What is S1Q3T3?
S1Q3T3 is a term for a specific ECG pattern defined by Paul White and Sylvester McGinn four years before WW2 [1].
The occurrence of this waveform on the ECG is an indicator for right heart problems. One of the most common conditions when the pattern emerges is pulmonary embolism [1].
Technically, S1 means deep S waves on ECG in the lead I. Q3 stands for the presence of a Q wave in the lead III, and T3 means inverted T waves in the lead III.
In what conditions do the S1Q3T3 pattern occur on ECG?
Aside from pulmonary embolism, the S1Q3T3 wave pattern on the ECG can occur in other conditions. For example, it was found in nearly 5% of a group of patients with pneumonia [2] or long QT syndrome [3].
It also was found in COVID-19-infected people. Interestingly, its finding was strongly linked to death [4].
It shows that the S1Q3T3 pattern cannot be considered an exclusive sign of one disease. It should always be considered in conjunction with other examinations and, most importantly, with clinical presentation and patient history.
How accurate is the pulmonary embolism diagnosis based on the S1Q3T3 pattern?
The accuracy in diagnosing pulmonary embolism (PE) according to S1Q3T3 ECG is not high. The pattern can be observed in less than 3% of all pulmonary embolism cases [5].
Additionally, the pattern can also occur in other diseases. This makes it very difficult to accurately diagnose a pulmonary embolism based only on the presence of the S1Q3T3 pattern.
What is pulmonary embolism, and what can cause it?
Pulmonary embolism is a dangerous condition that occurs when the embolus blocks a vessel in the pulmonary circulation. The embolus can obstruct one of the pulmonary arteries. The blood flow disturbance leads to a fall in the oxygen levels in the blood. If untreated, pulmonary embolism can be fatal [6, 7, 8, 9].
An embolus is most commonly a blood clot that originates in a deep vein in the leg [10]. However, in rare cases, an embolism can also be caused by an air bubble, fat tissue, or other large particles in the blood that are moved and occlude a vessel [11, 7].
Factors that can contribute to the formation of blood clots and increase the risk of embolism include:
- bone fractures,
- muscle tears,
- vessel injury,
- long period without movement (like recovery time after disease or long sitting),
- surgeries [10, 12].
What are the symptoms of a pulmonary embolism?
Symptoms depend on the location and the size of the embolism. It is possible to have little to no symptoms if the pulmonary embolism is small and does not obstruct the main arteries.
The most common symptom of pulmonary embolism is sudden or slowly onset shortness of breath. Pain in the chest that can spread to the arm, jaw, or neck is also common [10, 12].
Other symptoms include:
- coughing (sometimes with blood) [10, 13],
- limb swelling [13],
- syncope (fainting) [13],
- anxiety [10],
- pale or bluish skin [10],
- irregular heartbeat [13],
- lightheadedness [10],
- rapid breathing [13],
- rapid heartbeat [13],
- a weak pulse [10].
Diagnosis of Pulmonary Embolism
Diagnosis of pulmonary embolism is based on clinical presentation of symptoms, imaging methods, and laboratory results.
When the doctor has a suspicion that you can have a pulmonary embolism, he will use laboratory results of D-dimer [14] and blood gas analysis [15] to see whether you have a blood clot in your lungs.
To further examine the suspected pulmonary embolism the physician can use techniques like:
- ECG,
- X-ray,
- computed tomography pulmonary angiogram (CTPA),
- ventilation-perfusion scintigraphy,
- lung ultrasound,
- echocardiography [16, 17, 18, 15].
Treatment of Pulmonary Embolism
The treatment of pulmonary embolism can be pharmacological and sometimes an intervention. However, the course of the therapy is always determined by the size and location of the embolus.
Typical therapy is based on anticoagulation. It starts with a heparin or fondaparinux and later a vitamin K antagonist [16, 17].
In cases when the embolism is life-threatening, fast thrombolytic therapy can be applied [16]. However, if normal treatment fails or is contraindicated, embolectomy can be used to resolve the issue [17].