The Electrocardiogram is a test that measures the electrical impulses of the heart. The heart is a muscular pump which consists of four rooms. The two upper chambers are called atria and the other two are called ventricles. A natural electrical system causes the heart muscle to contract and pump blood to the lungs and to the body.
The electrical activity of the heart can be detected on the skin with the use of some small metal discs called electrodes. During the ECG, the electrodes are attached to the skin on the chest, arms and legs. They are connected to a device that converts the electrical impulses into a graphic representation which is recorded on paper. This graphical representation that appears as a line, is analyzed by the device and then by the doctor.
An electrocardiogram can show:
-signs of volume enlargement of the heart
-signs of insufficient blood flow to the heart
-signs of new and old injuries of the heart
-problems with the rhythm of the heart (arrhythmia)
-change in the electrical activity caused by an electrolyte imbalance
-signs of inflammation of the sac that surrounds the heart (pericarditis)
An electrocardiogram does not predict a myocardial infarction.
An electrocardiogram is indicated for:
– the evaluation of an unexplained chest pain, especially when a heart attack is suspected; other possible causes of chest pain that can be diagnosed through electrocardiogram are arrhythmias, hypertrophy of a room (the walls of a room are thickened), inflammation of the sac that surrounds the heart (pericarditis), decreased blood flow to the heart (ischemia).
– monitoring the electrical activity of the heart
– diagnosticating of ventricular hypertrophy
– monitoring the effectiveness and side effects of certain medications that can affect the electrical activity of the heart
– checking the function of some mechanical devices (peace-maker or defibrillators) implanted in the heart in order to maintain a regular heart rhythm.
An electrocardiogram can be used to assess the symptoms of a heart disease (such as a chest pain, unexplained dyspnea, dizziness, palpitations or weakness) or the cardiac function when there are risk factors for heart disease (such as diabetes, hypercholesterolaemia, smoking, hypertension, or a family history of heart disease at a young age).
Preparing for the electrocardiogram
The doctor who performs the electrocardiogram should be informed about the medication that the patient is taking. Some medicines may affect the results of the electrocardiogram.
Mode of execution
The ECG is usually performed by a health professional, and the result is interpreted by an internist, a family physician or cardiologist. The patient usually gets the ECG as proof of the examination done by a physician. The ECG is portable, so it can be performed virtually anywhere. In case of hospitalization, the patient can be monitored continuously through an electrocardiograph; This process is called telemetry. Before performing the EKG, the patient must remove their all jewelry and clothing from the upper half of the body, the hands and from the feet.
During the ECG, the patient lies on a table or a bed. The chest, hands and feet are cleaned and even shaved as to provide a clean and smooth surface. Between the skin and the electrodes a special gel can be placed or some small alcohol tissues in order to improve the electrical impulse conduction. Disposable electrodes can be used, which do not require gel or alcohol.
In the case of older devices, the electrodes must be repositioned during testing. When the investigation is over, the gel and the electrodes are removed.During the test, the patient should not move or speak because the muscle activity can influence the outcome. For best results, the patient must lie flat and breathe normally. Sometimes the doctor may ask the patient to hold their breath for a few seconds. An electrocardiogram lasts for about 5 to 10 minutes. In some cases, this period may be extended, for example, when measuring the heart rate.
The ECG is a painless investigation. The electrodes and the gel may be cold when applied. The patient may feel a sensation of warmth or stinging when the area on which the electrode is applied is cleaned and smooth. The skin and hair can be pinched when the electrodes are removed, which may cause a little discomfort.
There are no risks associated with an electrocardiogram. This is a very safe test. In most of the cases, there is no reason why a patient can not perform an electrocardiogram.
The electrodes detect the pulses produced by the heart. There is no electric wave going through the body, so there is no risk of electric shock.
The ECG is a graphical representation of a characteristic pattern of electrical impulses generated by the heart.
The component parts are referred as P wave, QRS complex, ST segment and T wave:
-The P wave is the electrical recording of the activity in the upper chambers (atria)
-The QRS complex is the recording of the electrical activity of the lower chambers (ventricles)
-The ST segment appears as a straight line between the QRS complex and the T wave; a bigger or smaller ST segment corresponds to a damaged heart muscle or not getting enough blood
-The T wave corresponds to the period in which the ventricles are electrically relaxed and are preparing for a new contraction.
