Electrocardiography Health Article

Definition

Electrocardiography is a commonly used, noninvasive procedure for recording electrical changes in the heart. The record, which is called an electrocardiogram (ECG or EKG), shows the series of waves that relate to the electrical impulses which occur during each beat of the heart. The results are printed on paper or displayed on a monitor. The waves in a normal record are named P, Q, R, S, and T, and follow in alphabetical order. The number of waves may vary, and other waves may be present.

Purpose

Electrocardiography is a starting point for detecting many cardiac problems. It is used routinely in physical examinations and for monitoring a patient's condition during and after surgery, as well as in the intensive care setting. It is the basic measurement used in exercise tolerance tests and is also used to evaluate symptoms such as chest pain, shortness of breath, and palpitations.

Precautions

No special precautions are required; however, patients are asked not to eat for several hours before a stress test.

Description

The patient disrobes from the waist up, and elec trodes (tiny wires in adhesive pads) are applied to specif ic sites on the arms, legs, and chest. When attached, these electrodes are called leads; three to twelve leads may be employed.

Muscle movement may interfere with the recording, which lasts for several beats of the heart. In cases where rhythm disturbances are suspected to be infrequent, the patient may wear a small Holter monitor in order to record continuously over a 24-hour period. This is known as ambulatory monitoring.

In 2001, the role of prehospital EKG in caring for patients with acute coronary syndromes was examined by the University of California San Diego School of Medicine, University of California San Diego Medical Center, San Diego, California, USA. Reported benefits of the prehospital 12-lead EKG include prompt initiation of reperfusion therapy (restoration of blood flow), and overall improved management and outcome of patients with acute myocardial infarction. Concerns remain regarding the best means of providing real-time field interpretation of the prehospital EKG and the potential for field time delay, triage concerns, and treatment of patients. Questions are raised regarding the overall clini cal and cost benefit of expanding this resource.

Preparation

The skin is cleaned to obtain good electrical contact at the electrode positions and, occasionally, shaving the chest may be necessary.

KEY TERMS

Ambulatory monitoring—ECG recording over a prolonged period during which the patient can move around.

Arrhythmia or dysrhythmia—Abnormal rhythm in hearts that contract in an irregular way.

ECG or EKG—A record of the waves which relate to the electrical impulses produced at each beat of the heart.

Ectopic beat—Abnormal heart beat arising elsewhere than from the sinoatrial node.

Electrodes—Tiny wires in adhesive pads that are applied to the body for ECG measurement.

Fibrillation—Rapid, uncoordinated contractions of the upper or the lower chambers of the heart.

Lead—Name given the electrode when it is attached to the skin.

Reperfusion therapy—Restoration of blood flow to an organ or tissue; following a heart attack, quickly opening blocked arteries to reperfuse the heart muscles to minimize damage.

Aftercare

To avoid skin irritation from the salty gel used to obtain good electrical contact, the skin should be thoroughly cleaned after removal of the electrodes.

Complications

No complications from this procedure have been observed.

Normal results

When the heart is operating normally, each part contracts in a specific order. Contraction of the muscle is triggered by an electrical impulse. These electrical impulses travel through specialized cells that form a conduction system. Following this pathway ensures that contractions will occur in a coordinated manner.

When the presence of all waves is observed in the electrocardiogram, and these waves follow the order defined alphabetically, the heart is said to show a normal sinus rhythm, and impulses may be assumed to be following the regular conduction pathway.

The heart is described as showing arrhythmia or dysrhythmia when time intervals between waves, or the order or the number of waves do not fit this pattern. Other features that may be altered include the direction of wave deflection and wave widths.

In the normal heart, electrical impulses—at a rate of 60–100 times per minute—originate in the sinus node. The sinus node is located in the first chamber of the heart, known as the right atrium, where blood reenters the heart after circulating through the body. After traveling down to the junction between the upper and lower chambers, the signal stimulates the atrioventricular node. From here, after a delay, it passes by specialized routes through the lower chambers or ventricles. In many disease states, the passage of the electrical impulse can be interrupted in a variety of ways, causing the heart to perform less efficiently.