Overview

An electrocardiogram — abbreviated as EKG or ECG — is a test that measures the electrical activity of the heartbeat. With each beat, an electrical impulse (or “wave”) travels through the heart. This wave causes the muscle to squeeze and pump blood from the heart. A normal heartbeat on ECG will show the timing of the top and lower chambers. The right and left atria or upper chambers make the first wave called a “P wave” — following a flat line when the electrical impulse goes to the bottom chambers. The right and left bottom chambers or ventricles make the next wave called a “QRS complex.” The final wave or “T wave” represents electrical recovery or return to a resting state for the ventricles. An abnormal EKG can mean many things. Sometimes an EKG abnormality is a normal variation of a heart’s rhythm, which does not affect your health. Other times, an abnormal EKG can signal a medical emergency, such as a myocardial infarction (heart attack) or a dangerous arrhythmia.

What Can EKG Or ECG Do?

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. Finding out how long a 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.
EKG or ECG can detect:

The underlying rate and rhythm mechanism of the heart.

The orientation of the heart (how it is placed) in the chest cavity.

Evidence of increased thickness (hypertrophy) of the heart muscle.

Evidence of damage to the various parts of the heart muscle.

Evidence of acutely impaired blood flow to the heart muscle.

Patterns of abnormal electric activity that may predispose the patient to abnormal cardiac rhythm disturbances.

When Is An ECG (EKG) Performed?

As part of a routine physical examination or screening evaluation.

As part of a cardiac exercise stress test.

As part of the evaluation of symptoms of chest pain, shortness of breath, dizziness or fainting, palpitations.

As part of the preoperative workup for surgery in patients who may be at an age where heart disease could potentially be present.

What Medical Condition Can EKG Diagnose?

Abnormally fast or irregular heart rhythms.

Abnormally slow heart rhythms.

Abnormal conduction of cardiac impulses, which may suggest underlying cardiac or metabolic disorders.

Evidence of the occurrence of a prior heart attack (myocardial infarction).

Evidence of an evolving, acute heart attack.

Evidence of an acute impairment to blood flow to the heart during an episode of a threatened heart attack (unstable angina).

Adverse effects on the heart from various heart diseases or systemic diseases (such as high blood pressure, thyroid conditions, etc.).

Adverse effects on the heart from certain lung conditions (such as emphysema, pulmonary embolus [blood clots to lung]).

Certain congenital heart abnormalities.

Evidence of abnormal blood electrolytes (potassium, calcium, magnesium).

Evidence of inflammation of the heart or its lining (myocarditis, pericarditis).

What Does An Abnormal EKG Indicate?

Because an EKG measures so many different aspects of the heart’s function, abnormal results can signify several issues. These include:

Defects or abnormalities in the heart’s shape and size: An abnormal EKG can signal that one or more aspects of the heart’s walls are larger than another. This can signal that the heart is working harder than normal to pump blood.

Electrolyte imbalances: Electrolytes are electricity-conducting particles in the body that help keep the heart muscle beating in rhythm. Potassium, calcium, and magnesium are electrolytes. If your electrolytes are imbalanced, you may have an abnormal EKG reading.

Heart attack or ischemia: During a heart attack, blood flow in the heart is affected and heart tissue can begin to lose oxygen and die. This tissue will not conduct electricity as well, which can cause an abnormal EKG. Ischemia, or lack of blood flow, may also cause an abnormal EKG.

Heart rate abnormalities: A typical human heart rate is between 60 and 100 beats per minute (bpm). An EKG can determine if the heart is beating too fast or too slow.

Heart rhythm abnormalities: A heart typically beats in a steady rhythm. An EKG can reveal if the heart is beating out of rhythm or sequence.

Medication side effects: Taking certain medications can impact a heart’s rate and rhythm. Sometimes, medications given to improve the heart’s rhythm can have the reverse effect and cause arrhythmias. Examples of medications that affect heart rhythm include beta-blockers, sodium channel blockers, and calcium channel blockers.

How Does It Work?

Each beat of your heart is triggered by an electrical impulse normally generated from special cells in the upper right chamber of your heart (pacemaker cells). An electrocardiogram records the timing and strength of these signals as they travel through your heart. An electrocardiogram is also called a 12-lead EKG or 12-lead ECG because it gathers information from 12 different areas of the heart. These views are created by electrodes, typically 10, placed on the skin of your chest and sometimes your limbs. The electrical activity is recorded as waves on a graph, with different patterns corresponding to each electrical phase of your heartbeat. The EKG machine doesn’t generate electricity. Instead, it conducts and measures electrical activity. Typically, the heart conducts electricity in a standard pathway from the right atrium to the left atrium. The electrical current then goes to the atrioventricular (AV) node, which signals the ventricles to contract. The current then flows to an area known as the bundle of His. This area divides into fibers that provide current to the left and right ventricles.