What does the presence of a delta wave indicate on an ECG?

• A. Pre-excitation via an accessory pathway
• B. Delays in AV nodal conduction
• C. Myocardial ischemia
• D. Prolonged QT interval

Answer: (A)

A delta wave indicates pre-excitation of the ventricles via an accessory pathway that bypasses the AV node. This means the heart’s impulse reaches the ventricular myocardium earlier than normal through an extra conduction route (as seen in Wolff-Parkinson-White syndrome), producing the slurred initial upstroke of the QRS complex. Because part of the ventricles activates sooner, the PR interval is shortened and the overall QRS becomes widened due to simultaneous activation through two pathways. This pre-excitation sets up a substrate for certain tachyarrhythmias, making WPW a classic context for seeing a delta wave. If the issue were AV nodal delays, the PR interval would be prolonged instead; ischemia would show ST-T changes, and a prolonged QT affects repolarization rather than the QRS onset.