Many clinicians have considered premature atrial contractions/depolarizations (PACs) to be a benign dysrhythmia with little risk of developing serious consequences. However, there is recent evidence that PACs may be associated with severe clinical consequences. Frequent PACs and atrial tachycardias (with or without symptoms) have been shown to be strong independent predictors of atrial fibrillation. Some scientists propose that frequent PACs contribute to the development of an atrial myopathy that causes atrial fibrillation, which alone is associated with an increased risk of stroke, heart failure, and death.

Premature atrial contractions, both conducted and blocked, are common. Typically, a PAC is characterized by the presence of a premature P wave, often found buried in the T wave in the preceding beat (Figure 1), followed by a QRS-T complex. The QRS complex may be normal, resembling the sinus beats, or aberrantly conducted.

A blocked or nonconducted PAC is a premature...

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