ECG Findings In Different Types Of Heart Block.

Heart Block is an abnormality in the electrical rhythm of the heart and it occurs when the electrical signals that moves through the heart are slowed or disrupted. There are different types of heart blocks that are mostly diagnosed by the finding on the ECG.

Normal Electrical Activity Of the Heart:A normal heartbeat is initiated when the heart’s natural pacemaker in the sino-atrial node located at the top of the right atrium creates the electrical signal which then travel through the atrium and reaches the atrio-ventricular node. After crossing the AV node these signals pass through the bundle of His. This bundle then divides into thin structures called as bundle branches which then extend into the right and the left ventricles. Through these bundle branches the signals finally reach within the muscle cells of the ventricles causing them to contract. In this way the ventricular muscles contracts as a whole and pumps the blood to the body. If this normal electrical passage is interrupted anywhere it leads to a condition known as heart block.

1. First Degree Heart Block:
In the first degree heart block the electrical impulses are slowed as they move from the atria to the ventricles, but they all reach successfully to the ventricles. This condition rarely causes any symptoms and usually do not require any treatment. On ECG patients with a first degree heart block will have a longer , flatter line between the P and the R wave. In other words the PR interval is prolonged.

2. Second Degree Mobitz type I:
In this type of heart block the electrical impulses are gradually delayed more and more with each heart beat until an impulse fails to reach the ventricles entirely resulting in a skipped beat. This condition sometimes may cause dizziness and usually does not require treatment. On ECG patients with Second degree Mobitz type I heart block shows a characteristic gradual prolongation of the PR interval until a dropped beat with an absent QRS complex.

3. Second Degree Mobitz type II:
In this type of heart block some of the electrical impulses don’t reach the ventricles but the pattern is less regular as compared to Mobitz type I. This condition is less common but more serious than Mobitz type I and may need a pace maker as it may progress into a third degree complete block. On ECG patients with this condition shows QRS wave follows the P wave at a normal speed but some of the QRS waves are missing that indicates a block. 

4. Third Degree Heart Block:
Also known as complete heart block in which none of the electrical impulses reach the ventricles. When the ventricles do not receive the impulse they start generating their own electrical activity but this backup is much slow than the normal heart rate and so the patient will feel light headed or may feel dizzy as the blood is not pumped to the body appropriately. The symptoms may be life threatening leading to medical emergency and conditions like cardiac arrest. Treatment is done with an artificial pacemaker. On ECG the normal patteren is disrupted and the P waves are at a faster rate and are not coordinated with the QRS complex.