STEPTRACKERHEMATOLOGY + CARDIOVASCULAR | PATHOLOGY | HIGH-YIELD REVIEW

Embolism

A mass travels in the blood and lodges downstream — clot, fat, amniotic fluid, gas, cholesterol, bacteria or tumor.

FOCUS ON
Most emboli are thrombi, and most pulmonary emboli start as DVT in the proximal deep leg veins. Each other embolus has a setting: fat after a long-bone fracture, amniotic fluid during labor, gas in divers, cholesterol after catheterization. Know the PE workup.
EMBOLUS
SOURCE · MECHANISM
CLINICAL PICTURE
CLASSIC CLUE
Pulmonary thromboembolism
most common
DVT in femoral, popliteal or iliac veins travels through the right heart to the pulmonary arteries.
Sudden dyspnea, tachycardia, pleuritic pain, hypoxemia; often silent if small. Large/saddle → RV failure, sudden death
Infarct is uncommon (dual blood supply) unless there is heart failure; repeated PEs → pulmonary hypertension
Systemic thromboembolism
left-sided source
Mural thrombus after MI, left atrium in AF, dilated cardiomyopathy, valve vegetations, aortic atheroma.
Stroke, renal or splenic infarct, mesenteric ischemia, cold pale limb
AF + sudden painful pale leg
Paradoxical embolism
crosses a shunt
Venous clot passes through a PFO or ASD into the arterial side.
Stroke in a young patient with a DVT
Bubble study on echo
Fat embolism
trauma
Marrow fat enters veins after long-bone (femur) fracture or liposuction; fat globules injure vessels.
1–3 days later: hypoxemia, confusion, petechial rash (axillae, chest)
Fat droplets in pulmonary and cerebral vessels
Amniotic fluid embolism
obstetric
Amniotic fluid and fetal debris enter maternal circulation during labor or delivery.
Sudden dyspnea, hypoxia, shock, seizures, then DIC; high mortality
Fetal squamous cells and lanugo in maternal lung vessels
Gas embolism
decompression
Fast ascent → dissolved nitrogen forms bubbles; also air via central lines or chest trauma.
"Bends" (joint pain), "chokes" (dyspnea), neurologic signs; chronic: avascular necrosis of femoral head
Divers, high-altitude flyers → hyperbaric O₂
Cholesterol (atheroembolism)
iatrogenic
Plaque fragments break off during catheterization or vascular surgery.
Blue toes, livedo reticularis, AKI, transient eosinophilia, low complement
Needle-shaped cholesterol clefts in arterioles
Septic & tumor emboli
Infected vegetations break off · tumor invades veins.
Right-sided endocarditis → lung abscesses; left-sided → brain, spleen, kidney · RCC, HCC
IV drug use with cavitary lung nodules

Mechanism — DVT to PE

Deep leg vein clotVirchow's triad
→
IVC → right heartEmbolus travels
→
Pulmonary artery blockedDead space (V/Q mismatch)
→
Hypoxemia, ↑ A–aRespiratory alkalosis
→
↑ PVRRV strain → shock if large

PE workup & treatment

STEP
DETAIL
Low pretest probability
D-dimer — normal result rules out PE
Imaging
CT pulmonary angiography; V/Q scan if contrast is a problem (pregnancy, renal failure)
ECG / ABG
Sinus tachycardia (most common); S1Q3T3 (RV strain); hypoxemia + respiratory alkalosis
Leg
Compression ultrasound for DVT
Treat
Anticoagulate (heparin → DOAC or warfarin); thrombolysis if unstable; IVC filter if anticoagulation impossible

How it's tested

COMMON CONFUSIONCalf-vein clots rarely cause big PEs. The dangerous source is the proximal deep veins — popliteal, femoral, iliac.
THE TRAPA patient with a femur fracture is confused, hypoxic and has petechiae in the axillae two days later. That is fat embolism, not a PE from DVT.
YOUR APPROACHThe setting picks the embolus (surgery/immobility, fracture, labor, diving, catheterization, IV drug use); then predict where it lodges.

If you see… think…

Postoperative patient, sudden pleuritic pain, tachycardia, ↑ A–a → PE
Sudden death with clot straddling the pulmonary bifurcation → saddle embolus
Femur fracture, then confusion, hypoxia, axillary petechiae → fat embolism
Shock in labor followed by DIC; lanugo in maternal lungs → amniotic fluid embolism
Diver with joint pain and dyspnea after rapid ascent → decompression sickness
Young patient with stroke and leg DVT → paradoxical embolism via PFO
After cardiac cath: blue toes, livedo, AKI, eosinophilia → cholesterol emboli
AF and a suddenly cold, pale, painful leg → arterial embolism from left atrium
IV drug user with multiple cavitating lung nodules → septic emboli (tricuspid IE)
Progressive dyspnea after several PEs → chronic thromboembolic pulmonary hypertension