Moderate to severe pulmonary embolism may result in several ECG changes. The following ECG findings reflect right ventricular strain and are not specific for acute pulmonary embolism.
They may be useful when combined wih other clinical and laboratory findings.


  T wave inversions in precordial leads V1-V4 with or without accompanying ST segment changes.

  Complete or incomplete right bundle branch block (RBBB).

  QR or qR pattern in lead V1.

 
S1Q3T3 pattern: S wave in lead I; new or increased Q wave in lead III; T wave inversion in lead III.

      S1Q3T3 pattern is seen in approximately
10% of patients with acute pulmonary embolism.

  Sinus tachycardia.

  Arrhythmias: most commonly atrial fibrillation.

  Right atrial abnormality.

  Right axis deviation.

  Low voltage.




Absence of typical ECG findings is not enough to exclude the diagnosis of acute poulmonary embolism.

Early and successful treatment of acute pulmonary embolism may revert the ECG abnormalities.



References

  European Heart Journal 2008,29:2276-2315.

  Am J Cardiol 1994;73:298-303.

  Am J Cardiol 2007;99:817-821.





ECG 1a. ECG in acute pulmonary embolus. The patient had an acute onset chest pain. D-dimer level was 2 mcg/mL.
Even though it is not specific, T wave negativity in C1, C2 and C3 is the most common ECG sign of acute pulmonary embolism.
S wave is present in lead I (S1) and the T wave is negative in lead III (T3) but there is no Q wave in lead III (Q3).
S1Q3T3 is NOT frequently observed in acute pulmonary embolism. There is also right axis deviation: QRS complex is
biphasic in aVR, positive in III and negative in aVL. This ECG was recorded before the onset of thrombolytic therapy.

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ECG 1b. The same patient's ECG just after the completion of thrombolytic therapy with tPA.

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Figure 1a. The same patient's telecardiography shows prominent right pulmonary artery.

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Figure 1b. Thorax CT showed enlarged right pulmonary artery and thrombus inside.

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ECG 2. The ECG above belongs to a 43 years-old woman with acute pulmonary embolism.
The diagnosis was confirmed by thorax CT angiography.
This ECG was recorded at the 10th day of the onset of her symptoms.
ECHOcardiography showed dilated right atrium and right ventricle. Coronary angiography showed normal coronary arteries.
Although not specific, the most common ECG sign of acute pulmonary embolism is T wave negativity in leads V1 to V3.
Mild right axis deviation is also present in the above ECG.
S1Q3T3 is not always seen in acute pulmonary embolism, as is the case in this patient.

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ECG 3. The ECG above belongs to a middle-aged man with acute pulmonary embolism.
Two weeks before this ECG, he was diagnosed as having coronary artery disease and two coronary stents were implanted to
his Left Anterior Descending (LAD) and Intermediate coronary arteries.
Unlike isolated acute pulmonary embolism, the T wave negativity in this patient (with accompanying coronary artery disease)
extends to the lead C5.
S1Q3T3 is also seen. However leads II and aVF are lacking q waves (he did not have inferior myocardial infarction).
The basic rhythm is sinus with VPS and frequent APS.

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Figures 4a, 4b, 4c. The thorax CT images above belong to a 72 years-old woman who complained of dyspnea and chest pain.
Her symptoms started one week ago. The CT images show thrombi in the right and left pulmonary arteries.




ECG 4. The above ECG was recorded on the same day with the thorax CT.
There are no typical ECG findings to suggest the diagnosis of acute pulmonary embolism.
This ECG clearly shows that absence of typical findings is not enough to exclude the diagnosis of acute pulmonary embolism.

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ECG 5. The ECG above belongs to a woman with long-standing chronic systemic arterial hypertension.
She had experienced syncope 4 days ago due to acute pulmonary embolism.
The ECG shows accelerated junctional rhythm. Heart rate (ventricular rate) is about 83/minute. There is also ectopic atrial
tachycardia. The atrial rate is about 165/minute.
P waves are not related to the QRS complexes: complete AV block.
The increased voltage in this ECG suggests left ventricular hypertrophy.

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ECG 6. The ECG above belongs to a 66 years-old woman with a complaint of recent-onset (< 2 days) severe dyspnea.
She can hardly walk 5 meters and becomes dyspneic. She has no known coronary artery disease.
Her echocardiography showed a dilated and hyopokinetic right ventricle with severe tricuspid regurgitation and
moderate pulmonary hypertension. She had normal left ventricular systolic function.
The above ECG shows negative T waves in leads V1 to V3 and flattened T wave in lead V4.
The S1Q3T3 sign is also positive.
No additional ECG signs of pulmonary embolism are seen in this woman.



 
Figures 6a and 6b. The above figures are thorax CT scan from the same woman,
showing
large thrombus occluding the right main pulmonary artery. Ao:Ascending aorta.





ECG 7a. The ECG above belongs to a 69 years-old woman with the complaint of severe fatigue for the last 6 days.
She could not even walk 5 meters. However, she did not complain of dyspnea or chest pain.
The rhythm is sinus tachycardia with a heart rate of 110/minute.
ECHOcardiography showed a dilated and hypokinetic right ventricle. The left ventricle was normal.

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ECG 7b. The compact ECG above is the summary of ECG 7a.
The negative T waves in this ECG was first interpreted as acute coronary syndrome and the patient was referred to us
for urgent coronary angiography.
However, the above compact ECG shows typical signs of acute pulmonary embolism:
- Negative T waves in leads V1 to V4 (not specific but the most common ECG sign of acute pulmonary embolism).
- Low voltage in chest leads
- S1Q3T3.
The patient was referred to pulmonary angiography by computed tomography (CT).



 
Figures 7a, 7b and 7c are the images from CT pulmonary angiography. and show thrombi in
the main pulmonary artery and left pulmonary artery .
Thrombolytic therapy with Alteplase was administered immediately. Anticoagulant therapy was also started.
Her fatique improved within hours. Next day, her ECHOcardiography showed a regression in the right ventricular abnormalities.
Ao:Ascending aorta., MPA: Main Pulmonary Artery., dAo:Descending Aorta.




ECG 7c. The compact ECG above was recorded 9 days after the administration of thrombolytic therapy.
By the time, her symptoms almost disappeared.
T wave negativity in the right precordial leads showed regression.




ECG 7d. The compact ECG above was recorded 6 weeks after the administration of thrombolytic therapy.
It is almost normal. The T wave negativity is confined only to leads III and V1.
Now she is asymptomatic and her ECHOcardiogram shows normal size and function of the right ventricle.
This case clearly shows that early and successful treatment of acute pulmonary embolism may revert the ECG abnormalities.