Arrhythmia and its types in detail

Arrhythmia refers to irregular heartbeat or disturbance in the rhythm of heart. In arrhythmia, heartbeat may be fast or slow or there may be an extra beat or a missed beat. It occurs in physiological and pathological conditions.

CLASSIFICATION

In arrhythmia, SA node may or may not be the pacemaker. If SA node is not the pacemaker, any other

part of the heart such as atrial muscle, AV node and ventricular muscle becomes the pacemaker.

Accordingly, arrhythmia is classified into two types:

A. Normotopic arrhythmia

B. Ectopic arrhythmia.

NORMOTOPIC ARRHYTHMIA

Normotopic arrhythmia is the irregular heartbeat, in which SA node is the pacemaker.

Normotopic arrhythmia is of three types:

1. Sinus arrhythmia

2. Sinus tachycardia

3. Sinus bradycardia.

SINUS ARRHYTHMIA

Sinus arrhythmia is a normal rhythmical increase and decrease in heart rate, in relation to respiration.

It is also called respiratory sinus arrhythmia (RSA). Normal sinus rhythm means the normal heartbeat with SA node as the pacemaker. Normal heart rate is 72 per minute. However, under physiological conditions, in a normal healthy person, heart rate varies according to the phases of respiratory

cycle. Heart rate increases during inspiration and decreases during expiration.

ECG Changes

ECG is normal during sinus arrhythmia. Only the duration of R-R interval varies rhythmically according to phases of respiration . It is shortened during inspiration and prolonged during expiration.

Cause

Sinus arrhythmia is due to fluctuation in the discharge of impulses from SA node . During inspiration,

the lungs are inflated and the intrathoracic pressure

decreases. This increases the venous return. Inflation

of lungs stimulates the stretch receptors of lungs, which

send impulses to vasodilator area (cardioinhibitory

center) through afferent fibers of vagus. It leads to

reflex inhibition of vasodilator area and reduction in

vagal tone. Because of these two factors, heart rate

increases. Simultaneously, increased venous return

initiates Bainbridge reflex that causes increase in heart

rate (Chapter 101).

During expiration, the lungs are deflated and

intrathoracic pressure increases. This decreases the

venous return. During deflation of lungs, the stretch

receptors are not stimulated and vasodilator area is not

inhibited. So, vagal tone increases, resulting in decreased

heart rate. Simultaneously, decreased venous return

abolishes Bainbridge reflex. It also decreases the heart

rate.

„ SINUS TACHYCARDIA

Sinus tachycardia is the increase in discharge of

impulses from SA node, resulting in increase in heart

rate. Discharge of impulses from SA node is very rapid

and the heart rate increases up to 100/minute and

sometimes up to 150/minute.

ECG Changes

ECG is normal in sinus tachycardia, except for short R-R

intervals because of increased heart rate

Conditions when Sinus Tachycardia Occurs

Sinus tachycardia occurs in physiological as well as

pathological conditions.

Physiological conditions when tachycardia occurs

1. Exercise

2. Emotion

3. High altitude

4. Pregnancy.

Pathological conditions when tachycardia occurs

1. Fever

2. Anemia

3. Hyperthyroidism

4. Hypersecretion of catecholamines

5. Cardiomyopathy

6. Valvular heart disease

7. Hemorrhagic shock.

Features of Sinus Tachycardia

1. Palpitations (sensation of feeling the heartbeat)

2. Dizziness

3. Fainting

4. Shortness of breath

5. Chest discomfort (angina).

„ SINUS BRADYCARDIA

Sinus bradycardia is the reduction in discharge of

impulses from SA node resulting in decrease in heart

rate. Heart rate is less than 60/minute.

ECG Changes

ECG shows prolonged waves and prolonged R-R

interval (Fig. 96.4).

Conditions when Sinus Bradycardia Occurs

Sinus bradycardia occurs in both physiological and

pathological conditions. It occurs during sleep. It is

common in athletes due to the cardiovascular reflexes,

in response to increased force of contraction of heart.

Physiological conditions when sinus

bradycardia occurs

1. Sleep

2. Athletic heart.

Pathological conditions when sinus

bradycardia occurs

1. Disease of SA node

2. Hypothermia

3. Hypothyroidism

4. Heart attack

5. Congenital heart disease

6. Degenerative process of aging

7. Obstructive jaundice

8. Increased intracranial pressure

9. Use of certain drugs like beta blockers, channel

blockers, digitalis and other antiarrhythmic drugs

10. Atherosclerosis. Bradycardia due to atherosclerosis

of carotid artery, at the region of carotid sinus is

called carotid sinus syndrome.

Features of Sinus Bradycardia

1. Sick sinus syndrome

2. Fatigue

3. Weakness

4. Shortness of breath

5. Lack of concentration

6. Difficulty in exercising.

Sick sinus syndrome

Sick sinus syndrome is the common feature of sinus

bradycardia. It is the condition characterized by dizziness

and unconsciousness.

ECTOPIC ARRHYTHMIA

Ectopic arrhythmia is the abnormal heartbeat, in which

one of the structures of heart other than SA node

becomes the pacemaker. Impulses produced by these

structures are called ectopic foci.

Subtypes of Ectopic Arrhythmia

Ectopic arrhythmia is further divided into two subtypes:

1. Homotopic arrhythmia, in which the impulses for

heartbeat arise from any part of conductive system

2. Heterotopic arrhythmia, in which the impulses arise

from the musculature of heart other than conductive

system.

Different Ectopic Arrhythmia

1. Heart block

2. Extrasystole

3. Paroxysmal tachycardia

4. Atrial flutter

5. Atrial fibrillation

6. Ventricular fibrillation.