Identifying Arrhythmias (Part-1)

The heart beats at a regular rate of 60-100bpm with the impulse originating from the SA node and ending at the ventricular musculature traversing the AV node, Bundle of His and Purkinjee fibres. Any defect in this circuit resulting in irregular beating of the heart is termed as Arrythmia. Lets look at some arrythmias, We commonly encounter in clinical practice.

Classification:

Broadly Arrythmias can be classified into

1. Sinus Arrhythmia
2. Brady Arrhythmia
3. Tachy Arrhythmia
4. Extra Systole

Sinus Arrhythmia:

It is mostly physiological, characterised by by irregular R-R interval, i.e lenghtheing and shortening of R-R interval, corresponding to the respiratory cycle.

• P wave is normal in size and morphology
• Every P wave is followed by QRS complex
• PR interval is normal and constant

Bradyarrhythmia:

Sinus Bradycardia:

HR less than 60bpm with otherwise normal ECG morphology is termed as sinus bradycardia. It is declared physiological after ruling out all pathological causes.

Trivia:The lowest heart rate recorded in a healthy individual is 24bpm, that of Mr.Daniel Green, then 81 years old

Usain Bolt has a resting heart rate of 33bpm.

Sick Sinus Syndrome:

As the name implies, the SA node is sick and may result in bradycardia  with paroxysmal tachycardias. The SA node at times dozes off, fails to fire. Some other part of the heart, takes up the pacemaking activity and fires at its own pace. Suddenly the SA node wakes up and start firing at its normal pace resulting in sinus rhythm or may fire excessively resulting in tachyarryhythmias. It may manifest as

• Sinus Bradycardia
• Sinus Arrhythmia
• Sinus Arrest
• Brady-Tachy Syndrome.

Sinus Arrest

Brady-Tachy Syndrome

Heart blocks:

1st Degree Heart block:

Prolonged PR interval more than 5 small boxes indicate 1st degree Heart block.

2nd Degree Heart block:(Mobitz Type 1):

This is characterised by progressive lengtheing of PR interval with each beat, untill a QRS complex is dropped and then the cycle repeats.

2nd Degree Heart block:(Mobitz Type 2):

Unlike Mobitz Type 1, here the PR interval is constant, but a QRS complex is dropped occasionally.

3rd Degree/ Complete Heart Block:

Complete heart block occurs when the atrium and ventricle beats independent of each other. Atrium contracts regularly but the impulse is not conducted to the ventricles.So ventricles contract at their their own pace of about 40/min. P waves and QRS shows no relationship

Extra Systole

When any part of the heart is depolarised earlier than expected, the beat is termed as an extrasystole. Since the heart contracts earlier, it is also termed as premature contraction and since the origin of the impulse is elsewhere the normal circuit, it is also termed as ectopic.

Atrial Extra Systole:

• Inverted P wave indicates Atrial ectopic

1. If PR interval is less than 3 small boxes, the origin of ectopic is AV node
2. If PR interval is more than 3 small boxes,the origin is elsewhere from the atrium.

Ventricular Extra Systole:

Look at the ECG as a whole for any bizzare, oddly placed beat. PVC is characterised by

• Wide QRS
• Premature-occurs before the next expected beat
• ST-T changes
• Compensatory pause

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Dr.Praful JK, MBBS