Please refer to the EKG tracing below if
you are not familiar with the labeling of the EKG waveforms.
The first step is to determine the RATE, which can be eyeballed by the following technique. Locate the QRS (the big spike) complex that is closest to a dark vertical line. Then count either forward or backwards to the next QRS complex. For each dark vertical line you pass, select the next number off the mnemonic "300-150-100-75-60-50" to estimate the rate in beats per minute (BPM).In other words if you pass 2 lines before the next QRS, the heart rate (HR) would be less than 150. Remember that this is merely an estimate. You should use real measurements to determine the exact HR (for precise measurement: each large box represents 200msec and small boxes represent 40msec). As an example of using the mnemonic, in the segment of the EKG below, start at the QRS that lines up with the vertical line at "0". Now counting back each vertical line to the previous EKG "300-150-100" we notice the HR to be slightly less than 100 (probably around 90-95).
Next we need to determine the RHYTHM both its source and its regularity. The prime concern is whether the source of the rhythm is the SA node (sino-atrial) or an ectopic pacemaker. To determine whether the source of the rhythm is "sinus" or an ectopic rhythm, you need to look at the relationship of the P-wave, if present, to the QRS-complex. If there is a P wave before each QRS and the P is in the same direction as the QRS, the rhythm can be said to be sinus. For instance note in the EKG segment below that there is a P-wave before each QRS (highlighted in blue) and that it is pointing up as is the QRS segment.
Also look at the quality and quantity of P-waves before each QRS. There should only be one P-wave before each QRS. The P-wave should be in only one direction, and not biphasic (except for leads V1 and V2). It should also be closer than 200ms to the QRS. The shape of the P-wave should also be gently rounded and not peaked.
