Precordial concordance on ECG is diagnostic of ventricular tachycardia when the QRS complexes in V1-V6 are which of the following?

• A. All negative
• B. All positive
• C. All negative or all positive
• D. Mixing positive and negative

Answer: (C)

Precordial concordance means the depolarization wave spreads in a single direction through the ventricles, so the QRS in the chest leads has the same orientation in every lead. In ventricular tachycardia, the impulse originates in the ventricle and propagates abnormally, producing a uniform polarity across V1 through V6. When all precordial leads are either entirely positive or entirely negative, this uniformity is present and strongly points to VT.

If the QRS polarity varies across the chest leads—mixing positive and negative—that pattern is discordant and less consistent with VT, fitting more with supraventricular tachycardia with aberrant conduction or other rhythms.