the dissection extends along the aorta or involves other arteries or organs. Three modern imaging techniques have contributed to a better understanding of the development, natural history and diagnosis of these uncommon aortic pathologies: computerized tomographic angiography (CTA), magnetic resonance angiography (MRA), and transoesophageal echocardiography (TEE) [9–12].

Table 5.2 Demographics and history of patients with acute aortic dissection
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Management

Initial management of AAS, particularly dissection, is directed at limiting propagation of dissected wall components by control of blood pressure and reduction in dP/dt (pressure development). Reduction in pulse pressure to just maintain sufficient end-organ perfusion is a priority with the use of intravenous β-blockade as first-line therapy [13].

Risk of Misdiagnosis

Diagnostic imaging studies in the setting of clinical suspicion of dissection have important primary goals such as confirmation of clinical suspicion, classification of dissection, localization of tears and assessment of both extent of dissection and indicators of urgency (e.g. pericardial, mediastinal, or pleural hemorrhage); in addition, biomarkers (such as myocardial markers, D-dimer elevation >500 μg/L and smooth muscle myosin heavy chain) may be used strategically in concert with swift aortic imaging, although an ideal algorithm has yet to be determined [12, 14–17]. Selection of imaging is often hospital-specific, but CT angiography is most readily available and accurate (Table 5.3). Clinical suspicion of acute aortic syndrome is high with abrupt or severe retrosternal or interscapular chest pain often migrating down the back; associated findings can produce signs of acute aortic insufficiency, pericardial effusion or occluded aortic sidebranches causing ischemia or pulse differential [4]. With predisposing factors such as hypertension, connective tissue disorders, bicuspid aortic valve, coarctation and previous cardiac surgery or recent percutaneous instrumentation, undelayed diagnostic imaging is required for any of the above symptoms and suspected acute aortic syndrome (Table 5.4) [13]. While transthoracic ultrasound provides vital information (new-onset aortic insufficiency, pericardial effusion or even visualisation of proximal dissection), additional transoesophageal (TEE) interrogation of the thoracic aorta is the logical next step, or MD-CT scanning of the entire aorta if considered safe [5, 10, 11, 17]. Both imaging modalities provide further detail beyond classification as type A and B (or distal) dissection and allow for strategic planning; ultrasound technology is portable, avoids transport of a critically-ill patient and may even be held in the operating theatre [17]. MRI has no place in the urgent diagnostic work-up of acutely symptomatic patients. Additional information not essential for immediate management decisions such as coronary, arch vessel and side-branch involvement is usually depicted on CT-angiograms without the need for invasive angiography, even in the presence of ST-changes [5, 11].

Table 5.3 Comparative diagnostic utility of imaging techniques in aortic dissection
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Table 5.4 Management of patients with suspected aortic dissection
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Medical Management

All patients must receive the best medical treatment available at admission [5, 13]. Initial management of AAS is directed at limiting propagation of diseased wall components by control of blood pressure and reduction in dP/dt. Reduction in pulse pressure with a target systolic pressure of 100–120 mmHg and a heart rate of 60–80 bpm to just maintain sufficient end-organ perfusion is a priority with the use of intravenous ß-blockade as first-line therapy. Often multiple agents are required, with patients ideally managed in an intensive care setting. Opiate analgesia should be prescribed to attenuate the sympathetic release of catecholamines to pain with resultant tachycardia and hypertension (Table 5.5). High-risk but asymptomatic patients with AAS, with the exception of type A aortic dissection, can probably be followed up without urgent intervention if they do not reveal any early complications [2, 18, 19]. All symptomatic patients will need surgical or interventional treatment, since the evolution is unpredictable with a high likelihood of severe complications. Moreover, it is clearly necessary to distinguish IMH and PAU from classic acute aortic dissection. The site of lesion and evidence of complications, as well as evidence of disease progression on serial imaging dictate the management strategy besides the initial medical management.

Table 5.5 Initial medical treatment in patients with acute aortic dissection and hypertension
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Control of Pain

First-line therapy is pain relief by morphine sulphate and intravenous β-blockade. The use of benzodiazepines and labetalol, with both α- and β-blockade, is useful for lowering both blood pressure and dP/dt, with target systolic pressure of 100–120 mmHg and heart rate of 60–80 beats/min. Often multiple agents are required, with patients ideally managed in an intensive care setting. Opiate analgesia should be prescribed to attenuate the sympathetic release of catecholamines to pain with resultant tachycardia and hypertension. Further management is dictated by the site of the lesion and evidence of complications (persisting pain, organ malperfusion), as well as evidence of disease progression on serial imaging.

