Figure 18.17 Atrial depolarization, initiated - PowerPoint Presentation

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Figure 18.17

Atrial depolarization, initiated

by the SA node, causes the

P wave.

P

R

T

Q

S

SA node

AV node

With atrial depolarization

complete, the impulse isdelayed at the AV node.

Ventricular depolarizationbegins at apex, causing theQRS complex. Atrialrepolarization occurs.

P

R

T

Q

S

P

R

T

Q

S

Ventricular depolarizationis complete.

Ventricular repolarizationbegins at apex, causing theT wave.

Ventricular repolarizationis complete.

P

R

T

Q

S

P

R

T

Q

S

P

R

T

Q

S

Depolarization

Repolarization

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2

3

4

5

6

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Figure 18.18

(a) Normal sinus rhythm.

(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.

(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.

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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.

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The answers to the following EKGs is on the

last slide.

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1. A flutter

2. PVC3. 1st degree block4. Inverted T wave5. A fib6. A fib with PVC7. Tachycardia8. normal

9. A flutter

10. 1

st

degree block

11. A fib

12. 1

st

degree block

13. A fib

14. PVC

15. A flutter with inverted

16.2

nd

degree