3.2 Massive & Submassive Pulmonary Embolism

ABIM Critical Care Medicine Study Guide Exam

Track your progress as you read

Finished sections get a check mark.

1 Chapter 1: Exam Orientation: Format, Blueprint & Study Strategy

1.1 ABIM Critical Care Medicine Exam: Format, Blueprint & Study Strategy

2 Chapter 2: Acute Respiratory Failure & ARDS

2.1 ARDS Definition, Pathophysiology & Phenotypes 2.2 Lung-Protective Mechanical Ventilation 2.3 Refractory ARDS: Prone Positioning, Neuromuscular Blockade & VV-ECMO

3 Chapter 3: Obstructive Airways, Pulmonary Vascular & Pleural Emergencies

3.1 Severe Asthma & COPD Exacerbations in the ICU 3.2 Massive & Submassive Pulmonary Embolism 3.3 Pulmonary Hypertension & Right Ventricular Failure in the ICU 3.4 Massive Hemoptysis, Complex Pleural Effusions & Thoracic Drainage

4 Chapter 4: Airway, Parenchymal & Nonthrombotic Pulmonary Emergencies

4.1 Airway Management, Upper-Airway Obstruction & Artificial-Airway Complications 4.2 Diffuse Alveolar Hemorrhage, Interstitial Lung Disease, Pulmonary Vasculitis & Noncardiogenic Edema 4.3 Severe Community-Acquired & Viral Pneumonia 4.4 Nonthrombotic Embolism (Air, Fat, Amniotic Fluid, Tumor, Septic) & Acute Chest Syndrome

5 Chapter 5: Mechanical Ventilation Modes, Dyssynchrony & Liberation

5.1 Mechanical Ventilator Modes & Advanced Breath Delivery 5.2 Patient-Ventilator Dyssynchrony & Waveform Analysis 5.3 Ventilator Liberation, Spontaneous Breathing Trials & Post-Extubation Support

6 Chapter 6: Shock Syndromes & Hemodynamic Principles

6.1 Shock Classification, Cellular Pathophysiology & Biomarkers 6.2 Hemodynamic Monitoring: Arterial Lines, CVP & Pulmonary Artery Catheter 6.3 Dynamic Assessment of Fluid Responsiveness & Resuscitation Targets

7 Chapter 7: Vasoactive Therapies & Mechanical Circulatory Support

7.1 Vasopressors & Inotropes: Pharmacology & Clinical Titration 7.2 Temporary Mechanical Circulatory Support: IABP, Impella & TandemHeart 7.3 Venoarterial ECMO (VA-ECMO) & Differential Hypoxemia 7.4 Post-Cardiac Arrest Care, Targeted Temperature Management & Neuroprognostication

8 Chapter 8: Acute Kidney Injury & Renal Replacement Therapy

8.1 KDIGO AKI Classification, Etiologies & Diagnostic Evaluation 8.2 Continuous Renal Replacement Therapy (CRRT) vs Intermittent Hemodialysis 8.3 Indications & Timing for RRT in Critical Illness: AKIKI & STARRT-AKI

9 Chapter 9: Electrolyte, Acid-Base & Endocrine Emergencies

9.1 Severe Dysnatremias: Hyponatremia, Hypernatremia & Osmotic Demyelination 9.2 Potassium, Calcium, Magnesium & Phosphate Disorders 9.3 Complex & Mixed Acid-Base Disorders: Boston vs Copenhagen vs Stewart 9.4 Endocrine Crises: DKA, HHS, Thyroid Storm, Myxedema Coma & Adrenal Crisis

10 Chapter 10: Glycemic Control, Hyperammonemia, Pituitary & Adrenal Disorders

10.1 ICU Glycemic Control & Severe Hypoglycemia 10.2 Non-Hepatic Hyperammonemia & Metabolic Encephalopathy 10.3 Pituitary Emergencies, Adrenal Excess & Critical Illness-Related Corticosteroid Insufficiency

11 Chapter 11: Acute Coronary Syndromes & Cardiac Arrhythmias

11.1 Acute Coronary Syndromes & Mechanical Complications of Myocardial Infarction 11.2 Critical Tachyarrhythmias: Atrial Fibrillation with RVR, VT & VF 11.3 Critical Bradyarrhythmias, Conduction Blocks & Temporary Cardiac Pacing

