Clotting Disorders

1. THE 2-MINUTE PHYSIOLOGY (Rapid Pathophysiology)

Clotting disorders arise when the normal hemostatic balance is tipped so that coagulation exceeds fibrinolysis. This is classically driven by Virchow's Triad: endothelial injury, stasis, and hypercoagulability,.

• Hypercoagulable States: Genetic defects, such as Factor V Leiden, produce a mutated procoagulant protein that cannot be inhibited by regulatory proteins like Protein C,. Other inherited defects involve deficiencies of antithrombin, Protein C, or Protein S,.
• The Pulmonary Embolism (PE) Death Spiral: When a thrombus obstructs the pulmonary arterial circulation, it causes ventilation-perfusion (V/Q) mismatch and acutely elevates pulmonary vascular resistance (PVR). If the pulmonary artery systolic pressure exceeds 40 mm Hg, the thin-walled right ventricle (RV) rapidly dilates and fails,. This RV dilation compresses the left ventricle (LV), decreasing LV preload and cardiac output, leading to severe hypotension, cardiogenic shock, and potentially pulseless electrical activity (PEA) or asystole.
• Disseminated Intravascular Coagulation (DIC): Driven by profound endothelial damage (e.g., from sepsis or trauma), causing massive release of Tissue Factor. This sparks uncontrolled thrombin generation and widespread microvascular fibrin deposition. The process rapidly consumes circulating platelets and clotting factors, leading to a paradoxical state of profound bleeding amidst systemic micro-thrombosis,,.

2. THE BEDSIDE ACTION PLAN (Rapid ER Management)

• Airway & Breathing: Hypoxemia and hypercapnia drastically worsen pulmonary vascular resistance and RV failure. Target SpO2 > 90%. Use High-Flow Nasal Cannula (HFNC) or Non-Invasive Ventilation (NIV) to avoid mechanical ventilation, as positive pressure severely impedes RV venous return.
• Circulation (The "Crashing RV"): Avoid excessive IV fluids. Aggressive fluid resuscitation worsens RV distension and impairs cardiac output; limit fluids to small 250 mL boluses. Initiate early vasopressors (Norepinephrine is preferred) to support RV function and maintain perfusion.
• Anticoagulation: Initiate IV Unfractionated Heparin (UFH) with an 80 units/kg bolus followed by an 18 units/kg/h infusion,. Do not delay empiric anticoagulation for imaging if clinical suspicion is high and bleeding risk is low.
• Reperfusion for High-Risk/Massive PE: Systemic thrombolysis (Alteplase or Tenecteplase push) is indicated for catastrophic PE causing refractory shock or cardiac arrest,. Veno-Arterial ECMO (VA-ECMO) should be initiated early as a bridge to intervention for refractory shock,.
• Catastrophic Antiphospholipid Syndrome (CAPS): For rapid multiorgan failure due to micro-thromboses, treat immediately with heparin, high-dose glucocorticoids (1g methylprednisolone), and consider plasma exchange or IVIG.

3. THE DIAGNOSTIC GRID (Differential Diagnosis & Workup)

• Critical "Can't-Miss" Differential Diagnoses:
• Acute Aortic Dissection
• Acute Coronary Syndrome (ACS) / STEMI
• Cardiac Tamponade
• Esophageal Rupture (Boerhaave Syndrome)
• Prioritized Diagnostic Workup:
• D-Dimer: Use for low to intermediate-risk patients. Apply age-adjusted cutoffs for patients >50 years (Age × 10 ng/mL). Under the YEARS criteria, use a threshold of 1,000 ng/mL if no clinical YEARS criteria are met.
• CT Pulmonary Angiography (CTPA): The gold standard imaging modality. Look for filling defects and an RV/LV ratio > 0.9 (which indicates RV strain).
• Cardiac Biomarkers: Troponin and BNP are critical to risk-stratify normotensive patients. Elevation indicates RV strain and classifies the patient as intermediate-risk (submassive), portending a higher risk of short-term complications and mortality,.
• DIC Panel: Look for profound thrombocytopenia, prolonged PT/aPTT, Fibrinogen < 100 mg/dL, elevated D-Dimer, and schistocytes on the peripheral smear indicating microangiopathic hemolytic anemia,,.

