Answer: The electrical current has difficulty traveling down the normal conduction pathway.

Transcription

1 1 Electrocardiography for Healthcare Professionals Chapter 8: Heart Block Dysrhythmias Learning Outcomes 8.1 Describe the various heartblock dysrhythmias 8.2 Identify first degree heartblock 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. Learning Outcomes (Cont d) 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. 8.1 Introduction to Heart Block Dysrhythmias Occur when electrical activity has difficulty traveling along normal conduction pathway Ventricular depolarization is delayed or absent Three levels of heart blocks 8.1 Apply Your Knowledge What is the cause of a heart block dysrhythmia? 8.1 Apply Your Knowledge What is the cause of a heart block dysrhythmia? Answer: The electrical current has difficulty traveling down the normal conduction pathway First Degree AV Block Delay in electrical conduction around the AV node Electrical stimulus is prevented from traveling to ventricular conduction system 8.2 First Degree AV Block Criteria Rhythm regularity between P-P interval and R-R interval is constant. Rate normal, beats per minute P wave configuration Same configuration and shape P wave occurs before each QRS complex 1

2 First Degree AV Block Criteria (Cont d) PR interval -is constant -measures greater than 0.20 second QRS duration -normal between 0.06 to 0.10 second 8.2 First Degree AV Block Patient will maintain normal cardiac output No change in the patient will occur with this rhythm Monitor and report further degeneration and development of other heart blocks ANSWER: First degree AV block What is unique about First Degree AV Block? What is unique about First Degree AV Block? Answer: With first degree AV block, the PR interval is constant and measures greater than 0.20 seconds. 8.3 Second Degree AV Block, Mobitz I (Wenckebach) Some electrical impulses are blocked/non-conducted at AV junction region AV node conducts electrical impulse to ventricular conduction pathway until it fails, then resets in a repetitious pattern Irregular ventricular response 8.3 Second Degree AV Block, Mobitz I (Cont d) 8.3 Second Degree AV Block, Mobitz I Criteria 2

3 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 8.3 Second Degree AV Block, Mobitz I Criteria (Cont d) P wave configuration Normal size, upright One P wave for every QRS, with additional P waves PR interval varies, starts short, gets progressively longer until QRS wave is dropped, then cycle is restarted QRS duration normal second 8.3 Second Degree AV Block, Mobitz I Patient may not exhibit signs of low cardiac output until rate decreases to 40 beats per minute or lower Condition usually results from inflammation around AV node and is often temporary 8.3 Second Degree AV Block, Mobitz I (Cont d) If patient exhibits signs of low cardiac output, notify licensed practitioner If no low cardiac output signs are exhibited, monitor patient for progression to third degree heart block ANSWER: Second degree AV block type I What is unique about Second Degree AV Block, Mobitz I? What is unique about Second Degree AV Block, Mobitz I? 3

4 Answer: A Mobitz I rhythm has a cyclical prolonging PR interval until the QRS is dropped. Then the cycle resets and begins again. 8.4 Second Degree AV Block, Mobitz II Referred to as the classical heart block AV node selects which electrical impulses to block No pattern or reason for dropping QRS complex exists Frequently progresses to third degree AV block 8.4 Second Degree AV Block, Mobitz II 8.4 Second Degree AV Block, Mobitz II Criteria Rhythm P-P interval is regular R-R interval is irregular Rate Atrial rate is within normal limits Ventricular rate is slower than atrial rate 8.4 Second Degree AV Block, Mobitz II Criteria (Cont d) P wave configuration Normal size Upright One P wave for every QRS complex, but additional P waves PR interval constant, even after QRS drop occurs QRS duration normal, second 8.4 Troubleshooting In second degree type I, the PR interval in front of the dropped QRS complex is longer than the PR interval behind the dropped QRS complex In second degree type II, the interval is constant Both rhythms should be reported 8.4 Second Degree Mobitz II Observe patient for signs of low cardiac output Highly unstable dysrhythmia Critical condition can progress quickly to third degree AV block or complete heart block 8.4 Apply Your Knowledge What is the mnemonic to remember to distinguish between 2 nd degree AVB, Mobitz I and 2 nd degree AVB, Mobitz II? 8.4 Apply Your Knowledge What is the mnemonic to remember to distinguish between 2 nd degree AVB, Mobitz I and 2 nd degree AVB, Mobitz II? Answer: Lengthen, Lengthen, drop equals Wenckebach Third Degree Atrioventricular (AV) Block 4

5 Also known as complete heart block (CHB) All electrical impulses originating above the ventricles are blocked No correlation exists between atrial and ventricular depolarization Criteria Rhythm P-P interval is regular R-R interval is regular, but different from P-P interval Rate Atrial rate is 60 to 100 beats per minute Ventricular is 20 to 40 beats per minute Criteria (Cont d) P wave configuration Normal size and shape, but may be buried in QRS complex Number of P waves does not correlate to number of QRS complexes P waves outnumber QRS complexes Criteria (Cont d) PR interval Intervals will vary A long PR interval followed by a short PR interval indicates complete heart block QRS duration Constant May be within normal limits or wider depending on the location of the block Patient will show signs of low cardiac output and may be unconscious Initiate Code Blue when patient shows first signs of low cardiac output Immediate medical intervention may be required temporary pacemaker Rhythm strips should be mounted and identified in patient s record 8.5 Apply Your Knowledge What is unique about 3 rd Degree (Complete) Heart Block? 8.5 Apply Your Knowledge What is unique about 3 rd Degree (Complete) Heart Block? Answer: The P-P and R-R intervals are regular, but firing at different rates. Chapter Summary The current has difficulty traveling the normal pathway. Causes a delay or absence of ventricular depolarization. The degree of blockage is dependent on the area affected and the cause of delay or blockage. First degree AV block -delay in conduction from the SA node to the AV node -prevents an impulse from traveling to the ventricular conduction system 5

6 42 Chapter Summary (Cont d) Second degree AV block, type I -has blocked or non-conducted impulses from SA node to ventricles at the AV junction -the conduction through the AV node is delayed -the impulse does not get to the ventricles and becomes blocked Second degree AV block, type II -referred as the classical heart block -AV node selects which impulses it will block -missing QRS complex -this dysrhythmia can progress to third degree AV block 43 Chapter Summary (Cont d) Third degree AV block -referred to as complete heart block (CHB) -all impulses above the ventricles are blocked and cannot reach the ventricles -no correlation between atrial and ventricular depolarization -P-P and R-R intervals are firing at different rates 6