Control of Blood Pressure

On admission, any AAS patient is subject to standardised protocol management including ICU transfer, continuous arterial pressure monitoring, central venous access for administration of intravenous antihypertensive agents, and urine output monitoring via a bladder catheter. The initial goals are to halt progression of dissection by decreasing impulse force (of systolic pressure) and control pain; β-blocking agent (labetalol, metoprolol), calcium channel blockers, nitroglycerine and sodium nitroprusside are used in that order to ensure anti-impulse management with the goal of keeping blood pressure <120 mmHg and mean arterial pressure <80 mmHg. Patients remain in cardiovascular intensive care until pressure and pain are well controlled and medication is oralised. In presence of uncontrollable pain or pressure elevation, evidence of a complicated setting of type B dissection is likely and endovascular management is usually warranted; the spectrum of complicated type B dissection is widening with ongoing pain and hypertension as recent, but nevertheless, classic complications [13, 20, 21]. There is no evidence for endovascular repair of uncomplicated type B dissection with no ongoing symptoms and well-controlled blood pressure and no evidence of malperfusion or impending rupture. The INSTEAD trial showed no survival advantage of stenting as opposed to best medical therapy at 2 years (best medical therapy 95.6 % vs. stenting 88.9 %; P = 0.15) [22] The study, however, showed a beneficial impact of stent-graft on aortic remodelling and beneficial long-term outcomes [23–25].

Management of Complications

In the case of suspected aortic dissection, prompt and competent interpretation of diagnostic contrast-enhanced CT or other imaging is mandatory for undelayed triaging and proper treatment. A high clinical index of suspicion after a “negative” result from the initial diagnostic imaging study may warrant subsequent transoesophageal ultrasound interrogation at the bedside. Moreover, focused cardiac ultrasound (FOCUS) can be useful for time-sensitive rapid assessment of aortic root size, valvular function and presence of dissection or intramural haematoma. Beyond transthoracic evaluation, transoesophageal imaging offers clear depiction of both ascending and descending aorta at high temporal resolution with clear depiction of entry size and location, secondary communications, extra-aortic blood collection and of true lumen collapse or compression; such information has a major prognostic impact and identifies patients at risk for ongoing or impending complications. As a consequence, all features of aortic wall disintegration or dissection involving the ascending aorta requires immediate surgical attention or prompt transfer to an appropriate tertiary care centre. Conversely, with features of complications such as impending rupture or organ malperfusion including true lumen collapse, type B dissection also requires undelayed attention by use of endovascular technology to reconstruct the true lumen of the dissected aorta. In particular, in presence of shock symptoms, the assumption of a scenario of complicated dissection is highly likely either caused by loss of blood by rupture, by hypotension secondary to bowel ischaemia from malperfusion and obstruction of the superior mesenteric artery and/or the celiar trunk. Similarly, but not as acutely, the emergence of renal dysfunction may be due to proximal aortic true lumen collapse or bilateral renal artery obstruction from dissection, and of course, requires endovascular revascularisation procedures, along with immediate volume expansion and fluid hydration.

Shock

Shock with diagnostic confirmation of a type A dissection (or any aortic pathology involving the ascending aorta) should prompt undelayed surgery and open repair. Cardiogenic shock is either caused by pericardial tamponade (frequent with proximal dissection), by acute aortic valve regurgitation or by coronary compromise from the dissection lamella either progressing into the left coronary mainstem or just obstructing any coronary ostium or from rare other conditions (Table 5.6). Interventions such as pericardiocentesis or coronary percutaneous procedures are not advised because they can worsen the acute problem and cost precious time until life-saving surgery. Shock from acute blood loss indicates rupture or contained rupture of the aorta and the need for immediate surgery, but is often fatal.

Table 5.6 Clinical findings in aortic dissection
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In a type B setting, shock symptoms call for immediate volume expansion (including blood transfusion) and swift endovascular management of such a life-threatening complication in an attempt to seal major communications to the false lumen and thereby stop further blood loss via the ruptured outer media layer of the false lumen.

