An atrial premature complex (APC) or Premature atrial complex (PAC) results from a premature, ectopic, supraventricular impulse that originates somewhere in the atria outside of the SA node. A single complex occurs earlier than the next expected sinus complex. After the APC, sinus rhythm usually resumes.
- Normal finding
- Stress, caffeine, alcohol
- Heart failure, MI, valvular disease, CAD
- Chronic lung disease, hyperthyroidism, infection
- Electrolyte abnormalities (hypokalemia); medications (digoxin)
- R-R interal is irregular.
- Shape of ectopic premature P wae is different from the sinus P wave.
- Premature P wave is followed by a QRS complex if the impulse is conducted into the ventricles. If the APC occurs so early that the AV node has not fully repolarized from the previous impulse, the AV node will be unable to conduct to the ventricles and the Premature P wave will not be followed by a QRS complex. This is known as a blocked or non-conducted APC and is the most common cause of a pause during sinus rhythm.
- Narrow QRS complex if conduction in the ventricles is undisturbed. If the AV node conducts a premature complex into the ventricles when they have not fully repolarized, the resulting QRS complex may appear wide and abnormally shaped. This is known as APC conducted with abberation and must be differentiated from a ventricular premature complex (VPC).
- PR interval may be normal, short, prolonged or absent.
- APC occurs so early that it distorts the T wave of the previous QRS complex. An abnormal or notched T wave followed by an early QRS complex should always arouse the suspicion of an APC.
In patients with heart disease, frequent PACs may precede paroxysmal supraventricular tachycardia (PSVT), A-fib, or A-flutter. If drug therapy is recommended, agents such as quinidine, procainamide, and disopyramide may be used.