12 Chapter 12: Acute Heart Failure, Valvular & Pericardial Emergencies

12.1 Acute Decompensated Heart Failure & Cardiogenic Pulmonary Edema 12.2 Acute Valvular Regurgitation & Prosthetic Valve Emergencies 12.3 Pericardial Tamponade & Acute Aortic Syndromes

13 Chapter 13: Myocardial Disease, Hypertensive & Cardiac Device Emergencies

13.1 Fulminant Myocarditis, Stress & Peripartum Cardiomyopathy, and Hypertrophic Cardiomyopathy 13.2 Hypertensive Emergencies & Ruptured Abdominal Aortic Aneurysm 13.3 Implanted Cardiac Devices, LVAD Emergencies & Electrical Storm

14 Chapter 14: Sepsis & Systemic Infectious Diseases

14.1 Sepsis-3 Definitions & Surviving Sepsis Campaign 2026 Guidelines 14.2 Refractory Septic Shock & Adjunctive Therapies 14.3 Multidrug-Resistant Pathogens & Antimicrobial Stewardship in the ICU

15 Chapter 15: ICU-Acquired & Severe Focal Infections

15.1 Hospital-Acquired & Ventilator-Associated Pneumonia 15.2 Central Line-Associated Bloodstream Infections & Catheter-Associated UTIs 15.3 Intra-Abdominal Sepsis, Necrotizing Soft Tissue Infections & CNS Infections

16 Chapter 16: Focal, Special-Host & Systemic Infections

16.1 CNS Infections Beyond Bacterial Meningitis: Encephalitis, Brain Abscess & Epidural Abscess 16.2 Infections in the Immunocompromised Host, Tropical & Bioterror Infections 16.3 Infective Endocarditis, Device Infections & Other Focal Cardiovascular Infections 16.4 Antimicrobial Pharmacokinetics, Allergy, Toxicity & Infection Prevention 16.5 Gastrointestinal & Hepatobiliary Infections: Fulminant C. difficile, Typhlitis, CMV Colitis & Abscesses

17 Chapter 17: Neurocritical Care & Coma

17.1 Coma, Altered Mental Status & Acute Delirium in the ICU 17.2 Status Epilepticus & Non-Convulsive Status Epilepticus 17.3 Acute Ischemic Stroke & Intracranial Hemorrhage

18 Chapter 18: Cerebrovascular Syndromes, Encephalopathy & Withdrawal States

18.1 Cerebral Venous Sinus Thrombosis, PRES & Reversible Cerebral Vasoconstriction Syndrome 18.2 Alcohol & Sedative Withdrawal, Wernicke Encephalopathy & Drug-Induced Encephalopathy

19 Chapter 19: Intracranial Hypertension & Neuromuscular Weakness

19.1 Intracranial Pressure Monitoring, Cerebral Perfusion & Tiered ICP Management 19.2 Acute Neuromuscular Respiratory Failure, ICU-Acquired Weakness & Brain Death Determination

20 Chapter 20: Traumatic Brain Injury, Spinal Cord Injury & Toxin-Mediated Paralysis

20.1 Traumatic Brain Injury Management & Paroxysmal Sympathetic Hyperactivity 20.2 Acute Spinal Cord Injury, Neurogenic Shock & Autonomic Dysreflexia 20.3 Toxin-Mediated Paralysis & Neuromuscular Crises: Botulism, Tetanus, Tick Paralysis & Myasthenic Crisis

21 Chapter 21: Gastrointestinal, Hepatic & Abdominal Emergencies

21.1 Acute Upper & Lower Gastrointestinal Bleeding in the ICU 21.2 Acute Liver Failure & Severe Acute Pancreatitis 21.3 Abdominal Compartment Syndrome & Acute Mesenteric Ischemia

22 Chapter 22: Luminal GI Emergencies & Complications of Cirrhosis

22.1 Esophageal, Gastric & Bowel Emergencies: Perforation, Obstruction, Ogilvie Syndrome & Colonic Ischemia 22.2 Complications of Cirrhosis: Alcohol-Associated Hepatitis, Hepatorenal Syndrome & Pulmonary Vascular Syndromes

23 Chapter 23: Trauma, Burns & Perioperative Critical Care

23.1 Polytrauma Resuscitation, Damage Control & Massive Transfusion 23.2 Severe Burn Injury, Inhalation Injury & Environmental Emergencies 23.3 Perioperative Critical Care for High-Risk Surgical Patients

