Electrocardiogram (ECG or EKG)

An electrocardiogram (ECG or EKG) measures the heart's electrical activity.

The heart is a pump. To allow blood to circulate in the body, the heart muscle cells need to contract and relax in a coordinated way and make a heartbeat. When the heart muscle contracts and relaxes, a small electrical current is generated.

An electrocardiogram (ECG or EKG) is a painless, non invasive test that uses electrodes on the skin to measure these small electrical changes and produces a graph showing the electrical changes over a period of time.

Commonly, an ECG will use six electrodes (or leads) placed across the chest, as well as one on each arm and leg. These electrodes capture the electric currents coming from the heart from different directions, which produces an ECG (referred to as a 12 lead ECG -- the 12 views are produced by the 10 electrodes) that can be interpreted and help diagnose issues with the heart’s electrical system, the heart’s blood supply, and other medical conditions that may affect the heart’s function.

In certain settings only a couple of leads are placed on the chest or limbs and a monitor strip is produced and most often is used to help diagnose issues with heart rate and rhythm.

ECG, EKG, electrocardiogram, and electrocardiograph are slightly different names for the same test.

ECG vs. EKG

EKG is the abbreviation for elektrokardiogramm, a German term for the test. ECG is the English abbreviation for electrocardiogram.

There are 3 common types of ECG. They include:

1. Resting ECG – A 12 lead tracing taken at a single moment in time with the patient laying down.
2. Ambulatory ECG – The ambulatory ECG measures a patient’s heart rate and rhythm continually for a longer period of time from days to weeks, most often trying to capture heart rate and rhythm disturbances that may not be detected in a single office visit. Holter monitors record the heart for periods of a couple days. MCOT (Mobile cardiac observation telemetry) can be used to observe the heart for up to a month at a time.
3. Exercise stress test – This test measures the heart function while the patient exercises on a treadmill or a bicycle. In patients who cannot perform physical activity, medications may be injected to make the heart work harder while the test is being done.

The heart is a two-stage electrical pump. The upper chambers of the heart (atrium) collect blood from the body and the lower chambers (ventricle) pump blood to the body. There is an electrical conducting system in the heart that helps coordinate each heart beat (cardiac cycle) of collecting blood and then pumping it out.

The ECG can measure how electricity is generated and show how it travels in the heart muscle.

The normal cardiac cycle looks like this electrically:

• The sinoatrial (SA) node located in the atrium contains specialized cells that begin the cycle.
• Electricity spreads quickly to all the muscle cells in the atrium causing them to contract and send blood to the ventricle.
• The electrical signal travels from the SA node to a junction box located between the atrium and ventricle, the atrioventricular (AV) node, where the signal is delayed for a split second, allowing the blood to flow from the atrium and allow the ventricle to fill.
• The electrical signal then spreads to the heart muscle in the ventricle, allowing them to contract and pump blood to the body.
• After the heart muscle contracts, it must relax and the electrical signal in the SA needs to reset for the next beat.
• The ECG measures the electrical pathway through the cardiac cycle. Abnormal or damaged heart muscle cells conduct electricity abnormally and the ECG can help with the diagnosis of coronary artery disease and heart attack (myocardial infarction).

What does an ECG show?

The ECG provides significant information about the heart and its function.

• The heart rate: how fast the heart beats per minute.
• The heart rhythm: How the electrical conduction system is functioning. Is the heart beating regularly or irregularly? Normal sinus rhythm is how the heart should beat (see cardiac cycle above). Atrial fibrillation is an example of an irregular heart rhythm. Other irregular heartbeats include premature atrial contractions (PAC), premature ventricular contractions (PVC), and different types of heart block.
• Increased thickness (hypertrophy) of the heart muscle.
• Heart muscle damage or inflammation.
• Acute loss of blood flow to the heart muscle causing a heart attack due to blocked coronary arteries -- the arteries that supply the heart muscle itself with blood.
• Some non-heart medical conditions can affect the electrical conduction of the heart. For example, electrolyte abnormalities (calcium or potassium) or hypothermia (low body temperature) can lead to recognizable changes in the ECG.

Does an ECG show clogged arteries?

Heart muscle that does not have adequate blood supply conducts electricity differently than heart cells with normal blood supply. The ECG can detect these changes when a patient presents with chest pain or other symptoms that might be heart related. An abnormal ECG can help diagnose clogged or narrow arteries caused by coronary artery disease.

