Steam Pop During Cavotricuspid Isthmus Ablation
A 66-year-old man with recurrent typical atrial flutter (EF 55%, INR 2.4 on warfarin) is under conscious sedation. An 8-mm non-irrigated tip catheter is positioned in the cavotricuspid isthmus, and RF is begun at 50 W with a 60 C target; baseline impedance is 108 ohms. After 12 seconds the impedance climbs steadily to 182 ohms and there is an audible pop; the generator then cuts out with an impedance error. The flutter terminates to sinus rhythm at 88 bpm. The patient reports sudden chest pressure and becomes diaphoretic; BP falls from 122/76 to 76/44, the heart rate rises to 118, and SpO2 holds at 96% on 2 L. IV access is in place and the ACT drawn 20 minutes ago was 280 s.
1. Give your differential for the acute deterioration and list your immediate actions in priority order.
Read the worked answer
Differential, in the order you must act on it:
- Perforation with tamponade - the pop plus hypotension plus chest pressure is a perforation until an echo says otherwise.
- Vasovagal response to pain/ablation - possible, but never the assumed answer when there has been a pop.
- Sedation-related hypotension or hypoventilation - check the airway and ETCO2.
- Air embolism or coronary injury/myocardial infarction - less likely but on the list.
Immediate actions:
- Stop ablation and stop heparin, call for the attending and additional staff.
- Airway, breathing, circulation: 100% oxygen, confirm ventilation, place the patient supine with legs elevated.
- Rapid crystalloid bolus of 500-1000 mL through a large-bore line.
- Stat bedside echocardiogram; have the pericardiocentesis tray open and the fluoroscopy ready.
- Protamine ready given the ACT of 280 s; do not reverse until you have decided the effusion picture.
- Continuous monitoring for pulsus paradoxus, electrical alternans, and falling BP. Abandon the procedure.
2. The echocardiogram shows a 1.4 cm circumferential effusion without diastolic collapse, and BP is 104/62 after 1 L of saline. ACT is 290 s. Do you complete the isthmus line? Justify your answer.
Read the worked answer
No - abort the case. A steam pop with a new effusion is an evolving injury, and effusions after perforation can enlarge over hours; completing an elective line in an anticoagulated patient with fresh pericardial blood is an unjustified risk. The isthmus line is incomplete, but flutter ablation can be staged safely in 4-6 weeks.
What to do instead:
- Reverse heparin with protamine titrated to the ACT, accepting that the ACT was only modestly elevated.
- Repeat the echo in 15-30 minutes and again before leaving the lab, then serially over the first 6-12 hours.
- Admit for monitored observation with IV access maintained; keep the patient NPO in case intervention is needed.
- Hold anticoagulation until the effusion is shown to be stable or resolving, and involve the attending in that decision.
The judgment being tested is resisting the urge to finish a nearly complete line.
3. If the patient returns for a repeat attempt, how would you change your energy delivery strategy on the isthmus?
Read the worked answer
The impedance rise from 108 to 182 ohms before the pop is the signature of coagulum and tissue overheating, so the repeat strategy should target heat control:
- Lower power - 30-40 W rather than 50 W with an 8-mm tip; titrate upward only if lesions are ineffective.
- Shorter applications (20-30 s) with continuous impedance surveillance; stop for any abrupt or sustained rise.
- Watch for the expected 5-10 ohm impedance fall as a marker of effective heating; a flat or rising impedance means stop.
- Keep the electrode clean - wipe the tip between applications and exchange the catheter if char develops.
- Maximize stable contact and catheter orientation across the isthmus, with attention to the anatomic variants (pouch, prominent Eustachian ridge).
- Consider an open-irrigated catheter, which reduces coagulum and allows cooler, deeper lesions, if the lab has one available.
- Confirm the ACT is therapeutic throughout, and document the prior event so the team plans for it.