The major function of the heart is to force blood in to a closed system of blood vessels within which the blood is confines and circulated to the entire body. Heart’s activity can be compared to a muscular pump equipped with one way valves. With each heartbeat, an electrical impulse travels through the heart and causes the heart muscle to squeeze and pump blood from the heart. These electrical impulses, transmitted through the heart, are spread throughout the body. This electrical activity of the heart can be detected on the body’s surface and recorded with an instrument called an electrocardiograph.
A graphic record of heart activity is called an electrocardiogram. An electrocardiogram is also called an EKG or ECG. Sometimes the test is called a 12-lead EKG or 12-lead ECG. This is because the heart's electrical activity most often is recorded from 12 different places on the body at the same time. A healthcare provider may recommend an electrocardiogram if a person has signs and symptoms that suggest a heart problem (National Institutes of Health, 2010). Examples of signs and symptoms may include chest pain, breathing problems, unusual heart sounds, palpitation etc.
However, this test can screen for early heart disease that has no symptoms. An ECG may be done as part of a routine health exam and may be used for routine screening before major surgery. Also, this test can be ordered to check how well heart medicine or a medical device, such as a pacemaker, is working (National Institutes of Health, 2010). ECG results can be used by the healthcare provider to help plan treatment for a heart condition. Different types of electrocardiograms Many heart problems are present all the time, and thus a commonly used 12-lead ECG test is sufficient to detect any of these problems.
However, certain issues, such as those related to irregular heartbeats, can come and go. They may be present for only a few minutes out of the day, or while performing specific daily activities (e. g. , exercising). In these situations, special types of ECGs are used to help diagnose these types of problems. The different ECGs that can be used in these situations are:
Stress test: During stress testing, exercise or medications are used to make heart beat faster and work harder while conducting the ECG. •Holter monitor: This is a portable device that records the electrical signals of he heart for a full 24 to 48 hour period (Pagana & Pagana, 2010). This is also called as an ambulatory ECG, as daily activities can be performed while wearing it.
Event monitor: This is a portable device like holter monitors, but they can be worn for more than a month and are used to detect abnormalities of short duration and that occur infrequently. This paper discusses 12-lead ECG that is most commonly used in health care settings. Explanation of ECG test and related physiology A typical ECG has three distinguishable waves or deflections.
The relationship between the deflections waves of an ECG and sequential excitation of the heart is shown below (The Biology corner, 2011) Figure1. The sequence of excitation of the heart related to deflection waves of an ECG tracing. The first wave, the small P wave, lasts about 0. 08 s (Marieb & Mitchell, 2010). This wave results from movement of the depolarization wave from the heart’s SA node through atria. The second wave, the QRS complex is the largest waves of all the three waves. It results from ventricular depolarization and precedes ventricular contraction.
Average duration of the QRS complex is 0. 08 s (Marieb & Mitchell, 2010). A prolonged QRS complex may indicate a right or left bundle branch block in which one ventricle is contracting later than the other. The third wave, the T wave is caused by ventricular depolarization and typically lasts about 0. 16 s (Marieb & Mitchell, 2010). The P-R interval represents the time between the beginning of atrial depolarization and ventricular depolarization and it lasts about 0. 16 to 0. 18 s. A longer interval may suggest a partial AV heart block caused by damage to the AV node (Marieb & Mitchell, 2010).
Lack of impulses through AV node may indicate a total heart block. The Q-T interval is the period from the beginning of ventricular depolarization and repolarization that normally lasts 0. 31 to 0. 41 s (Marieb & Mitchell, 2010). The shorter Q-T interval may indicate tachycardia, and a longer may indicate bradycardia. Normal/abnormal findings In a healthy heart, the size, duration and timing of the deflection waves tend to be consistent. For this reason, changes in the pattern or timing of the ECG may reveal a diseased or damaged heart or problems with the heart’s onduction system (Marieb & Mitchell, 2010). An ECG gives two major kinds of information. First, by measuring time intervals on the ECG, a doctor can determine how long the electrical wave takes to pass through the heart (Pagana & Pagana, 2010). Finding out how long the wave takes to travel from one part of the heart to the next shows if the electrical activity is normal or slow, fast or irregular. Second, by measuring the amount of electrical activity passing through the heart muscle, a cardiologist may be able to find out if parts of the heart are too large or are overworked (Pagana & Pagana, 2010).
Normal ECG values include a heart rate of 60 to100 beats /min and an even and consistent heart rhythm (National Institutes Of Health, 2010). Abnormal ECG results may indicate a sign of following health issues:
Abnormal heart rhythms (arrhythmias)
Cardiac muscle defect
Congenital heart defect
Faster than normal heart rate (tachycardia)
Slower than normal heart rate (bradycardia)
Heart valve disease
Inflammation of the heart (myocarditis)
Changes in the amount of electrolytes (chemicals in the blood)
Past heart attack
Present or impending heart attack
An electrocardiogram may be performed to diagnose additional conditions which are not listed above. ECG Procedure and Patient preparation The patient does not need to take any special steps before having an electrocardiogram. However, the nurse may ask about the medicines the patient is taking as some medicines can affect the results. Also, the nurse performing the test may instruct the patient to avoid exercising or drinking cold water immediately before an ECG, as it may cause false results. The procedure of an ECG is painless and harmless. A nurse will attach soft, sticky patches called electrodes to the skin of chest, arms, and legs.
The patches are about the size of a quarter. Often, 12 patches are attached to patient’s body. This helps detect the heart's electrical activity from many areas at the same time. The nurse may have to shave areas of the skin to help the patches stick. After the patches are placed on patient’s skin, he/she will lie still on a table while the patches detect heart's electrical signals (Pagana & Pagana, 2010). During the ECG recording, nurse may instruct the patient to lie quietly for 10-20 seconds, because the electrocardiograph will detect any muscle or body movement.
A machine will record these signals on graph paper or display them on a screen. The entire test will take about 10 minutes. After an electrocardiogram, the nurse will remove the electrodes (soft patches) from the patient’s skin. Patient may develop a rash or redness where the EKG patches were attached. This mild rash often goes away without treatment. Patient usually can go back to his/her normal daily routine after an ECG. Summary An electrocardiogram is a painless, non-invasive diagnostic test that records heart’s electrical activity.
This test shows, how fast a heart beats, whether the rhythm of the heart is regular or irregular and the strength and timing of electrical signals as they pass through each part of the heart. Healthcare providers use this test to study and detect many heart problems and the results of this test can also suggest other disorders that affect heart function. Conducting an ECG when appropriate is a primary step in increasing a patient’s survival, and leads to a clearer, gained understanding of what is actually happening to a patient’s heart.