Question:

What is the most common abnormal ECG finding in pulmonary embolism (PE)?

1. Atrial fibrillation
2. Left bundle branch block (LBBB)
3. Sinus tachycardia
4. Right bundle branch block (RBBB)

Answer: 3. Sinus tachycardia is the most common finding in PE.

Pulmonary embolism (PE) can be difficult to diagnose and has few ECG findings that are specific or sensitive. PE cannot be diagnosed on the basis of ECG alone. The most common ECG finding in PE is sinus tachycardia. This is seen in just under half of PE cases. A right bundle branch block is seen in less than 20% of PE cases. Another “classic” ECG finding is referred to as S1Q3T3, describing a large S-wave in lead I, a Q-wave in lead III, and an inverted T-wave in lead III.

This S1Q3T3 is commonly taught as associated with PE; but is neither sensitive nor specific – it is found in less than 15% of PE and is also found in many other conditions. It is more appropriately termed a “respiratory pattern” and is associated with severe and/or chronic pulmonary conditions.

Many ECG changes found in PE are due to strain on the right side of the heart caused by the right ventricle attempting to circulate blood against resistance in the blood vessels of the lung. When a blood clot (an embolus) partially or fully obstructs one of the pulmonary arteries, the right ventricle must work against higher pressure to perfuse the lungs. This first leads to tachycardia as the heart attempts to maintain the same cardiac output (volume of blood pumped over a given time). As the right ventricle becomes increasingly strained, it may lead to RBBB and right axis deviation.

Learn more about this condition.

Pregnant patients are at increased risk of venous thromboembolism (VTE) disease which may manifest as DVT, PE, or other less-common conditions. The pregnant woman’s body increases her ability to form blood clots to prevent post-partum hemorrhage. While this is generally protective, it leads to a five-fold increase in VTE events during pregnancy. [1]

Many of the normal symptoms of pregnancy may mimic pulmonary embolism. Dyspnea, the most common symptom of PE, is also a common complaint during late pregnancy due to pressure on the diaphragm and increased circulating blood volume. Thus, it is important to remember that pregnant patients are at an increased risk of PE and this condition should be considered in any pregnant patient complaining of unilateral leg swelling, dyspnea, or chest pain.

Treatment of the unstable PE patient is tricky, there is conflicting evidence on the role of fluids for hypotension secondary to a PE. For the prehospital treatment of this patient, follow TP 1213, Cardiac Dysrhythmia – Tachycardia. This would allow you to administer normal saline with reassessment every 250 mL for signs of pulmonary edema or fluid overload. In case the patient becomes hypotensive or exhibits signs of shock, follow TP 1207 Shock/Hypotension and consider push-dose epinephrine.

After official diagnosis in the hospital, treatment of PE involves starting the patient on “blood thinner” medications that slow down formation of blood clots and prevent growth of the already existing clot, giving the body time to break down the clot naturally. For rare patients with hemodynamic instability due to large clots, mechanical clot retrieval (thrombectomy) may be performed or clot-busting drugs, like those used for acute strokes, may be given in the hospital.

ECG Case Follow-Up

After transporting the patient to the ED, the patient is diagnosed with an acute DVT and PE. She is started on a blood thinner, enoxaparin and is discharged after two days of observation. She delivers a healthy baby two months later and continues treatment with blood thinners for 6 weeks post-partum. [2]