Type A Aortic Dissection

Written by Saleem Jahangeer, Consultant Cardiothoracic and Aortic Surgeon, St James’s Hospital, Dublin

The 19th of September is the global Aortic Dissection Awareness Day. To raise awareness, especially among healthcare professionals, about this silent killer, this article will focus mainly on Acute Type A Aortic Dissection (ATAD). ATAD is a life-threatening, time sensitive emergency with a high pre-hospital and peri-operative mortality.

Introduction

An aortic dissection is a partial tear in the wall of the aorta between the intimal and the medial layer of the aortic wall (Figure 1).

This separation results in the creation of a false channel of blood. This false lumen may extend into branches of the aorta in the chest or abdomen, causing malperfusion, ischemia, or occlusion with resultant complications. The dissection can also progress proximally, to involve the aortic sinus, aortic valve, and coronary arteries. Dissection can lead to aneurysmal change and early rupture, which represents a life- threatening emergency.

Aortic dissections are classified using the Stanford or DeBakey Classification (Figure 2). A Stanford A represents an intimal tear proximal to the left subclavian artery.

Type A Aortic Dissection – The Facts

• Most lethal condition of the aorta

• Worldwide prevalence of 0.5 to 2.95 per 100,000 per year. Recent data : 10.4 cases per 100,000/year.

• 65% males.

• Up to 26% of aortic dissections die prior to hospital admission.

• 58% to 68% of acute dissection cases die prior to definitive operative intervention.

• Mortality is often quoted at 1% per hour.

• About 74% of patients die within the first two weeks.

• Less than 10% of untreated patients live for one year, and almost all patients die within 10 years.

• 33% of patients with a dissection are misdiagnosed.

• Over 2000 lives per year are lost to dissections in the UK and Ireland.

• 10 lives per week can be saved with the correct diagnosis and treatment.

Risk Factors

The most common risk factors for acute dissection are hypertension, connective tissue disease and known aortic aneurysm. Other significant risk factors include:

• Atherosclerosis

• Iatrogenic trauma

• Previous aortic manipulation (including cardiac surgery)

• Vasculitis – Takayasu’s arteritis, Giant cell arteritis

• Infection – Syphilis, Tuberculosis

• Congenital abnormalities – Bicuspid Aortic valve, Coarctation of the aorta

• Age (60-80 yrs. old)

• Family history

• Trauma

• Pregnancy

• Illicit drug use

Clinical Presentation

The vast majority of patients with dissection present with chest pain. This can be described as a ripping or tearing pain. The onset is very often abrupt and sudden in nature. Patients can also present with clinical features underlying malperfusion: acute organ ischaemia, neurological symptoms or acute heart failure. Unfortunately, in some patients the first sign can be sudden death, caused by free rupture or shearing of the coronary arteries. The physical signs and clinical features are summarised in Figure 3.

Since the most common presentation is chest pain, acute dissections are very often misdiagnosed as acute coronary syndromes (ACS). Up to 33% of dissection patients are misdiagnosed. This can have very drastic consequences. Not only does this represent a delay in diagnosis and ultimately treatment, but mis-managing a dissection as an ACS with antiplatelets or even an angiogram can lead to severe complications including rupture. The diagnosis of an acute aortic dissections always requires a high level of suspicion.

Imaging modalities in aortic dissection

Plain Chest X-ray (CXR)

Most if not all patients presenting to ED will have a CXR as part of their investigations. Patients with an acute dissection may have some radiological signs on CXR such as a widened mediastinum or a pleural effusion. Comparison with old films can be very helpful but a normal CXR should not deter further investigations.

CT scan

CT scan remains the gold standard diagnostic imaging modality. It is 95% sensitive and shows both the true and false lumens with an intimal flap often visible (Figure 4). It is critical to emphasise that diagnosis of a dissection might not be visible on a Non-contrast CT or one with the wrong contrast phase (e.g. CTPA). In such cases, it is paramount that a proper arterial, ideally gated CT aorta is performed straight away.

