The term "heart rate" normally refers to the rate of ventricular contractions. However, because there are circumstances in which the atrial and ventricular rates differ (e.g., second and third degree AV block), it is important to be able to determine both atrial and ventricular rates. This is easily done by examining an ECG rhythm strip, which is usually taken from a single lead (e.g., Lead II). In the example below, there are four numbered R waves, each of which is preceded by a P wave. Therefore, the atrial and ventricular rates will be the same because there is a one-to-one correspondence. Atrial rate can be determined by measuring the time intervals between P waves (P-P intervals). Ventricular rate can be determined by measuring the time intervals between the QRS complexes, which is done by looking at the R-R intervals. Show
 There are different short-cut methods that can be used to calculate rates, all of which assume a recording speed of 25 mm/sec, which corresponds to 5 large squares (dark red boxes) in the ECG recording. With this recording standard, the time dimension (width) of each large square represents 0.2 sec and each small square represents 0.04 sec. One method is to divide 1500 by the number of small squares between two R waves. For example, the rate between beats 1 and 2 in the above tracing is 1500/22, which equals 68 beats/min. Alternatively, one can divide 300 by the number of large squares, which is 300/4.4 (68 beats/min). Another method, which gives a rough approximation, is the "count off" method. Simply count the number of large squares between R waves with the following rates: 300 - 150 - 100 - 75 - 60. For example, if there are three large boxes between R waves, then the rate is 100 beats/min. One must extrapolate, however, between boxes. Atrial rate can be determined like the ventricular rate, but using the P waves. Remember, if the heart is in sinus rhythm and there is a one-to-one correspondence between P waves and QRS completes, then the atrial rate will be the same as ventricular rate. The rate is considered normal if the interval lies between 5 and 3 large squares (60 - 100 beats/min). Intervals less than 3 large squares or greater than 5 large squares represent tachycardia or bradycardia, respectively. In the above examples, the ventricular rate was determined based on the interval between the first two beats. However, it is obvious that the rate would have been faster had it been calculated using beats 2 and 3 (104 beats/min) because of a premature atrial beat, and slower if it had been calculated between beats 3 and 4 (52 beats/min). This illustrates an important point when calculating the rate between any given pair of beats. If the rhythm is not regular, it is important to determine a time-averaged rate over a longer interval (e.g., over ten seconds or longer). For example, because the recording time scale is 25 mm/sec, if there are 12.5 beats in 10 seconds (50 large squares), the rate will be 75 beats/min (1.25 beats/sec X 60 sec/min). Revised 11/08/2022 DISCLAIMER: These materials are for educational purposes only, and are not a source of medical decision-making advice. Step 1: Determine the heart rate There are a number of strategies for determining the heart rate. A simple, quick technique is to find a QRS complex that falls on a major vertical grid-line (1), then count the number of large squares to the next QRS complex (2). Dividing this number into 300 gives you the heart rate. In the ECG below, there are 2 large squares between QRS complexes. 300/2 gives a heart rate of 150 beats per minute.
« Previous | Next » We will now look at determining heart rate on an ECG or EKG six second strip. If you do not understand the PQRST wavs, I suggest you take a look at my previous article first regarding PQRST waves and the cardiac cycle. So let us begin. Method 1: Count the number of R-waves and multiply by 10.The first step in analyzing an EKG or ECG strip is to calculate the heart rate. There are different ways to calculate ECG heart rate on a 6 second strip. One of the easiest ways to calculate heart rate on a 6 second strip is to count the amount of R waves on a 6 second strip and and multiply it by 10. This can be done if a heart rhythm is regular or irregular. To determine if a rhythm is regular, measure the R to R intervals. If the intervals between each R wave is equal, then you can say this is a regular rhythm. If there is an abnormality within the R to R interval, then the rhythm will be considered irregular. In the above EKG strip, you see the R to R intervals are equal so we can say that this is a regular rhythm. If R-R intervals vary by less than 1.5 boxes, the rhythm is still considered a regular rhythm. We see that there are 7 R-waves. We multiply 7 x 10 and that equals 70 bpm (beats per minute). So the ECG heart rate in the above is 70 bpm. This technique also works well for slow heart rates as well. There are other ways to calculate heart rate on a 6 second ECG strip, but the rhythm must be regular to do so. There is also the 300 method, the 1500 method, and the sequence method. Method 2: The 300 MethodFor the 300 method, you count the number of large boxes between two R waves and divide it by 300. In the example below, there are 5 large boxes between these two R waves, 300 divided by 5 is 60. So the heart rate is 60 bpm. Method 3: The 1500 MethodWith the 1500 method, you count the number of small boxes between two R waves and divide it by 1500. In the example below, there are 21 small boxes between each R-R interval. You take 1500 and divide it by 21 which equals 71.43, which rounds to 71 bpm. Method 4: The Sequence MethodFor the sequence method, you count the bolded lines between each R wave. You start at 300, then 150 at the next bolded line, then 100, then 75, then 60 and 50. You continue to count down until you reach the next R wave. This just the beginning with analyzing a 6 second EKG or ECG strip. See below my other articles that address differentiating and classifying different heart rhythms and cardiac dysrhythmias. Related Articles:ECG Basics and Rhythm Review: Sinus Rhythms and Sinus Arrest ECG Basics and Rhythm Review: Atrial Rhythms ECG Basics and Rhythm Review: Junctional Rhythms ECG Basics and Rhythm Review: Ventricular Rhythms and Asystole ECG Basics and Rhythm Review: AV Blocks and Pacer Rhythms What are the 3 methods of calculating heart rate?Three Methods to Calculate the Heart Rate. Method #1: Identify an R-wave that is on a line. ... . Method #2: 300 divided by the number of large squares between the QRS complexes. ... . Method #3: The number of QRS complexes per 6-second strip multiplied by 10.. What is 300 in heart rate calculation?Simply identify two consecutive R waves and count the number of large squares between them. By dividing this number into 300 (remember, this number represents 1 minute) we are able to calculate a person's heart rate. Rate = 300 / number of large squares between consecutive R waves.
What is the big box method ECG?The big block method is very similar to the small box method explained above. In the big block method we count the number of big blocks between R waves as opposed to small boxes. You then take 300, which is the number of big boxes in a minute on an EKG, and divide that by the number of big blocks counted.
What is the triplicate method?This method consists of concatenating the three 10-second sequences of the triplicate electrocardiogram set as if it were a single 30-second electrocardiogram, and then processing as above (semiautomated QTcF determination using a unique superimposed median beat).
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