Acute aortic dissection

Background

Aortic dissection is the separation of the aorta into two areas of blood flow, - the true and false lumen held apart by an arterial flap resulting from the tear. In the false lumen, interrupted blood flow can compromise blood flow in the true lumen due to compression, and when the two lumens communicate due to re-entry, blood flow is present in both but can cause aneurysmal degeneration. Rupture, extensive hemorrhage, aortic valve incompetence, coronary dissection, cardiac tamponade, stroke and malperfusion are likely complications of acute aortic dissection. Surgery will usually involve placing a Dacron graft; medication will be a combination of nitrates and beta-blockers.
Symptoms can vary according to where the tear is localised, and where it migrates to. Tear in the ascending aorta would bring on pain in the anterior, midline chest. A tear in the aortic arch might bring on pain in the jaw or neck. Intra scapular back and abdominal pain are more common with the descending aorta. 
Intramural hematoma, symptomatic aortic ulcer, and symptomatic aneurysm syndrome together with acute aortic dissection traditionally make up the wider spectrum of aortic disease. However, intramural hematoma and hemorrhage, and aortic ulcers can be seen as signs of evolving dissections according to the 2001 ESC guidelines on aortic dissection, which offered 5 classes of aortic dissection according to that staging of the disease: 1) classical (intimal flap between true and false lumen), 2) medial disruption (with formation of intramural haemotoma), 3) subtle dissection (without haematoma, eccentric bulge at tear site) 4) rupture (leading to aortic ulceration, penetrating aortic atherosclerotic ulcer with surrounding haemoatoma usually sub adventitial), or 5) iatrogenic and traumatic.
With onset of symptoms as reference point, aortic dissection is acute within two weeks; sub acute from 2 to 6 weeks and it is chronic beyond 6 weeks. 
Previous to the ESC's disease staging, two anatomic systems widely served to describe it: 1) The Stanford system involving the ascending artery (type A) or not (type B) and 2) the DeBakey system which refers to the original site of intimal tear: I - ascending aorta propagating to aortic arch and II - ascending arch only and III - descending aorta and extending distally or proximally
A third, descriptive classification refers to proximal aortic dissection: (Stanford type A or DeBakey Type I and II 2) or distal: Stanford Type B or DeBakey Type III. (Fig. 1)
Cardiovascular morbidity and mortality associated with this condition are high. Hospital-based mortality rates are approximately 30%. Patients with type A aortic dissection who undergo surgical treatment have a 30% mortality rate; patients who receive medical treatment have a mortality rate of 60%.   The annual incidence of aortic dissection - 5 to 30 per million is low compared to that of myocardial infarction which is 4,000 per million. 

I - Presentation: Pain, heart sounds and other symptoms

A sudden, painful, ripping sensation in the chest or back is the usual complaint. The severe, sharp or ‘tearing’ back pain follows a tear in the aortic intima. Anterior chest pain in dissection is related to the ascending aortic artery distal to the left subclavian artery. (1)
Painless dissection is rare. Only 63 patients in the International Registry of Acute Aortic Dissection experienced no pain, which represent 6.3% of patients of the 977 patients of the Registry. (2)
Diastolic murmur from aortic regurgitation and neurological deficits can occur. Distant heart sounds secondary to pericardial effusion may be noted if the dissection causes bleeding into the pericardium. Tamponade symptoms and signs may be seen in extreme cases.
Symptoms suggestive of congestive heart failure, stroke, shock or loss of distal pulse can be noted - most often in the older population.

II - Diagnostic tools: determination of tear and acute management

In ascending aortic dissection in particular, early diagnosis is critical: prompt intervention can reverse the mortality rate, which is estimated to increase by 1% to 1.4% in the first 48 hours.

