How to Interpret an EKG
This article is based off of information from the The University of Texas Medical Branch Health Pediatrics, Cardiology Textbook. For more information, please visit their website here.
An electrocardiogram (ECG or EKG) is a graph of electrical activity in different areas of the heart. Different numbers or letters labelling separate lines are called “leads,” or areas of the heart measured, in the cardiogram. Standard cardiograms usually have 12 leads in total. Electrocardiograms are not to be confused by echocardiograms, which are ultrasounds, so many people call them by their German name, EKG. EKGs can be very important in determining the rhythm, heart rate, and different characteristics of an abnormal heart rate to detect any heart diseases. In this section, we will look at different parts of the EKG and how we can interpret them.
When looking at an EKG, we must take into account the patient’s age, standardization, and paper speed.
Image of an electrocardiogram. I, I, and III signify different “leads,” or areas of the heart measured, in the cardiogram.
In order to interpret the rhythm, we need to look at the SV node, the main pacemaker, and then the atrial, AV node, and ventricle pacemakers.
The SV node is responsible for the PR interval, which is why we usually look at the “P wave” at the beginning before the QRS complex. We can analyze the slope of the wave and its angle to determine whether or not it is a normal sinus rhythm.
Problems with the P wave can result in different diseases.
Advanced Interatrial Block (IAB): delayed connection between right and left atrium (e.g. AV node or bundle of His cells)
P Terminal Force: The duration and amplitude of the P terminal force can be a sign of left sided valvular lesions (aortic and mitral valves), commonly caused by high blood pressure.
Atrial, AV, and Ventricular Rhythms
Atrial rhythms are caused when the SV node does not work anymore, and the atrium takes over as the automatic pacemaker. This causes a slower resting heart rate. It is characterized by a P wave (which is good) but no normal sinal wave we would expect from a function SV node.
If the atrial rhythm fails, then the heart moves on to the AV node, which causes a narrow QRS complex and loses a P wave.
If the AV node fails, then the last resort is relying on the ventricular rhythm, which is characterized by a wide QRS complex (meaning a very slow heart rate) and no P waves.
Axis Deviations
Reading the tilt of a peak can tell us a lot about where an electrical impulse came from. Some hints can tell us whether it is a Right Axis Deviation (RAD) or a Left Axis Deviation (LAD). Spotting these in an ECG can be critical in a diagnosis for hypertrophy, a bundle branch block (meaning a loss of connection between ventricles and atria), a fascicular block (block in electrical charges), hyperkalemia (high potassium, which can result in abnormal heart rate), pneumothorax (lung collapsion), and emphysema (which means your alveoli in your lungs are not working properly).