Developing the ability to read and interpret an ECG tracing is time-consuming and requires a great deal of clinical experience. Use a paper rhythm strip and a metric ruler to measure the exact height and width of the various waveforms to develop the highest level of clinical expertise.
- Learn about electrocardiograms
An electrocardiogram is the technology used to create the tracing seen on a heart monitor. An ECG consists of waveforms that correspond to the electrical events that occur in the heart during a single heartbeat. These waveforms are called the P, Q, R, S, T and U waves. Identifying these is essential to understanding the ECG. An ECG is often performed in several different configurations known as leads. The following information pertains to tracings obtained in Lead II.
- Identify the P wave
The P wave is the first visible electrical event on an ECG tracing and represents the depolarization of the left atrium, which is the event that initiates the contraction of the heart. A normal P wave deflects upwards above the baseline.
- Identify the QRS complex
The QRS complex represents the depolarization and contraction of the left ventricle. It begins with a downward-deflected Q wave followed by an upward-deflected R wave and then a downward-deflected S wave. A normal QRS complex looks like an upside down "V." An abnormally shaped QRS complex often indicates some type of heart block.
- Identify the T wave
The T wave represents ventricular repolarization. It normally appears as a small, somewhat flattened waveform that deflects upward. High, spiked T waves sometimes indicate an abnormally high potassium level in the blood, while a high, broad T wave is often indicative of a type of heart attack known as ST-elevation myocardial infarction, or STEMI.
- Identify the U wave
The U follows the T wave and appears as a slightly flattened wave form that deflects upwards. It represents repolarization of specialized fibers in the heart called Purkinje conduction fibers. The U wave is not visible in every ECG.
- Determine the heart rate
A simple way to determine the heart rate is to count the number of QRS complexes per minute on the heart monitor. When using EKG paper, count the number of large squares between each R wave, and divide that number by 300 to determine the rate. Use this calculation only for ECG tracings in which the heart rate falls within the normal limit of 60 to 100 beats per minute.
- Determine the heart rate for fast or slow rhythms
If a person has a very fast heartbeat, determine the rate by counting the number of small squares between R waves and divide the number by 1,500. For very slow or irregular rhythms, count the number of R waves in a 10-second rhythm strip, and multiply the number by 6.