CONDUCTION ABNORMALITIES (HEART BLOCK)

• Conduction Abnormalities or heart block is a disease in the electrical system of the heart, in which the transmissions of electrical impulses are daily or fail to transmit.
• A heart block can be a blockage at any level of the electrical conduction system of the heart. Blocks that occurs –
  • Within the SA node are called SA nodal blocks
  • Within the AV node are called AV nodal blocks.
  • Below the AV node are known as infra-Hisian blocks
    • Within the left or right bundle branches are known as bundle branch blocks
    • Within the fascicles of the left bundle branch are known as hemiblocks
• Clinically most of the important heart blocks are AV nodal blocks

ATRIOVENTRICULAR BLOCK

• AV blocks occur when the conduction of the impulse through the AV nodal or His bundle area is decreased or stopped.
• These blocks can be caused by-
  • Medications - digitalis, calcium channel blockers, beta-blockers
  • Lyme disease - Lyme disease is a bacterial infection (Borrelia burgdorferi) spread through the bite of the blacklegged tick
  • Myocardial ischemia and infarction
  • Valvular disorders
  • Cardiomyopathy
  • Endocarditis or myocarditis
• If the AV block is caused by increased vagal tone (eg, long-term athletic training, sleep, coughing, suctioning, pressure above the eyes or on large vessels, anal stimulation), it is commonly accompanied by sinus bradycardia.
• It may be temporary (resolve on its own), or permanent (require permanent pacing)
• The clinical signs and symptoms of a heart block vary with the resulting ventricular rate and the severity of any underlying disease processes.
• The treatment is based on the hemodynamic effect of the rhythm.
• AV blocks or Heart Block is Classify as –
  • First-Degree Atrioventricular Block
  • Second-Degree Atrioventricular Block,
    • Mobitz Type I (Wenckebach)
    • Mobitz Type II
  • Third-Degree Atrioventricular Block

FIRST-DEGREE ATRIOVENTRICULAR BLOCK

• First-degree AV block occurs when all the atrial impulses are conducted through the AV node into the ventricles at a rate slower than normal.

CHARACTERISTICS

• Rate: Depends on the underlying rhythm
• Rhythm: Depends on the underlying rhythm
• P wave: In front of the QRS complex; shows sinus rhythm, regular shape
• PR interval: prolong; constant and > 0.20 sec
• QRS shape and duration: Usually normal, but may be abnormal
• P:QRS ratio: 1:1
• Causes: MI, seen in healthy children, seen in healthy athletes
• Usually does not require treatment

 

 

SECOND-DEGREE ATRIOVENTRICULAR BLOCK

• Second-degree AV block is diagnosed when one or more (but not all) of the atrial impulses fail to conduct to the ventricles due to impaired conduction.
• It is further classify into two types –
  • Type 1 Second-degree AV block – Mobitz-I / Wenckebach periodicity
  • Type 2 Second-degree AV block, also known as "Mobitz-II"

SECOND-DEGREE AV BLOCK TYPE 1

• Type 1 is characterized by progressive prolongation of the PR interval on consecutive beats followed by a blocked P wave (a 'dropped' QRS complex). After the dropped QRS complex, the PR interval resets and the cycle repeats.

Characteristics

• Rate: Depends on the underlying rhythm
• Rhythm: The PP interval is regular if the patient has an underlying NSR; the RR interval reflects a pattern of change. Starting from the longest RR then RR interval gradually shortens until the another long RR interval.
• P wave: In front of the QRS complex; shape depends on underlying rhythm
• PR interval: PR interval becomes longer with each succeeding ECG complex until there is a P wave not followed by a QRS. The changes in the PR interval are repeated between each "dropped" QRS, creating a pattern in the irregular PR interval measurements.
• QRS shape and duration: Usually normal but may be abnormal
• P:QRS ratio: 3:2, 4:3, 5:4, and so on…
• It is almost always a disease of the AV node.
• This is almost always a benign condition for which no specific treatment is needed. In symptomatic cases, intravenous atropine or isoproterenol may transiently improve conduction.

