Immediate Management of Type A and Type B Aortic Dissection

Definition and Pathophysiology

Aortic dissection is a major form of acute aortic syndrome (AAS), alongside intramural haematoma, penetrating atherosclerotic ulcer, aortic pseudoaneurysm and traumatic aortic injury. In classic dissection, an intimal tear permits blood to enter the diseased aortic media. Blood then propagates along the wall, creating a true lumen and a false lumen separated by an intimal flap. Propagation may be antegrade or, less commonly, retrograde. Distal re-entry tears may allow blood to return to the true lumen, whereas disruption of the adventitia can result in rupture.

An alternative proposed mechanism is primary rupture of the vasa vasorum, followed by disruption of the intima. Intramural haematoma differs from classic dissection because haemorrhage occurs within the media without imaging evidence of an intimal tear or flap.

AAS is classified anatomically according to involvement of the ascending aorta:

• Stanford type A: involves the ascending aorta, with or without extension into the arch or descending aorta.

• Stanford type B: does not involve the ascending aorta and includes dissections involving the arch or descending aorta.

In the DeBakey system:

• Type I: originates in the ascending aorta and extends through the arch, usually into the descending aorta.

• Type II: is confined to the ascending aorta.

• Type III: originates in the descending aorta, usually just distal to the left subclavian artery.

• Type IIIa: remains confined to the descending thoracic aorta.

• Type IIIb: extends below the diaphragm.

The temporal classification is also clinically relevant:

• Hyperacute: less than 24 hours from symptom onset.

• Acute: 1–14 days.

• Subacute: 15–90 days.

• Chronic: more than 90 days.

The central clinical danger is progressive aortic wall disruption, rupture and compromise of branch vessels. Type A disease may cause cardiac tamponade, severe acute aortic regurgitation, coronary malperfusion, myocardial ischaemia, heart failure, shock and cerebral or visceral malperfusion. Type B disease may produce rupture, renal, mesenteric or limb malperfusion, spinal cord ischaemia, paraplegia or paraparesis, rapid aortic expansion, refractory pain and hypertension despite treatment.

A related entity is non-A non-B dissection, which involves the arch without involvement of the ascending aorta or represents retrograde extension from the descending aorta into the arch that stops before reaching the ascending aorta. Conservative treatment in this group is associated with high mortality when malperfusion or rupture develops; surgery or endovascular treatment is therefore generally favoured within 14 days of symptom onset in the source material.

Clinical Presentation and Symptoms

Aortic dissection is an uncommon cause of acute chest pain but carries a particularly high mortality when diagnosis is delayed. The typical presentation is sudden-onset, severe chest, back or abdominal pain. Pain may be described as ripping, tearing, sharp or stabbing. Its location and radiation may reflect the segment of aorta involved, although the source material does not provide a detailed symptom-to-anatomy correlation.

Pain may be absent, particularly in iatrogenic aortic injury. Iatrogenic lesions commonly follow cardiac surgery, coronary angiography or other invasive procedures, and affected patients may be relatively painless compared with those with spontaneous dissection.

Clinical manifestations may result from rupture, aortic valve involvement, coronary compromise or malperfusion. Important presentations include:

• Hypotension or shock

• Acute severe aortic regurgitation with heart failure

• Cardiac tamponade from haemopericardium

• Myocardial ischaemia from coronary ostial compromise

• Focal neurological deficits or non-haemorrhagic stroke

• Renal, mesenteric or lower-limb ischaemia

• Paraplegia or paraparesis

• Persistent or recurrent pain

• Hypertension that remains uncontrolled despite optimal therapy

Acute type A dissection has a particularly rapid early mortality. Medical treatment alone is associated with a death rate of approximately 0.5% per hour in the early period, with mortality reported at roughly 20% by 24 hours and 30% by 48 hours in historical descriptions. The risk is especially high when tamponade, coronary involvement, malperfusion or shock is present.

