11. Acute Aortic Syndromes (Dissection, IMH, PAU)

Quick Recap

Cardiovascular System, Protocol 12/12 — completing the Cardiovascular System.

1. Definition & Types

Acute aortic syndrome (AAS) encompasses three related entities:

• Classic aortic dissection: intimal tear allows blood into the media, propagating antegrade/retrograde to create a false lumen; re-entry tears may reconnect with the true lumen
• Intramural hematoma (IMH): 10-20% of AAS; hemorrhage within the aortic media WITHOUT a visible intimal tear or lumen communication; may show focal intimal defects, progress to classic dissection, form an aneurysm, or spontaneously resolve; managed the same as dissection by anatomic type (type A = surgery, type B = medical)
• Penetrating atherosclerotic aortic ulcer (PAU): atherosclerotic ulceration penetrating the intima/media, most common in descending/abdominal aorta, may form a pseudoaneurysm that dissects or ruptures

Incidence ~3-6 per 100,000/year; mortality up to 0.5-1% PER HOUR in the first several hours of untreated type A dissection — among the most time-critical diagnoses in critical care.

2. Classification

Anatomic (defines management pathway):

Ascending aorta involvement occurs ~2x more often than descending-only. Type A -> emergency surgery. Type B (uncomplicated, no high-risk features) -> initial medical management.

Temporal (IRAD classification, stratifies mortality risk by symptom duration): hyperacute (0-24h), acute (2-7 days), subacute (8-30 days), chronic (>30 days). Serious complications (rupture, branch vessel occlusion) are far more likely in the acute phase than the chronic phase.

3. Pathophysiology

Once dissection occurs, propagation of the tear is driven by shear stress, which is a function of dP/dt (rate of pressure rise) and mean arterial pressure — this is the direct physiologic rationale for beta-blocker-first therapy (Section 7): beta-blockade reduces dP/dt independent of its BP-lowering effect, while an isolated vasodilator (without beta-blockade) triggers reflex tachycardia that INCREASES dP/dt and can worsen propagation.

Malperfusion syndrome (branch vessel compromise from the dissection) occurs via two mechanisms: static obstruction (dissection flap extends directly into a branch vessel with false lumen thrombosis — fixed obstruction) or dynamic obstruction (the more common mechanism — the dissection flap intermittently prolapses over/blocks the branch vessel ostium, causing fluctuating perfusion). Recognizing which branch territory is affected (coronary -> MI-like presentation; carotid -> stroke/syncope; mesenteric -> abdominal pain/ischemia; renal -> AKI/renal hypertension; iliofemoral -> limb ischemia) is central to why dissection mimics so many other emergencies.

4. Risk Factors

5. Immediate Stabilization (ABCDE)

"Think Aorta" — unexplained acute chest, neck, or back pain and/or syncope should trigger active consideration, given AAS's ability to mimic MI, PE, heart failure, syncope, and limb ischemia.

Airway/Breathing: support per standard indications; be mindful that induction agents/positive pressure can affect hemodynamics in a patient who needs precise BP control.

Circulation — the defining, time-critical intervention:

• Immediate IV beta-blocker (unless contraindicated) BEFORE or simultaneous with diagnostic confirmation — do not wait for imaging to start beta-blockade if clinical suspicion is high
• Target: SBP <120 mmHg AND HR <60-70 bpm, titrated as low as possible without compromising end-organ perfusion — more aggressive than the generic hypertensive emergency target
• First-line: esmolol (bolus 250-500 mcg/kg, infusion 50-100 mcg/kg/min — short half-life allows rapid titration) or labetalol (bolus 20mg over 2min, then 20-80mg q10min to max 300mg, then infusion 0.5-2mg/min)
• If beta-blockers contraindicated: diltiazem (0.25mg/kg IV over 2min, then infusion 5-15mg/h)
• If SBP remains elevated despite adequate beta-blockade, ADD a vasodilator (nicardipine 5mg/h titrated by 2.5mg/h q5-15min to max 15mg/h; clevidipine 1-2mg/h up to 16-32mg/h; or sodium nitroprusside 0.3-0.5 mcg/kg/min, caution with thiocyanate toxicity)
• CRITICAL SEQUENCING RULE: NEVER start a vasodilator before beta-blockade is established — unopposed vasodilation triggers reflex tachycardia, increasing dP/dt and risking dissection propagation
• Opioids for pain control are an important adjunct — pain itself drives sympathetic tone and BP

Checklist:

6. Focused History / ADD-RS Risk Stratification

Aortic Dissection Detection Risk Score (ADD-RS): bedside tool scored 0-3 based on high-risk conditions (Marfan/HTAD, family history, known aortic valve disease, recent aortic manipulation, known thoracic aortic aneurysm), high-risk pain features (abrupt onset, severe intensity, ripping/tearing quality), and high-risk exam features (pulse deficit, SBP differential between limbs, focal neuro deficit with pain, new murmur of aortic insufficiency with pain, hypotension/shock). 0 = low risk, 1 = moderate risk, 2-3 = high risk/high pretest probability — guides the intensity of the imaging workup.

