Is premature atrial contraction (PAC) significant?

Significance of Premature Atrial Contractions

Premature atrial contractions (PACs) are not merely benign findings but are associated with an increased risk of developing atrial fibrillation, stroke, and all-cause mortality. 1

Clinical Significance of PACs

Risk Assessment

• PACs were previously considered benign electrocardiographic findings, but recent evidence shows they can be markers of underlying pathology
• Frequent PACs (>700 per day) are associated with:
  • Increased risk of developing atrial fibrillation 2
  • Higher risk of stroke even independent of AF occurrence 2
  • Increased all-cause mortality 1
  • Potential marker of atrial cardiomyopathy 2

Prevalence and Symptoms

• PACs occur in nearly all individuals at some point 1
• Most PACs are asymptomatic, but some patients experience:
  • Palpitations
  • Sensation of skipped beats
  • Chest discomfort
• Approximately 6.5% of patients with PACs are severely symptomatic 3

Diagnostic Considerations

ECG Identification

• A PAC is identified as a premature P wave that occurs before the next expected sinus P wave 4
• PACs typically have different morphology and mean vector from sinus P waves 4
• PACs may be:
  • Conducted to ventricles normally
  • Conducted with ventricular aberration
  • Not conducted ("blocked") 4

Important Diagnostic Pitfalls

• Blocked atrial bigeminy: When PACs occur in a bigeminal pattern but are not conducted, they can simulate sinus bradycardia; careful examination of T waves for hidden P waves is essential 4
• PACs may be confused with atrioventricular block on ECG 4
• In atrial bigeminy, repetitive PACs could be associated with normal conduction, AV delay, or blocked conduction, potentially leading to erroneous diagnosis of AV block 4

Management Approach

Initial Evaluation

• Exclude potentially reversible causes:
  • Electrolyte abnormalities
  • Hyperthyroidism
  • Stimulant drug use
  • Excessive caffeine or alcohol consumption 1
• Consider echocardiography to evaluate for structural heart disease, especially with frequent PACs 1

Treatment Algorithm

1. For asymptomatic patients with infrequent PACs:

   • No specific treatment required
   • Regular follow-up to monitor for increasing frequency

2. For symptomatic patients:

   • First-line therapy: Beta-blockers 1
   • Alternative: Non-dihydropyridine calcium channel blockers
   • Consider antiarrhythmic drugs for refractory symptoms

3. For patients with frequent PACs (>700/day) or PACs triggering AF:

   • Consider catheter ablation, especially if:
     • Symptoms are refractory to medical therapy
     • Patient cannot tolerate antiarrhythmic medications
     • Evidence of PACs triggering atrial fibrillation 5

Ablation Outcomes

• Catheter ablation has shown good efficacy for symptomatic, frequent, drug-refractory PACs 5
• Success rates of approximately 80-90% have been reported 5, 6
• Ultra-high-density mapping techniques have improved localization and ablation success 6

Special Considerations

• PACs with shorter coupling intervals (especially <400ms) are more likely to trigger atrial fibrillation than those with longer coupling intervals 5
• The concept of "atrial cardiomyopathy" suggests that structural, functional, and biochemical changes in the atria may lead to both PACs and thromboembolic events 2
• Frequent PACs are more common in elderly individuals and those with enlarged left atria 3

In conclusion, while isolated and infrequent PACs may not require specific intervention, frequent PACs warrant careful evaluation and consideration of treatment options given their association with increased risk of atrial fibrillation, stroke, and mortality.