The impulse which generated in SA node suddenly fails to be transmitted in both ventricles than –

Options

A. Only atria contract, ventricles not contract
B. Only ventricles contract
C. Atria and ventricles contract at different rate
D. The whole heart stop contraction

Answer

To solve the question regarding the failure of impulse transmission from the SA node to the ventricles, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Heart's Structure**:
- The human heart consists of four chambers: two atria (right and left) and two ventricles (right and left). The SA node (sinoatrial node) is located in the right atrium and is responsible for generating electrical impulses that initiate heartbeats.

2. **Role of the SA Node**:
- The SA node generates electrical impulses that cause the atria to contract first, pushing blood into the ventricles. This impulse is then transmitted to the ventricles through the AV node (atrioventricular node) and the Purkinje fibers.

3. **Implication of SA Node Failure**:
- If the SA node fails to transmit impulses to the ventricles, the normal coordinated contraction of the heart is disrupted. The atria may still contract due to the SA node's activity, but the ventricles will not receive the impulse to contract in sync.

4. **Function of the AV Node**:
- The AV node can also generate impulses, but at a slower rate compared to the SA node. If the SA node fails, the AV node may take over, leading to a situation where the atria and ventricles contract at different rates.

5. **Analyzing the Options**:
- Option 1: Only atria contract, ventricles do not contract - This is partially true, but the ventricles may still contract due to the AV node.
- Option 2: Only ventricles contract - This is incorrect as the atria would still contract.
- Option 3: Atria and ventricles contract at different rates - This is correct as the AV node would take over but at a different rate.
- Option 4: The whole heart stops contraction - This is incorrect as the heart can still function with the AV node.

6. **Conclusion**:
- Therefore, the correct answer is **Option 3: Atria and ventricles contract at different rates**.