SECOND-DEGREE AV BLOCK TYPE 2

• Type 2 is characterized on a surface ECG by intermittently nonconducted P waves not preceded by PR prolongation and not followed by PR shortening.

Characteristics

• Rate: Depends on the underlying rhythm
• Rhythm: The PP interval is regular if the patient has an underlying NSR; the RR interval is usually regular but may be irregular, depending on P:QRS ratio.
• P wave: In front of the QRS complex; shape depends on underlying rhythm
• PR interval: PR interval is constant for those P waves heaving QRS complexes
• QRS shape and duration: Usually normal but may be abnormal
• P:QRS ratio: 2:1, 3:1, 4:1, 5:1, and so forth
• The medical significance of this type of AV block is that it may progress rapidly to complete heart block, in which no escape rhythm may emerge.
• In this case, the person may experience a Stokes-Adams attack, cardiac arrest, or sudden cardiac death.
• The definitive treatment for this form of AV Block is an implanted pacemaker.

THIRD-DEGREE ATRIOVENTRICULAR BLOCK

• Third-degree AV block occurs when no atrial impulse is conducted through the AV node into the ventricles because of complete electrical block at or below the AV node. This is known as AV dissociation.
• "Complete heart block" is another name for this rhythm.

CHARACTERISTICS

• Rate: Atrial: 60–100 bpm; ventricular: 40–60 bpm if escape focus is junctional, <40 bpm if escape focus is ventricular
• Rhythm: Usually regular, but atria and ventricles act independently
• P wave: Normal (upright and uniform); may be superimposed on QRS complexes or T waves
• PR interval: Varies greatly
• QRS shape and duration: Normal if ventricles are activated by junctional escape focus; wide if escape focus is ventricular
• P:QRS ratio: More P waves than QRS complexes

MANAGEMENT

• Third-degree AV block can be treated by use of a dual-chamber artificial pacemaker.
• It is an artificial pacemaker with two leads, one in the atrium and one in the ventricle, so that electromechanical synchrony can be approximated.
• Treatment may also include medicines to control blood pressure and atrial fibrillation, as well as lifestyle and dietary changes to reduce risk factors associated with heart attack and stroke.
• Treatment in emergency situations ultimately involves electrical pacing.

NURSING MANAGEMENT

ASSESSMENT

• Assess indicators of cardiac output and oxygenation, especially changes in level of consciousness.
• Physical assessment includes:
  • Rate and rhythm of apical and peripheral pulses
  • Assess heart sounds
  • Blood pressure and pulse pressure
  • Signs of fluid retention
• Health history: include presence of coexisting conditions and indications of previous occurrence
• Medications

NURSING DIAGNOSES

• Decreased cardiac output
• Anxiety related to fear of the unknown
• Deficient knowledge about the dysrhythmia and its treatment

NURSING INTERVANTION

DECREASED CARDIAC OUTPUT

• Monitoring
  • ECG monitoring
• Assessment of signs and symptoms
• Administration of medications and assessment of medication effects
• Adjunct therapy: cardioversion, defibrillation, pacemakers

ANXIETY

• Use a calm, reassuring manner.
• Measures to maximize patient control to make episodes less threatening
• Communication and teaching

HEALTH EDUCATION

• Explain to the patient the importance of taking all ordered medications at the proper time intervals.
• Teach him how to take his pulse and recognize an irregular rhythm, and instruct him to report alterations from his baseline to the physician.
• Teach the adverse effects of medication and signs to report. Warn the patient not to take over-the-counter medications unless he has talked with his physician first.
• If the patient has a permanent pacemaker, warn him about environmental and electrical hazards as indicated by the pacemaker manufacturer.
• Tell the patient to report any light-headedness or syncope. Stress the importance of scheduling and keeping appointments for regular checkups.