Acute Aortic Syndrome

Definition

Acute aortic syndrome is the clinical umbrella for the life-threatening conditions in which the integrity of the aortic wall is breached — classic aortic dissection, intramural haematoma and penetrating aortic ulcer, and, in the four-item formulation, incomplete dissection. They are grouped because they present identically (abrupt severe aortic pain), are diagnosed by the same imaging, and can convert into one another. The definition is of a syndrome, not a diagnosis: naming the constituent changes the treatment. (sources/AD-JACC-2021, rating: high)

Of the constituents, dissection dominates: it is the commonest, the one with an operation defined for it, and the one in which blood-pressure and heart-rate control in the first hour does more for survival than anything done afterwards.

Key Concepts

The constituents

• The three-item and four-item definitions disagree. Both major guidelines describe dissection, intramural haematoma and penetrating ulcer; the JACC review adds incomplete dissection, arguing it is commonly missed and represents roughly 5% of cases. (sources/AD-JACC-2021; sources/AD-AHA-2022)
• Intramural haematoma may simply be dissection with a thrombosed false lumen. The vasa vasorum model is the textbook account, but tears found at surgery that imaging had missed argue for a single mechanism. The practical consequence is that an "IMH" with an ulcer-like projection is treated as a dissection. (sources/AD-JACC-2021)
• The entities can coexist or follow one another — synchronous in different segments or metachronous over years — and any of them can rupture, most often in the first week.

Classification by segment, and its limits

• Stanford A involves the ascending aorta whatever else is involved; Stanford B spares it. This remains the operative distinction: A goes to surgery, B is medical unless complicated. DeBakey adds nothing to that decision and is now largely historical.
• Non-A non-B involves the arch without the ascending aorta — 7–11% of dissections, requiring more invasive treatment than type B and carrying a retrograde type A risk of up to 26% after TEVAR. Frozen elephant trunk is the effective operation, not TEVAR. (sources/AD-EHJ-2023, rating: high)
• The TEM classification adds entry location (E0 not seen, E1 ascending, E2 arch, E3 descending) and malperfusion (M0–M3, + clinical/− radiological). It exists because the Stanford letter alone does not predict which operation is needed: an arch entry with visceral malperfusion will not be fixed by ascending replacement.
• Entry at the lesser curvature of the arch propagates retrogradely to type A, because the supra-aortic vessels at the greater curvature are an anatomical barrier. An entry within 2 cm of the left subclavian, or a proximal communication >10 mm, predicts a complicated course in type B.
• The Society for Vascular Surgery/Society of Thoracic Surgeons proposal to call any dissection with an entry distal to the innominate a "type B" is rejected by the JACC authors, on the grounds that it understates the prognostic weight of ascending involvement.

Recognition and diagnosis — a three-step algorithm

• Suspect it with chest, back or abdominal pain together with unequal pulses — which may be absent — or acute aortic regurgitation.
• Step 1, pretest probability: risk conditions (Marfan or connective tissue disease, family history, known aortic valve disease, recent aortic manipulation, known thoracic aneurysm), pain characteristics (abrupt, severe, tearing or ripping), and examination findings (pulse deficit or interarm difference, focal neurological deficit, new aortic regurgitation murmur, hypotension). One point per category gives a 0–3 score.
• Step 2, the alerting triad: in a patient with aortic pain, a normal ECG plus a normal troponin plus a raised D-dimer points to acute aortic syndrome and away from acute coronary syndrome. D-dimer is highly sensitive; a value above 1,600 ng/mL raises the likelihood substantially. A normal chest radiograph is common and excludes nothing.
• Step 3, imaging: ECG-gated CT from neck to pelvis is first-line, with and without contrast, in all patients with a score ≥1 and a raised D-dimer. Focused bedside TTE helps assess effusion, regurgitation and ventricular function but a normal TTE does not exclude the diagnosis. TEE and MRI are reasonable alternatives for initial imaging. Aortography is now rarely needed. (sources/AD-AHA-2022, rating: very high)
• Troponin positivity does not exclude dissection. It can rise from coronary ostial involvement or acute regurgitation, and must not delay imaging when suspicion is high. An abnormal ECG, including ST elevation from coronary malperfusion, carries the same warning. Acute coronary syndrome is the commonest misdiagnosis, and thrombolysis in unrecognised dissection is lethal.
• High-risk conditions are incompletely captured. Hypertension — present in 86% of people who later dissect — is absent from the ADD-RS, and a score of 0 does not exclude the diagnosis. (sources/AD-JACC-2021)