1. Classic type A dissection (involving the ascending aorta) needs rapid surgical intervention, whereas classic type B dissection (not involving the ascending aorta) requires medical management only - unless complications render surgery necessary.
2. Transthoracic echo (TTE): A bedside transthoracic echo is an invaluable tool. It provides information on the function of the heart, and the possible presence of complications, such as pericardial effusion and mediastinal hematoma. Flap determination by echocardiogram can be challenging and is dependent on operator experience. Using two-dimensional echocardiography, the intimal flap, point of entry and possible re-entry, and true and false lumens can be located. TTE is most useful in ascending aortic dissections. However, quality of image won't be enough for decision-making. 
3. Transesophageal echo (TEE) can also be performed in the emergency room for patients who present with acute chest pain and/or are hemodynamically unstable. It is the best technique to evaluate the morphology and the function of the aortic valve. Transesophageal echo (TEE) is more accurate than transthoracic echo (TTE) and is as sensitive and specific as CT scanning and magnetic resonance imaging. It will be able to assess the flow or no-flow in the false lumen.  
4. Computed tomography is the most frequently performed first imaging modality, with near perfect sensitivity and specificity, however it will not evaluate aortic valve insufficiency adequately.  Computed tomography (CT) scan with contrast is reserved for situations in which both TEE and MRI are unavailable or contraindicated. 
5. Magnetic resonance imaging (MRI) also has near perfect sensitivity and specificity, and is especially suited for evaluation of chronic dissection - however it will not detect intimal tear (limited dissection) without hematoma and eccentric aortic bulge, which can only be diagnosed with aortography. 
6. Aortography is used when ascending aortic dissection is strongly suspected and noninvasive tests are unavailable or inconclusive. It is an invasive procedure and requires the use of contrast. Its use is limited in critically ill and unstable patients. Nevertheless, it remains the method of choice in diagnosing intimal tear without hematoma and eccentric aortic bulge. 
7. Coronary angiography is generally safe in stable patients, although some retrospective data suggest no in-hospital benefit from coronary angiography.

A recent meta-analysis by Shiga et al (8) reviewed published studies of the diagnosis of aortic dissection by TEE, helical CT and MRI and observed that these tests have equal and reliable diagnostic value (9). 

Fig. 1 Common classification systems of aortic dissections: Stanford and DeBackey.

Patients with suspected aortic dissection should be admitted to an intensive care unit as rapidly as possible for: 

1. Diagnosis confirmation
2. Control of pain
3. Systolic blood pressure reduction to between 100 mmHg and 120 mmHg
4. Intubation if the patient is hemodynamically unstable 
5. Surgery as an emergency when the ascending aorta (type A) is involved or if there is progression or continued hemorrhage into the pleural or retroperitoneal space.
6. Medical treatment for dissections confined to the descending or distal aorta (type B): a combination of nitrates and β-blockers. 

Predisposing conditions are: 

1. Systemic hypertension is the most important predisposing factor for acute aortic dissection - it has been reported in 70% of the patients with aortic dissection. 
2. Weakening of the aortic wall: All mechanisms that weaken the aortic wall, the aortic lamina media in particular, lead to higher wall stress, which can induce aortic dilatation and aneurysm formation, eventually resulting in aortic dissection or rupture (10). Atherosclerosis is a big contributing factor.
3. Aortic aneurysms may manifest with symptoms late in their development. Progressive dilation of the ascending aneurysm may cause dilation of the aortic annulus, with resultant aortic regurgitation. This represents a significant volume overload on the left ventricle, resulting in progressive left ventricular dilation and failure. Compression of the adjacent structure may lead to chronic chest pain.
4. Other factors such as disorders of collagen, Marfan syndrome, Ehlers-Danlos syndrome, bicuspid aortic valve, aortic coarctation, Turner syndrome, coronary artery bypass graft surgery, previous aortic valve replacement, crack cocaine use, strenuous resistance training and trauma are others.
5. High-speed accidents, aortic chest trauma, interventional procedure can count for a very small percentage of aortic dissection.

Differential diagnosis should include myocardial infarction and ischemia, pericarditis, pulmonary embolus, aortic regurgitation without dissection, aortic aneurysm without dissection, musculoskeletal pain, mediastinal tumors, pleuritis, cholecystitis, atherosclerotic or cholesterol embolism, peptic ulcer disease or perforating ulcer and acute pancreatitis. 
Follow-up will aim to minimise aortic stress:

1. Oral beta-blocker: All patients should receive lifelong therapy with an oral beta-blocker to reduce a) systemic blood pressure and b) the rate of rise in systolic pressure. Both effects of will minimise aortic wall stress. 
2. Avoid strenuous physical activity
3. Thoracic magnetic resonance: A baseline thoracic magnetic resonance scan before discharge, with serial follow-up examinations at three, six and 12 months, even if the patient remains asymptomatic, is recommended.

