HEART BLOCK

RATHEESH R.L

Normal conduction pathway:

SA node -> atrial muscle -> AV node -> bundle of His -> Left and Right Bundle Branches -> Ventricular muscle

DEFINITION

Heart block is an abnormal heart rhythm where 

the heart beats too slowly (bradycardia). 

In this condition, the electrical signals that tell the heart to 

contract are partially or totally blocked between the upper 

chambers (atria) and the lower chambers (ventricles).

TYPES

• They are further classified as,

First degree heart block ( first degree AV 

block)

 second degree heart block (second degree AV 

block)

 third degree heart block (third degree AV 

block)

FIRST DEGREE HEART BLOCK

• First-degree atrio-ventricular block (AV block), or PR 

prolongation, is a disease of the electrical conduction 

system of the heart in which the PR interval is 

lengthened beyond 0.20 seconds.

The following are the most common causes of first-

degree AV block:

• Intrinsic AVN disease

• Acute myocardial infarction (MI), particularly acute 

inferior wall MI

• Myocarditis

• Electrolyte disturbances (eg, hypokalemia, 

hypomagnesemia)

• Drugs (especially those drugs that increase the refractory 

time of the AVN, thereby slowing conduction)

First Degree Heart Block (1º)• SA Node – normal

• Normal P wave• AV Node conducts more slowly than normal

• Prolonged PR Interval• Rest of conduction is normal

• Normal QRS

Significance

• Clinical significance• None

• Treatment• None

• Note – this can progress to 2º or 3º heart block  

Second Degree Heart Block (2º)

• Mobitz Type I (Wenkebach)

• Mobitz Type II

Second Degree Heart Block (2º)Mobitz Type I(Wenkebach)

• Conduction through the AV Node – progressively delayed until a drop beat is seen

Second-degree atrio-ventricular (AV) block, or 

second-degree heart block, is characterized by 

disturbance, delay, or interruption of atrial impulse 

conduction through the AV node to the ventricles.

CAUSES• Drugs (beta-blockers, calcium channel blockers, 

amiodarone)

• Cardiomyopathy

• rheumatic fever, myocarditis

• varicella-zoster virus infection

• Rheumatic diseases

• Hypoxia

• Hyperkalemia

• Hypothyroidism

•  inferior wall myocardial infarction 

Second Degree Heart Block (2º)Mobitz Type I(Wenkebach)

• PR Interval prolongs with each beat until a dropped beat is seen

• The PR Interval is NOT constant• After each dropped beat, the PR interval is normal

and the cycle starts again 

Second Degree Heart Block (2º)Mobitz Type I(Wenkebach)

   PR      PR     PR DROPPED BEAT

Significance• Clinical Significance

• Slight symptoms e.g.. Lethargy, Confusion

• Treatment• Pacemaker if during day &/or symptoms• No treatment if at night

• Note – this can progress to 3º Heart Block

Second Degree Heart Block (2º)Mobitz Type II

• Conduction through the AV node is constant.• PR interval is normal and constant• Occasionally a dropped beat is seen

Second Degree Heart Block (2º)Mobitz Type II

        PR                            PR                   DROPPED BEAT     PR                            

Significance• Clinical significance – this is more significant

disease

• Treatment – pacemaker

• Note – this can progress to 3º Heart Block

Third Degree Heart Block (3º)(Complete)• Complete failure of the AV Node

• No impulses from Sinus Node will pass through to the ventricles

• Some part if the conducting system will take over as pacemaker of the heart (even a myocardial cell 10-15 bpm)

Third-degree atrioventricular (AV) block, also referred to 

as third-degree heart block or complete heart block, is a 

disorder of the cardiac conduction system where there is 

no conduction through the atrioventricular node.

Third Degree Heart Block (3º)(Complete)

• P wave rate – normal

• Ventricular rate – slow

• Ventricular complex may be broad• Idioventricular rhythm

• Complete dissociation between P waves & QRS

Third Degree Heart Block (3º)(Complete)

  P                        P                          P                         P                         P                     

                            QRS                                                            QRS

Significance

• clinical significance• Symptoms LOC, Confusion, Dizziness, Low BP• Can lead to standstill, VT or VF (stokes Adams)

• Treatment - pacemaker

NURSING MANAGEMENT1. Assess the high risk patients2. Monitor ECG of the patient3. Assess the family history of heart disease4. Assess the history of smoking and alcoholism5. Monitor lab values frequently especially serum 

cholesterol levels.6. Assess for CAD7. Monitor vital signs8. Instruct to avoid high fat and oil rich diet