What is the preferred electrode placement for cardioversion, anterior-posterior (AP) or anterior-lateral (AL)?

Anterior-Posterior vs. Anterior-Lateral Electrode Placement for Cardioversion

The anterior-posterior (AP) electrode configuration is superior to anterior-lateral (AL) placement for external cardioversion of atrial fibrillation, with higher success rates (87% vs. 76%) and lower energy requirements. 1, 2

Evidence Supporting Anterior-Posterior Placement

The evidence strongly favors AP electrode positioning for several reasons:

• Randomized controlled studies demonstrate AP configuration achieves higher overall success rates (87% vs 76%) compared to AL positioning 2
• AP placement requires lower energy levels for successful cardioversion 1, 3
• AP positioning creates a more homogeneous shock-field gradient throughout the atria 3
• AP configuration is particularly beneficial when pathology involves both atria (e.g., atrial septal defects or cardiomyopathy) 2, 1

A landmark randomized trial by Kirchhof et al. (2002) found that AP positioning was successful in 96% of patients compared to only 78% with AL positioning 3. When crossover was performed after failed cardioversion, 8 of 12 patients were successfully cardioverted when switching from AL to AP, while none were successful when switching from AP to AL.

Optimal Electrode Placement Technique

For optimal AP electrode placement:

• Anterior pad: Place to the left of the sternum, directly against the chest wall 2, 1
• Posterior pad: Position below the left scapula 2
• Use pads with a diameter of 8-12 cm for optimal current flow 1
• Place pads directly against the skin (not over clothing) 1
• For patients with breasts, place the anterior pad under rather than over breast tissue 1
• Use electrolyte-impregnated pads to minimize electrical resistance 1

Special Considerations

• For patients with emphysema: The amount of pulmonary tissue between the anterior paddle and heart can reduce effectiveness. Place the anterior electrode further to the left of the sternum to reduce this distance 2, 1
• Timing: Deliver shocks during expiration when possible, as this compresses pulmonary tissue and allows more current to reach the heart 2, 1
• For patients with implanted devices: Position pads at least 8 cm away from pacemakers/ICDs 1
• For patients with high BMI: Consider fluoroscopic guidance for electrode placement to ensure current traverses through atrial tissue 4
• Active compression: Recent research shows applying active compression on the anterior electrode during cardioversion can further improve success rates (96% vs 84%) and lower defibrillation thresholds 5

Electrode-to-Heart Distance Matters

Recent research indicates that the distance from electrodes to the cardiac silhouette significantly impacts cardioversion success. Patients requiring only a single 100J shock had significantly shorter distances from electrodes to the heart compared to those requiring multiple or higher energy shocks 6. The xiphoid process can serve as an anatomical landmark to guide optimal anterior electrode placement.

Conclusion

While both AP and AL configurations are mentioned in guidelines, the evidence clearly demonstrates that AP positioning should be the first-choice approach for external cardioversion of atrial fibrillation. This recommendation is supported by multiple randomized trials, pathophysiological principles, and recent research showing superior outcomes with AP placement.