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Electrocardiography for Healthcare Professionals

Electrocardiography for Healthcare Professionals. Chapter 8: Heart Block Dysrhythmias. Kathryn A. Booth Thomas O’Brien. Learning Outcomes. 8.1 Describe the various heart block dysrhythmias .

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Electrocardiography for Healthcare Professionals

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  1. Electrocardiography for Healthcare Professionals Chapter 8: Heart Block Dysrhythmias Kathryn A. Booth Thomas O’Brien

  2. Learning Outcomes 8.1 Describe the various heart block dysrhythmias. 8.2 Identify first degree atrioventricular (AV) block using the criteria for classification, and explain how the rhythm may affect the patient, including basic patient care and treatment. 8.3 Identify second degree atrioventricular (AV) block, Mobitz I, using the criteria for classification, and explain how the rhythm may affect the patient, including basic patient care and treatment.

  3. Learning Outcomes (cont.) 8.4 Identify second degree atrioventricular (AV) block, Mobitz II, using the criteria for classification, and explain how the rhythm may affect the patient, including basic patient care and treatment. 8.5 Identify third degree atrioventricular (AV) block using the criteria for classification, and explain how the rhythm may affect the patient, including basic patient care and treatment.

  4. 8.1 Introduction toHeart Block Dysrhythmias Occur when electrical activity has difficulty traveling along normal conduction pathway Ventricular depolarization is delayed or absent Degree of blockage depends on cause of delay or blockage and the area effected Three levels of heart blocks

  5. 8.1 Apply Your Knowledge ANSWER:The electrical current has difficulty traveling along the normal conduction pathway. What is the cause of a heart block dysrhythmia?

  6. 8.2 First Degree Atrioventricular (AV) BlockKey Term Cardiac output parameters

  7. 8.2 First Degree AV Block Delay in electrical conduction from SA node to AV node Causes longer than normal PR interval

  8. 8.2 First Degree AV Block Criteria • Rhythm: P-P and R-R intervals are regular and constant. • Rate: 60 to 100 bpm (atria and ventricles) • P wave morphology • Consistent morphology and shape • P wave occurs before each QRS complex • Same number of P waves and QRS complexes

  9. 8.2 First Degree AV Block Criteria (Cont.) PR interval: Greater than 0.20 second QRS duration and morphology: 0.06‒0.10 second, within normal limits

  10. 8.2 First Degree AV Block:What You Should Know Cardiac output consistent with underlying rhythm Monitor for further degeneration and development of other heart blocks. Observe cardiac output parameters. Report developments that occur.

  11. 8.2 Apply Your Knowledge ANSWER:False. A first degree AV block causes a delay in electrical conduction, but the impulse is not completely blocked from reaching the ventricles. True or False: A first degree atrioventricular block prevents impulses generated in SA node from reaching the ventricles.

  12. 8.2 Apply Your Knowledge ANSWER:The PR interval is constant and measures greater than 0.20 second. What are the distinguishing characteristics of first degree AV block?

  13. 8.3 Second Degree Atrioventricular (AV) Block, Type I (Mobitz or Wenckebach)Key Term Blocked or nonconducted impulse

  14. 8.3 Second Degree AV Block Second degree AV blocks are the only blocks that have an irregular ventricular response. • Some electrical impulses are blocked at AV junction region. • Types of second degree AV block: • Type I (Mobitz I or Wenckebach) • Type II (Mobitz II)

  15. 8.3 Second Degree AV Block, Type I (Mobitz I or Wenckebach) Impulses are conducted with increasing difficulty. PR interval increases until a QRS complex is dropped, then resets in a regular pattern.

  16. 8.3 Second Degree AV Block, Type I: Criteria • Rhythm • P-P interval regular • R-R interval irregular due to blocked impulses • Rate • Atrial rate: within normal limits • Ventricular rate: slower than atrial rate

  17. 8.3 Second Degree AV Block, Type I: Criteria (Cont.) • P wave morphology • Normal size • Upright • One P wave for every QRS, with additional P waves • PR interval: becomes progressively longer until QRS wave is dropped, then cycle restarts. • QRS duration and morphology: 0.06‒0.10 second, within normal limits

  18. 8.3 Second Degree AV Block, Type I: What You Should Know • Patient may show signs of low cardiac output if rate decreases to 40 beats per minute or lower. • Condition usually results from inflammation around AV node. • Often temporary • May resolve itself • Monitor for further progression to third degree heart block.

