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Understanding EKG Graphs (Part I) | Learning Healthcare | Americation Career and Training School

Updated: Apr 15, 2020

Americation Career and Training School (ACTS)

Take the Graph one Step At a Time

EKG graphs to the untrained eye can appear to be just random wiggles on a piece of paper. However, each line, wiggle, and the peak has meaning behind it and points to something in a patient’s health that may require medical attention. To understand EKG graphs the best way to approach it is to know what a normal graph looks and go from there.

Background Knowledge you need to know before we get into the graphs

  • EKG’s technicians can monitor the electrical activity of the heart by placing electrodes on the patients’ bodies and attaching them to an EKG machine. The graph depicts the heart's electrical function.

  • The electrical conductors or pacemakers of the heart are the Sino Atrial (S.A.) Node, Atrioventricular (AV) node, Bundle of His and Purkinje Fibers. The pacemakers are located in different areas of the heart.

  • The waves on the graph represent the signals being sent from pacemaker to pacemaker allowing the heart to contract and relax pumping blood throughout the body.

  • Depolarization means contraction of the heart muscle. Repolarization means relaxation of the heart muscle.


The P Wave

The flat line prior to the p wave is when the S.A. node fires. The upslope of the p wave is the depolarization (contraction) of the right atria (D.R.A) by the S.A. stimulus and also represents the spreading of impulse from the S.A. node to the A.V. node. The downslope of the p wave is the depolarization of the left atria (D.L.A).

Abnormalities to look out for:

  • Absence of P wave: may indicate S.A. node not firing in heart.

  • Peak in P wave: Indicates atrial enlargement or chronic obstructive pulmonary disease (COPD)

  • P wave irregular baseline: indicates atrial fibrillation

The QRS Complex

QRS complex mainly represents the depolarization of the ventricles. The upslope of the wave is the depolarization of the interventricular septum. The Downward slope represents the impulse being sent to the L.B.B (left bundle branch) and the R.B.B (Right bundle branch). The line past the isoelectric line represents the signal being sent into the P. Fibers.


Is the negative wave (below the isoelectric line) right after the p-wave represents the depolarization of the inter-ventricular septum.

Abnormalities to Look Out For:

  • The Q wave is usually 1 small box if the Q wave is not one small box in duration this can indicate myocardial infarction (death of heart tissue)


This was is the spike you see right after the Q wave. This positive wave represents the depolarization of the ventricles.

Abnormalities to Look Out For:

  • Tall R-wave indicates ventricular hypertrophy


This negative wave is right after the R wave represents the depolarization of the ventricles at the base.

Abnormalities to Look Out For:

  • A long S-Wave indicates left ventricular hypertrophy.

The T Wave

The T-Wave is the wave after the s wave and represents ventricular repolarization.

Abnormalities to Look Out For:

  • Tall T – wave can indicate a left or right ventricular enlargement, left bundle branch block, myocardial infarction, hyperkalemia.

  • Inverted T wave can also indicate left and right ventricular enlargement.

  • Pointed T Wave can indicate pericarditis.

Take your Time with It

Understanding the basic waves first will help with understanding the graph as a whole later on. Each wave presents a pacemaker, and each pacemaker is in a different area of the heart. When abnormalities of certain waves happen, you will be able to tell which area of the heart is affected. For example, the S.A. node is located in the atria and if the wave is outside normal bounds this represents an issue pertaining to the atria such as atrial enlargement. Being able to put the pieces together will come in time but having the basics down pat will help you in the long run.

Learn more about a Career as an EKG technician

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