7. Examination + POCUS

BP differential between arms (>20mmHg), pulse deficits, new diastolic murmur (aortic insufficiency from annular involvement), focal neurologic deficits, signs of tamponade if proximal dissection ruptures into the pericardium (see Cardiac Tamponade protocol — aortic dissection with hemopericardium has special drainage considerations there), signs of malperfusion by territory (Section 3).

POCUS/TTE: can identify type A dissection with 85-90% sensitivity/93-96% specificity, but sensitivity for type B dissection is much lower — a normal TTE does NOT exclude dissection, especially type B. TEE (98-99% sens/95% spec) can be performed at bedside without contrast, excellent for aortic root/descending thoracic aorta/valve/pericardium, but requires esophageal intubation (hemodynamic effects) and experienced operators.

8. Differential Diagnosis

9. Investigations

• CXR: may show widened mediastinum, abnormal aortic contour, pleural effusion (hemothorax), or the "calcium sign" (intimal calcification displaced >10mm from the outer aortic wall). 20% of CXRs are normal in dissection — a normal CXR does NOT exclude the diagnosis.
• ECG: often nonspecific; may show ischemia/injury if a coronary artery is involved by the dissection (risk of the STEMI-mimicry trap above)
• D-dimer: typically markedly elevated in classic dissection; <500 ng/mL within 24h of symptom onset has ~95% negative predictive value — useful for ruling OUT dissection in lower-probability patients, but may NOT be elevated in IMH or PAU, so a normal D-dimer should not override high clinical suspicion for these variants
• Labs for complications: CBC, CMP, lactate, troponin, LDH, CK
• Definitive imaging comparison:

CT is the most commonly used first-line imaging modality given speed/availability; choice of imaging should be based on hemodynamic stability and operator/scanner availability — an unstable patient may go straight to bedside TEE rather than to a distant CT scanner.

10. Evidence-Based Management

Type A (Stanford A / DeBakey I-II): EMERGENCY SURGERY — medical therapy alone carries very high morbidity/mortality; do not delay surgical consultation/OR mobilization once type A is confirmed (or even strongly suspected in an unstable patient).

Type B (Stanford B / DeBakey III):

• Uncomplicated (no high-risk features): initial medical management — beta-blocker/vasodilator per Section 5, pain control, ICU monitoring
• High-risk imaging features that raise concern even in "uncomplicated" type B: primary entry tear diameter >10mm, initial aortic diameter >40mm, false lumen diameter >22mm, partially thrombosed false lumen, saccular false lumen formation
• Complicated type B (rupture, malperfusion syndrome, rapidly expanding diameter, refractory pain, uncontrolled hypertension despite maximal medical therapy, or high-risk imaging features per some algorithms): Thoracic Endovascular Aortic Repair (TEVAR) is recommended — covers the intimal tear, decompresses the false lumen, restores true lumen/branch perfusion
• Open surgery for type B reserved for complications not manageable by TEVAR — carries higher risk
• Randomized trial data on TEVAR for UNCOMPLICATED type B dissection is still being developed; current standard remains initial medical therapy for uncomplicated type B, with TEVAR reserved for complicated cases or high-risk feature-driven escalation

IMH and PAU: managed by the same anatomic-type logic as classic dissection (type A -> surgery, type B -> medical), given their shared propagation risk and potential to evolve into classic dissection.

11. Organ Support

Beta-blocker/vasodilator titration per Section 5; pain control; standard ICU supportive care; management of malperfusion-related organ dysfunction (renal, mesenteric, limb) per the affected territory's own protocol logic once source (the dissection) is addressed.

12. Consultation Matrix

13. Monitoring Framework

Continuous arterial line BP monitoring during titration, continuous cardiac monitoring, serial exam for new malperfusion signs (pulse checks, neuro checks, urine output), serial imaging as clinically indicated to monitor for propagation/expansion in medically managed type B.

14. Complications

Aortic rupture (most catastrophic, especially type A), cardiac tamponade (proximal dissection into pericardium — see Cardiac Tamponade protocol's special hemopericardium-with-dissection management pathway), acute severe aortic regurgitation, malperfusion syndrome by territory (Section 3), stroke, MI (coronary ostial involvement), paraplegia (spinal artery malperfusion, particularly a TEVAR/open surgery risk), death. Prevention: rapid beta-blocker-first BP/HR control, correct sequencing avoiding unopposed vasodilation, timely surgical/TEVAR referral for type A/complicated type B. Rescue: emergent surgery, TEVAR, pericardiocentesis (controlled, per Cardiac Tamponade protocol) if tamponade develops.

