Electrophysiology Study

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What is an Electrophysiology Study (EPS)?

An EP study is a low risk procedure that has been performed in major medical centres for many years.

The EP study makes it possible to study your abnormal heart rhythm under controlled conditions and diagnose your particular problem.

Who requires EPS?

Patients are referred for EPS for many reasons.

Some of the more common reasons are:

Rapid or irregular heart beat (often associated with shortness of breath, chest pain or dizziness). Common terms used are palpitations, racing heart or missed beats.
Blackout or dizziness.
Abnormal findings on an ECG.

The Heart

The heart is a pump responsible for maintaining blood supply to the body. It has four chambers. The two upper chambers (the right atrium and left atrium) are the chambers which receive blood as it returns from the body via the veins. The lower chambers (the right and left ventricle) are the chambers responsible for pumping the blood out to the body via the arteries. Like any pump, the heart has an electrical system that controls how it functions.

Normal heart rhythm

In order for the heart to do its work (pumping blood throughout the body), it needs a sort of spark plug or electrical impulse to generate a heartbeat. Normally this electrical impulse begins in the upper right chamber of the heart (in the right atrium) in a place called the sino-atrial (SA) node. The SA node is the natural pacemaker of the heart.

The SA node gives off electrical impulses to generate a heartbeat in the range of 60 to 100 times per minute. If you are exercising, doing strenuous work or you are under a lot of stress, your heart rate may be faster. When you rest or sleep your heart rate will slow down. If you take certain medications, your heart rate may be slower. All of this is appropriate.

From the SA node, the electrical impulse is relayed along the heart’s conduction system. It spreads throughout both the right and left atria causing them to contract evenly.

When the impulse spreads over the right atrium it reaches the atrio-ventricular (AV) node.This is a very important structure in the heart because it is the only electrical connection between the top chambers and the bottom chambers. It is therefore the only way in which an electrical impulse can reach the pumping chambers (the ventricles). The impulse spreads through the AV node and down into the lower chambers or ventricles of the heart. This causes them to contract and pump blood to the lungs and body.

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How do abnormal heart rhythms occur?

In some hearts, an abnormal heart rhythm develops when an electrical impulse either starts from a different location, other than the SA node, or follows a route (or pathway) that is not normally present.

Your doctor will explain the exact nature of your abnormal heart rhythm and the following diagrams should help you understand the mechanism.

Types of abnormal heart rhythms include:

1. AV Nodal Re-entry Tachycardia (AVNRT)

This is the most common form of SVT. An abnormal short circuit (circular conduction) occurs near the AV node. Instead of a single AV node between the top and bottom chambers, there is a second connection that is abnormal. This extra connection has been present since birth. As a result of having 2 connections a short-circuit can occur.

2. Re-entrant Tachycardia and Wolff Parkinson White Syndrome

Abnormal circular conduction utilising the AV node and an “accessory pathway” connecting the atria and ventricles. This extra connection has been present since birth. As a result of having 2 connections a short-circuit can occur. This condition is sometimes termed the Wolff-Parkinson-White Syndrome or WPW.

3. Atrial Tachycardia

This is the least common form of SVT. There is an extra abnormal origin of the electrical impulse from a small area in the atria other than the SA node. It is not known when or why such an extra focus develops.

4. Atrial Flutter

In atrial flutter, abnormal electrical signals circulate in the heart's upper chambers, or atria, which causes the rhythm of the lower chambers to be fast. Because contractions are not timed as in the normal heartbeat, the heart does not pump blood as effectively to the rest of the body. Irregular heartbeats can be seen on an electrocardiogram, or ECG

5. Atrial Fibrillation

In atrial fibrillation, disorganized electrical signals originate in the heart's upper chambers, or atria, causing the rhythm to be irregular. These signals come from small areas in the heart represented here by stars. Irregular heartbeats can be seen in an Electrocardiogram or "ECG". Because contractions are not coordinated as in the normal heartbeat, the heart does not pump blood effectively to the rest of the body.

6. Ventricular Tachycardia

Ventricular Tachycardia is a heart arrhythmia, or irregular heartbeat. In ventricular tachycardia, abnormal electrical pulses in the lower chambers, or ventricles, disrupt the normal firing of the SA node, causing the heart to beat rapidly. These signals can be seen in an Electrocardiogram or ECG. A rapid heartbeat does not give the heart enough time to refill with blood before pumping, which causes diminished blood flow to the rest of the body. This may lead to symptoms of dizziness, lightheadedness, unconsciousness.