Evaluation and Physical Examination

Evaluation should begin with bedside assessment of the probability of AAS while immediate haemodynamic treatment is initiated. The Aortic Dissection Detection Risk Score incorporates three domains:

High-risk conditions

High-risk pain features

High-risk examination features

A score of 0 represents low risk, 1 intermediate risk and 2–3 high risk. Two or more high-risk features strongly support the possibility of dissection. Patients with high-risk presentations require expedited imaging and urgent surgical consultation. Even lower-risk patients require aortic imaging when no alternative diagnosis is established.

The physical examination should specifically assess:

• Blood pressure in both arms when feasible

• Peripheral pulses and evidence of pulse deficit

• Signs of shock or impaired perfusion

• Cardiac murmurs, particularly a murmur of aortic regurgitation

• Signs of heart failure

• Pericardial tamponade

• Focal neurological abnormalities

• Features of limb, renal or mesenteric malperfusion

A normal examination does not exclude dissection. Likewise, the absence of typical pain does not reliably exclude the diagnosis, particularly in iatrogenic disease.

Diagnostic Strategy

Immediate Stabilisation During Diagnostic Evaluation

Diagnostic assessment and initial treatment proceed concurrently. Patients should receive immediate pain control and reduction of aortic wall stress while definitive imaging and surgical assessment are arranged. Diagnostic testing should not delay imaging in patients with a high probability of dissection.

Routine chest radiography and ECG are useful in evaluating alternative causes of chest pain, but normal results do not exclude AAS and should not postpone definitive investigation.

Computed Tomography

ECG-gated cardiovascular computed tomography from the neck to the pelvis is the preferred confirmatory test when AAS is suspected. It provides information on:

• Presence or absence of dissection

• Ascending-aortic involvement

• Entry-tear location

• Proximal and distal extent

• True- and false-lumen anatomy

• Branch-vessel involvement

• Malperfusion

• Rupture or periaortic complications

The source material reports sensitivity of 100% and specificity of 98% for this approach. ECG gating helps reduce motion artefact, particularly around the ascending aorta, which can otherwise mimic or obscure a dissection flap.

When acute coronary syndrome or pulmonary embolism remains in the differential diagnosis, a triple-rule-out ECG-gated CT protocol may be used. However, this approach exposes the patient to greater contrast and radiation doses, may be less accurate for AAS and does not eliminate the need for additional imaging.

Transoesophageal Echocardiography

Transoesophageal echocardiography is an important alternative when CT is unavailable or the patient is haemodynamically unstable. It is also valuable before, during and after surgery to assess the aortic anatomy and detect operative or postoperative complications.

Transthoracic Echocardiography

Focused transthoracic echocardiography can be performed rapidly at the bedside. It may identify:

• Pericardial effusion or haemopericardium

• Aortic regurgitation

• Regional wall-motion abnormalities

• Aortic dilatation

• Occasionally, a dissection flap, particularly with contrast enhancement

TTE may detect type A dissection with sensitivity as high as 85%–90%, but it is substantially less sensitive for type B disease. A negative study therefore does not exclude AAS.

Cardiovascular Magnetic Resonance

Cardiovascular magnetic resonance provides good diagnostic accuracy but is less frequently used in the acute setting. Limitations include reduced availability, longer examination time and dependence on patient cooperation.

Electrocardiography and Chest Radiography

The source material supports obtaining ECG and chest radiography in patients with chest pain to investigate alternative diagnoses. It does not provide a characteristic ECG pattern or a sufficiently reliable radiographic sign to diagnose or exclude aortic dissection. Their principal role is complementary; neither should delay definitive aortic imaging when clinical suspicion is significant.

Biomarkers and Laboratory Findings

Laboratory testing should be obtained as part of the initial assessment, but results should not delay imaging when the likelihood of AAS is high.

The most commonly described laboratory abnormality is an elevated D-dimer concentration. This finding is nonspecific because D-dimer may also rise in pulmonary embolism, infection and other conditions. A D-dimer level below 500 ng/mL makes AAS unlikely in the appropriate low-risk clinical setting. D-dimer cannot exclude dissection in patients with a higher pre-test probability.

