Atrial depolarization, initiated by the SA node, causes the P wave. Q Repolarization R R P T Q P T S 1 Atrial depolarization, initiated by the SA node, causes the P wave. Q S Ventricular depolarization is complete. 4 AV node R R P T P T Q S With atrial depolarization complete, the impulse is delayed at the AV node. 2 Q S Ventricular repolarization begins at apex, causing the T wave. 5 R R P T P T Q S Q 3 S Ventricular depolarization begins at apex, causing the QRS complex. Atrial repolarization occurs. 6 Ventricular repolarization is complete. Figure 18.17

(a) Normal sinus rhythm. (b) Junctional rhythm. The SA node is nonfunctional, P waves are absent, and heart is paced by the AV node at 40 - 60 beats/min. (c) Second-degree heart block. Some P waves are not conducted through the AV node; hence more P than QRS waves are seen. In this tracing, the ratio of P waves to QRS waves is mostly 2:1. (d) Ventricular fibrillation. These chaotic, grossly irregular ECG deflections are seen in acute heart attack and electrical shock. Figure 18.18

In catheter ablation, catheters are threaded through the blood vessels to the inner heart, and electrodes at the catheter tips transmit energy to destroy a small spot of heart tissue.

The answers to the following EKGs is on the last slide.

1

2

3

4

5

6

7

8

9

10

11

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14

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16

1. A flutter 2. PVC 3. 1st degree block 4. Inverted T wave 5. A fib 6 1. A flutter 2. PVC 3. 1st degree block 4. Inverted T wave 5. A fib 6. A fib with PVC 7. Tachycardia 8. normal 9. A flutter 10. 1st degree block 11. A fib 12. 1st degree block 13. A fib 14. PVC 15. A flutter with inverted 16.2nd degree