How To Read An EKG

How To Read An EKG

What is an EKG?
An electrocardiogram (EKG or ECG) is a test that checks for problems with the electrical activity of your heart. An EKG translates the heart’s electrical activity into line tracings on paper. The spikes and dips in the line tracings are called waves.

The heart is a muscular pump made up of four chambers . The two upper chambers are called atria, and the two lower chambers are called ventricles. A natural electrical system causes the heart muscle to contract and pump blood through the heart to the lungs and the rest of the body.

An electrocardiogram (EKG or ECG) is done to:

-Check the heart’s electrical activity.
-Find the cause of unexplained chest pain, which could be caused by a heart attack, inflammation of the sac surrounding the heart (pericarditis), or angina.
-Find the cause of symptoms of heart disease, such as shortness of breath,dizziness, fainting, or rapid, irregular heartbeats (palpitations).
-Find out if the walls of the heart chambers are too thick (hypertrophied).
-Check how well medicines are working and whether they are causing side effects that affect the heart.
-Check how well mechanical devices that are implanted in the heart, such aspacemakers, are working to control a normal heartbeat.
-Check the health of the heart when other diseases or conditions are present, such as high blood pressure, high cholesterol, cigarette smoking, diabetes, or a family history of early heart disease.

Reading an EKG
An EKG is a graph (thusly named an electrocardiograph) tracing the strength and direction of this electrical signal. Leads equipped with conductive goo are placed on different parts of the body allowing a view of the heart from different angles.   If the electrical activity of the heart at any given moment is traveling toward the lead being viewed, the line on the graph goes up (positive deflection).  If the electrical activity is traveling away from the lead, the line goes down (negative deflection). This graph (pictured) is being traced by a stylus on a moving piece of graph paper.  

 That first petite little hump, affectionately called the P wave, represents the electrical signal that starts in a group of cells called the Sinoatrial Node. This signal then travels through the atria (the smaller and upper two chambers of the heart) causing them to contract and push blood in to the larger and more powerful ventricles below.

The “PR Interval” segment represents a delay in the signal at another grouping of cells called the AtrioVentricular Node.  This delay allows time for the atria to completely deliver their bounty into the Ventricles. With perfect timing this signal continues through the Bundle of His.  The signal splits and speeds along down the left and right bundle branches, making its way to the Purkinje fibers and turning north again. This stimulates those Ventricular beefcakes to contract and deliver their payload to the lungs and body (if hearts had biceps, the left ventricle would be the proverbial “gun show”….it’s such a glory hog!).

The journey causing this second contraction through the ventricles is represented by the QRS portion of the EKG. The larger T wave which then finishes off our heartbeat is the repolarization of the ventricles.  I know what you’re thinking, either “what in the what now goes where?” or hopefully, “what wave represents the repolarization of the atria”?  Well, the repolarization of the atria is buried in the larger signal of the QRS and therefore not visible on the graph.

This pattern is called normal sinus rhythm.  It is the basic EKG of any normal healthy heart.  Naturally, there are variations of normal within the healthy population.

Sources:
http://www.webmd.com/heart-disease/electrocardiogram
http://en.wikipedia.org/wiki/Electrocardiography
http://www.todayifoundout.com/index.php/2011/10/how-to-read-an-ekg-electrocardiograph/