Integration of D-dimer with the Aortic Dissection Detection Risk Score may help exclude dissection in patients with very low clinical suspicion, particularly those with an ADD score of 0 or 1. It should not replace definitive imaging in patients with high-risk clinical features.

Immediate Medical Management

All patients with suspected or confirmed AAS require immediate medical treatment while the need for surgery or endovascular intervention is determined. The initial objectives are to reduce aortic wall stress, limit propagation and lower the risk of rupture.

Haemodynamic Targets

The principal acute targets are:

• Systolic blood pressure below 120 mmHg

• Heart rate ≤60 beats per minute

These targets are intended to reduce pulse pressure and the rate of rise in left-ventricular contraction force, thereby reducing stress on the dissected aortic wall. In patients with malperfusion, a higher blood pressure may be tolerated temporarily when necessary to maintain perfusion to threatened organs.

Beta-Blockade

Intravenous beta-blockade is the preferred initial pharmacological strategy. Labetalol is generally favoured because it combines alpha- and beta-adrenergic blockade. Esmolol is an alternative with an ultra-short duration of action that permits rapid titration, making it particularly suitable when frequent adjustment is required.

Beta-blockade should precede vasodilator therapy. This sequence is intended to avoid reflex tachycardia and a consequent increase in aortic wall stress.

Alternative Rate Control

When beta-blockers are contraindicated, intravenous non-dihydropyridine calcium-channel blockers may be used for heart-rate control. The source material does not specify individual agents or doses for this indication.

Additional Blood-Pressure Reduction

If the blood-pressure target is not achieved after rate control, intravenous vasodilators may be added. Options described include:

• Nitrates

• Dihydropyridine calcium-channel blockers, such as nicardipine

These agents should be administered concomitantly with a rate-controlling drug rather than used alone.

Analgesia

Effective analgesia is an integral component of acute management because pain can impede haemodynamic control. Intravenous morphine may be titrated cautiously to relieve pain. The source material does not provide a dose.

Monitoring and Location of Care

Early invasive arterial blood-pressure monitoring is considered mandatory in the source material. Intensive-care admission is advisable, with continuous ECG surveillance and monitoring of urine output. Once haemodynamic targets are achieved and gastrointestinal transit is normal, intravenous treatment can be transitioned progressively to oral antihypertensive therapy.

Management should be centralised in experienced centres with dedicated aortic teams whenever possible.

Type A Aortic Dissection

Rationale for Emergency Surgery

Acute type A aortic dissection requires emergency surgical evaluation and immediate operative management because of the risks of rupture, tamponade, acute severe aortic regurgitation, coronary ischaemia and malperfusion. Medical treatment alone has substantially higher mortality than surgery.

Emergency surgical consultation is recommended for all patients with suspected or confirmed type A disease. Patients stable enough to travel may reasonably be transferred from a low-volume facility to a high-volume aortic centre, where survival is improved. Age alone should not be regarded as an exclusion criterion for surgery; the source material reports lower mortality with surgery than conservative treatment even among very elderly patients.

Non-haemorrhagic stroke complicating acute type A dissection is not, by itself, a reason to withhold operation. Surgical treatment is considered reasonable over medical therapy to reduce mortality and improve neurological outcomes.

Operative Considerations

The source material emphasises several anatomical and functional decisions:

• The aortic valve is often structurally normal despite acute aortic regurgitation and may therefore be preserved.

• Valve replacement may be required when pre-existing structural valve disease is present.

• Aortic-root replacement depends on tears involving the sinuses, extensive dissection of the sinuses or coronary ostia, or substantial root dilatation.

• Ascending-aortic or hemi-arch replacement may close the proximal entry site but leaves more distal diseased aorta untreated.

• Extended repair, including frozen elephant trunk repair, may be considered when the primary tear is in the descending aorta and visceral or renal malperfusion is present, although technical complexity is greater.

In patients with cardiac arrest due to pericardial tamponade, emergency pericardial puncture may be considered as a temporary life-saving measure before transfer to the operating room.

