How to Perform 3-Dimensional Entrainment Mapping to Treat Post–AF Ablation Atrial Tachycardia/AFL
Philipp Sommer, MD; Christopher Piorkowski, MD; Gerhard Hindricks, MD
In the past decade, ablation of AF has become standard procedure in the treatment of AF patients. Wide atrial circumferential ablation lines are drawn around the ipsilateral PVs in order to isolate this region in almost all patients as the cornerstone of ablation procedures. During the development of today’s techniques, noncontinuous ablation lines with gaps due to bad tip-to-tissue contact caused post–AF ablation atrial tachycardias and atypical AFL in up to 20% of patients (Figure 23.1). With improved mapping and catheter navigation technologies, the rate of these iatrogenic tachycardias has decreased to approximately 5%. With increasing use of different ablation strategies (especially defragmentation of the atria) we observed an increase in the rate of atypical flutters in the past years. Understanding of the tachycardia mechanism is crucial for a successful treatment of these arrhythmias.
Before their initial AF ablation procedure, all patients undergo cardiac imaging, mostly MRI imaging. For all post–AF arrhythmia ablations, the initial imaging is being used for the reablation as well. Nevertheless, it can be very helpful to redo the 3-dimensional (3D) reconstruction of the DICOM data because not only the LA but also the RA may play a role in this form of arrhythmias. Otherwise, a combination of electroanatomical reconstruction and registered (superimposed) 3D/MRI CT model is necessary (Figure 23.2).
Echo Before Ablation
In all patients with a moderate or high thrombembolic risk atrial thrombus formation is ruled out the day before the ablation procedure by TEE. Furthermore, LVEF is measured in all patients with TTE to identify patients who developed a tachycardiomyopathy with impaired LVEF under their atrial tachycardia and fast conduction over the AV node. This might have implications on the periprocedural planning and sedation regimens (e.g., negative inotropic effects of propofol in patients with impaired LVEF) as well as follow-up.
All patients undergo their PVI as well as their post–PVI AT ablation under deep analgosedation. Before puncture of the femoral veins, midazolam and fentanyl are administered in low doses. Then a bolus of propofol is delivered followed by continuous application. The LFV accommodates a 5-Fr (RVA) and 6-Fr (CS) sheath for the standard diagnostic catheters. We routinely use deflectable decapolar CS catheters that can be inserted via a femoral access. On the right side, a short 12-Fr sheath is placed for insertion of the transseptal sheath. Additionally, an arterial line (4-Fr) is punctured for invasive blood pressure measurement. Finally, a temperature probe is inserted in the esophagus to monitor temperature increase during ablation.
Single transseptal puncture for LA access is typically performed after initial entrainments within CS and HRA have suggested a LA origin of the arrhythmia. The puncture is guided by contrast dye injection and fluoroscopy mainly. Another tool is pressure recording at the needle tip with the RR measurement line. Successful puncture is confirmed by contrast dye injection and fluoroscopical control. TEE guided transseptal punctures are only rarely necessary (< 1%). After the transseptal puncture, an initial bolus of 100 U/kg is given and the ACT controlled every 20 minutes in order to maintain target ACT values between 250 and 350 seconds. If necessary, repeated heparin boluses are delivered during the ablation.
Selection of Guiding Sheaths and Catheters
The guiding sheath for the spiral and the ablation catheter is a deflectable sheath that allows bidirectional movement during the ablation procedure (Agilis®, St. Jude Medical, St. Paul, MN). In patients with normal or moderately enlarged LA diameter (< 45 mm), we use the small curve; in enlarged left atria, “med” curve is preferred. The sheath is constantly flushed with a heparinized saline drip at a flow rate of 2 mL/h. In clinical routine, we use RF as the energy source exclusively. An open irrigated-tip catheter (Flexability, St. Jude Medical, St. Paul, MN) is the standard ablation catheter, irrigation rate is 17 mL/min, and the preferred spiral catheter is an adjustable (15–25 mm) Reflexion (St. Jude Medical).
3D Mapping System
For ablation of AF, but especially for AT/AFL procedures, the use of 3D mapping systems has increased efficacy significantly. When combined with image integration, 3D mapping systems allow reproducible identification and visualization of reentrant circuits. For AT/AFL ablations, we routinely use the Ensite Precision (St. Jude Medical, St. Paul, MN).
Registration of 3D CT Model
After the transseptal puncture, the spiral diagnostic catheter is inserted into all PVs and separate geometries are acquired over all 10 poles. The 3D MRI model is superimposed visually (Figure 23.3; Video 23.1) and registration is completed with additional 10 to 15 characteristic points acquired manually with the ablation catheter (e.g., mitral annulus 3, 6, 9, 12 o’clock, roof).2 Once the MRI model is registered, the electroanatomical information can be displayed on this shell without acquiring any further geometries.