Aortic Pathologies — General BroadCAST

Diseases affecting the Aorta have been known for Centuries and were, historically, due to trauma or infectious disease. The Scientific advances of the 17th and 18th Centuries saw huge leaps in our understanding of anatomy, biology, medicine and germ theory and, as a result, the near disappearance of syphillitic aneurysms and an increasing understanding of how to successfully manage these conditions. But with the modern world comes modern problems - as our diets and lifestyles have changed, we have seen the emergence and rise of atherosclerotic degenerative aneurysms, inflammatory arterial disease and aortic dissection. These conditions, often misunderstood and misdiagnosed, can present a challenge to clinicians in the pre-hospital arena. So, this month, we're looking at some Aortic disease pathologies and everything you aorta know about them..

Aorta Anatomy

The aorta has 2 main segments – the thoracic and abdominal aortas. The thoracic aorta is further subdivided into three – ascending, arch and descending respectively.

The ascending aorta begins at the aortic valve and ends before the innominate artery (Brachiocephalic trunk) and is approx 5cm long.

The Aortic arch begins at the brachiocephalic trunk and contains three major branches; the brachicocephalic trunk, the left common carotid artery and the left subclavian artery. The aortic arch runs slightly posterior and to the left of the trachea and ends following the left subclavian artery, after which comes the descending aorta.

Pressures in the aorta are obviously highly variable with a “normal” textbook pulse pressure of 40mmHg (dependent on actual blood pressure) – This means that the aorta in particular needs to be somewhat expansile and flexible to accommodate these rapid pressure changes.

Aortic dissection occurs when there is a tear or break in the smooth layer of endothelial tissue inside the aorta - the tunica intima. This, combined with high ejection pressures from the left ventricle allows blood to enter the intermural space, forcing it’s way between the tunica intima and the tunica media creating a ‘false lumen’ in which blood collect and flows, often in surpsingly large volumes. [1] The length of the false lumen inside the aorta is variable, but typically involves the antire aorta beyond the point of the tear. As the dissection grows, more blood enters the tunica media and increases the OUTSIDE diameter of the aorta. [2]

Classification

Aortic dissections are usually classified using either the Stanford or DeBakey classifications which classify dissections according the location of the inital intimal tear and how extensive the false lumen is along the aorta’s length. [1]

In the Stanford classification system, a Type A dissection has the initial tear in the ascending aorta, proxmal to the brachiocephalic artery and Type B distal to the left subclavian artery and affecting only the descending thoracic aorta.

The DeBakey system further divides the classifications into four - Type I and Type II are broadly similar to Stanford Type A in that they begin in the ascending aorta but inType II DeBakey dissection false lumens are contained in the ascending aorta and Type I involve the ascending and descending thoracic aorta. Two further subtypes (Type IIIa and Type IIIb) have an initial tear in the descending aorta and a differentiated by the extent of dissection - Type IIIa does not extend beyond the diaphragm.

Image from Aortic Dissection Charitable Trust

Aortic dissection has an estimated incidence of 4.5 per 100,000/year in the UK [1] (around 2500 cases) and dissection most commonly affects the ascending aorta – (70% ascending, 15-20% descending thoracic, 10% arch, <5% abdominal) [2.] Dissection has serious complications which are largely related to the exact location of the dissection, the volume of the false lumen and the direction of blood flow, which can sometimes be retrograde – expansion of the dissection up to and around another blood vessel such as the subclavian artery or renal arteries can cause significant ischemia and associated symptoms.

If a dissection is large enough or left untreated it can rupture, resulting in catastrophic bleeding into different body cavities – Aortic rupture may cause haemopericardium (syncope and/or sudden death), left or right haemothorax (invariably sudden death,) mediastinal haemorrhage, compression of the pulmonary trunk and, rarely – intraperitoneal (abdominal) or oesophageal (descending) haemhorrage. [2]

Ruptured aortic dissection has a very high mortality rate (up to 80%) [3] and 50% of aortic issections are misdiagnosed,with up to 33% being actively treated for the wrong condition [1] BUT, if identified and treated in a timely fashion 80% of patients will survive the dissection- these figures demonstrate exactly how important it is that pre-hospital care clinicians have a good awareness of dissection and it’s presentation.

Aortic aneurysm occurs when there is an enlargement or ballooning of the aorta. The UK National screening programme suggests that Abdominal Aortic Aneurysm (AAA) has a prevalence of around 1.3% [4] amongst men who are screened (that is, men aged 65 or older) and ruptured abdominal aneurysm (rAAA) is responsible for approx. 6000 deaths/year – 20% of whom die before reaching hospital and 50% before reaching specialist care. Interestingly, although aortic aneurysm is up to six times more prevalent in men [5], women with AAA are more likely to experience rupture and women actually account for 1/3 of all rAAA deaths.

There is a scarcity of data on ‘normal’ aortic diameters, possibly due to differing imaging modalities, but by common convention aortic dilation is an aorta larger than 95th percentile for sex, body size and age.

*Aneurysm is distinguished from ectasia as* ***localised, fusiform*** *dilation of the aorta >50% of expected diameter whereas ectasia is* **widespread** *dilation. There is little consensus on the cut off between dilation and aneurysm.*

Abdominal aortic aneurysm is most common presentation- 80-95% of aneurysms are below the renal arteries [6], likely due to lower levels of elastin and collagen in the tunica media below this point meaning that the aorta is more pre-disposed to experience enlargement.

Complications of aortic aneurysm are similar to those of dissection – most significantly, rupture, but aneurysm can also be linked to emboli formation and compression of surrounding structures (e.g. the Vena Cava.)

