Boxes and Sizes

The pen will record the electrocardiogram (ECG) waves and segments onto the paper. To keep things simple, we have drawn straight horizontal lines to represent the complexes in Figure 3-1.

Figure 3-1 ECG paper. Height is measured in millimeters (mm) and width in milliseconds (ms).

© Jones & Bartlett Learning.

Description

The ECG paper passes under the pen at a rate of 25 mm/sec. Each little box is, therefore, ¹/₂₅th of a second, or 0.04 seconds. Because a big box is made up of five little boxes, it represents 5 × 0.04 sec = 0.20 sec, so five big boxes make 1 second.

There are usually some small marks along the bottom of the strip every 3 seconds so that you can keep tabs on the time more easily. The lead should be appropriately labeled by the machine or the person obtaining the strip for easy identification. In addition, the patient’s name and hospital number (when appropriate) should be labeled at the beginning or end of the strip.

When we talk about the vertical height of a wave or segment, we use millimeters; for instance, a wave that is five little boxes high would, in reality, be 5 millimeters high. Likewise, a darker big box is 5 millimeters high.

It will be very useful to keep these measurements in mind, especially when we discuss rates and widths of waves and segments. Everything on the rhythm strip is measured in millimeters or milliseconds, and you will use these measurements to describe your findings when examining the strip.

As an example, a wave can be described as being 15 mm high and 0.06 seconds wide. This would tell us that the height of the wave is 15 little boxes or 3 big boxes, and the width is 1.5 little boxes. With a bit of practice, you’ll have this mastered.