PACs, like every other wave or complex on an ECG strip, can sometimes occur at such a point that they overlap another wave or complex. When this occurs, they may be difficult to spot (thus the term buried P wave). Let’s go over some of these possible pitfalls in diagnosis.
Every once in awhile the P wave of a PAC will fall right over the T wave of the previous complex. Most of the time, the two waves will be easily distinguishable (Figure 13-26). Occasionally, however, the presence of the P wave makes the T wave appear to be double humped or biphasic (Figure 13-27). At other times, the P wave and the T wave can be indistinguishable because they fuse. In these cases, the presence of the P can only be inferred from the added height or width that the P wave gives to the underlying T wave due to the fusion (Figure 13-28).
Figure 13-26 P wave superimposed on previous T wave. In this example, the P is easily identifiable and is obviously superimposed on the T wave of the previous complex.
From Arrhythmia Recognition: The Art of Interpretation, courtesy of Tomas B. Garcia, MD.
Figure 13-27 P wave superimposed on previous T wave. In this example, the P wave appears to be blending into the T wave of the previous complex. Note that this is the only T wave in the strip that shows a double-humped appearance. These PACs are difficult to pick up, and a keen eye is needed to make the definitive diagnosis.
From Arrhythmia Recognition: The Art of Interpretation, courtesy of Tomas B. Garcia, MD.
Description
Figure 13-28 P wave superimposed on previous T wave. In this example, the P-wave amplitude has been added to the T-wave amplitude of the previous complex to create an extra-high and wide T wave. This is a common occurrence and is often confused with PJCs. Always be aware of the possibility of the fusion of two waves when you are evaluating an arrhythmia.
From Arrhythmia Recognition: The Art of Interpretation, courtesy of Tomas B. Garcia, MD.
DescriptionThe key to spotting hidden or partially hidden P waves is to look closely at your strip. Look over each wave and see if any of them has a big difference in its morphology when compared to its brothers and sisters in the other complexes. If you do spot something that is unusual, spend the time to evaluate that area closely. When interpreting ECGs or arrhythmias, the key lies with the abnormality.