by Dr Pandula Siribaddana

Created on: November 19, 2010

Heart is one of the many but yet vital natural creations in our body and performs a lifelong function of pumping blood throughout the body in order to support the oxygen and other energy requirements of different tissues. The effective pumping action of the heart will be dependent on coordinated movements and contractions taking place cyclically in the heart musculature and is regulated by self generated electrical impulses within the heart itself.

How does Impulse generate in the heart for contractions?

These electrical impulses are generated mainly in the SA node or the sino-atrial node of the right atrium and will be transmitted to the ventricles through a specialized set of cells placed within the wall of the atrium. It secondly reaches a place known as the AV node located at the beginning of the inter-ventricular septum and will propagate the same through the septum and back up through the ventricular wall during each cycle. Thus, when the signals travel through the ventricular wall, it would contract to push the blood within the ventricular chambers into the aorta and in to the pulmonary vasculature.

How will it be shown in the electrocardiogram?

The electrical activity within the heart will be shown in the ECG as different waves and the atrial contraction taking place following generation of the signal at the SA node will be shown as a single wave known as the ‘p’ wave. It will be followed by a brief flat line known as the PR interval and will then be followed by a larger complex of waves known as the ‘QRS’ complex.

What is meant by a ‘heart block’?

When the electrical signal generated in the SA node do not travel into the ventricle to generate a ventricular contraction, it is defined as a heart block and several such heart blocks have been identified in the clinical setting. Although some heart blocks are harmless and do not require treatment, some would give rise to symptoms which needs correction and some would be fatal if emergency treatment is not given. Thus, let us take a look at the different types of heart blocks.

What are the different types of heart blocks?

First degree block : In this instance, the impulses generated in the SA node does carry into the ventricle although the pace at which the impulses are relayed will become slow. Thus, the length of the PR interval will be increased in such individuals although it would not manifest as clinical symptoms in most instances.

Second degree heart blocks : There

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