15. Escalation & De-escalation

Escalate: any type A dissection -> emergent surgery; type B developing rupture, malperfusion, refractory pain/hypertension, or rapid expansion -> TEVAR.

De-escalate: uncomplicated type B with BP/HR at goal, no evolving high-risk features -> continue medical management, transition to oral beta-blocker, plan long-term surveillance imaging.

16. ICU Discharge Criteria

Type A: post-surgical stabilization per cardiothoracic surgery criteria. Type B: BP/HR at goal on oral regimen, no malperfusion/expansion on surveillance imaging, pain controlled, genetic/family counseling initiated if indicated, long-term BP target and follow-up imaging schedule established.

17. Long-Term Management (relevant to discharge planning)

Goal BP <=120/80 mmHg long-term. Smoking cessation essential (active tobacco use is an established dissection risk factor). Long-term "anti-impulse" beta-blockade (lowering both resting HR and SBP) is recommended indefinitely. Genetic screening indicated if: syndromic features on exam, family history of aortic dissection/aneurysmal disease, or dissection age <60 — up to 20% of nonsyndromic thoracic aortic dissection patients have a first-degree relative with aortic dilation/disease, making family screening/counseling a real, actionable finding, not just an academic point.

18. Documentation & Medicolegal Checklist

19. Key Guidelines

Hiratzka LF, Bakris GL, Beckman JA, et al. 2010 ACCF/AHA/AATS/ACR/ASA/SCA/SCAI/SIR/STS/SVM guidelines for the diagnosis and management of patients with thoracic aortic disease. J Am Coll Cardiol. 2010;55(14):e27-e129 (note: a more recent joint guideline update may exist — verify current edition given the field's active evolution). Braverman AC, Schermerhorn. Diseases of the Aorta, in Braunwald's Heart Disease, 12th ed.

20. Landmark Evidence

• IRAD (International Registry of Acute Aortic Dissection): foundational registry data underpinning temporal classification, survival curves by type/management strategy, and the ADD-RS risk score derivation/validation (Rogers et al., Circulation 2011).
• Tadros RO, Tang GHL, Barnes HJ, et al. Optimal treatment of uncomplicated type B aortic dissection: JACC review. J Am Coll Cardiol. 2019;74:1494-1504 — summarizes the high-risk imaging feature criteria and medical-vs-TEVAR decision framework for type B.

21. Controversies

TEVAR for UNCOMPLICATED type B dissection (as opposed to reserving it for complicated cases) remains an active area of investigation — randomized trials are being planned/conducted, and current practice of medical-therapy-first for uncomplicated type B may evolve as this evidence matures. The precise set of "high-risk imaging features" that should prompt earlier TEVAR in nominally uncomplicated type B varies somewhat between society guidelines and individual expert algorithms. Nitroprusside's maximum safe dose in this specific population is cited inconsistently across sources (some cap at 2 mcg/kg/min to avoid toxicity, others allow up to 10) — individualize based on duration of use and renal/hepatic function rather than anchoring to a single number.

22. References

1. Diseases of the Aorta / Acute Aortic Syndromes chapter. Washington Manual of Critical Care, 4th ed, 2025 (Ch. 22).
2. Hiratzka LF, Bakris GL, Beckman JA, et al. 2010 ACCF/AHA/AATS/ACR/ASA/SCA/SCAI/SIR/STS/SVM guidelines for thoracic aortic disease. J Am Coll Cardiol. 2010;55(14):e27-e129.
3. Rogers AM, Hermann LK, Booher AM, et al. Sensitivity of the aortic dissection detection risk score (ADD-RS). Circulation. 2011;123(20):2213-2218.
4. Booher AM, Isselbacher EM, Nienaber CA, et al. The IRAD classification system for characterizing survival after aortic dissection. Am J Med. 2013;126(8):730.e19-730.e24.
5. Tadros RO, Tang GHL, Barnes HJ, et al. Optimal treatment of uncomplicated type B aortic dissection: JACC review topic of the week. J Am Coll Cardiol. 2019;74(11):1494-1504.
6. Nienaber CA, Eagle KA. Aortic dissection: new frontiers in diagnosis and management, Part I. Circulation. 2003;108(5):628-635.
7. Braverman AC, Schermerhorn. Diseases of the aorta. In: Libby P, Bonow RO, Mann DL, et al., eds. Braunwald's Heart Disease. 12th ed. Elsevier; 2022:806-836.

See also: Hypertensive Emergencies (beta-blocker-first sequencing detail), Cardiac Tamponade (dissection-associated hemopericardium drainage nuance) — Cardiovascular System.