The heart rate (normally between 60 and 100 beats per minute) and pace are regular. The atrial activity is normal.
The P wave, QRS complex and the T wave are normal.
The ST segment is not elevated or flattened.
A normal ECG does not exclude the possibility of a heart disease. For this reason, the ECG has to be interpreted taking into account the symptoms, medical history, clinical examination and, if necessary, other investigations.
When changes in the ECG result occur, they show the existence of a heart disease. In some cases, the EKG can detect abnormalities only during exercise or when symptoms occur. In these cases, a special form of ECG is required, called exercise electrocardiogram.
There are several types of cardiac arrhythmias. A heart rate below 60 beats per minute is called bradycardia. A heart rate above 100 beats per minute is called tachycardia. Tachycardias include a fast, irregular rhythm in the ventricles (ventricular fibrillation) or a rapid pace regularly starting in the atria (atrial flutter). Also, the abnormalities in the conduction of electrical impulses are placed in the category of arrhythmias.
If the coronary arteries that provide blood the heart muscle are blocked, it gets less oxygen than it needs, causing the occurrence of ischemia or necrosis (death of heart muscle). This lesion appears on the electrocardiogram. Early signs of cardiac ischemia (decreased coronary blood flow) are represented by a depression in the ST segment. Early signs of heart attack are represented by the elevated ST segment. In time, after an infarction, the Q wave in the QRS complex on the ECG appears deeper.
Some ECG changes suggest thickening of the heart muscle in one or more rooms. Diseases that can cause hypertrophy are hypertension, coronary heart disease, cardiomyopathy and valvular diseases.
An elevated ST occurs in the inflammation of the heart muscle (myocarditis) or the sac that surrounds the heart (pericarditis).
Chemical changes (electrolyte imbalances). The normal activity of the heart depends on normal blood levels of certain chemicals (called electrolytes) such as calcium and potassium. Increased or decreased levels of these electrolytes cause certain arrhythmias, such as changes in the P-wave, the QRS or T wave.
Certain medicines used for heart diseases or other illnesses cause changes in the ECG.
Factors that may change the ECG
Factors that may interfere with the accuracy of the test and its results are:
-defects of the electrocardiograph or electrical interference due to inadequate grounding or because of other electrical equipment in the vicinity
-the inappropriate attachment of the electrodes to the skin
-If the patient speaks during testing
-effort before performing physical testing
-anxiety or dyspnoea
An ST segment raised or a negative T wave may occur in black people, but disappear during effort.
If an electrocardiogram is performed during a heart attack, it may initially appear normal or unchanged from the previous EKGs; therefore, the ECG should be repeated (called serial ECGs) a few hours or days later; specific blood tests for heart muscle damage should also be done.
There are several specific types of electrocardiograms such as telemetry, ambulatory ECG monitoring (Holter) and effort electrocardiogram.
-telemetry and Holter monitoring are used for continuous monitoring of the ECG during hospitalization or at home
-telemetry is used during hospitalization; it requires the attachment of at least two electrodes connected to a small device that can be placed in your pocket; This device emits a signal which is captured and displayed by a central monitoring system; heart rhythm abnormalities are recorded and can trigger an alarm.
-Holter monitoring continuously records the heart activity for 24 to 48 during the patient’s daily activities.
-the effort electrocardiogram is used to detect changes that occur during exercise.
Before making an effort electrocardiogram, a normal one should be done, because certain abnormalities that occur during exercise are harder to interpret. Also, resting ECG can detect decreased coronary blood flow, making an effort electrocardiogram dangerous.
Some doctors recommend an electrocardiogram to all patients over 35 years, to compare subsequent amendments. This test is particularly useful for people with risk factors for cardiac diseases. Sometimes, the ECG changes occur only during exercise or while showing symptoms. In order to detect these changes and effort of Holter ECG is performed. It is possible that after obtaining the results from an electrocardiogram other tests will be needed to make a definite diagnosis