Introduction

 In order for the heart to do its work of pumping oxygen-rich blood to the body, it needs a trigger or electrical impulse to generate a heart beat. This electrical impulse originates from the sinus node-- the heart's natural pacemaker. The sinus node (SA node) is located in the upper right chamber of the heart called the right atrium. From the sinus node, the impulse travels to the atrioventricular (AV) node causing the atria to contract. The AV node takes the signal from the atria and passes it across the His bundle to the ventricles. This causes the ventricles to contract and completes one cardiac cycle.

Problems Related to The Heart's Electrical System

Normally, the sinus node delivers electrical impulses at a rate of 60-100 beats per minute. This is called "sinus rhythm" Your heart determines its optimum rhythm depending on your activity. For example, you heart may beat slower when sleeping or faster when exercising.

Heart rates below 60 beats per minute are called bradycardia. When your heart rate exceeds 100 beats per minute, that's known as tachycardia. If the tachycardia comes from the upper chambers of the heart it is called supraventricular tachycardia or SVT. If it comes from the lower chambers it is ventricular tachycardia or VT. Either too slow or too fast a heart beat may cause the following symptoms:

• Dizziness or light-headedness
• Fatigue
• Palpitations (pounding in the chest)
• Shortness of breath
• Chest pain or pressure
• A fainting spell

 © 1998, 2000, 2002 by Hall-Garcia Cardiology Associates - Last revised August 18,2002

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