Imaging mimics

Medical therapy — identical for every constituent

• Targets: systolic pressure 100–120 mmHg — or <120 mmHg with the lowest pressure that maintains end-organ perfusion — and heart rate ≤60/min. Managed in an ICU with an arterial line and continuous ECG, started before confirmatory imaging returns. (sources/AD-PAD-ESC-2024, rating: very high)
• Intravenous beta-blockade first (labetalol or esmolol). A non-dihydropyridine calcium channel blocker substitutes where beta-blockade is contraindicated; vasodilators are added only after rate control, because reflex tachycardia increases dP/dt and propagates the tear.
• Raise the target in spinal cord ischaemia or concomitant brain injury — a specific exception the ESC guideline writes into the same recommendation.
• Doses (Hospital Authority protocol). Labetalol 20 mg IV, then 20–80 mg every 10 minutes to a maximum total of 300 mg; maintenance 0.5–2 mg/min in D5, titrated up to 10 mg/min in some patients. Sodium nitroprusside 0.25–0.5 µg/kg/min, increased every 5 minutes by 0.5 µg/kg/min, to a maximum of 10 µg/kg/min; limit to <3 µg/kg/min if eGFR <30 mL/min/1.73 m², protect from light, discard after 12 hours. (sources/Handbook-HA-2024, rating: high)
• Nitroprusside must not be used while the heart rate is uncontrolled. Vasodilatation provokes reflex tachycardia, which increases the rate of rise of aortic pressure (dP/dt) — the force that propagates the dissection. This sequencing rule is the pharmacological core of the section.
• Hydralazine and diazoxide are actively avoided, for the same reflex-tachycardia reason. Where beta-blockers are contraindicated (e.g. COAD), diltiazem or verapamil are acceptable alternatives.
• Supportive care: nil by mouth, bed rest, IV access, oxygen to keep SaO₂ ≥90%, morphine 2–5 mg IV, arterial line sited on the arm with the higher pressure, and input/output charting.
• Actively look for the modes of death: cardiac tamponade, severe aortic regurgitation, massive haemorrhage, and myocardial, cerebral or renal ischaemia.
• Oral therapy is started as soon as the patient is stable, unless surgery is planned; beta-blockade continues lifelong where tolerated, with ACE-I or ARB added as needed.
• Pain control is a haemodynamic intervention, not a comfort measure.

Operating on the ascending aorta

• Emergency surgery for all type A dissections (Class I). Transfer to a high-volume centre where the patient is stable enough — outcomes track to individual surgeon volume, not institutional size. (sources/AD-AHA-2022)
• Aortic valve resuspension rather than replacement where the root is partially dissected but the leaflets are intact (I/B). Root replacement with a valved conduit where the root is destroyed, there is a root aneurysm, or there is a known genetic disorder (I/B).
• Open distal anastomosis is Class I — it improves survival and increases false lumen thrombosis. A simple supracoronary interposition graft is the operation to avoid.
• Hemiarch over total arch where there is no arch tear or arch aneurysm (I/B). Total arch and frozen elephant trunk are reserved for arch tears, arch dilatation or branch-vessel dissection.
• Immediate proximal repair for renal, mesenteric or limb malperfusion (I). For mesenteric malperfusion, immediate mesenteric revascularisation before or alongside aortic repair is reasonable (IIa) — the alternative to waiting.
• Axillary cannulation over femoral where feasible (IIa), to reduce stroke and retrograde malperfusion.

The Type B boundary

• Medical therapy for every uncomplicated type B, without exception (I). TEVAR is first-line for complicated disease — shock, rupture, malperfusion, rapid expansion, periaortic or mediastinal haematoma, refractory pain or refractory hypertension.
• TEVAR in the subacute phase (14–90 days) is now IIa for selected high-risk but uncomplicated cases, on the strength of INSTEAD and ADSORB: false lumen thrombosis 91% versus 19%, and better aortic-related survival at five years. (sources/AD-PAD-ESC-2024)
• Chronic type B carries its own numbers: intervene at a descending diameter ≥60 mm (I), or ≥55 mm in low procedural risk (IIa). These are not the same as aneurysm thresholds and apply only after dissection.
• Connective tissue disease argues against endovascular repair for elective indications, but not in an emergency.

Management of the other constituents

• Type A intramural haematoma: emergency surgery is Class I in both guidelines, with a "wait-and-see" option at Class IIb for selected higher-risk patients without high-risk imaging features.
• Type B intramural haematoma and PAU: medical therapy with imaging surveillance; TEVAR for complications or high-risk features. PAU with rupture, or ascending PAU with IMH, requires urgent repair; open repair for zones 0–1, either modality for zones 2 and beyond.
• Blunt traumatic aortic injury is graded 1–4 and managed by grade: non-operative for grade 1, intervention for grades 3–4, and TEVAR over open repair where anatomy allows.

