Cardiology Menu

The Heart

Symptoms of Heart Disease

Diagnosing Heart Disease

Introduction to the ECG

Rhythms and Arrhythmia

Rhythms and Arrhythmia

The Sinus Node

• Sinus Rhythm

• Sinus Tachycardia

• Sinus Bradycardia

• Sinus Node Disease

The Atria

• Atrial Ectopic Beats

• Atrial Fibrillation

• Atrial Flutter

• Supraventricular Tachycardia

The Atrioventricular Node

• First Degree Block

• Second Degree Block

• Third Degree Block

• Bundle Branch Block

The Ventricles

• Ventricular Ectopic Beats

• Ventricular Tachycardia

• Ventricular Preexcitation

• Myocardial Ischaemia

Rhythms and Arrhythmia

First Degree Atrioventricular Block

If each wave of depolarisation that originates in the sinus node is conducted to the ventricles, but there is a delay in conduction through the atrioventricular node, then the PR interval will be prolonged.

If the PR interval is more than 0.20 seconds (one box) then this prolongation is referred to as first degree atrioventricular block.

In the ECG trace below, the PR interval (shaded) is prolonged to wider than one box.