Anterior-Posterior vs. Anterior-Lateral Placement in Medical Procedures
For cardioversion of atrial fibrillation, anterior-lateral electrode positioning is more effective than anterior-posterior positioning, with higher first-shock success rates (54% vs 33%) and better overall conversion rates (93% vs 85%). 1
Cardioversion Electrode Placement
Efficacy Comparison
- The most recent high-quality evidence from a 2021 multicenter randomized trial involving 468 patients showed anterior-lateral (AL) electrode positioning was significantly more effective than anterior-posterior (AP) for biphasic cardioversion of atrial fibrillation 1
- This contradicts earlier guidelines and smaller studies that suggested AP positioning was superior
- Key findings from the 2021 study:
- First shock success: 54% with AL vs 33% with AP (22% absolute difference)
- Overall success after maximum 4 shocks: 93% with AL vs 85% with AP
- No significant differences in safety outcomes between approaches 1
Technical Considerations
For AL placement:
For AP placement:
- Allows current to reach sufficient atrial myocardium when pathology involves both atria (e.g., atrial septal defects, cardiomyopathy)
- Drawback: Amount of pulmonary tissue between anterior paddle and heart, particularly in patients with emphysema 3
Optimization Techniques
- Use pads with diameter of 8-12 cm for optimal current flow 3
- Ensure direct contact with skin (no clothing in between) 2
- Use electrolyte-impregnated pads to minimize electrical resistance 2
- Consider removing excessive chest hair if necessary 2
- Deliver shocks during expiration when possible to optimize current flow 2
Per-Oral Endoscopic Myotomy (POEM) Approach
For POEM procedures, both anterior (2 o'clock) and posterior (5 o'clock) tunnel orientations show:
- Comparable efficacy
- Similar safety profiles
- Equivalent post-procedure reflux rates 3
The 2024 AGA Clinical Practice Update recommends:
- Selection between anterior vs posterior POEM should depend primarily on endoscopist's preference and patient characteristics
- For patients with prior surgery (including LHM or POEM), use an approach opposite in orientation from the site of prior surgery to avoid fibrosis 3
Surgical Approaches in Total Hip Arthroplasty
When comparing direct anterior approach (DAA) versus posterior approach (PA) or lateral approach (LA):
- DAA shows better early functional outcomes with higher Harris Hip Scores at 6 weeks compared to PA and at 12 weeks compared to LA
- DAA has shorter length of hospital stay compared to PA
- No significant differences in risk of complications (dislocations, neurapraxias, periprosthetic fractures, VTE) between approaches 4
Endoscopic Adrenalectomy Approaches
Three main approaches are used:
- Lateral (transperitoneal)
- Posterior (retroperitoneal)
- Anterior (transperitoneal)
Key considerations:
- Anterior approach requires advanced laparoscopic skills
- Both transperitoneal approaches (anterior and lateral) are suitable for larger adrenal masses
- Posterior approach may be better for obese patients or cases with small lesions 5
Common Pitfalls and Caveats
- Outdated guidelines may still recommend AP positioning for cardioversion based on older studies using monophasic waveforms, but the most recent evidence supports AL positioning with modern biphasic defibrillators 1
- For patients with implanted cardiac devices, position pads at least 8 cm away from the device 2
- Body mass index significantly affects operative time in transperitoneal approaches for adrenalectomy 5
- In POEM procedures, interpretation of data comparing anterior vs posterior approaches is limited by short follow-up and heterogeneity in myotomy length, objective pH testing, and outcome definitions 3