The Rule of 300s (also known as the triplicate method) is useful for measuring heart rateThe number of QRS complexes per minute; note that HR may not equal perfused pulse rate. See also: - Step 1 Heart Rate - Rate - Rule of 300s (Triplicate Method) - Six Second Count - The Caliper Method 1.... over shorter periods (less than 3 seconds) or for calculating heart rates of rapid tachycardias. This method is quick but not quite as accurate at measuring heart rateHeart Rate; calculated by counting the number of QRS complexes in six seconds and multiplying by 10; rate is also determined by measuring the number of large squares between two R waves; i.e. –1 large square = heart rate of 300/minute. as the six second countPerhaps the simplest and most common method to determine heart rates involves multiplying the number of QRS complexes found over six seconds by a factor of 10 to get the number of QRS complexes in a minute (60 seconds). Figure... method. Note: the rhythmOften refers to a discernible pattern in time or distance between QRS complexes and/or P waves. must be regular (consistent R-R intervalThe distance between the top of the R waves. Figure 4.15 The Normal Q Wave and QT Interval Figure 4.15 illustrates the Q wave, QT interval and the R-R interval. A normal QT interval should be less than half the...) for the Rule of 300s to be of any use.
Understanding the Rule of 300s calls on the fact that a large square on ECG paperAn ECG is a graphical display of electrical energy generated by the heart over time. ECG graph paper records this cardiac electrical activity, printing at a rate of 25 mm/second. The paper graph is divided into small 1 mm squares... equals 5 mm or 0.20 seconds (5 mm x 0.04 = 0.20 seconds or 1/5 of a second). Begin by finding an R waveFollowing the depolarization of the interventricular septum, ventricular depolarization then progresses from the endocardium through to the epicardium across both ventricles producing an R wave and an S wave. An R wave is the first positive deflection of the QRS... that falls on a thicker vertical line. If the next R wave and every subsequent R wave occurred only one large square apart, how fast is the resulting heart rate?
1 QRS every 1/5 of a second = 5 QRS/second = 300 QRS/minute
Fast. If the R waves consistently arrived two large squares apart, the heart rate would be half of 300 at 150/minute. If the R waves are three large squares apart, the heart rate would be a third of 300/minute at 100/minute. Four large squares in between R waves equals a heart rate of 75/minute. A rate of 60/minute occurs with R-R intervals of five large squares.
In figure 4.20, the second QRS complexThe electrical representation of ventricular depolarization; the atrial repolarization is also a part of the QRS. ECG interpretation relies heavily on the QRS complex. The QRS complex represents the depolarization of the ventricles. The repolarization of the atria is also... falls on a thick vertical line. The next R wave is between three large squares (thick lines) and four large squares away. The heart rate is estimated between 75/minute and 100/minute. Because the next R wave falls closer to the fourth thick line, the rate is closer to 75/minute. The heart rate is about 80/minute, a safe approximation from a treatment perspective. Would a heart rate of 77/minute or 85/minute be any more meaningful? Not likely.
Figure 4.20 illustrates the Rule of 300s to estimate heart rate. The rule is particularly useful when measuring the heart rate of an underlying rhythmWhile a rhythm as a whole may be irregular, segments may be regular. These regular periods are often referred to as the underlying rhythm. Apply the three step method to the underlying rhythm first. When naming a rhythm, the underlying... when frequent ectopicA depolarizing wave that originates anywhere outside of the SA node. 1. Six Second ECG Guidebook (2012), T Barill, p. 196 beats are also present. This method can be used only for rhythms with a consistent R-R intervalA period measured on rhythm strip paper that measures a wave and a segment; the distance measured is equal to time taken as an ECG is voltage over time; a PR interval for example is measured from the beginning of.... For rhythms with irregular patterns, the six second count is preferable for measuring heart rate.
1. Six Second ECG GuidebookA Practice Guide to Basic and 12 Lead ECG Interpretation, written by Tracy Barill, 2012 Introduction The ability to correctly interpret an electrocardiogram (ECG), be it a simple six second strip or a 12 lead ECG, is a vital skill... (2012), T Barill, p. 92-93