A negative deflection before the R wave is called which wave?

• A. Q waves
• B. R waves
• C. S waves
• D. T waves

Answer: (A)

In ventricular depolarization, the QRS complex shows three successive deflections: a downward one, then an upward R wave, followed by a downward S wave. The downward deflection that occurs before the first positive R wave is called the Q wave. It represents the initial depolarization of the interventricular septum, usually moving from left to right. The R wave is the first upward deflection, and the S wave is the downward deflection after the R wave, with the T wave representing ventricular repolarization. Keep in mind that not all leads show a noticeable Q wave; when present, it’s typically small, but if a Q wave is unusually deep and wide, it can signal prior myocardial infarction.