Premature Atrial Contraction

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Premature Atrial Contraction

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A premature atrial complex (PAC) is a premature beat that originates from an ectopic (abnormal) location within the atria rather than from the normal sinoatrial node (SA node). It is common for healthy individuals to have PACs that go unnoticed until they start occurring more frequently and/or cause troublesome symptoms. Although benign in most individuals, PACs can be a trigger for the onset of detrimental tachyarrhythmias like atrial flutter, atrial fibrillation, and atrioventricular nodal reentrant tachycardia. Therefore, they have been referred to as "a wolf in sheep's clothing."

Clinical Significance

Frequent and excessive PACs are one of the most potent predictors of an incident AF. ≥30 PACs per hour or an episode of ≥20 consecutive PACs as detected via a Holter monitor delineates excessive PACs.


What exactly causes the atria to depolarize before the normal pacemaker is unclear; however, several factors can increase the frequency of PACs. These include:

  • Anxiety
  • Sympathomimetics (like beta-agonists, ephedrine etc.)
  • Excess caffeine
  • Heavy alcohol intake
  • Digoxin toxicity
  • Myocardial ischaemia
  • Hypokalaemia
  • Hypomagnesemia

Signs and Symptoms

While being asymptomatic in a vast majority of the population, frequent PACs can trigger the following symptoms:

  • Palpitations
  • A strong thump or a jolt in the chest: This is because the normal beat that follows a premature contraction is extremely forceful
  • A skipped beat


The diagnosis of PACs typically requires an ECG or a 24-hour heart rate tracing via a Holter monitor. A PAC can be appreciated as an abnormal P wave, usually followed by a normal QRS complex.


Frequent PACs warrant treatment that includes controlling the heart rate with AV nodal blockers like beta-blockers, and avoidance of the precipitating factors. When due to reduced potassium levels, administration of magnesium sulfate is beneficial in converting PACs to normal sinus contractions. PAC ablation is reserved for cases that do not respond to medical therapy or are triggering AF.