Surgical Risk

Despite improvements in surgical and anaesthetic care, operative mortality and neurological complications remain substantial. Predictors of poor postoperative outcome include:

• Cardiogenic shock due to tamponade

• Coronary malperfusion

• Mesenteric, renal, lower-extremity or cerebral malperfusion

• Coma

• Significant comorbidity

The GERAADA score may be used in patients undergoing surgery to estimate 30-day mortality.

Type B Aortic Dissection

Type B dissection excludes the ascending aorta. Management is determined principally by whether the disease is uncomplicated or complicated and whether high-risk anatomical features are present.

Uncomplicated Acute Type B Dissection

Medical therapy is the recommended initial treatment for uncomplicated acute type B dissection. This consists of aggressive heart-rate and blood-pressure control, pain relief, close clinical observation and imaging surveillance.

Adherence is a major limitation of chronic medical treatment, with reported compliance below 50%. Adherence is more likely to improve when patients have undergone previous aortic surgery, have more severe hypertension or understand the disease process. Surveillance and education are therefore essential components of long-term care.

Complicated Acute Type B Dissection

Complications requiring intervention include:

• Aortic rupture

• Malperfusion

• Rapid aortic expansion

• Paraplegia or paraparesis

• Aortic haematoma

• Refractory pain

• Hypertension despite optimal therapy

Conservative treatment of complicated disease is associated with an approximately 50% mortality risk in the source material.

When anatomy is suitable, endovascular therapy—principally thoracic endovascular aortic repair—is the preferred treatment for complicated type B dissection. For rupture, endovascular stent-graft placement is recommended over open repair when anatomy is appropriate. For other complications, an endovascular approach is considered reasonable rather than open surgery.

Open surgery is reserved primarily for patients with unsuitable anatomy for endovascular repair. Fenestration may be considered as a last-resort strategy, and in selected patients correction of side-branch compression before proximal sealing may be appropriate.

High-Risk Uncomplicated Type B Dissection

Endovascular management may be considered in patients who are clinically uncomplicated but have high-risk anatomical features. Features associated with a more adverse course include:

• Primary entry tear larger than 10 mm, particularly when located on the inner aortic curvature

• Initial aortic diameter greater than 40 mm

• Initial false-lumen diameter greater than 20 mm

• Multiple or large communications between the true and false lumens

• Partial false-lumen thrombosis

• Stent-graft-induced new entry tear

The DISSECT system integrates the duration from symptom onset, intimal-tear location, aortic size, segmental extent, clinical complications and false-lumen thrombosis to support therapeutic decision-making.

Early intervention in otherwise uncomplicated acute or subacute type B dissection remains an area of debate. Available evidence in the source material indicates that early endovascular treatment may reduce later events and improve aortic remodelling compared with medical therapy alone, although the matter is not completely settled. Intervention may be considered within 90 days of symptom onset and may be safer during the subacute phase, after 14 days, but available data remain limited. Prophylactic TEVAR may be considered in suitable patients with high-risk features.

Endograft Planning

Accurate endograft sizing is essential for TEVAR. Aortic dimensions may fluctuate during haemorrhagic shock and subsequent resuscitation, making admission CT measurements potentially imprecise despite appropriate centreline assessment.

Real-time imaging, particularly intravascular ultrasound, may improve sizing accuracy, especially in hypovolaemic patients. The roles of intravascular ultrasound, transoesophageal echocardiography and three-dimensional CT in optimising sizing and improving long-term outcomes remain incompletely defined.

Non-Aortic and Special Anatomical Patterns

Non-A Non-B Dissection

Non-A non-B dissection involves the aortic arch without ascending-aortic involvement or represents a retrograde process from the descending aorta that extends into the arch but not the ascending aorta. Conservative treatment has been associated with high mortality when malperfusion or rupture occurs. Accordingly, surgery or endovascular treatment is favoured within 14 days of symptom onset. In complicated disease with an arch tear, frozen elephant trunk repair may be considered; when feasible, stent-graft coverage of the primary tear is an alternative.

