Download Electrocardiography for Healthcare Professionals Chapter 8: Heart

8/20/2012
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Electrocardiography for Healthcare Professionals
Chapter 8:
Heart Block Dysrhythmias
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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.
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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.
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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
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8.1 Apply Your Knowledge
What is the cause of a heart block dysrhythmia?
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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.
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8.2 First Degree AV Block
 Delay in electrical conduction around the AV node
 Electrical stimulus is prevented from traveling to ventricular conduction system
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8.2 First Degree AV Block Criteria
 Rhythm – regularity between P-P interval and R-R interval is constant.
 Rate – normal, 60-100 beats per minute
 P wave configuration
Same configuration and shape
P wave occurs before each QRS complex
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8.2 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
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8.2 First Degree AV Block
What You Should Know
 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
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8.2 Apply Your Knowledge
Identify this type of AV block:
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8.2 Apply Your Knowledge
Identify this type of AV block:
ANSWER: First degree AV block
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8.2 Apply Your Knowledge
What is unique about First Degree AV Block?
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8.2 Apply Your Knowledge
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.
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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
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8.3 Second Degree AV Block, Mobitz I (Cont’d)
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8.3 Second Degree AV Block, Mobitz I Criteria
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 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
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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 0.06-0.10 second
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8.3 Second Degree AV Block, Mobitz I
What You Should Know
 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
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8.3 Second Degree AV Block, Mobitz I
What You Should Know (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
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8.3 Apply Your Knowledge
Identify this type of AV block:
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8.3 Apply Your Knowledge
Identify this type of AV block:
ANSWER: Second degree AV block type I
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8.3 Apply Your Knowledge
What is unique about Second Degree AV Block, Mobitz I?
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8.3 Apply Your Knowledge
What is unique about Second Degree AV Block, Mobitz I?
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Answer: A Mobitz I rhythm has a cyclical prolonging PR interval until the QRS is dropped.
Then the cycle resets and begins again.
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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
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8.4 Second Degree AV Block, Mobitz II
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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
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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, 0.06-0.10 second
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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
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8.4 Second Degree Mobitz II
What You Should Know
 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
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8.4 Apply Your Knowledge
What is the mnemonic to remember to distinguish between 2nd degree AVB, Mobitz I and 2nd
degree AVB, Mobitz II?
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8.4 Apply Your Knowledge
What is the mnemonic to remember to distinguish between 2nd degree AVB, Mobitz I and 2nd
degree AVB, Mobitz II?
Answer: “Lengthen, Lengthen, drop equals Wenckebach.”
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8.5 Third Degree Atrioventricular
(AV) Block
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 Also known as complete heart block (CHB)
 All electrical impulses originating above the ventricles are blocked
 No correlation exists between atrial and ventricular depolarization
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8.5 Third Degree AV Block
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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 is 60 to 100 beats per minute
Ventricular is 20 to 40 beats per minute
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8.5 Third Degree AV Block
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
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8.5 Third Degree AV Block
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
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8.5 Third Degree AV Block
What You Should Know
 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
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8.5 Apply Your Knowledge
What is unique about 3rd Degree (Complete) Heart Block?
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8.5 Apply Your Knowledge
What is unique about 3rd Degree (Complete) Heart Block?
Answer: The P-P and R-R intervals are regular, but firing at different rates.
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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
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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
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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
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