17- pulmonary Embolism

KYJ17- Pulmonary Embolism

Of all the causes of chest pain that are non cardiac, a pulmonary embolism (PE) has to be high on the hit list of acute killers.

A common cause is a clot in a peripheral vein breaking of and becoming liberated in blood returning to the heart.   With the venous returning blood merging into larger and larger veins enroute, the clot (now called an embolism) is free to journey all the way into the right heart, and through to the lungs.  Once in lungs, the pulmonary blood vessels become narrower and narrower, to the point where the traveling embolism gets lodged inside a lung vessel. This is a pulmonary embolism.

A person experiencing a pulmonary embolism most often experiences a classic triad of symptoms.
Shortness of breath
Tachycardia
Low oxygen saturations (Hypoxaemia)

There are other symptoms that relate to right heart failure (ankle swelling, ECG changes) in large PEs.

 The classic ECG change is a right Bundle branch block, and S1Q3T3 pattern seen in 10-50% of large PEs

S1Q3T3 is literally :
-a large S wave in lead I,
-a large Q wave in lead III and
-an inverted T wave in lead III

While it is commonly seen in those diagnosed with big PEs, it is one of those supporting signs of an already confirmed diagnosis, and is present in up to 20% of other right lung failure inducing conditions. It's value in diagnosis is negligible.

Diagnosis of PE is based on a criteria called the Wells Score.
It uses history, evaluation of risk factors, blood tests and with radiology.
The gold standard is pulmonary angiogram (CTPA) though VQ Scans are also used.

Risk factors include
Immobilisation post operatively
Long haul travel
Dehydration
Smoking
Pregnancy and hormone replacement
History of Deep Vein Thrombosis

Thus a patient who presents with these risk factors, and demonstrates the classic presentation of chest pain, shortness of breath and desaturation <94%, is a likely candidate for a CTPA.

In weak or low probability patients, a blood test called D-Dimer can be used to rule out PE. D-Dimer looks for breakdown products of a clot in the blood.  It would be present anytime someone is post op, or post injury of any kind, so s positive D-Dimer is not diagnostic.  A negative D-Dimer however, means there is no PE, do its negative predictive value is very good to rule out PE. It saves the patient from needing a risky CT scan.

Treatment.
Like a clot blocking a coronary blood vessel, a PE can be dissolved directly using a lysis agent, but contraindications (eg recent surgery) exist. For large life threatening PEs, thrombolysis or surgical (Thrombectomy) treatment is available.

The most common management is supportive reoxygenation therapy, and anticoagulant medication to prevent thrombus growth (snowballing).  The aim is to inhibit fibrin formation, to allow the patient to slowly dissolve the clot over time.

There you have it. PE. A deadly killer with 25% mortality. Don't forget to walk around that plane when you are next flying home from Europe!! And if you are on the Pill, for goodness sake stay active and quit the fags!!! (Disclaimer :  in Australia Fags are cigarettes)

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