Electrical activity in nerve and muscle cells occurs because of the flow of ions--electrically-charged particles--between the inside and outside of the cell membrane. Electricity is vital to the functioning of the brain, nerves and muscles, including the heart. Because the body conducts electricity, electrical changes detected on the body's surface by electrodes from an EKG machine, can be an extremely effective diagnostic tool. ECG and EKG can be used interchangeably.
Significance
The heart normally contracts and relaxes in a regular pattern. The signals that tell the muscle to contract come from the sinoatrial node, the heart's pacemaker. These signals travel from one part of the heart to another by electrical impulses. These electrical impulses, when detected and recorded, will show abnormalities in the heart's rate or rhythm. This test is useful for diagnosing disorders and monitoring treatment, particularly certain medications.
Process
The first little blip on the EKG is called the "P" wave. It represents the electrical trigger that causes the contraction of the atria, or upper chambers of the heart. The "P" wave is typically small, but may be larger if the right atrium is enlarged. The next wave is the QRS complex, signifying the positive and negative deflection or trigger for the contraction of the ventricles, or lower chambers of the heart. The final "T" wave represents the electrical recovery of the ventricles to their normal resting state. The "P," "QRS," and "T" waves signify a complete electrical pathway that takes approximately 0.6 second in a normal, healthy heart.
Test
Electrodes from an EKG machine are placed on the arms, legs and chest. Electrical impulses from the body travel through wires, enabling the machine to record the impulses. The electrical activity produces an image on paper, screen or both. During the procedure, a person lies still, relaxes and breathes naturally. If the patient moves or speaks, the tracing can be distorted, causing an inaccurate result.
Uses
A physician may ask for an EKG if his patient has experienced chest pain, breathlessness, dizziness, palpitations or fainting attacks. The test can show signs of coronary heart disease, heart attack, arrhythmia or disturbances of the heart rhythm, and a variety of other heart disorders. An EKG can also identify abnormal levels of certain minerals in the blood that control electrical activity in the heart. If a patient is being treated with medication for a heart disorder, an EKG may be suggested to keep track of the safety and effectiveness of the treatment.
Abnormalities
An EKG can identify numerous cardiac abnormalities. Sinus tachycardia is when the heart beats regularly, but rapidly, at more than 100 beats per minute. Tachycardia can be a normal response to exercise, stress, caffeine or drugs. Atrial fibrillation occurs when the atria beats randomly and rapidly at 300 to 500 beats per minute and not every impulse reaches the ventricles. This often occurs with hypertension or heart muscle disease, as well as with alcohol use. Ventricular tachycardia is a rapid heartbeat, usually greater than 140 beats per minute, originating in the ventricles and occurring due to a faulty conduction through a damaged area of heart muscle after a heart attack.
