An electrocardiogram or EKG measures the electrical activity of the heart over a period of time. This activity is measured using electrodes placed on the surface of the skin, and recorded by an external device on the body. Although a person's heart rate can be easily calculated by means of their pulse, an EKG will help determine the presence of a heart problem, the effectiveness of the device or medication, whether the heart is beating normally, or determine the location and size of the heart chambers. This test can also be done to check for heart disease, or determine if a person's heart is strong enough to undergo surgery.
Method 1 of 2: Using the Distance Between QRS Complexes
Step 1. Know what the normal “waveform” looks like in the ECG trace
This way, you can determine the area of the ECG that reflects a single heartbeat. You can calculate the heart rate using the length of the heartbeat on the ECG trace. A normal heartbeat consists of a P wave, a QRS complex, and an ST segment. You need to pay close attention to the QRS complex because it is the easiest to use for calculating heart rate.
- The P wave is a semicircle that lies just before the high QRS complex. These waves reflect the electrical activity of the atria ("atrial depolarization"), the small chambers at the top of the heart.
- The QRS complex is the highest part that can be seen on an ECG trace. These complexes are usually tall, sharp triangular in shape, and very easy to spot. This shape reflects the electrical activity of the ventricles ("ventricular depolarization"), which are the two chambers located at the bottom of the heart and forcibly pump blood throughout the body.
- The ST segment is located just after the QRS complex. This segment is actually the flat area before the next semicircle on the ECG trace (T wave). The flat segment (ST segment) just after the QRS complex is important because it provides doctors with crucial information regarding the chance of a heart attack.
Step 2. Identify the QRS complex
The QRS complex is usually the highest part of the repeating pattern on the ECG trace. This complex is a tall and narrow pointed triangle (for people with normal heart function) that occurs repeatedly at the same rate throughout the ECG trace. For every one QRS complex, one heartbeat has occurred. Therefore, you can use the distance between the QRS complexes on the EKG to calculate the heart rate.
Step 3. Calculate the distance between the QRS complexes
The next step is to determine the number of large squares on the ECG trace that separates one QRS complex from the next. The EKG usually has a small and a large square. Make sure you use the large square as a reference point. Count from one peak of the QRS complex to the next QRS complex. Record the number of large squares separating the two points.
- Often, the result is a fractional number because the complex doesn't land on exactly one square; for example, the distance separating the QRS complexes may be as much as 2.4 square or 3.6 square.
- Usually there are 5 small squares embedded in each large square so you can calculate the distance between the QRS complex to the nearest 0.2 units (1 large square consists of 5 smaller squares to get 0.2 units per small square).
Step 4. Divide the number 300 by the answer obtained
After you've counted the number of large dividing squares that separate the QRS complex (say the sum is 3, 2 squares), perform the following calculations to determine the heart rate: 300/3, 2 = 93, 75. After that, round up your answer. In this case, his heart rate is 94 per minute.
- The normal human heart rate is between 60-100 beats per minute. That way, you can find out if the heart rate calculation is on track.
- However, the 60-100 beats per minute range is just a rough guide. Many athletes are in good physical condition so their resting heart rate is low.
- There are also diseases that cause a slowing of the heart rate (called pathological bradycardias), and diseases that cause an abnormal acceleration of the heart rate (called pathological tachycardias).
- Consult a doctor if the person whose heart rate is counted shows abnormal results.
Method 2 of 2: Using the 6 Second Method
Step 1. Draw two lines on the ECG trace
The first line should be close to the left hand side of the ECG trace paper. The second line must be exactly 30 large squares from the next first line. The large 30 square spacing on this EKG trace represents exactly 6 seconds.
Step 2. Count the number of QRS complexes between the two lines
As a reminder, the QRS complex is the highest peak of each wave reflecting a single heartbeat. Count the total number of QRS complexes between the two lines and write down the number.
Step 3. Multiply the result by 10
Since 6 seconds x 10 = 60 seconds, multiplying the answer by 10 gives the number of heartbeats that occur in one minute, which is a standard measure of heart rate). For example, if you count 8 beats in 6 seconds. This means that your calculated heart rate is 8 x 10 = 80 beats per minute.
Step 4. Understand that this method is effective for detecting abnormal heart rhythms
If the heartbeat is regular, the first method of simply determining the distance between one QRS and the next is quite effective because the distance between all QRS complexes is approximately equal to the rate of a regular heartbeat. On the other hand, if the heartbeats are irregular (thus the distance between the QRS complexes is not the same), the 6-second method is more effective because it averages the distance between heartbeats so that the overall result is more accurate.