24 Chapter 24: Thoracic Trauma, Environmental Injury & Obstetric Critical Care

24.1 Thoracic Trauma: Flail Chest, Pulmonary Contusion, Great Vessel & Tracheobronchial Injury 24.2 Environmental Injury: Drowning, Diving, Altitude, Heat, Cold, Electrical & Radiation 24.3 Obstetric & Genitourinary Emergencies and the Physiology of Pregnancy

25 Chapter 25: Transplantation, Donor Management & Post-Cardiac Surgery Care

25.1 Solid Organ Transplant Recipients & Deceased Donor Management 25.2 Post-Cardiac Surgery Critical Care: Bleeding, Tamponade, Low Output & Vasoplegia

26 Chapter 26: Hematologic Emergencies, Toxicology, Critical Ultrasound & ICU Liberation

26.1 Hematologic Emergencies in the ICU: HIT, DIC, TMA & Anticoagulant Reversal 26.2 Critical Care Toxicology, Toxidromes & Specific Antidotes 26.3 Critical Care Point-of-Care Ultrasound (POCUS) 26.4 ICU Liberation, Analgosedation, Goals of Care & Critical Care Ethics

27 Chapter 27: Transfusion Medicine, Hematologic & Oncologic Disorders

27.1 Transfusion Medicine: Products, Thresholds, Reactions & Apheresis 27.2 Red and White Cell Disorders, Hemoglobinopathies, Factor Deficiencies & Hypercoagulable States 27.3 Oncologic Emergencies, Hematopoietic Cell Transplant Complications & Cellular Therapy Toxicity

28 Chapter 28: Clinical Pharmacology, Adverse Drug Reactions & Specific Poisonings

28.1 Pharmacokinetic Principles, Dose Adjustment & Drug Interactions in Critical Illness 28.2 Adverse Drug Reactions: Anaphylaxis, Severe Cutaneous Reactions & Hyperthermic Syndromes 28.3 Specific Poisonings: Sodium-Channel Blockers, Lithium, Valproate, Theophylline, Iron, Sulfonylureas & Methemoglobinemia

29 Chapter 29: Ethics, Research Methods, Administration & Abdominal Ultrasound

29.1 Advance Care Planning, Nonbeneficial Treatment, Informed Consent & Confidentiality 29.2 Critical Care Research Methods, Statistics, IRB Oversight & Quality Improvement 29.3 Abdominal, Vascular & Procedural Point-of-Care Ultrasound

3.2 Massive & Submassive Pulmonary Embolism

Key Takeaways Explain This Topic AI

Massive (high-risk) pulmonary embolism is defined by sustained hypotension (systolic blood pressure <90 mmHg or a drop ≥40 mmHg for >15 minutes), requirement for vasopressors, or cardiac arrest.

Submassive PE (AHA 2011) is a normotensive PE with RV dysfunction OR myocardial necrosis; ESC intermediate-high risk requires BOTH RV dysfunction and elevated troponin, and the 2026 AHA/ACC guideline replaces these labels with Categories A-E.

For PE with cardiopulmonary failure (massive PE; 2026 AHA/ACC Category E), systemic alteplase 100 mg over 2 hours with anticoagulation is reasonable when bleeding risk is acceptable; in submassive PE, the PEITHO trial showed that routine upfront thrombolysis reduces hemodynamic decompensation but significantly increases major bleeding and hemorrhagic stroke without reducing overall mortality.

Catheter-directed therapies (ultrasound-assisted thrombolysis or large-bore mechanical thrombectomy) and surgical embolectomy represent preferred treatment options when systemic thrombolysis is contraindicated or has failed.

The 2026 AHA/ACC guideline recommends LMWH over UFH when hospitalized patients need initial parenteral anticoagulation; UFH remains reasonable for the sickest patients, imminent procedures, or severe renal failure.

Last updated: October 2026

Acute pulmonary embolism (PE) is a life-threatening cardiovascular emergency in which an occlusive thrombus lodges in the pulmonary arterial circulation. In the ICU, clinical presentations range from stable dyspnea to catastrophic obstructive shock and pulseless electrical activity (PEA) arrest. Successful management hinges on rapid, accurate risk stratification that balances the immediate benefits of pulmonary arterial reperfusion against the severe risk of major hemorrhage.

