A premature atrial complex (PAC) is an extra beat that arrives early, originating from the atria. The P wave often has a different shape to normal. The QRS may be conducted normally (narrow), conducted with aberrancy (wide, often RBBB shaped), or non-conducted (absent). Nonconducted beats may be so early that the AV node is still refractory. There is usually a pause afterwards.
PACs are common and generally benign.
See also: Extra Beats
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