What does a short PR interval with a delta wave indicate on ECG?

• A. Wolff-Parkinson-White pattern with pre-excitation
• B. Left bundle branch block
• C. Inferior STEMI
• D. Posterior MI

Answer: (A)

A short PR interval with a delta wave points to pre-excitation of the ventricles via an accessory pathway, as seen in Wolff-Parkinson-White syndrome. The PR interval is shortened because the atrial impulse bypasses the AV node and reaches the ventricles earlier through this accessory tract. The delta wave is a slurred, initial upstroke of the QRS representing early ventricular activation starting at the accessory pathway before the normal His-Purkinje system takes over. This early activation broadens the overall QRS complex, producing the widened QRS with a notchless, slurred start.

In contrast, a pattern consistent with left bundle branch block shows a wide QRS with characteristic BBB morphology but no delta wave; inferior STEMI would show ST elevations in the inferior leads; posterior MI presents with reciprocal changes in the anterior leads, not a delta wave.