Risk Stratification & Clinical Classification

The traditional AHA (2011) and ESC (2019) schemes classify acute PE based on hemodynamic stability, right ventricular (RV) strain, and myocardial biomarker elevation. The terms differ in one important way: the AHA defined submassive PE as normotension with RV dysfunction or myocardial necrosis, whereas the ESC labels a patient intermediate-high risk only when both RV dysfunction on imaging and an elevated troponin are present, and intermediate-low risk when one or neither is present in a patient with an elevated PESI class III-V or sPESI ≥ 1 \ge 1 ≥ 1 . A normotensive patient with PESI class I-II or sPESI 0 is low risk.

PE Classification Hemodynamic Status RV Dysfunction (Echo / CT) Cardiac Biomarkers (Troponin / BNP) In-Hospital Mortality Primary Management Strategy

Massive (High-Risk) Sustained hypotension (SBP < 90 <90 < 90 or drop ≥ 40 mmHg \ge 40\text{ mmHg} ≥ 40 mmHg for > 15 min >15\text{ min} > 15 min ), shock, or arrest Present (severe RV dilation, hypokinesis) Elevated or indeterminate > 25 – 50 % >25–50\% > 25–50% Immediate systemic thrombolysis; rescue surgical embolectomy or catheter thrombectomy if contraindicated

Submassive: Intermediate-High Hemodynamically stable (SBP ≥ 90 mmHg \ge 90\text{ mmHg} ≥ 90 mmHg ) Present (RV/LV ratio > 0.9 – 1.0 >0.9–1.0 > 0.9–1.0 , McConnell's sign) Elevated troponin (BNP/NT-proBNP adds prognostic information) 3 – 12 % 3–12\% 3–12% Therapeutic parenteral anticoagulation (LMWH generally preferred; UFH if a procedure is imminent); close ICU monitoring; rescue reperfusion or catheter intervention for deterioration

Submassive: Intermediate-Low Hemodynamically stable (SBP ≥ 90 mmHg \ge 90\text{ mmHg} ≥ 90 mmHg ) Present OR absent (Only one positive: either RV strain OR elevated biomarker, but not both) Normal or minimally elevated 1 – 3 % 1–3\% 1–3% Therapeutic anticoagulation (LMWH or direct oral anticoagulant); intermediate telemetry monitoring

Low-Risk Hemodynamically stable (SBP ≥ 90 mmHg \ge 90\text{ mmHg} ≥ 90 mmHg ) with PESI class I-II or sPESI 0 Absent (not required to assess) Normal (not required to assess) < 1 % <1\% < 1% Anticoagulation (DOAC preferred); consider early discharge or outpatient management

The 2026 AHA/ACC Acute PE Clinical Categories

The 2026 AHA/ACC/multisociety guideline (Creager et al., Circulation 2026) introduced five categories that replace the massive/submassive vocabulary. Expect both systems in questions, so learn to translate between them:

• 2026 Category Clinical Picture Approximate Older Equivalent
• A Subclinical (incidental, asymptomatic) PE Low risk
• B Symptomatic PE with a low clinical severity score Low risk

C (C1-C3) Elevated clinical severity score; graded by RV imaging and biomarkers (C1 neither abnormal, C2 one abnormal, C3 both abnormal) Intermediate-low to intermediate-high risk

D (D1-D2) Incipient cardiopulmonary failure: transient hypotension or normotensive shock (hypoperfusion with preserved blood pressure) High end of submassive

E (E1-E2) Cardiopulmonary failure: E1 persistent hypotension or cardiogenic shock; E2 refractory shock or cardiac arrest Massive (high risk)

Key recommendations: a multidisciplinary PE response team (PERT) is recommended to speed decisions; systemic thrombolysis plus anticoagulation is reasonable for Category E1 when bleeding risk is acceptable, and is a rescue option in E2; catheter-directed thrombolysis, mechanical thrombectomy, and surgical embolectomy are reasonable for Category E1 and may be considered for D1-D2; for E2 (refractory shock or arrest), VA-ECMO or other mechanical circulatory support at a capable center can bridge to reperfusion; mechanical thrombectomy is not recommended for Categories A to C1, and routine systemic thrombolysis is not recommended in the lower-risk categories; LMWH is recommended over UFH when initial parenteral anticoagulation is needed; and DOACs are the preferred oral agents.