4. THE VISUAL BOARD (ECG / POCUS / Imaging)

• ECG Findings: Sinus tachycardia is the most common finding (<30% of cases),. To confirm RV strain, look for new T-wave inversions in the right precordial leads (V1-V4), a rightward axis, a new right bundle branch block (RBBB), and the classic (though poorly sensitive) S1Q3T3 pattern,,.
• Point-of-Care Ultrasound (POCUS) / RUSH Exam: Look for direct signs of obstructive shock. You must assess for:
• RV Dilation: RV/LV ratio > 1.0.
• The D-Sign: Bowing of the interventricular septum into the LV during systole, representing RV pressure overload.
• McConnell's Sign: Akinesia of the RV free wall with visible sparing (hyperkinesia) of the RV apex.
• Plethoric IVC: An IVC > 2.5 cm with < 50% inspiratory collapse, indicating elevated right-sided pressures,.

5. THE SCORING MATRIX (Risk Stratification & Guidelines)

• PERC Rule (PE Rule-Out Criteria): Safely excludes PE without testing in patients with a low pre-test probability (<20%),.
• Wells Score for PE: Stratifies patients into low, moderate, or high probability. Key criteria: clinical signs of DVT (3 pts), alternative diagnosis less likely than PE (3 pts), HR > 100 (1.5 pts), prior PE/DVT (1.5 pts),.
• PESI & sPESI (Pulmonary Embolism Severity Index): Predicts 30-day mortality. Low-risk patients (sPESI = 0) with normal biomarkers and no RV strain on imaging can be safely managed as outpatients with Direct Oral Anticoagulants (DOACs),,.
• Hestia Criteria: A clinical rule to determine eligibility for outpatient management. If all criteria are "No," the rule is negative, and the patient may be safely discharged,.

6. THE DANGER ZONE (Pitfalls & Critical Actions)

• Deadly Pitfall (Airway): Intubating a patient with an unstable PE without hemodynamic optimization. Positive pressure ventilation drops venous return and worsens pulmonary vascular resistance, frequently triggering cardiac arrest.
• Critical Action: Use hemodynamic resuscitation first: initiate Norepinephrine and augment preload with small (250 mL) fluid boluses prior to definitive airway management.
• Deadly Pitfall (Fluids): Routinely slamming 2 to 3 liters of crystalloids into a hypotensive PE patient. This causes RV over-distension, further crushing the LV (interventricular dependence) and destroying cardiac output.
• Critical Action: Avoid excessive IV fluids. Administer a strict maximum of 250 mL while closely monitoring response.
• Deadly Pitfall (Testing): Delaying anticoagulation while waiting for a CTPA in an unstable patient with high clinical gestalt for PE.
• Critical Action: Administer empiric Unfractionated Heparin immediately if no contraindications exist.

7. MCQ MASTERCLASS (Written Exam Tips)

• Distractor: The S1Q3T3 ECG pattern. While famously taught and highly tested, examiners will often use it in the stem. Do not rely on it as a sensitive or specific rule-out; it simply suggests RV strain,. Look instead for T-wave inversions in V1-V4.
• Buzzword: "Phlegmasia cerulea dolens." Describes a swollen, severely painful, dusky/blue limb due to a massive proximal DVT causing near-total venous occlusion. This is a limb-threatening emergency requiring aggressive clot disruption. (Contrasted with phlegmasia alba dolens, which is pale/white).
• Pathophysiology Fact: Factor V Leiden is the most commonly tested inherited thrombophilia. The mutation results in the synthesis of a procoagulant protein that is resistant to breakdown by activated Protein C,.

8. THE BOARDROOM SCRIPT (OSCE & Oral Board Tips)

• The Initial Assessment: "I am highly concerned for a massive pulmonary embolism causing obstructive shock. I will immediately place the patient on a monitor, provide supplemental oxygen targeting SpO2 > 90%, and establish two large-bore IVs. I am holding off on intubation to prevent hemodynamic collapse from positive pressure."
• The Resuscitation: "Because aggressive fluids will worsen RV distension and bow the septum into the left ventricle, I will limit my fluid bolus to 250 mL. I want a Norepinephrine infusion started immediately to support right ventricular perfusion."
• The Diagnostics: "I am bringing the ultrasound machine to the bedside for a RUSH exam, specifically looking for RV dilation, a D-shaped left ventricle, McConnell's sign, and a plethoric IVC. Given the high probability of PE, I am ordering an 80 unit/kg bolus of Unfractionated Heparin right now, before sending the patient for a CT Pulmonary Angiogram."
• The Escalation: "If the patient loses pulses, we will initiate ACLS protocols and I will immediately order systemic thrombolysis with an Alteplase push for presumed catastrophic PE."