Scenario: This 12-lead ECG was obtained in a 60-year-old man presenting for a preoperative workup prior to a throat biopsy procedure. The patient is in good health and has no prior history of any medical problems. The surgeon canceled surgery based on the ECG interpretation of Q waves in leads II, III, and aVF.

Sinus rhythm, Wolff-Parkinson-White (WPW) pattern, type A

In WPW syndrome, the electrical impulse traveling from the atria to the ventricles does so via an accessory pathway (or pathways), thus bypassing the normal conduction system. The result is early activation of the ventricles, or “preexcitation.” The ECG characteristics of WPW include (1) shortened PR interval (typically < 0.12); (2) slurring of the initial part of the QRS complex, called a “delta wave”; and (3) a wide QRS complex (> 0.12 seconds) due to the delta wave.

In this example, the Q waves visible in leads II, III,...

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