Defining RV Dysfunction

Echocardiographic Criteria: Right ventricular enlargement with an RV/LV end-diastolic diameter ratio > 0.9 >0.9 > 0.9 to 1.0 1.0 1.0 in the apical 4-chamber view; McConnell's sign (akinesis of the mid-free RV wall with normal or hyperdynamic apical contraction); decreased tricuspid annular plane systolic excursion ( TAPSE < 16 mm <16\text{ mm} < 16 mm ); tricuspid regurgitant jet peak velocity > 2.8 m/s >2.8\text{ m/s} > 2.8 m/s ; and systolic flattening of the interventricular septum ("D-shaped" left ventricle).

Computed Tomography Pulmonary Angiography (CTPA) Criteria: RV/LV transverse diameter ratio > 1.0 >1.0 > 1.0 in the axial reconstructed views; bowing of the interventricular septum toward the left ventricle; and retrograde reflux of intravenous contrast medium into the inferior vena cava and hepatic veins.

Defining Myocardial Injury

Cardiac Troponin I or T: Elevation above the 99th percentile upper reference limit reflects acute ischemic necrosis of RV subendocardial myocytes subjected to high wall tension.

Brain Natriuretic Peptides (BNP / NT-proBNP): Elevation reflects acute neurohormonal stretch of the overloaded right ventricular myocardium.

• Systemic Thrombolytic Therapy
• Indications

Systemic thrombolysis is the long-standing first-line reperfusion therapy for massive (high-risk; 2026 Category E) pulmonary embolism in patients without absolute contraindications (Class 2a in the 2026 AHA/ACC guideline; Class 1 in ESC 2019). In patients with submassive (intermediate-high-risk) PE, routine upfront systemic thrombolysis is not recommended; it is reserved as rescue therapy for patients who develop objective clinical signs of hemodynamic decompensation (hypotension, worsening lactic acidosis, end-organ hypoperfusion) despite therapeutic anticoagulation.

Dosing Regimens

Standard Infusion Regimen: Recombinant tissue plasminogen activator ( Alteplase / rtPA ) 100 mg IV administered as a continuous infusion over 2 hours .

Cardiac Arrest / Peri-Arrest Regimen: In patients with PE-induced cardiac arrest or imminent hemodynamic collapse, an accelerated bolus of 50 mg IV over 2 minutes is administered. If return of spontaneous circulation (ROSC) is not attained after 15 minutes, a second 50 mg IV bolus may be given.

Tenecteplase: Weight-based single IV bolus (30 to 50 mg over 5 to 10 seconds), studied extensively in clinical trials.

Evidence & Landmark Trials: The PEITHO Trial

The PEITHO Trial ( Pulmonary Embolism Thrombolysis Study , NEJM 2014) was a randomized, double-blind trial that evaluated 1,006 patients with intermediate-risk PE (normotensive with both RV dysfunction on echo/CT and elevated troponin). Patients were assigned to receive tenecteplase plus unfractionated heparin versus placebo plus unfractionated heparin:

Primary Efficacy Endpoint: Tenecteplase significantly reduced the composite endpoint of all-cause mortality or hemodynamic collapse within 7 days ( 2.6 % 2.6\% 2.6% vs. 5.6 % 5.6\% 5.6% , p = 0.02 p = 0.02 p = 0.02 ). This reduction was driven almost entirely by the prevention of hemodynamic collapse.

Bleeding Harm: Tenecteplase caused a significant, unacceptable increase in major extracranial bleeding ( 6.3 % 6.3\% 6.3% vs. 1.2 % 1.2\% 1.2% , p < 0.001 p < 0.001 p < 0.001 ) and a tenfold increase in intracranial hemorrhage / hemorrhagic stroke ( 2.0 % 2.0\% 2.0% vs. 0.2 % 0.2\% 0.2% , p = 0.003 p = 0.003 p = 0.003 ).

30-Day Mortality: There was no statistically significant difference in 30-day all-cause mortality ( 2.4 % 2.4\% 2.4% vs. 3.2 % 3.2\% 3.2% , p = 0.42 p = 0.42 p = 0.42 ).

Warning

The PEITHO trial established that routine upfront systemic thrombolysis in submassive PE trades an unacceptable rate of fatal or disabling intracranial hemorrhage (2.0%) for a modest reduction in hemodynamic decompensation, without any overall survival benefit. Upfront systemic thrombolysis must be strictly restricted to massive PE or decompensating patients.