BUT … a normal ECG does not mean that coronary heart disease is not present. Blood tests, stress tests, heart CT, heart MRI scans, and other tests may be needed to uncover partially blocked arteries that cause heart-related symptoms.

AND … an abnormal ECG may be caused by heart illnesses or non-heart illnesses unrelated to blocked arteries.

Abnormal rate or irregular heart rhythms:

• Abnormally fast heart rates: tachycardia = tachy (fast) + cardia (heart)
• Abnormally slow heart rhythms: bradycardia = brady (slow) + cardia (heart)
• Abnormal electrical conduction
  • There are many examples including atrial fibrillation, heart block, premature atrial contractions (PAC), and premature ventricular contractions (PVC).
  • Some conduction abnormalities are lethal, because they do not generate a heartbeat. For example. ventricular fibrillation.
• Previous evidence of heart muscle damage
• Evidence of a complete blockage of a coronary artery during a heart attack (acute myocardial infarction), or
• Evidence of decreased blood flow to the heart but without complete blockage of the coronary artery. In combination with symptoms, this might help diagnose angina or unstable angina.
• Heart issues associated with systemic diseases like high blood pressure, thyroid conditions, or hypothermia.
• Electrical conduction changes in the heart associated with abnormal blood electrolytes (potassium, calcium, magnesium).
• Heart strain associated with lung conditions like COPD, emphysema, or pulmonary embolus (blood clots to lung).
• Inflammation of the heart or its lining (myocarditis, pericarditis).
• Congenital heart abnormalities.

Why would you need an ECG?

An ECG is performed when there is concern that there might be a heart-related condition present. This may be due to a direct heart issue like coronary artery disease or a heart rhythm issue, or because of indirect issues like high blood pressure or lung disease.

ECGs are a routine test for patients experiencing chest pain or fainting (syncope).

The ECG or a monitor is a routine part of the evaluation of most acutely ill patients, where many organs are being evaluated and monitored.

ECGs may be part of the routine heart evaluation prior to surgery, often to determine the potential risk of anesthesia.

A single ECG is just a snapshot in time, and some illnesses and injuries may need repeated ECGs or prolonged monitoring to help assess and diagnose a patient’s condition.

There is little preparation needed for an ECG if it is being planned and done electively (not in an emergency).

It is best to avoid skin creams or oils, since electrodes need to be place on the skin and oily skin makes it more difficult for the electrodes to stick.

Wear loose fitting clothing since the test requires electrodes to be placed across the chest and on the arms and legs.

What should you not do before an ECG?

There are no activity or diet restrictions prior to an ECG.

The ECG is a simple procedure.

The patient is asked to lay down, the chest is exposed and 6 electrodes are placed across the chest, adhering to the skin with a gel that is preapplied to the electrode pads. 4 more electrodes are placed, one each on each arm and leg.

Once the electrodes are in place, the patient is asked to hold still and the ECG tracing will take only a few seconds to complete.

How long does an ECG test take?

It takes a couple of minutes or less to place the electrodes in their proper place on the chest and limbs. The ECG recording should be completed within a few seconds afterward.

The ECG is very good at assessing heart rate and rhythm issues, but only when the machine is attached. If the patient has had a fainting spell, or complained of lightheadedness or palpitations, a single ECG may miss the cause of the symptoms. Longer-term heart monitoring as an outpatient may be needed.

Similarly, with a patient experiencing chest pain due to a myocardial infarction, the ECG may be relatively normal initially and then change over time to show heart muscle damage. Subtle changes may be difficult to appreciate. Repeated ECGs, blood tests, and monitoring may be necessary if the health care provider remains concerned about narrowing of the coronary arteries.

There are situations where the ECG will show evidence consistent with an acute myocardial infarction, but the changes in the tracing are due to conditions other than a blocked coronary artery. These might include inflammation of the heart muscle (myocarditis) or the heart muscle lining (pericarditis).

In some patients, previous heart conditions like left bundle branch block or heart rhythm disturbance, may make it difficult to evaluate changes in the ECG due to heart attack.

How accurate is an ECG?

The ECG is very accurate at evaluating heart rate and rhythm disturbances when they are present as the patient is being tested.

Evaluating chest pain is more difficult because ECG can be relatively normal, even in a patient with significant narrowing of a coronary artery. Clinical judgement and further testing may be needed in patients suspected of having heart disease whose ECG is relatively normal.

There are also potential differences in the ability of health care providers to adequately interpret ECGs. As expected, cardiologists (heart specialists) are often best able to interpret ECGs, but other providers are quite capable, and get better with more experience.