Type A aortic dissection in a non-pregnant woman, 37 years of age. 

Approximately half of all observed cases of aortic dissections in women under 45 years of age have been reported to be related to pregnancy - pregnancy is considered to be an independent risk factor for aortic dissection. Acute aortic dissection represents a rare pathology in women younger than 45 years of age; however, it is associated with a high rate of sudden death. In pregnancy, acute aortic dissection has an overall incidence of 0.4 cases per 100,000 person years.
We present a case of type A aortic dissection diagnosed in a 37-year-old non-pregnant woman. We want to show that aortic dissection is diverse in its manifestations, and not uncommon or impossible in a young healthy and previously asymptomatic female.  
A 37 year old woman was admitted with complaints of acute onset, non-exertional, severe and stabbing lower chest and epigastric pain that lasted the previous hour and is increased with each movement and deep inspiration.
Nausea, one episode of vomiting and syncope were present at onset. There was no history of hypertension, diabetes or bronchial asthma in this mother of two children, the last of which was born 5 years prior. The patient had no known allergies. She is a nonsmoker and has no family history of congenital heart defects. 
On presentation the patient is afebrile with a temperature of 36.7°C, a blood pressure reading of 110/60 mmHg, a pulse rate of 50 beats/min and a respiratory rate of 18 breaths/min. The patient is alert and oriented. 
On physical examination, the patient' pupils are round, equal, and reactive to light and accommodation. There is no jugular venous distension or hepatojugular reflux. There are no carotid bruits. The chest wall is symmetric and there is no deviation of the trachea. There was good bilateral air entry with clear breath sounds. The point of maximal impulse is located in the left fifth intercostal space anterior axillary line. Heart sounds have a regular rate and rhythm, with a grade II/VI mid-systolic murmur located in aortic area. There are no audible gallop or clicks. Heart sounds were not muffled and there was no pulsus paradoxus. The second heart sound was physiologically split. The abdomen was obese with no visible pulsations. 
Bowel sounds were normoactive and there were no palpable masses; abdomen was soft and nontender. The patient's extremities were warm to the touch, with no pallor, finger clubbing or cyanosis. Pulses were symmetrical; there was neither radio femoral delay nor peripheral edema. There was no femoral bruit or focal neurological signs.
Due to the systolic murmur noted on physical examination, the patient was referred to a cardiologist for evaluation. On evaluation, a detailed history directed at symptoms and risk factors for aortic dissection was taken but was noncontributory. Chest X ray was reported normal by radiologist. An electrocardiogram and echocardiogram were ordered as preliminary tests along with D dimer and cardiac markers. 
The electrocardiogram showed a normal sinus rhythm with a rate of 50 beats/min (Fig. 2).

Fig. 2 ECG showing sinus bradycardia

The echocardiogram showed a dilated aortic root (5.3 cm) with intimal flap in the ascending aorta (Fig. 3).

Fig. 3 The intimal flap seen in echocardiogram

D dimer was elevated 1.68 mg/l (normal <0.50 mg/l). Cardiac markers were within normal range. 
With regard to risk factors, the patient had no previous cardiac catheterisation, intra-aortic balloon pump or any cardiac surgery such as valve replacement.
A diagnosis of acute aortic dissection was made and patient was immediately referred to the cardiovascular surgeon for further management. The patient was eventually taken up for emergency surgery and underwent a Bentall operation with valve replacement and aortic root replacement conduit and IABP and inotropic support post operatively. Patient was successfully weaned and recovered completely. 

III - Prevention

Preventive measures of before and after the events of aortic dissection are:

• Treatment of hypertension
• Elective aortic surgery in patients with dilated ascending aortas. Guidelines for timing of aortic root repair are based on clinical observations by experienced clinicians and surgeons, and consensus. One consensus is that surgery to prevent rupture or dissection of the ascending TAA should be recommended when the ascending aortic diameter reaches 5.5 cm for non-Marfan patients and 4.5 cm in Marfan patients.
• Marfan syndrome: reduced physical activity endocarditis prophylaxis, serial imaging of the aorta, beta-blocker medication for aortic protection and prophylactic replacement of the aortic root. Prophylaxis surgery: At least one criteria must be met among the following (11)
  