Transthoracic and Transoesophageal echocardiogram (TTE and TOE)

TTE and TOE have a sensitivity of 80% and 89% respectively. There has been recent interest in the use Point of Care Ultrasound (POCUS) at the bedside upon presentation to diagnose an acute dissection (Figure 5). It is important to note that the use of TTE and TOE might be limited to the proximal aortic segment and a tear in the proximal arch may be missed.

Any suspicious findings on echocardiogram should trigger an immediate CT scan to confirm the diagnosis.

The European Society of Cardiology has published a risk-scoring method based on High Risk Condition, High Risk Pain features, High Risk Examination features (Figure 6 – Table 2 on page 22).

The diagnosis of an acute aortic dissections always requires a high level of suspicion. Unless you think of an aortic dissection, it will be missed. And if you think of an aortic dissection, it needs to be immediately confirmed or ruled-out by a contrast CT scan without delay.

Management of Acute Type A Dissection

The definitive treatment for acute type A dissection is surgery. Once the diagnosis is confirmed, immediate referral needs to be made to the cardiothoracic on call team, with preparation for prompt patient transfer.

Blood Pressure Management

Blood Pressure control is critical in the first line management and should be initiated immediately – Anti-impulse therapy. The aim is to decrease δP/ δT – the force of ejection of blood, while maintaining organ perfusion. Antiimpulse therapy aims to titrate systolic BP to less than 120mmHg and HR to less than 60bpm.

The first line agent is usually intravenous labetolol. GTN or nipride should generally be avoid as they can cause a reflex tachycardia which may increase δP/ δT.

Surgical Management of Acute Type A Dissection

The definitive management remains surgical repair. The surgical strategy aims at resecting the primary tear/tears and obliterating the false lumen. The aortic valve is usually resuspended to maintain competence. If the initial tear involves the root, a root replacement with a composite conduit and re-implantation of the coronary arteries is warranted (Figure 7).

The aortic arch should be inspected at the time of surgery to ensure there are no intimal tears. This is accomplished during Deep Circulatory Hypothermic Arrest (DHCA). Presence of any intimal tears in the arch would warrant a hemi-arch or a total arch replacement (Figure 8).

Surgical repair of Acute Type A Dissections are high risk surgeries. The operative and in-patient mortality rates are around 18% and 33% respectively. In an effort to improve surgical outcomes, surgical management of Type A dissections has been centralised to specialist “Aortic” centres in many European countries and in the UK. This has seen an improvement in outcomes, mainly due to a volume-outcome relationship.

Frozen Elephant Trunk procedure in acute dissection

Even in patients who underwent successful surgery for a Type A dissection, the rates of reintervention or aortic-related complications can be as high as 70%.

The poor long-term prognosis related to a Type A dissection has led to a shift in the treatment paradigm of these patients. The focus currently has changed to performing a lifesaving, durable repair which will address the poor long-term prognosis of this condition.

The introduction of the Frozen Elephant Trunk (FET) graft prosthesis has revolutionised the acute surgical management of acute Type A dissections. A FET prosthesis allows for a ‘2 in 1’ hybrid procedure which includes both a surgical repair and an endovascular stenting performed simultaneously (Figure 9).

The Frozen Elephant Trunk (FET) technique is invaluable in patients with distal aortic malperfusion with compression of the true lumen, complex primary and re-entry tears involving the distal arch or proximal descending thoracic aorta (DTA). FET prosthesis can fully open the compressed true lumen and also cover additional entry tears located in the proximal DTA.

The presence of the stented graft of the FET prosthesis also provides a landing zone for future aortic endovascular stenting if required. This facilitates the long-term management of patients who might have an expanding false lumen after their index operation.

Currently, both in the USA and the UK, FET procedures are performed by aortic surgeons trained in such procedures. Figure 10 shows a recent trifurcated FET prosthesis done by our Aortic team at St James’s Hospital, with excellent clinical and radiological outcome.

Follow-up following Acute Type A Dissection

Survivors of Type A dissection need long-term/life-long surveillance as the rate of post dissection complications and reintervention are quite high. Strict BP control along with enrolment in a surveillance programme are mandatory for these patients.

Interval CT imaging is required to monitor the aorta. Echocardiograms are required to monitor the competence of the aortic valve if affected during the initial presentation.

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