In a previous column, several key steps in assessing pacemaker functioning were discussed: knowledge of the type of pacemaker implanted (single, dual, or biventricular), basic programmed parameters, and basic functional assessment. The next step in this process is an understanding of pacemaker timing cycles to interpret the paced electrocardiogram (ECG). Paced ECG tracings are interpreted through the use of intervals measured in milliseconds, and not in beats per minute. An interval is the amount of time between 2 consecutive events. Nurses are typically taught to express intervals in seconds and rates in beats per minute when interpreting ECG tracings. However, because of the brief duration between cardiac rhythm events, the units must be expressed in milliseconds.2 It is easy to convert between intervals and rates and vice versa by using the equation in Figure 1. For example, a rate of 60 beats per minute would translate to 1000 ms (60 000/60 = 1000 ms). An interval of 800 ms would translate to 75 beats per minute. It should be noted that the longer the interval in milliseconds, the slower the rate in beats per minute.
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