Iatrogenic Dissection

Iatrogenic aortic injury may follow cardiac surgery, coronary angiography or other invasive procedures. Risk factors include advanced age, cardiovascular risk factors, atherosclerosis, aortic aneurysm and peripheral arterial disease. These patients are often less likely to report chest or back pain.

Management depends on the lesion, its location and the presence of coronary involvement. In selected small type A iatrogenic dissections with preserved coronary flow, conservative treatment may produce good results. Within the Dunning classification, the available data support an evolution-based conservative approach for type 1 and 2 lesions, whereas surgery is favoured for type 3 lesions. If the coronary artery is involved, stent implantation to seal the flap may be considered.

Pregnancy

The management of type A dissection during pregnancy is trimester-dependent:

• During the first or second trimester, urgent aortic surgery with fetal monitoring is recommended.

• During the third trimester, urgent caesarean delivery followed immediately by aortic surgery is recommended.

• Type B dissection during pregnancy should generally be treated medically unless endovascular or surgical intervention is required for acute complications.

• Prophylactic aortic surgery may be considered for progressive aortic dilatation during pregnancy, depending on individual circumstances.

Intramural Haematoma as a Related Acute Aortic Syndrome

Although distinct from classic dissection, intramural haematoma follows similar initial principles: immediate pain relief and blood-pressure control.

Type A Intramural Haematoma

Emergency or urgent surgery is recommended for type A intramural haematoma. Prompt open repair is also recommended in uncomplicated cases. In selected patients with increased operative risk, uncomplicated disease and no high-risk imaging features, an initial expectant strategy may be considered in an experienced reference centre.

Type B Intramural Haematoma

Uncomplicated type B intramural haematoma should initially be managed medically with close clinical and imaging surveillance. Endovascular intervention may be considered when high-risk imaging features are present.

Complicated type B intramural haematoma warrants consideration of TEVAR. Open repair remains an alternative when anatomy is unsuitable for endovascular treatment.

Intimal disruption may be identified in type B intramural haematoma. Small disruptions measuring 3 mm or less are generally not associated with acute aortic events, whereas some evolve into larger focal intimal disruptions with prognostic implications. All patients with intimal disruption require close imaging follow-up. In the acute phase, focal disruptions have a poor prognosis because of rupture risk and should be treated early and invasively, particularly when they are at least 10 mm long and 5 mm deep.

Guideline-Based Management Summary

Prognosis and Follow-Up

AAS has high early mortality, particularly when the ascending aorta is involved. Prognosis is strongly influenced by anatomical type, treatment strategy, comorbidities and complications. Tamponade, coronary involvement, malperfusion, rupture, shock and coma are associated with increased mortality.

Emergency surgery improves survival in type A dissection compared with medical treatment alone, and long-term outcomes also favour surgical treatment. High-volume centres have lower mortality, supporting transfer of stable patients when necessary.

For type B dissection, uncomplicated disease is generally managed medically initially, whereas complicated disease requires intervention. Endovascular treatment has largely replaced open repair for complicated type B disease because of more favourable morbidity and mortality outcomes when anatomy is suitable. In selected uncomplicated patients with high-risk anatomy, early TEVAR may reduce later aortic events and improve remodelling, although the optimal timing and broad application of prophylactic treatment remain unsettled.

Long-term care requires:

• Continued blood-pressure and heart-rate control

• Transition from intravenous to oral antihypertensive therapy once stable

• Assessment and reinforcement of treatment adherence

• Education regarding the disease process and warning symptoms

• Ongoing clinical surveillance

• Serial imaging, particularly after type B dissection, intramural haematoma or focal intimal disruption

• Follow-up in an experienced multidisciplinary aortic service

Chronic type B dissection is defined as disease more than three months after symptom onset and also includes residual type B dissection after type A repair. Aortic complications, especially aneurysmal degeneration, occur in up to half of these patients. New symptoms, rapid expansion, malperfusion or rupture are indications for intervention. In asymptomatic patients, aneurysmal dilatation is the principal risk factor for rupture; elective treatment is suggested when the aortic diameter reaches approximately 50–55 mm, with lower thresholds considered in heritable thoracic aortic disease.