What is the commonest foci (drivers) of atrial fibrillation (AF)?

The Commonest Foci (Drivers) of Atrial Fibrillation

The pulmonary veins are the most common foci (drivers) of atrial fibrillation, with approximately 94% of AF triggers originating from this location. 1

Anatomical Distribution of AF Foci

The distribution of AF triggers follows this pattern:

• Pulmonary Veins (PVs): The predominant source of AF triggers

  • Left Superior PV: Most common individual location
  • Right Superior PV: Second most common
  • Left Inferior PV: Third most common
  • Right Inferior PV: Fourth most common

• Non-Pulmonary Vein Foci: Less common but clinically significant

  • Superior Vena Cava
  • Ligament of Marshall
  • Left Posterior Free Wall
  • Crista Terminalis
  • Coronary Sinus
  • Left Atrial Appendage
  • Right Atrial Appendage

Electrophysiological Mechanisms

The initiation and maintenance of AF involve two primary mechanisms:

1. Focal Activation Theory: Rapidly firing ectopic foci, predominantly in the pulmonary veins, trigger AF 2

   • These foci demonstrate abnormal automaticity and triggered activity
   • Pulmonary vein myocytes have shorter refractory periods than other atrial tissue
   • Earliest activation typically occurs 2-4 cm inside the pulmonary veins 1

2. Multiple-Wavelet Hypothesis: Involves fractionation of wavefronts propagating through the atria, creating self-perpetuating "daughter wavelets" 2

   • These mechanisms are not mutually exclusive and often coexist in the same patient

Clinical Implications

The recognition of pulmonary veins as the predominant source of AF triggers has revolutionized treatment approaches:

• Pulmonary vein isolation has become the cornerstone of catheter ablation strategies for AF 2
• Recurrence of AF after pulmonary vein isolation indicates the presence of non-PV foci 3
• More proximal disconnection of the PVs by performing ablation within the left atrium may be required in some cases 3

Special Considerations

• In patients with persistent AF, right atrial appendage may also serve as an important driver, with cycle lengths even shorter than those in the left atrial appendage in some patients 4
• The left atrial appendage can harbor foci maintaining AF after pulmonary vein isolation 5
• Unique anatomic and electrophysiological features of the pulmonary veins contribute to their arrhythmogenic nature:
  • Abrupt changes in fiber orientation
  • Relatively depolarized resting potentials
  • Abbreviated action potentials and refractoriness 2

Therefore, based on the most recent and highest quality evidence, the answer to the multiple-choice question is: B. Pulmonary veins (not listed in the options but is the correct anatomical location).

Among the given options, none correctly identifies the most common foci of AF. The left atrial appendage (option B) can harbor AF foci but is not the most common location.