  19. 8.3 Apply Your Knowledge ANSWER:Second degree AV block, type 1 Identify this type of AV block:

  20. 8.3 Apply Your Knowledge ANSWER:It has a cyclical prolonging PR interval until the QRS is dropped; then the cycle resets and begins again. What are the distinguishing characteristics of second degree AV block, type I?

  21. 8.4 Second Degree Atrioventricular (AV) Block, Type II (Mobitz II) AV node selects electrical impulses to block. Pattern may or may not exist. Frequently progresses to third degree AV block.

  22. 8.4 Second Degree AV Block, Type II Criteria • Rhythm • P-P interval is regular. • R-R interval may be regular or irregular. • Rate • Atrial rate: within normal limits • Ventricular rate: slower than atrial rate

  23. 8.4 Second Degree AV Block, Type II: Criteria (Cont.) • P wave morphology • Normal size • Upright • At least one P wave for every QRS complex • More P waves than QRS complexes • PR interval: Constant, even after QRS drop occurs • QRS duration and morphology: 0.06‒0.10 second, within normal limits

  24. 8.4 Second Degree AV Block, Type II: What You Should Know Highly unstable dysrhythmia Observe patient for signs of low cardiac output Critical condition can progress quickly to third degree AV block or complete heart block

  25. 8.4 Differences between Second Degree Heart Blocks Remember: Lengthen, lengthen, drop equals Wenckebach. • Type I • PR interval varies • Temporary condition • Type II • PR interval constant • Chronic condition and more critical

  26. 8.4 Apply Your Knowledge ANSWER:“Lengthen, lengthen, drop equals Wenckebach” What is the mnemonic to help you remember how to distinguish between second degree AV block, types I and II?

  27. 8.5 Third Degree Atrioventricular (AV) Block (Complete)Key Term Dissociative

  28. 8.5 Third Degree Atrioventricular (AV) Block All electrical impulses originating above the ventricles are blocked. No correlation between atrial and ventricular depolarization. P-P and R-R intervals are dissociative.

  29. 8.5 Third Degree AV Block: Criteria • Rhythm • P-P interval is regular. • R-R interval is regular, but different from P-P interval. • Rate • Atrial rate: 60 to 100 bpm • Ventricular rate: 20 to 40 bpm or 40 to 60 bpm, depending on pacemaker site

  30. 8.5 Third Degree AV Block: Criteria (Cont.) Third degree block is the only heart block in which the P waves can be buried inside a QRS complex or T wave. • P wave morphology • Normal size and morphology • May be buried in QRS complex or may occur before or after QRS complex • P waves outnumber QRS complexes

  31. 8.5 Third Degree AV Block: Criteria (Cont.) • PR interval: Varies because atria and ventricles are firing at different rates. • QRS duration and morphology • All complexes have the same duration and morphology. • May be within normal limits or wider depending on the location of the block.

  32. 8.5 Third Degree AV Block:What You Should Know • AV dissociation results in loss of atrial kick. • First responsibility: observe patient for signs of low cardiac output • When ventricular heart rate is 40 or lower, patient may become unconscious. • Immediate medical intervention may be required. • Rhythm strips should be mounted and identified in patient’s record.

  33. 8.5 Comparing Heart Blocks

  34. 8.5 Apply Your Knowledge ANSWER:The P-P and R-R intervals are regular, but firing at different rates. What are the distinguishing characteristics of third degree heart block?

  35. Chapter Summary In heart block rhythms, the current has difficulty traveling the normal pathway. First degree AV block is a delay in conduction from the SA node to the AV node that prevents an impulse from traveling to the ventricular conduction system. Second degree AV block, type I, has blocked or nonconducted impulses from the SA node to the AV junction; also called Wenckebachor Mobitz type I.

  36. Chapter Summary (Cont.) Second degree AV block, type II, selects which impulses it will block, resulting in periodic missing QRS complexes; also called Mobitz type II. Third degree AV block is complete heart block (CHB); all impulses above the ventricles are blocked, so there is no correlation between atrial and ventricular depolarization.

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