Renal Insufficiency

In the setting of both proximal and also distal dissection, acute renal insufficiency can be the result of kidney malperfusion from obstructed renal arteries. The obstruction often results from true lumen collapse or from static obstruction of renal arteries by either thrombus or invagination of dissected aortic wall components. In most cases, local interventions are not helpful and would delay urgent proximal repair in type A dissection; in type B dissection, malperfusion of renal arteries are best managed by endovascular scaffolding of the descending thoracic aorta with stent-graft in the true lumen, an intervention that depressurises the false lumen, redirects blood to the true lumen only, and opens the true lumen by virtue of systolic pressure even at the level of abdominal side branches and iliac arteries. After such a procedure, stents in the ostia of renal arteries are rarely needed and fenestration procedures are obsolete. Renal function usually recovers even after days of malperfusion.

Anticoagulation

Risk/Benefit of Anticoagulation and Antithrombotics

Once a proximal or distal aortic dissection has been diagnosed, therapeutic management is focused on surgical repair in cases of type A involvement and on proper triaging for complications and thus endovascular treatment of type B dissection. There is no place for anticoagulation strategies besides the use of prophylactic heparin to avoid deep venous thrombosis during immobilisation and bed rest. With ambulation, patients do not require anticoagulants either in the short term, or long-term. Similarly, no antiaggregation with agents such as aspirin or thienopyridiues is required except for unrelated independent indications such as coronary or peripheral artery disease. Even after TEVAR, specific antithrombotic medication is not indicated. On the other hand, chronic dissection without signs of acute complications is not a contraindication for antithrombotic or anticoagulant medication if they are needed for another prognostically relevant reason [2].

Interventional Management

In the acute setting with complications, endovascular repair for dissection of the descending thoracic aorta is now established owing to the high mortality of open repair [2, 21, 26]. Conversely, open surgical repair requires single-lung ventilation, cardiopulmonary bypass with circulatory arrest, profound hypothermia and cerebrospinal fluid drainage, and has been replaced by endovascular repair with an IA recommendation in the presence of organ or limb ischemia [27–29]. Particularly in the setting of malperfusion, outcomes with open surgery have been unpredictable and the risk of irreversible spinal cord injury and death in acute type B dissections has ranged from 14 to 67 % [2, 3, 30]. Contemporary in-hospital mortality rates are around 17 % with open surgery supporting a paradigm shift towards endovascular management as first-line treatment in patients with complicated type B dissection [21, 31, 32]. If malperfusion of a branch vessel persists, branch vessel stenting or the PETTICOAT (provisional extension to induce complete attachment) technique may be used with open bare-metal stents to relieve distal malperfusion [33, 34] (Fig. 5.2). In complex complicated scenarios, even the interventional closure of distal re-entry points appears reasonable with successful endovascular management the 30-day mortality of 10.8 % for complicated dissection with imminent rupture or end organ ischemia is similar to the mortality rate of uncomplicated patients [29]. Nevertheless, complications can occur with TEVAR including peri-intervention stroke and retrograde dissection particularly in inexperienced hands [35]. A relatively dated meta-analysis of outcomes for TEVAR in complicated acute type B aortic dissection, revealed in-hospital mortality of 9 %, and a low rate of major complications (stroke 3.1 %; paraplegia 1.9 %; conversion to type A dissection 2 %; bowel infarction 0.9 %; and major amputation 0.2 %); aortic rupture occurred in 0.8 % over 20 months concluding that endovascular treatment of (complicated) acute type B dissection is a therapeutic option with favourable initial outcomes; the long-term data regarding outcome and remodelling are promising [28]. Current observational evidence suggests that TEVAR improves survival in complicated distal dissection [21]. In patients with connective tissue disease, however, remodeling is achieved less frequently and endovascular strategies are discouraged or considered as bridging to definitive open repair [36].

Figure 5.2
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Malperfusion syndrome treated with endovascular stent-graft and PETTICOAT; (a) angiography of lower body malperfusion; (b) reperfusion after proximal stent-graft; (c) 3D CT reconstruction of acute complicated dissection with malperfusion; (d) reconstructed aorta and abolished malperfusion after stent-graft and PETTICOAT

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In the subacute phase of distal aortic dissection, mortality varies between 32 % for open surgery, 7 % for patients with endovascular management, and 10 % for medical treatment alone (P < 0.0001) [3, 32]. Approximately 60 % of late deaths result from rupture of the false lumen since long-term patency of the false lumen sets the stage for aneurysmal dilatation (Fig. 5.3). Previously accepted indications for surgical repair, such as refractory pain, ongoing malperfusion, expansion >1 cm per year, and a diameter over 55 mm are currently considered indications for TEVAR in subacute and chronic dissections. There is clear observational evidence that depressurisation and shrinkage of the false lumen are beneficial even beyond the acute phase of dissection, and placement of an individualised stentgraft has been shown to promote false lumen thrombosis and remodelling even late after dissection. Stent-graft placement has even been used to treat late evolution of retrograde extension into the ascending aorta, followed by remodelling and healing in a subacute state. This window of plasticity of dissected aorta is usually open until 90 days; in other words, the likelihood of successful remodelling with TEVAR is greater in the first 3 months than later in the chronic phase of dissection [26].

