107. What is the McGinn-White sign?

The McGinn-White Sign is the S1Q3T3 pattern seen on the ECG in the setting of acute pulmonary embolism or other causes of acute right heart strain (cor pulmonale). A large S wave in lead I, a Q wave in lead III, and an inverted T wave in lead III is the finding and only occurs in about 10% of people with pulmonary embolisms. This ECG finding should not be confused with that of a left posterior fascicular block.