HEART BLOCK

DEFINITION

Heart blocks are referred to junctional dysrrhythmias i.e, dysrrhythmias that originate in the area of the AV node, primarily because the SA node has failed to fire or the signal has been blocked. In this situation AV node becomes the pacemaker of the heart.

Types of Heart Block

1. First degree Atrio-Ventricular block
2. Second degree Atrio-Ventricular block
3. Third degree Atrio-Ventricular block

First Degree AV block

This is a type of AV block in which every impulse is conducted to the ventricles but the AV conduction is prolonged. After the impulse moves through the AV node it is usually conducted normally through ventricles.

Etiology:

• Myocardial Infarction
• Coronary Artery Disease
• Rheumatic fever
• Vagal stimulation
• Drugs such as digoxin, Beta adrenergic blockers, calcium channel blockers.

ECG characteristics:

• Heart rate is normal and rhythm is regular
• ‘P’ wave is normal, PR interval is prolonged >0.20 seconds and QRS complex usually has normal shape and duration.

Clinical manifestations:

• usually asymptomatic
• warning or a precursor for higher degree AV block.

Treatment:

• Treat the underlying causes like MI, Rheumatic fever.
• Monitor the patient for any changes in rhythm.

Second Degree block

Second degree AV block is further classified as

1. Second degree AV block (Mobitz Type 1) block
2. Second degree AV block (Mobitz Type 2) block

Second degree AV block (Mobitz Type 1) block: This is also called (mobitz Type I heart block or wenckebach Phenomenon. This includes a gradual lengthening of the PR interval. It occurs prolonged AV conduction time until atrial impulse is non-conducted a QRS impulse is blocked (missing).

Etiology: use of drugs such as digoxin or beta adrenergic blockers.

ECG characteristics:

• Atrial rate is normal
• Ventricular rate is slows as a result of non-conducted or blocked QRS complexes.
• Here there is progressive lengthening of PR interval until another QRS complex is blocked.

Clinical manifestations:

• Usually asymptomatic
• associated symptoms are hypotension
• bradycardia
• Signs of shock.

Treatment:

• Atropine is used to increase HR
• Temporary pacemaker may be needed esp. in patients with Myocardial Infarction
• If patients are asymptomatic closely observe the patient with a transcutaneous pacemaker at the bedside.

Second degree AV block (Mobitz type II)

It is also called as type II heart block. Here ‘P’ wave is non-conducted with progressive PR lengthening. This usually occurs when there is a block in bundle branches.

This is a severe type of block in which certain impulses from SA node are conducted. The ratio occurs 2:1, 3:1 i.e. 2 ‘P’ waves to one QRS wave and 3 ‘P’ waves to one QRS complex. This block occurs in bundle of His and purkinje system.

Etiology

• Coronary Artery Disease
• Rheumatic Heart Disease
• Anterior wall Myocardial Infarction
• Digitalis toxicity

ECG characteristics:

• Atrial rate usually normal
• But ventricular rhythm may be irregular
• QRS complex is usually more than 0.12 second because of bundle branch block.

Clinical manifestations:

• Decreased cardiac output
• Angina
• hypotension

Treatment:

• Withdraw or stop medications that slows the Atrio-ventricular node conduction such as Amiodarone, digoxin, beta adrenergic blockers & Calcium Channel blockers
• Temporary pacemaker is inserted immediately to treat symptoms of angina and hypotension
• Permanent pacemaker is recommended to treat severe bradycardia

Third degree AV block

It is also called as complete heart block that constitutes one form of AV dissociation in which no impulse from the atria are conducted to the ventricles. The ventricular rhythm is an escape rhythm and ectopic pacemaker may be above or below the bifurcation of bundle of HIS.

Etiology:

• Coronary Artery Disease
• Myocardial Infarction
• Cardiomyopathy
• Systemic disease like amyloidosis and progressive systemic sclerosis (scleroderma)

ECG characteristics:

• Atrial rate is usually a sinus rate ie, 60-100 beats/ min
• If the block is in Atrio-Ventricular node the rate is 40-60 beats/min
• ‘P’ wave has normal shape, PR interval is variable and there is no time relationship between P wave and QRS complex

Clinical manifestations:

• Syncope
• Bradycardia
• Decreased cardiac output
• Asystole
• Signs and Symptoms of shock and
• Heart failure

Treatment:

• Transcutaneous or temporary pacemaker is inserted.
• Drugs like atropine is administered to treat Bradycardia
• Epinephrine, Isoproterenol and Dopamine is administered to treat severe Hypotension as a temporary measure to increase heart rate and maintain BP.
• Permanent pace maker is inserted as soon as possible: Permanent Pacemakers is a device that is surgically placed in the right side of the heart to support the heart’s electrical activity. They can stabilize abnormal heart rhythms
• Epicardial spacing: Epicardial pacing wires are inserted into the endocardium via femoral cut down and are attached to a pacer box (pulse generator box) via a pacing cable.
• Defibrillation therapy: Defibrillators are devices used in severe Arrhythmias to generate an electric pulse or shock to the heart in order to revert back to normal Sinus rhythm. They are usually given during Cardiac arrest to aid in regaining heart’s contractility.
• Automatic external defibrillator(AED): An AED is a small, battery-operated, portable device that monitors the heart’s rhythm and delivers a shock to the heart to restore normal rhythm
• Insertion of Implantable cardioverterdefibrillator(ICD): An ICD is a battery-powered device placed surgically placed under the skin that monitors the heart rate. Thin wires connect the ICD to your heart. If an abnormal heart rhythm is detected the device will deliver a low energy electric shock to restore a normal heartbeat.

Patient and family teaching in case of permanent pacemaker or Implantable Cardioverter Defibrillation (ICD) Insertion

• Follow up with the consultant for inspection of ICD insertion and routine interrogation of the ICD
• Report any signs of infection at incision site like redness, swelling, drainage or fever
• Keep incision site dry for 4 days after insertion
• Avoid lifting arm on ICD side above shoulder until approval by consultants
• Avoid direct blows to ICD site
• Avoid large magnets and strong electromagnetic fields because it may interfere with the device
• While travelling in plane the airport must be informed of the presence of ICD because it may set off the metal detector
• If ICD fires inform consultant immediately.
• Teach family members on CPR procedure