A 57-year-old woman presents with occasional palpitations that she describes a precordial pounding. She has good exercise tolerance, and no other complaints:

• Marked sinus arrhythmia (respiratory), 84/min
• Otherwise a normal ECG

In sinus arrhythmia, there may be variations of the P wave morphology, probably due to different foci initiating and/or contributing to the sinus impulse. The term “wandering pacemaker” is sometimes used. The respiratory variations (decrease of rate during expiration, increase during inspiration) are common in sinus arrhythmia, particularly in younger subjects. It is quite unlikely that the palpitation described by this lady is related to her sinus arrhythmia.