Organisation of care

• Outcomes track to individual surgeon volume, not just institutional volume. Treating AAS at a high-volume centre with a low-volume surgeon is not the same as the reverse. (sources/AD-JACC-2021)
• The "aorta code" is a streamlined emergency pathway activated from any emergency department, with three jobs: raise recognition, speed transfer to an aorta centre, and activate a dedicated aortic surgeon.
• Annual volume of at least 30–40 aortic procedures is the ACC/AHA working threshold for a referral centre.
• AAS is a lifelong condition. Surveillance imaging continues indefinitely, because the remaining aorta is diseased and can dilate, re-dissect or rupture.

Contradictions / Open Questions

• Three sources give three heart-rate targets, all at Class I. ESC 2024 sets ≤60/min; ACC/AHA 2022 sets 60–80/min; the Hong Kong protocol uses 60–70/min. None is Level A, and a patient at 58/min is simultaneously at target and below it. (sources/AD-PAD-ESC-2024; sources/AD-AHA-2022)
• The blood-pressure target is lower than in any other hypertensive emergency, and the override is stated without explanation. Dissection targets a systolic of 100–120 mmHg, whereas every other emergency permits a fall of only 25% in the first hour. The usual caution about over-rapid reduction — that autoregulation has not shifted and perfusion falls with it — is set aside here for a reason the handbook does not give. See concepts/Hypertensive-Crisis. (sources/Handbook-HA-2024)
• The targets carry no citation. 100–120 mmHg and a heart rate of 60–70/min are stated as protocol with no reference attached, and no ingested source tests either number against an alternative.
• Rate-before-pressure sequencing is physiologically sound and unevidenced here. The rule is universally taught, both guidelines enforce it, and no source in the wiki grades it.
• "Acute aortic syndrome" has no agreed membership. Three constituents or four, depending on whether incomplete dissection counts; neither guideline uses the term. The wiki keeps both vocabularies and flags where they diverge.
• The conservative option in type A IMH is Class IIb in both guidelines but is routine practice in Asia, where guidelines have long accepted medical therapy with timely operation. The disagreement is regional and unresolved by evidence.
• The Type B boundary has moved without a trial of the question people ask. INSTEAD and ADSORB randomised TEVAR added to medical therapy in stable patients and showed remodelling and aortic-related survival; they did not compare intervention against a watch-and-wait strategy, so "operate on the high-risk uncomplicated patient at 14–90 days" remains an extrapolation.
• D-dimer's negative predictive value is doing more work than its evidence base supports. It is described as consistently ruling out the diagnosis, yet it cannot distinguish AAS from pulmonary embolism, and the rule-out is confined to low pretest probability.
• No trial compares immediate surgery with a delayed or conservative strategy in stable type A. Operative mortality ranges from 5% to 75% according to preoperative condition, so the population in which surgery is unambiguously right is narrower than "all type A".
• The endovascular type A devices have not been tested clinically. The Endo-Bentall conduit is anatomically feasible in about two-thirds of patients, but no device has been implanted in a trial.
• The AAS "type B" redefinition proposed by SVS/STS is a live dispute, with the JACC authors explicitly dissenting. Whether entry-based classification will displace segment-based classification is open.
• No trial has compared a diagnostic algorithm against standard care for AAS; the three-step proposal is explicitly unvalidated.

Connections

• Related to concepts/Thoracic-Aortic-Aneurysm — the substrate from which most AAS arises, and the reason most dissections occur below 55 mm
• Related to entities/Marfan-Syndrome and entities/Bicuspid-Aortic-Valve — the aortopathies that predispose to dissection
• Related to concepts/Heritable-Thoracic-Aortic-Disease — the populations in whom dissection happens at smaller diameters
• Related to concepts/Aortic-Regurgitation — acute AR is both a complication and a diagnostic clue
• Related to concepts/Cardiac-Tamponade — retrograde rupture into the pericardium produces tamponade and is a principal mode of death
• Related to concepts/Hypertensive-Crisis — dissection is the compelling indication that overrides the usual 25% first-hour rule
• Related to entities/Hypertension — chronic control is the mainstay of late survival after repair
• Related to concepts/Cardiogenic-Shock — shock in type B is an indication to operate, not a reason to delay
• Related to entities/Acute-Coronary-Syndrome — the misdiagnosis that makes thrombolysis lethal, and the reason for imaging before reperfusion

Sources

• sources/AD-JACC-2021
• sources/AD-EHJ-2023
• sources/AD-AHA-2022
• sources/AD-PAD-ESC-2024
• sources/Handbook-HA-2024