The Breathtaking Facts of Pulmonary Embolism

S1Q3T3….S1Q3T3… We are taught this time and time again when using a 12-lead ECG to help confirm the presence of PE. If you look at the literature, this sign is insensitive and non-specific for PE and only occurs in 20% of cases. This sign is shown in many types of respiratory issues that cause right ventricular strain. If you don’t know what I’m referencing, don’t worry about it because there are other/better ways to get your diagnosis. I was taught in school when you have a patient exhibiting signs of dyspnea, you put all of your diagnoses in a bucket. You then systematically take out each one that doesn’t fit until you have your main diagnosis and a few differential diagnoses. Listed below are some of the test that are typically performed in the setting of a suspected PE:

  1. ECG
  2. ABG/D-dimer (considerable amount of debate on these)
  3. Echocardiogram (ultrasound of the heart)
  4. VQ Scan
  5. Pulmonary Angiogram

In this post we’ll go over the ECG findings and briefly hit on ABG/D-dimer, and echocardiography.. But in the end, one of your greatest test will be something that requires no equipment, a thorough history! So what exactly is a pulmonary embolism?

A pulmonary embolism is simply a clot that’s caused a sudden blockage in an artery within a lung. In more severe cases, this can result in hemodynamic collapse and cardiac arrest. A lot of pulmonary embolisms occur as a result of a deep vein thrombosis (DVT) breaking loose and implanting itself in one of the lungs. In regards to history, you should look for the following: recent long distance travel, patient’s taking birth control medication, bed bound patients, recent surgery, smoking, obesity, and hypertension. Patient’s experiencing a PE can have symptoms such as dyspnea, chest pain, and syncope. In more severe cases, patient’s can present with low oxygen saturations and exhibit signs of obstructive shock (hypotension and tachycardia). While acquiring a thorough history on the patient, run a quick ECG.


On the ECG, you need to be on the lookout for rightward axis deviation, tachycardia, RBBB, ST-segment elevation in V1 and aVR, premature atrial contractions, and new onset of atrial fibrillation/flutter. Additionally, T wave inversions (TWI) in the “rightward looking” leads may also suggest PE. You should pay extra close attention for TWI when looking at Lead III, as this is the most rightward facing lead. The most common ECG manifestation is tachycardia.

In this specific patient, you see a sinus tachycardia with a rightward axis. Additionally, there’s TWI in V1-V5 which shows some degree of right ventricular strain. The reason you look for right ventricular strain is because once the clot has been implanted in the lung, blood backs up and puts pressure on the right ventricle.

Arterial Blood Gas (ABG)

An ABG measures the pH and levels of oxygen and CO2 in the bloodstream. The normal values for an ABG are:

  1. pH is 7.35-7.45
  2. Partial pressure of oxygen (PaO2) is 75-100 mmHg
  3. Partial pressure of carbon dioxide (PaCO2) is 35-45 mmHg
  4. Bicarbonate (HCO3) is 22-26 mEq/L
  5. Oxygen saturation is 94-100%


A D-dimer is a fibrin degradation product (FDP) which is, in simple terms, small protein fragments in the blood after a blood clot has been broken down. The normal range for this test is less than 0.50. Anything over this is considered positive. In low risk populations, this test has a high sensitivity but a low specificity for detecting a pulmonary embolism. This test is also able to determine if the patient has a DVT.


An echocardiogram (ultrasound) is a simple test used to determine right ventricular straining of the heart. This is done by sending out high frequency waves from a wand that allows the sonographer to see things such as right ventricular dilation and right ventricular hypokinesia. One of the most distinctive findings for a PE on echo is the presence of McConnell’s Sign.

“McConnell’s sign, that is regional RV dysfunction, with akinesia of the mid free wall but normal motion at the apex is a distinct echocardiographic finding described in patients with acute pulmonary embolism” (Oh, Bang, & Kim, 2015). Below is the McConnell’s sign.


Treatments for the hemodynamically unstable patient with PE include: Thrombolytics, an embolectomy if thrombolytics have failed or are contraindicated, or even an IVC filter. Hemodynamically stable patients receive anticoagulation.

Unfortunately for those in EMS, there aren’t many treatments for these patients. The best thing for these patients is early recognition through a thorough history/examination and getting the patient to the most appropriate facility while maintaining the ABCs enroute.

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This site is meant to be used for educational use only. We strive to push evidence based medicine with no bias to help you obtain all the important information. You should always follow your protocols that have been set in place.

Scopeduation Team (Matt)


Bounds, Emily J. “D Dimer.” StatPearls [Internet]., U.S. National Library of Medicine, 3 May 2020,,Dimer%20is%200.50%20or%20greater.

Gaines, Kathleen. “Know Your ABGs – Arterial Blood Gases Explained.”, 3 Apr. 2020,

Mansencal, Nicolas, and Olivier Dubourg. “Update on Echocardiography in Pulmonary Embolism.” European Society of Cardiology, 15 Feb. 2014,,hypertension%20(1%2C2).

Oh, Seong Beom, et al. “McConnell’s Sign; a Distinctive Echocardiographic Finding for Diagnosing Acute Pulmonary Embolism in Emergency Department.” Critical Ultrasound Journal, Springer Milan, 9 Mar. 2015,

Rodger MA, Carrier M, Jones GN, et al. Diagnostic value of arterial blood gas measurement in suspected pulmonary embolism. Am J Respir Crit Care Med. 2000;162(6):2105-2108. doi:10.1164/ajrccm.162.6.2004204

Sosland, Rachel P., and Kamal Gupta. “McConnell’s Sign.” Circulation, 7 Oct. 2008,

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