Recent studies have demonstrated that the myocardium around the pulmonary vein (PV) ostia plays an important role in the initiation and perpetuation of atrial fibrillation (AF).1–11 This important finding has led to the development of segmental PV ostial isolation,3–6 circumferential ablation or isolation around the PVs using circular linear lesions guided by 3D electro-anatomical mapping.7–11 Also, substrate modification with the use of limited linear ablation has been demonstrated to improve clinical outcome after PV isolation in patients with AF inducibility.12,13 However, the most useful method in the majority of ablation centres is PV isolation using either segmental PV isolation or complete PV isolation guided by 3D mapping and Lasso catheters. This article describes methods of left atrial ablation and clinical outcome after ablation in patients with paroxysmal or persistent AF.
Complete Pulmonary Vein Isolation Using 3D Mapping and the Lasso Technique
The ablation procedure is performed under sedation with a continuous infusion of propofol. All procedures comprise the following steps.10,11
First, three 8F SL1 sheaths (St Jude Medical, Inc.) are advanced to the left atrium (LA) by a modified Brockenbrough technique: two sheaths via one puncture site and the third sheath via a second puncture site. One puncture is always performed at the inferoposterior site of the foramen ovale for easy access to the right inferior vein and the atrial myocardium. After trans-septal catheterisation, intravenous heparin is administered to maintain an activated clotting time of 250–300 seconds. Additionally, continuous infusions of heparinised saline are connected to the trans-septal sheaths at a flow rate of 10ml/hour to avoid thrombus formation or air embolism.
Next, 3D mapping (CARTO or NavX) is performed using a 3.5mm-tip catheter (ThermoCool NaviStar, Biosense-Webster, US) or a 4mm-tip catheter (Biosense-Webster, US) during coronary sinus pacing, sinus rhythm or AF. Mapping is performed only in the LA. All mapping points deep within the PV have to be deleted to ensure that the posterior wall is flat in the right lateral and left lateral view (see Figure 1).
After LA reconstruction, each PV ostium is identified by selective venography and carefully tagged on the electro-anatomical map. The authors arbitrarily defined any point with clear PV–LA inflection and marked the opposite points perpendicular to the PV on the right anterior oblique (RAO) 30 or left anterior oblique (LAO) 40.
This step is the most important part in order to achieve a successful PV isolation. In our experience, lack of knowledge of the PV ostium may sometimes make the ablation more difficult or create a potential risk of PV stenosis.14,15 For example, the isolation of the left-sided PVs in the setting of a narrow ridge between the left atrial appendage and the left PVs can be difficult if the anterior edge of the left PV ostia is inappropriately marked in the left atrial appendage.14 On the other hand, severe PV stenosis can be produced if the PV ostium is tagged inside the PVs.15
Next, two decapolar Lasso catheters (Biosense-Webster) are placed within the ipsilateral superior and inferior PVs or within the superior and inferior branches of a common PV before radiofrequency (RF) delivery in the majority of patients with AF. In our series of >1,300 AF ablations, in only 2% of patients could only one Lasso catheter be placed in the PVs due to difficult trans-septal puncture or manipulation of the sheaths. Irrigated RF energy is then delivered with a target temperature of 45°C, a maximal power limit of 40W and an infusion rate of 17ml/min. In all patients, maximal power of 30W is delivered to the posterior wall to avoid the potential risk of LA–oesophageal fistulae. RF ablation sites are tagged on the reconstructed 3D LA. RF energy is applied for 30 seconds until the maximal local electrogram amplitude decreases to <70% or double potentials appear, and the sequence of PV activation recorded from the double Lasso catheters changes. RF ablation is performed in the posterior wall about 1cm from and in the anterior wall about 5mm from the angiographically defined PV ostia (see Figure 2).
In patients with paroxysmal or persistent AF, the ablation end-point of continuous circular lesions (CCLs) is defined as absence of all PV spikes during sinus rhythm (SR) documented with the two Lasso catheters within the ipsilateral PVs at least 30 minutes after PV isolation.10,11 Termination of AF is not included in the end-point in the authors’ procedure. Electrical cardioversion (CV) is performed after complete isolation of the bilateral PVs in case of AF persistence.