History taking

Since both of these conditions affect the aorta and both have a direct link to arteriosclerosis (hardening of the arterial wall), the significant history and risk factors are very similar, essentially anything which increases the likelihood of arteriosclerosis;

· The most important and strongly linked risk factors for both pathologies in is smoking [7] [8] – the association is directly linked in literature to the number of years smoking and decreases with the number of years since quitting. Smoking directly contributes to arteriosclerosis by promoting protease-anti-protease imbalance and inflammatory cytokynes which damage and reduce levels of elastin and collagen in the tunica media which can significantly reduce it’s elasticity and recoil. Smoking is also contributes to atherosclerosis development as well as being a major independent risk factor for chronic hypertension and the major factor in developing COPD – both of which furter increase the risk of aortic dissection/aneurysm.

· >60 years – partly due to calcification plus degeneration of collagen and elastin in aorta walls.

· Genetic conditions affecting collagen and elastin such as Ehlers Danlos syndrome or Marfan Syndrome, Turner’s syndrome

· Family history – 1st degree relative.

· Pregnancy

· Aortic valve replacement, bicuspid aortic valve, CABG or coarction of the aorta can also be linked due to an associated increase in aortic pressures

“Aortic Dissection is more common than brain cancer. For every 20 patients you see, between the ages of 65 and 70,suffering with an MI, one of these will be an Aortic Dissection. ”

— Parameducate Live 2022 - Aortic Dissection Charitable Trust

Examination

Aortic Dissection

Dissection typically (85%) [2] presents as very sudden, acute and maximal chest pain which is commonly described as ‘sharp’ as opposed to a more typically cardiac ‘ache’ or ‘tightness.’ It may present in the anterior chest (70-80%) if the ascending aorta or arch is affected (type A.) Back pain occurs in 50% of all dissection patients. The pain may also move – thought to be due to peripheral extension of dissection from the primary intimal tear.

The ‘classic’ symptom of acute aortic dissection, tearing interscapular pain, was found in only 50% of patients. [9]

Be aware – there may be no chest pain (5-15% no pain at all) – or pain may completely resolve if the dissection process has temporarily halted or if there is a reduction of pressure within the aortic wall. [2]

Other features:

Hypertension, pulse deficit (reduced or absent – represents occlusion of branch vessels), differential BP between arms (20mmHg difference significant – but not specific finding. A pulse deficit alone was found to be more suggestive of dissection than either differential BP OR differential BP plus pulse deficit. Several studies found that up to 20% of ambulatory ED patients had systolic or diastolic inter-arm difference of >20mmHg) – Positive finding might heighten suspicion with clinical context. [10] [11]

Limb parasthesia or weakness, diastolic murmur over aortic area and widened pulse pressure (caused by root dilation), systolic murmur over any part of the aorta (true lumen compression,) syncope, concurrent chest and abdominal pain.

Hypotension – late sign which may be caused by massive haemothorax, haemorrhage or loss of volume into extensive false lumen.

Aortic Aneurysm

Most patients with aortic aneurysm are not aware that they have one, it is usually discovered as an incidental finding, due to sudden rupture or as a result of routine screening, However – up to 30% of asymptomatic AAA is picked up as a pulsatile and expansive mass during abdominal assessment.

The classic triad of symptoms for ruptured AAA - Hypotension, flank or back pain and pulsatile mass may not be fully present in up to 50% of presentations [12] and therefore diagnosis of rAAA should be considered in people with new abdominal and/or back pain, cardiovascular collapse or loss of consciousness. [5]

Diagnosis and differentials

Diagnosis in terms of prehospital care with be dependent on symptoms, presentation and most importantly, history.

Formal diagnosis can only be made with imaging – Ultrasound, CXR, CT angio, MRI angio, Transoesophageal echo.

Be aware that 12 lead ECG may be normal in up to 30% of patients, however more than 40% have ST segment or T wave changes.

Treatments and management

These patients will invariably require hospital if presenting with any symptomatic features or suspected new dissection or aneurysm. Type A dissections are treated with emergency surgery with varying degrees of aortic replacement. Type B dissections can usually be managed medically with antihypertensives although in some cases they may still require surgery. However, in the context of pre-hospital care there is no way to reliably determine dissection presence or type and it is worth noting that there is no evidence that any single symptom, sign or prognostication risk assessment tool can be used to determine if suspected or confirmed aortic rupture or dissection should be transferred to a regional vascular service. If you have genuine concerns about the possibility of an aortic pathology, you should consider bypass to a vascular centre - even if the patient is unstable.

You could consider permissive hypotension and warming to reduce ‘traumatic’ coagulopathy in patients where bleeding is suspected although no high level evidence to support permissive hypotension. [5] There is currently no evidence to specifically support the use of TXA in aortic rupture, and could be considered for isolated interal bleeding but this is entirely dependent on the terms of your PGD if you give TXA under one.

Pitfalls

Insufficient history
failure to treat pain adequately
lowering threshold of suspicion due to resolution of symptoms, absence of BP differentials etc.

Resources

General BroadCAST has been kindly supported in this episode by the Aortic Dissection Charitable Trust - the ADCT has some fantastic resources, videos, patient stories and a fantastic primary care guide which is linked below.

Smoking Cessation

Smoking Cessation - Health Promotion Advice for Professionals

Health Matters: Stopping Smoking - What works?

Protease Activity in Vascular Disease

The Last Word

Hopefully, this has been a useful summary of aortic pathologies to support your practice, but don’t just take our work for it… navigate to the other resources to supplement your learning and make sure to reflect on this CPD in your portfolios. Remember, clinicians are responsible for their own practice. These podcasts are produced for informative purposes and should not be considered solely sufficient to adjust practice. See "The Legal Bit" for more info.

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