The MOPETT Trial and "Moderate PE"

The MOPETT trial ( Moderate PE Treated with Thrombolysis ) evaluated "safe-dose" alteplase (50 mg over 2 hours) in intermediate PE. It demonstrated accelerated reduction in pulmonary artery pressures without fatal bleeding complications, but was underpowered for hard clinical and mortality endpoints.

Contraindications to Systemic Thrombolysis Contraindications to Systemic Thrombolysis in Pulmonary Embolism:

ABSOLUTE CONTRAINDICATIONS (Reperfusion must use mechanical/surgical modalities):

• ├── Any prior history of intracranial hemorrhage or hemorrhagic stroke
• ├── Known structural cerebral vascular lesion (e.g., arteriovenous malformation, aneurysm)
• ├── Known malignant intracranial neoplasm (primary or metastatic)
• ├── Ischemic stroke within the preceding 3 months
• ├── Suspected aortic dissection
• ├── Active internal bleeding or bleeding diathesis (excluding menses)
• └── Significant closed-head or facial trauma within the preceding 3 months

RELATIVE CONTRAINDICATIONS (Weigh against immediate mortality risk of massive PE):

• ├── Severe uncontrolled hypertension on presentation (SBP >180 mmHg or DBP >110 mmHg)
• ├── History of chronic, poorly controlled hypertension
• ├── Ischemic stroke older than 3 months
• ├── Major surgery within the preceding 3 weeks
• ├── Recent internal bleeding within 2 to 4 weeks (e.g., gastrointestinal hemorrhage)
• ├── Non-compressible vascular punctures (e.g., subclavian/internal jugular lines)
• ├── Prolonged or traumatic cardiopulmonary resuscitation (>10 minutes)
• ├── Active therapeutic oral anticoagulation (e.g., INR ≥1.7 or direct oral anticoagulant)
• ├── Pregnancy or first postpartum week
• └── Active peptic ulcer disease
• Catheter-Directed Therapies & Percutaneous Thrombectomy

Catheter-directed therapies (CDT) have emerged as essential therapeutic modalities for patients with massive PE who harbor contraindications to systemic thrombolytic therapy, patients who have failed systemic thrombolysis, and select patients with intermediate-high-risk PE possessing high clinical bleeding risk. Pulmonary Artery Catheter Interventions

• │
• ┌──────────────────────────┴──────────────────────────┐
• ▼ ▼
• Ultrasound-Assisted Catheter Thrombolysis Large-Bore Mechanical Thrombectomy
• (EKOS System) (Inari FlowTriever, Penumbra Lightning)
• Combines high-frequency ultrasound + local rtPA • Aspiration / mechanical extraction
• Low rtPA dose: 0.5–1.0 mg/hr/catheter • Zero thrombolytic drug administered
• Total dose: 12–24 mg over 12–24 hours • Immediate mechanical clot debulking
• Studied in ULTIMA and SEATTLE II • Studied in FLARE and the FLASH registry
• Modalities

Ultrasound-Assisted Catheter-Directed Thrombolysis (EKOS): Utilizes multi-sidehole infusion catheters containing ultrasound cores. High-frequency (2.2 MHz), low-power acoustic ultrasound energy loosens and uncrosslinks fibrin strands, increasing clot permeability to low-dose local alteplase infusions (typically 0.5 to 1.0 mg/hour per catheter; total dose 12 to 24 mg). The ULTIMA trial demonstrated superior reversal of RV enlargement at 24 hours compared to heparin alone without major bleeding.

Large-Bore Mechanical Aspiration Thrombectomy: Systems such as the Inari FlowTriever (16–24 French) and Penumbra Lightning aspirate and extract large, organized thrombi directly from pulmonary arterial trunks without requiring any thrombolytic medication. The single-arm FLARE study and the FLASH registry showed immediate reductions in mean pulmonary artery pressure and RV/LV ratio with low major bleeding rates ( < 1.5 % <1.5\% < 1.5% ). These are surrogate outcomes; randomized trials with clinical endpoints (such as HI-PEITHO and PEERLESS) are reshaping the evidence base, and mechanical thrombectomy is not recommended for Categories A to C1.

