Arrhythmias

• An arrhythmia is…– disturbance of the electrical rhythm of the heart.

• Classification– Supraventicular (sinus, atrial, junctional) and..– Ventricular

• Main mechanisms– Disorders of impulse formation or automaticity – Abnormalities of impulse conduction– Re-entry– Triggered activity

Supraventricular I

• Sinus– Sinus arrhythmia -> alteration of heart rate during respiration –

not pathological, pronounced in children– Sinus bradycardia and tachycardia

• Atrial tachycardia – automaticity, sinoartial disease– Narrow complex tachycardia with abnormal P waves

• Atrial flutter – large re-entry circuit (RA encircling tricuspid)– 300/min, some form of AV block– Saw tooth flutter waves

• Atrial fibrillation – re-entry, or continued ectopic firing– Paroxysmal or persistent

Supraventricular II

• AV node re-entrant tachycardia (AVNRT)– 120-140 tachycardia, why polyuria?

• WPW Syndrome, atrioventricular re-entrant tachycardia– Abnormal band of conducting tissue connects the

ventricles and the atria– Resembles purkinje tissue, acts as an accessory pathway,

50% asymptomatic– If different pathways have different speeds -> re-entrant ->

with symptoms => WPW syndrome– Delta wave is characteristic

AV block

• First degree – delayed progression through AV node

• Second degree– Type 1 – PR gradually increase until a QRS complex

is missed.– Type 2 – Occasionally P wave does not result in a

QRS complex.• Third degree – complete heart block.

SA block

• First degree – delay between firing of the SA node and depolarisation of the atria

• Second degree– Type 1 – conduction time between SA node and

surrounding atrial tissue becomes progressively longer – eventually a cycle is missed.

– Type 2 – time between SA node and propagation to atria is normal but at some point a cycle is just missed.

• Third degree – failure to conduct impulses