  • 1.Aortic root diameter: > 55 mm (50 mm according to other authors)> 50 mm (45 mm to 50 mm according to other authors) in patients at high risk for aortic complications
  • 2.Family history of aortic dissection.
  • 3.Aortic root: Growth of the aortic root of > 10 mm/year
  • 4.Aortic sinus: Dilation of the aortic sinus involving the ascending aorta > mild aortic regurgitation
  • 5.Severe mitral regurgitation
  • 6.Special patients: Patient scheduled to undergo major non cardiovascular surgery
  • 7.A woman planning a pregnancy
  • 8.Ratio of the diameters of the aortic root and the descending aorta > 2

Endovascular stent grafting

Open repair of aortic dissection is involves a median sternototomy and cardiopulmonary bypass offered only to candidates who will be able to withstand the stress of surgery. Perioperative death rates exceed 10%, a risk of paraplegia of 4% to 5%, and a long recovery from thoracotomy make this a weighty undertaking for surgeon and patient alike.
Endovascular stent grafting of aneurysmal disease processes of the thoracic aorta is feasible and relatively safe (12).
Surgical intervention may involve the placing of stents or grafts to the aorta but accurate assessment are essential first, as there may be entry, re-entry and multiple tears.

• Acute type A (types I and II) dissection
  Surgery aims to prevent aortic rupture, pericardial tamponade and to relieve aortic regurgitation. Implantation of a composite graft in the ascending aorta, with or without re-implantation of coronary arteries, is performed.

• Acute type B (type III) dissection - surgery is indicated for the following criteria: Persistent, recurrent chest pain, Aortic expansion, Periaortic hematoma, Mediastinal hematoma.

Guidance of aortic stent-graft implantation in type-B aortic dissection is improved by complimentary use of contrast fluoroscopy, multiplane TEE with Doppler flow interrogation, and IVUS. This imaging approach implies no additional risk and provides online visualisation. Nevertheless, pre interventional and post interventional computed tomography/magnetic resonance, as well as peri interventional ANGIO, will not be replaced. However, procedural complications with stent-graft implantation are likely to be avoided, because TEE and IVUS help navigate guide wires and catheters in the true lumen, which improves safety of stent-grafting and, thus, may eventually improve procedural outcomes.

Aortic aneurysm

Aortic aneurysm is usually a progressive disease that needs to be monitored closely or treated. As aneurysms grow in size, there is increased incidence of rupture, dissection and death. Ascending aortic aneurysms grow an average of 1 mm to 4 mm each year, but in patients with bicuspid aortic valves and Marfan syndrome, growth is more rapid.  
The cumulative risk of rupture was 20% after five years. Seventy-nine per cent of ruptures occurred in women (P=0.01). The five-year risk of rupture as a function of aneurysm size at recognition was 0% for aneurysms less than 4 cm in diameter, 16% for those between 4 cm and 5.9 cm, and 31% for aneurysms 6 cm or larger (13, 14, 15). Once ruptured, emergent repair is extremely challenging with an associated mortality in the mid 90% range. 
Overall survival for TAA has improved significantly in the past 15 years. Aortic rupture and older age were risk factors for operative mortality, but the only variable associated with long-term mortality was increasing age. The patients who underwent surgery had an actuarial survival at one, five and 10 years of 92%, 77% and 57%, respectively. 

Conclusions

A sharp, tearing or gripping possibly migrating pain, worst at onset rather than crescendo-like- eventually migrating, known aortic disease or inherited diseases, diagnostic murmur, a high pressure amplitude, neurological abnormalities, pulse deficits, a history of hypertension, radiography findings are elements that might warrant the high index of suspicion necessary for this serious condition. Because acute aortic dissection may occur anywhere along the aorta, manifestations are diverse.
An initial diagnosis by chest radiography showing mediastinal widening and EKG excluding another diagnosis on one hand and transesophageal echocardiography, computed tomography or magnetic resonance imaging, on the other will be required to confirm or rule out the diagnosis. 
Treatment will depend on type or class or stage of condition - necessitating surgery or not. Perhaps in the future, biomarkers for example might help with the diagnosis of this condition, but in the meantime, we need to be all the more alert, even in atypical cases and presentations.