If heart sound recording and ECG are superimposed, the first heart sound would occurs

Options

A. At P-wave
B. Just after P-wave
C. Just before QRS complex
D. Just after QRS complex.

Answer

To determine when the first heart sound (S1) occurs in relation to the ECG, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Components of the ECG:**
- The ECG consists of several waves: P wave, QRS complex, and T wave.
- The P wave represents atrial depolarization (contraction of the atria).
- The QRS complex represents ventricular depolarization (contraction of the ventricles).
- The T wave represents ventricular repolarization (relaxation of the ventricles).

2. **Identify the Timing of Heart Sounds:**
- The first heart sound (S1), also known as the "LUB" sound, occurs when the atrioventricular (AV) valves close.
- This closure happens at the beginning of ventricular contraction (systole), which is initiated by the QRS complex.

3. **Locate the QRS Complex on the ECG:**
- The QRS complex is a sharp spike on the ECG that indicates the start of ventricular depolarization.
- The first heart sound (S1) occurs just before the peak of the QRS complex, as the ventricles begin to contract.

4. **Conclusion:**
- Therefore, when heart sound recording and ECG are superimposed, the first heart sound (S1) occurs at the beginning of the QRS complex, indicating the start of ventricular systole.

### Final Answer:
The first heart sound (S1) occurs just before the QRS complex on the ECG.

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