Pulmonary Embolism

Pathophysiology

Originate primarily from deep venous system of lower extremities Ilio - femoral thrombi and pelvic veins appear to be the most clinically recognized source air, amniotic fluid, and fat emboli are rarer causes.
The commonest scenario is a patient with a risk factor who becomes breathless suddenly, with a normal CxR and perhaps mild hypoxia, and no obvious cause.
Most pulmonary thrombi are multiple, with the lower lobes being involved in the majority of cases.

Most PE are small, and infarcts are usually associated with small PE:

• Small embolism may produce dyspnea, pleuritic, chest pain, and occasionally hemoptysis
• Small embolism will reach the periphery of the lung, sometimes producing wedge - shaped shadow on CxR, and may cause pulmonary infarction.• A large embolism suddenly obstructing a major pulmonary vessel has marked effects on cardiac function, often associated with anterior chest pain and collapse.
• Pulmonary infarct following a large embolism is less common.
• A distinguish between small and large embolism is important.• Chronic recurrent pulmonary embolism may develop pulmonary hypertension and right ventricular failure.

Risk Factors

The most common risk factors identified are:• Immobilization• Surgery or trauma within the last 3 months• Increasing age• Malignancy

Triad of Virchow

• Endothelial injury
• Stasis
• Hypercoagulation status

Idiopathic or primary venous thromboembolism should be further evaluated for the underlying abnormalities For example:
pancreatic cancer, prostate cancer, late in the course of breast, lung, uterine, or brain malignancies

PE Symptoms

The symptoms of pulmonary embolism may include:

• Shortness of breath that may occur suddenly
• Sudden, sharp chest pain that may become worse with deep breathing or coughing
• Rapid heart rate
• Rapid breathing
• Sweating
• Anxiety
• Coughing up blood or pink, foamy mucus
• Fainting
• Heart palpitations
• Signs of shock

DDX

Heart conditions often confused with pulmonary embolism:

• Heart attack
• Heart failure or pulmonary edema
• Irregular heartbeat (cardiac arrhythmia)
• Pericarditis or pericardial effusion

Lung conditions often confused with pulmonary embolism:

• Pneumonia
• Lung cancer
• Pleurisy or pleural effusions
• Asthma
• Chronic obstructive pulmonary disease (COPD)
• A collapsed lung (pneumothorax)

Other conditions often confused with pulmonary embolism:

• Dissecting aortic aneurysm
• Hyperventilation
• Panic attacks

Tests

• A chest X-ray:
Atelectasis or a pulmonary parenchymal abnormality is the most frequent radiographic abnormalities.
Westermark's sign: represents a focus of oligemia (leading to collapse of vessel) seen distal to a (PE).
Hampton’s hump:  consists of a shallow wedge-shaped opacity in the periphery of the lung with its base against the pleural surface.
If the chest X-ray is normal, you may need further testing.

• EKG:
Most commonly revealed nonspecific ST segment and T wave changes in submassive PE. More severe right ventricular dysfunction with obstruction of more than 50% of pulmonary vasculature in a previously healthy patient may reveal T wave inversion in the precordial leads V1- V3 or P pulmonale, RAD, RBBB. S1Q3T3 (seen in only 25% of large PE), or sinus tachycardia can also be found. On occasion, PE can precipitate atrial flutter or AF.

• Arterial blood gas analysis. A sudden drop in the blood oxygen level may suggest a pulmonary embolism.

Further testing may include:• D-dimer: <500 ng/ml is a powerful excluding tool for PE • Spiral (helical) computed tomography. This test is used commonly in most hospitals to check for pulmonary embolism. The test of choice if the X ray is abnormal.• Ventilation-perfusion scanning. This test scans for abnormal blood flow through the lungs after a radioactive tracer has been injected and you breathe a radioactive gas. the more normal the chest x ray, the more accurate the results will be.• Pulmonary angiogram. A pulmonary angiogram (also called a pulmonary arteriogram) is the most accurate way to diagnose pulmonary embolism. This test is not available at some smaller hospitals and is more invasive than other testing.• Computerized tomography (CT) angiogram. A CT angiogram uses a special dye and a series of X-rays to produce pictures of blood vessels. It can be done to look for a pulmonary embolism or for a blood clot that may cause a pulmonary embolism.• Doppler ultrasound. A Doppler ultrasound test uses reflected sound waves to determine whether a blood clot is present in the large veins of the legs.• Echocardiogram (echo). This test detects abnormalities in the size or function of the heart's right ventricle, which may be a sign of pulmonary embolism.• Magnetic resonance imaging (MRI). This test may be used to view clots in the deep veins and lungs.

Treatment

• LMWH are now first line treatment for DVT and are as effective as Heparin IVD. Could be used as an alternative choice of Heparin IVD in PE as 30mg, sc, bid.
• Thrombolytic therapy is used when there is significant cardiac compromise, RV strain, or hemodynamic changes not responding to IVF and vasopressor resuscitation. Thrombolytic therapy achieves faster resolution of the thrombus and more rapid recovery of normal vascular flow than simple anticoagulation.

Secondary Prevention

Oral anticoagulants (and LMWH subcutaneously):
• Oral warfarin can be given with the initiation of Heparin keep INR between 2-3 with initial dose of 5mg/day for 2 days.
• An overlap of 4-5 days with a therapeutic INR and aPTT is recommended.
• After the first episode of PE, treatment is recommended for 3-6 months.
• Permanent anticoagulation is recommended with repeated PE unless there is an obvious reversible cause.• Repeat Doppler ultrasound scans of the legs or repeat V/Q scans have been used to confirm complete resolution of thrombus before stopping anticoagulation.

Vena Cava Filters:
These have been used in patients with recurrent venous thromboembolic disease where anticoagulation is contraindicated or has been ineffective.