Some Additional Clinical Points

The biggest problem associated with sinus arrhythmia, and with the nonrespiratory variant in particular, is that it is frequently mislabeled as multiple premature atrial contractions (PACs). The inverse is also true; an ECG with many PACs is frequently considered sinus arrhythmia (Figure 11-5). The possibility of frequent PACs should always be considered before making the diagnosis of sinus arrhythmia.

A rhythm strip shows sharp peaks of the QRS complexes between fluctuations. Arrows point toward curved P waves occurring at irregular intervals.

Figure 11-5 Note the irregularity of the rhythm. The P waves identified with the green arrows are PACs.

From Arrhythmia Recognition: The Art of Interpretation, courtesy of Tomas B. Garcia, MD.

While we are on the topic of PACs . . . sinus arrhythmia is a cardiac rhythm. Just like any other cardiac rhythm, the pattern can be broken by an event, such as a PAC. The event can cause a further deterioration of the baseline irregularity caused by the sinus arrhythmia itself. In certain cases, an event overlying a respiratory variant sinus arrhythmia can look just like a nonrespiratory variant sinus arrhythmia (Figure 11-6). As we saw, the difference between the two possibilities can be of critical clinical importance. Always evaluate the P waves for any inconsistencies that could be caused by ectopic or premature complexes!

Two illustrations show sinus arrhythmia and sinus arrhythmia with events occurring at regular intervals.

Figure 11-6 Notice how just two well-placed events, in this case PACs, can change the appearance of an easily identifiable respiratory variant sinus arrhythmia.

© Jones & Bartlett Learning.

ARRHYTHMIA RECOGNITION

Sinus Arrhythmia

Rate: Usually around 60 to 100 BPM, but can be slow or fast
Regularity: Regularly irregular, but can be irregularly irregular
P wave:

Morphology:

Upright in II, III, and aVF:

 Present and sinus in origin

Same throughout

Yes
P:QRS ratio: 1:1
PR interval: Normal, consistent
QRS width: Normal or wide
Grouping: None
Dropped beats: None

NOTE

Because sinus arrhythmia is a relatively slow rhythm and the changes in rate due to respirations may take a few seconds to develop, the ECG strips in this section will be presented in landscape format. Keeping the original size of the rhythm strip is important in correctly learning to identify rhythm abnormalities.

We will continue to do this from time to time as the situation warrants. Next, full-size ECGs will be presented in landscape format to maintain the actual size of the tracing.