All Channels Noisy and a 38-Ohm Reading Mid-Case
A 62-year-old man is undergoing an EP study with a planned ablation for SVT. Decapolar and quadripolar catheters sit in the CS and RV apex, and the baseline study has been unremarkable, with diagnostic catheter impedances of 110-140 ohms. When the ablation catheter is connected to the pin box and the RF generator is switched on in standby, continuous 60-Hz artifact at 3-4 mV appears on all 12 intracardiac channels while the surface leads stay clean. The artifact disappears the moment the ablation catheter is unplugged from the pin box. The generator's impedance display for that catheter reads 38 ohms, and its dispersive-pad indicator shows adequate contact. The patient remains in sinus rhythm at 72 bpm with stable vital signs.
1. Interpret the findings, name the most likely fault, and state your immediate action. Why is the 38-ohm reading more important than the noise?
Read the worked answer
Normal diagnostic impedances, clean surface leads, and artifact that appears only when one catheter is connected all point to a fault in the ablation catheter or its connection, not the recording system. Combined with the 38-ohm reading, the most likely cause is an insulation breach creating a low-resistance path (short) to the blood pool or the return electrode.
The impedance is the more important finding. The noise is a symptom; the impedance tells you where the current will go. With a breach, RF current can exit at the defect rather than the tip, so energy is delivered to tissue you are not watching, and the generator's power/temperature feedback becomes unreliable. You cannot ablate safely with that reading.
Immediate action: do not deliver RF. Disconnect the catheter from the pin box and the generator, remove it, inspect it, and replace it with a new one. Verify the new catheter reads roughly 80-150 ohms before use, recheck the cables and pad, and document the event and the lot number. Continuing with 'the noise went away' would be the wrong call.
2. The catheter is replaced and impedance is now 108 ohms with no noise. At the first RF application the impedance climbs abruptly from 108 to 220 ohms and stays there. What do you do, and what does the pattern mean?
Read the worked answer
Stop RF immediately. An abrupt, sustained impedance rise means the electrode is no longer in good electrical contact with the tissue/blood interface - most often coagulum formation on the tip, which insulates the electrode. Continuing through a rise like this is how you get a steam pop or a charred tip that no longer records.
The pattern matters:
- Gradual rise over many seconds suggests heating and evolving tissue contact.
- Abrupt step-up suggests coagulum or loss of contact/movement.
- Abrupt step-down raises concern for an insulation breach or a short, and is a stop signal too.
After stopping: withdraw, clean or exchange the catheter, check the dispersive pad and all connections, verify the impedance has returned to the 80-150 ohm range, then resume at lower power with shorter applications. If the impedance will not stay stable, do not proceed - abort and reschedule rather than ablate blindly.