Step 1: Recall ECG components.
An ECG wave typically consists of the P wave, QRS complex, and T wave.
- P wave: Atrial depolarization.
- QRS complex: Ventricular depolarization (Q = initial downward deflection, R = tall upward deflection, S = downward deflection following R).
- T wave: Ventricular repolarization.
Step 2: Analyze the given ECG figure.
The figure shows a prominent upward spike (R wave), a downward deflection after it (S wave), and a rounded wave after that (T wave).
The initial small wave before QRS complex (P wave) is missing.
Step 3: Exclude wrong options.
- (A) R wave: Already visible in the figure.
- (B) S wave: Present after the R wave.
- (C) Q wave: Usually a small downward deflection before R, but here the P wave is entirely absent.
- (D) P wave: Missing wave; correct answer.
Step 4: Conclusion.
Thus, the missing wave in the ECG trace is the P wave.