Surgical Pulmonary Embolectomy

Surgical embolectomy under cardiopulmonary bypass with median sternotomy is indicated for:

• Massive PE with absolute contraindications to systemic thrombolysis
• Massive PE with refractory shock despite systemic thrombolysis or catheter intervention

Right ventricular thrombus-in-transit straddling a patent foramen ovale (high risk of paradoxical systemic arterial embolization and stroke)

In modern centers with dedicated multidisciplinary Pulmonary Embolism Response Teams (PERT), perioperative survival for surgical embolectomy exceeds 85% to 90% when performed prior to the onset of irreversible multi-organ failure or cardiac arrest.

Parenteral Anticoagulation: UFH vs. LMWH

Immediate parenteral anticoagulation must be instituted upon high clinical suspicion of acute PE, even while confirmatory imaging is being arranged, provided there is no active hemorrhage.

Unfractionated Heparin (UFH)

Dosing: Intravenous bolus of 80 units/kg , followed by a continuous maintenance infusion of 18 units/kg/hour , titrated to an anti-factor Xa level of 0.3 – 0.7 IU/mL 0.3–0.7\text{ IU/mL} 0.3–0.7 IU/mL (or aPTT 1.5 to 2.5 times control).

When UFH Is Still Chosen (sickest Category E patients, imminent procedures, severe renal failure):

Short biological half-life (60 to 90 minutes after stopping infusion).

Complete and rapid reversibility with protamine sulfate (1 mg protamine neutralizes ~100 units of UFH administered in the preceding 2 hours; maximum dose 50 mg).

Safe in severe renal insufficiency ( CrCl < 30 mL/min \text{CrCl} < 30\text{ mL/min} CrCl < 30 mL/min ), as UFH is cleared by the reticuloendothelial system and endothelial cells rather than renal excretion.

Seamless interruption prior to urgent catheter intervention or surgical embolectomy.

Low-Molecular-Weight Heparin (LMWH)

Dosing: Enoxaparin 1 mg/kg subcutaneously every 12 hours (or 1.5 mg/kg once daily); dalteparin 200 units/kg once daily.

Role: Recommended over UFH (2026 AHA/ACC) for hospitalized patients who need initial parenteral anticoagulation, because a meta-analysis showed less recurrent VTE without more bleeding, plus more predictable bioavailability, lower incidence of heparin-induced thrombocytopenia (HIT), and no requirement for laboratory monitoring. However, LMWH is contraindicated or requires dose reduction/anti-Xa monitoring in severe renal failure ( CrCl < 30 mL/min \text{CrCl} < 30\text{ mL/min} CrCl < 30 mL/min ) and cannot be fully neutralized by protamine (only ~60% reversed).

Mechanical Circulatory Support: Venoarterial (VA) ECMO

In catastrophic massive pulmonary embolism complicated by refractory obstructive shock or cardiac arrest (PEA), venoarterial extracorporeal membrane oxygenation (VA-ECMO) can be life-saving.

By draining deoxygenated venous blood from the femoral vein/right atrium and pumping oxygenated blood into the femoral artery, VA-ECMO accomplishes two critical goals:

Completely decompresses the acutely failing, overloaded right ventricle.

Restores systemic end-organ perfusion and arterial oxygenation.

VA-ECMO serves as an emergent hemodynamic bridge to definitive catheter thrombectomy, surgical embolectomy, or delayed clot dissolution under systemic thrombolysis or anticoagulation.

• Inferior Vena Cava (IVC) Filters
• Indications

Absolute contraindication to anticoagulation in the setting of acute proximal DVT or acute PE (e.g., active major intracranial or gastrointestinal bleeding, major trauma, planned urgent surgery).

Recurrent, objectively documented PE despite proven therapeutic anticoagulation.

Massive PE with severe residual cardiopulmonary compromise where a subsequent small embolus would be fatal (controversial; temporary protection).

Complications & Long-Term Outcomes (PREPIC Trial)

The landmark PREPIC trial demonstrated that permanent IVC filters significantly reduced the initial risk of recurrent PE, but significantly increased the long-term incidence of deep vein thrombosis ( 20.8 % 20.8\% 20.8% vs. 11.6 % 11.6\% 11.6% , p = 0.02 p = 0.02 p = 0.02 ) with no overall difference in survival.

Retrievable IVC filters should be removed as soon as the bleeding risk subsides and therapeutic anticoagulation can be safely initiated. Complications of indwelling filters include filter thrombosis, IVC occlusion, migration, strut fracture, tilt, and secondary perforation into the duodenum, aorta, or retroperitoneum.