What we set up and why
Several distinct sets of adhesive electrodes live on the patient during an EP case. Each has a different job, and confusion between them is a common source of pre-case fumbles. We’re talking about:
- ECG leads — surface ECG for the recording system and for monitor display
- Defibrillation pads — for shock delivery and external pacing
- RF dispersive (grounding) pad — return path for ablation current
- 3D mapping patches — for location and reference
- BIS or depth-of-anesthesia stickers — if used
Every one of them is placed before the sterile drape goes down, and once the drape is down, the goal is to never have to touch them again.
ECG leads
Placement
- Standard 10-lead configuration when we want 12-lead acquisition on the recording system
- Limb leads can be moved to the shoulders and hips (Mason-Likar) to keep them out of the fluoro field — flagged to the operator because morphology shifts slightly
- Precordial leads (V1–V6) placed accurately — these are clinical data, not decoration
- Avoid placing leads under defib pads, mapping patches, or BIS strips
Check before drape
- All leads connected to the harness, harness connected to the recording system
- Clean baseline on every channel, no 60 Hz noise, no lead-off
- Save a baseline 12-lead before any manipulation
Defibrillation pads
Placement
- Anterior-posterior is standard for EP — keeps the chest clear of the operator’s working field
- Anterior pad on the left chest, lateral to the apex
- Posterior pad on the left back, mirror position
- For ICD implant cases, pad position adapts to the surgical side
- Stay clear of mapping patches and the dispersive pad — at least 5–8 cm separation
Check before drape
- Plugged into the defibrillator/external pacer
- Defibrillator on, in monitor mode, pad-impedance reading normal
- External pacer tested if planned (capture threshold or backup mode set)
- Document time of placement
RF dispersive (grounding) pad
This is the patch that completes the electrical circuit for unipolar RF ablation. Without it, no RF current flows through the tissue to ground.
Placement
- Dry, well-vascularized skin — usually the upper back or thigh
- Avoid bony prominences, scars, tattoos, implant pockets
- Full surface contact — no wrinkles, no air gaps
- Some systems require two dispersive pads (split pad) — confirm the system’s needs
Why position matters
- Pad too small or partially adherent = high current density at the pad = skin burn
- Pad too far from the heart with intervening high-impedance tissue = inefficient delivery
- Pads near other patches can create unintended current paths
Check before drape
- Plugged into the RF generator
- Impedance baseline within range
- No overlap with other patches
3D mapping patches
Already covered in Mapping Station Setup. Two key reminders for the patch perspective:
- Placed early, in final patient position (arms tucked or boarded — match the case)
- Never overlapping defib pads or dispersive pad
- Confirmed plugged in and reading impedance before drape
Pre-case timeout checks
A useful sequence — say each one out loud:
- ECG leads on, signal clean, baseline 12-lead saved
- Defib pads on, plugged in, pad-impedance reading normal
- Dispersive pad on dry skin, fully adherent, plugged into RF generator
- Mapping patches on, plugged in, system reading reference
- BIS or depth monitor (if used) on and reading
- Foley placed if planned
- SCDs on and cycling
At the end of the case
Skin checks aren’t optional — especially under the dispersive pad and the defib pads.
- Peel patches gently, looking at the skin underneath each one
- Document any redness, blistering, or burns immediately
- Photograph anything beyond mild erythema
- Notify the operator before the patient leaves the room
- A small burn under a dispersive pad means the pad failed — investigate before next case
Safety habits
- Always have a backup set of pads in the room — one peels mid-case, we don’t scramble
- Use the same brand/system the generator expects — mismatches degrade contact and impedance
- For pediatric or small adult patients, use the appropriately sized pads — don’t assume adult defaults
- If a shock is delivered, recheck adhesion and skin under the pads before continuing