To read an EKG practice test strip, begin by counting the number of QRS-complexes in a six-second interval and multiplying that number by 10 to determine the heart rate. Each large square on the EKG paper represents 0.20 seconds; thus 30 large boxes is six seconds on the clock, reports Practical Clinical Skills. Assess the heart rhythm by measuring the height, appearance and spacing of the various wave forms.
To assess whether the ventricular heart rate is regular or irregular, count the number of boxes between the beginning of each QRS complex. If the number of boxes differs by greater than 10 percent, the heart rate is irregular, Practice Clinical Skills explains. If you note an irregularity, determine whether it occurs in a consistent pattern or appears random. To determine the atrial heart rate, count the number of boxes between each P-wave.
Next, assess the quality of the waveforms, beginning with the P wave. Note if the P wave is present before each QRS complex, and measure its height. Also measure the PR interval, which is the interval between the beginning of the P-wave and the start of the QRS complex. A normal PR interval is between 0.12 and 0.20 seconds, says Practical Clinical Skills.
Continue your assessment with the QRS complex, which typically is higher and wider than the P wave. Measure the QRS interval, or the number of boxes between the beginning and the end of the complex. This normally is between 0.08-0.12 seconds, according to Practical Clinical Skills. Next, assess the height of the T-wave that follows the QRS complex, taking note of any negative deflection or tall, spiked waves. Also note the QT interval and the ST segment, which is normally flat.