What is Pulmonary Embolism?
Pulmonary embolism (PE) is the obstruction of pulmonary arteries, most commonly by blood clots originating from deep vein thrombosis in the legs or pelvis, representing the most serious and potentially fatal clinical presentation of venous thromboembolism. 1
Definition and Pathophysiology
PE occurs when thromboemboli block the pulmonary vasculature, creating an acute increase in pulmonary vascular resistance that can lead to right ventricular failure—the primary cause of death in severe cases. 2, 3
- Deep vein thrombosis and pulmonary embolism are manifestations of the same disease entity: venous thromboembolic disease 3
- Over 70% of proven PE cases have proximal leg thrombus as the source, though this is usually clinically undetectable 1
- In up to 50% of PE patients, no deep vein thrombosis is found on imaging, suggesting either complete embolization of the source thrombus or alternative origins 4
Epidemiology and Clinical Impact
PE is the third most frequent cardiovascular disease with devastating mortality: untreated PE carries approximately 30% mortality, which drops to 2-8% with adequate anticoagulation. 1
- Annual incidence ranges from 100-200 per 100,000 inhabitants in Europe 1
- Over 317,000 deaths were related to venous thromboembolism in six European Union countries in 2004 1
- 59% of PE-related deaths occur undiagnosed during life, and only 7% are correctly diagnosed before death 1
- Risk approximately doubles with each decade after age 40 1
- Three-month mortality in acute PE ranges from 9-17.5%, with sustained hypotension conferring 52.4% mortality versus 14.7% in normotensive patients 1, 2
Clinical Presentation Spectrum
PE presents across a wide severity spectrum, requiring classification for appropriate management 1:
Massive PE
- Defined by shock and/or hypotension (systolic blood pressure <90 mmHg or pressure drop of 40 mmHg for >15 minutes not caused by arrhythmia, hypovolemia, or sepsis) 1
- Right ventricular failure from acute pressure overload is the mechanism of death 2, 3
Submassive PE
- Non-massive PE with echocardiographic evidence of right ventricular dysfunction 1
- This subgroup has different prognosis than those with normal right ventricular function 1
Non-massive PE
- All cases without shock or hypotension 1
Hemodynamic Consequences
The abrupt increase in pulmonary vascular resistance causes right ventricular dilation and dysfunction, with the interventricular septum bowing leftward and impairing left ventricular filling. 3
- Pulmonary artery pressure increases when >30-50% of the total cross-sectional area of the pulmonary arterial bed is occluded 3
- Systemic hypotension compromises coronary perfusion to the overloaded right ventricle, potentially causing right ventricular ischemia 2
Associated Complications
Acute Complications
- Sudden death can be the first presentation 1
- Pulmonary infarction (actually alveolar hemorrhage) causes hemoptysis, pleuritis, and pleural effusion 3, 5
- Distal emboli cause pleural irritation even without significant hemodynamic effects 5
Chronic Complications
- Chronic thromboembolic pulmonary hypertension develops in approximately 3.8% of patients within 2 years after initial PE 2, 3
- Post-thrombotic syndrome 6
Non-Thrombotic Causes
While thrombotic occlusion is the primary etiology, PE can result from other sources 2:
- Septic embolism (right-sided endocarditis, infected catheters) 2
- Fat embolism (long bone fractures, orthopedic procedures) 2
- Air embolism (lethal volume: 200-300 ml at 100 ml/s) 2
- Amniotic fluid embolism (1/8,000-1/80,000 pregnancies with 80% maternal mortality) 2
- Tumor embolism (seen in up to 26% of autopsies, rarely diagnosed ante-mortem) 2
- Foreign material from broken catheters or medical devices 2
Diagnostic Challenge
PE is both underdiagnosed and overdiagnosed in clinical practice: 70% of fatal PE cases were not suspected clinically, while 63% of clinically diagnosed PE cases were not confirmed at autopsy. 1