Catheter Ablation
Catheter Ablation
This domain tests whether you can select a target, deliver energy safely, and confirm success. Questions cover mapping (activation, entrainment, substrate), radiofrequency and cryothermal lesion physics, and complication recognition.
Core rules
- RF lesion size depends on power density, contact force, duration, and tissue temperature. Typical settings are 20–50 W with irrigation, a target temperature of 50–60°C at the electrode-tissue interface, and contact force of 10–20 g. Low contact force with high power causes steam pops; excessive force causes deep injury.
- Cryoablation uses cryomapping at about −30°C to test safety, then freezing at −80°C. Cryo is useful near the AV node and coronary arteries because it preserves architecture and creates reversible lesions during mapping.
- AVNRT: target the slow pathway in the triangle of Koch, guided by a slow-pathway potential and anatomy. Typical flutter: create bidirectional block across the cavotricuspid isthmus; prove it with pacing from both sides.
- WPW: map the earliest ventricular activation during pre-excited rhythm or atrial pacing, and test for mechanical block. After ablation, confirm loss of preexcitation and check for pathway recovery with isoproterenol and adenosine.
- AF ablation centers on pulmonary vein isolation. Complications include PV stenosis, phrenic nerve palsy (right superior PV, SVC), atrioesophageal fistula, stroke, tamponade, and coronary injury near the CS ostium.
Worked example
A 28-year-old with palpitations has a delta wave in V1–V2 and inducible orthodromic AVRT. During atrial pacing, the earliest ventricular signal is at the lateral tricuspid annulus, consistent with a right free-wall pathway. RF is applied during pacing; preexcitation disappears at 15 seconds. After 30 minutes, adenosine produces no delta wave and no pathway conduction. Success is confirmed by loss of preexcitation plus unidirectional and bidirectional block, not by loss of palpitations alone.
Traps
- Ablating the earliest atrial activation during orthodromic AVRT without confirming the ventricular insertion; retrograde mapping can mislead.
- Titrating power in thin-walled structures (PVs, SVC, atrial appendage) without reducing energy.
- Missing a steam pop or impedance rise and continuing to deliver energy.
- Assuming absent preexcitation equals success without testing for pathway recovery.