Figure 5.3
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3D-CT image of aneurysmal dilatation of uncomplicated type B aortic dissection after 3 years

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Surprisingly, the only randomised comparison demonstrated no statistical difference in all-cause mortality between patients treated with TEVAR compared with best medical therapy alone for up to 2 years of follow-up [22]. However, long-term outcome data support endovascular scaffolding (with stent-graft) for initially stable type B dissection in an attempt to prevent late complications and cardiovascular death [23, 24, 37]; therefore, in concert with antihypertensive medication, pre-emptive TEVAR provided at low risk is increasingly being accepted even for initially uncomplicated dissection [23, 37]. At 5 years of follow-up the INSTEAD-XL study showed that aortic rupture, disease progression and vascular mortality to be tempered by pre-emptive TEVAR in the sub-acute phase of dissection (Fig. 5.4). The pre-emptive TEVAR concept, as introduced above in the subacute phase of dissection, is supported by one meta-analysis and 2 retrospective registries [23, 37]; in particular observations from IRAD corroborate the late advantage of TEVAR beyond 2–3 years of follow-up [24]. Thus, anatomically-suitable patients with considerable life expectancy of >2 years should be offered pre-emptive TEVAR regardless of clinical presentation with the idea to prevent late complications. Such a conceptual change from a complication-specific indication for TEVAR to pre-emptive TEVAR also suggests that patients with dissection should be transferred to tertiary care at high-volume aortic centres for high-quality care and at a very low complication rate [38].

Figure 5.4
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Five years F/U INSTEAD-XL vascular mortality. Kaplan-Meier estimates of vascular mortality (death), and landmark analysis with the breakpoint at 24 month, 12 month and 1 month after randomization to the end of the trial are shown for OMT and OMT + TEVAR groups. Beyond 2 years of follow-up the observed mortality was lower with TEVAR than with OMT alone [23]

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Outlook

Different clinical patterns are being used to differentiate between sets of patients with aortic dissection, both in type A but, in particular, in type B. While management of type A dissection is straightforward with the need for timely surgical repair after initial pain control and blood pressure control by intravenous drugs, subclassification of type B dissections is more complex although all type B dissections represent a serious vascular event per se as the result of longstanding uncontrolled hypertension, connective tissue disorders or other risk conditions with the potential to shorten lifespan. Currently used recommendations suggest initial medical management (anti-impulse β-blockade, sartans and/or Ca++-channel blockers) with close surveillance for so-called uncomplicated type B dissections in the acute, subacute and chronic setting; emergent TEVAR is accepted and advised in all complicated scenarios of type B dissection. This complication-driven approach may soon be supplanted by a more liberal pre-emptive use of TEVAR (with advanced technology) in the light of long-term benefits from aortic remodeling, even in the setting of so-called uncomplicated type B dissection. Thus, with better understanding of adverse predictors, the concept of pre-emptive repair of any type B aortic dissection by endovascular interventions should be considered for all patients with type B dissection regardless of presenting symptoms and in addition to life-long pharmaceutical blood pressure control as long as they are anatomically suitable. All patients should be followed and offered sustained surveillance with focus on blood pressure control and progressive expansion; even renal sympathetic denervation may have a role [39]. With this novel approach, chances are that thoraco-abdominal aneurysmatic expansion of dissected aortas could be prevented in the future.

Intramural Haematoma and Penetrating Aortic Ulcer

Medical management of intramural haematoma and penetrating aortic ulcer follows the same logic as aortic dissection. In type A involvement, surgery should be considered in all cases except in presence of serious comorbidities. Before surgery or in cases where surgery is not indicated, medical treatment including control of symptoms and haemodynamic alterations is indicated.

In type B involvement, management is based on complications. In cases without complications, control of pain and blood pressure are paramount. Repeated imaging during the acute phase is necessary to monitor evolution of intramural or periaortic haemorrhage, progression of aorta size and disease extension.