Complete Pulmonary Vein Isolation by Continuous Circular Lesions
Our studies have demonstrated that CCLs can be performed during SR or coronary sinus (CS) pacing or during AF.10,11 During SR or CS pacing, CCLs resulted in progressive prolongation and sequence change of PV activation recorded from two Lasso catheters within ipsilateral PVs and, ultimately, isolation of the ipsilateral PVs.10 Also, CCLs during persistent AF resulted in progressively organised PV activity within the ipsilateral PVs and, ultimately, isolation of the ipsilateral PVs.11 In the authors’ experience, simultaneous isolation of the ipsilateral PVs during AF or SR occurred in >90% of the right-sided and left-sided PVs (see Figure 2).10,11
After the complete isolation of the PVs, regular or irregular automatic activity dissassociated from the atrial activity was observed in ~95% of patients with AF.10 Induced or spontaneously sustained fast PV tachyarrhythmias were observed within the isolated PV in ~45% of patients.10 The high incidence of automatic activity and fast PV tachyarrhythmias within the isolated PVs may be due to more myocardium within the isolated area compared with other studies using segmental PV isolation.3–6,10,16,17
Atrial Fibrillation Termination During Continuous Circular Lesions
In our recent study,18 51 patients with paroxysmal AF underwent complete PV isolation during AF. After complete PV isolation, external CV was required to terminate AF in only five patients (9.8%); in the remaining 46 patients (90.2%), AF termination occurred before or immediately after complete PV isolation. Importantly, a single PV as AF substrate was demonstrated in five patients (9.8%), in whom sustained PV fibrillation or tachycardia was always observed within the PV before isolation during AF and after isolation during SR. However, in patients with persistent AF lasting more than seven days and less than one year, AF termination occurred in only 30% of cases.11 Also, the majority of AF termination occurred before isolation of the bilateral PVs. Based on the authors’ data, AF termination should not be the end-point for catheter ablation, because in most cases AF terminated before complete isolation. More importantly, recovered PV conduction occurred in the majority of patients with recurrent atrial tachycardia during the second ablation procedure.19
Recovered Pulmonary Vein Conduction After the Initial Ablation Procedure
The recurrence rate after the initial PV isolation seems to be different depending on the ablation technique and the follow-up. In the authors’ experience, without any blanking period, the recurrence rate of atrial tachyarrhythmias was 25% in patients with ablation during stable rhythm and 37.5% in patients with ablation during AF.10,11 Interestingly, recovered PV conduction has been demonstrated in 80–90% of patients with recurrent tachycardia after CCLs, and the recovered PV activation presented as a significant delay during sinus rhythm compared with that before the initial ablation.10,11,19 During the second procedure, the conduction gap was found in all regions of the previous CCLs. All conduction gaps were easily identified in the previous CCL by using two Lasso catheters within the ipsilateral superior and inferior PVs, and could be successfully closed by a few RF applications in the previous CCLs during the second procedure.19
These data are consistent with previous studies showing that recovered PV conduction is a dominant finding in patients with recurrent atrial tachyarrhythmias after the initial procedure. Importantly, the majority of patients were free of recurrence after the second procedure. These data strongly support that permanent PV isolation should be the end-point of CCLs. In patients without recovered PV conduction, we attempted to uncover non-PV foci triggering AF by stimulation and provoked manoeuvres, and to abolish all non-PV foci by irrigated RF ablation.
Linear Lesion of the Left Atrium
Macro re-entrant tachycardia has been reported as a complication of circumferential PV ablation or isolation.7,10,11,19,20 The incidence of these tachycardias was 5–20% depending on the ablation techniques and additional linear lesions in the LA. In a recent study, additional linear lesions have been demonstrated to prevent macro re-entrant tachycardias after circumferential PV ablation.20 In clinical practice, it is difficult to create a conduction block over the left isthmus between the left PVs and the mitral annulus.21,22 However, clinical success was ~95% after permanent complete PV isolation (including the second ablation procedure) without additional linear lesion in the LA in patients with paroxysmal or persistent AF.10,11,19 Based on their data, the authors do not routinely create any additional linear ablation in the LA except in patients with left atrial macro re-entrant tachycardia after ablation for paroxysmal and persistent AF.
Complications
In the authors’ experience with >1,300 AF ablations using irrigated ablation and a 3D mapping system, cardiac tamponade occurred in only four patients. Arterial embolism to the right retinal artery occurred in one patient, and it was completely recovered three days after the ablation. Most complications were local haematomas (in ~2% of patients).
Conclusion
Based on the authors’ experience with low complication and high success rates, the ideal ablation procedure consists of performing minimal lesions. The authors’ current strategy is to achieve permanent PV isolation by CCLs. The permanent circumferential PV isolation is the preferable end-point for catheter ablation of paroxysmal and persistent AF.