Palpitations and narrow-complex tachycardia.

A 56-year-old patient with a history of Parkinson's disease presented with palpitations and an apparently irregular narrow-complex tachycardia on electrocardiogram. The discrepancy in ventricular rate between the limb and precordial leads was the result of myopotentials from his tremors mimicking the QRS complexes in the limb leads. These myopotentials can be differentiated from true QRS complexes by the fact that they are usually variable in amplitude and occur at a frequency similar to that of limb tremors.