The most common ECG finding in the setting of a pulmonary embolism is sinus tachycardia. However, the “S1Q3T3” pattern of acute cor pulmonale is classic; this is termed the McGinn-White Sign.
A large S wave in lead I, a Q wave in lead III and an inverted T wave in lead III together indicate acute right heart strain. This pattern only occurs in about 10% of people with pulmonary embolisms and is similar to the ECG findings of a left posterior fascicular block, or LPFB. Recall that sinus tachycardia is actually the most common ECG finding during a pulmonary embolus.
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