How to Use Balloon Cryoablation for Ablation of Atrial Fibrillation

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How to Use Balloon Cryoablation for Ablation of Atrial Fibrillation


Wilber W. Su, MD; Paul J. Wang, MD


Introduction


Electrical isolation of pulmonary veins (PVs) is the cornerstone of all atrial fibrillation (AF) ablation procedures and remains the most uniformly agreed upon strategy for patients with either paroxysmal or persistent AF.13 Achieving PV isolation (PVI) using conventional, point-by-point ablation lesions remains technically challenging with a shallow learning curve, mostly due to the highly variable anatomy of the posterior left atrium (LA) and difficulty in maintaining good, stable, catheter tip–tissue contact during ablation.4 PVI at the antral level is preferred to minimize the risk of PV stenosis and to include arrhythmogenic antral foci within the level of isolation. To this extent, antral ablation has been shown to be more effective than ostial segmental ablation in preventing AF recurrence.5 With these considerations in mind, an ablation technology that can deliver circumferential ablation centered on the PV antra should facilitate an effective AF ablation.


Although a range of different ablation energy sources such as RF energy, laser, and cryotherapy are available, cryothermal ablation offers theoretical advantages not found in other energy sources in that it does not disrupt target tissue architecture and could thus reduce the overall incidence of procedural complications such as LA perforation, thromboembolic phenomena, and atrioesophageal fistula formation.6 Symptomatic PV stenosis is rare after cryoballoon ablation but was reported for the first time in the STOP-AF trial.7 Coronary occlusions have not been reported in association with cryoablation for AF.


There has been considerable experience with balloon cryoablation of AF, including the STOP-AF trial7 and its Post Approval Follow-up Trial. The overall incidence of atrial esophageal fistula with cryoablation appears to be considerably less than compared to the rate observed with radiofrequency ablation. Despite recognizing the benefits of cryoablation, an efficient delivery platform to deliver contiguous lesions around the PV antra had been lacking until the introduction of the cryoablation balloon catheter system. PVI using earlier delivery platforms (e.g., the 6-mm tipped and expandable circular cryoablation catheters) required lengthy procedures of more than 6 hours, and these novel cryoablation catheters were associated with unsatisfactory clinical outcomes.810 The low rate of long-term efficacy was thought to be due to the effects of competitive warming by the blood pool as it flowed past the catheter. Simply, the flowing blood pool increases the available heat sink area, and consequently, it reduces the cryoballoon cooling potential and ultimately limits the final lesion size. By comparison, the cryoablation balloon catheter obstructs blood flow from the PV being treated, thereby removing this biophysical limitation. In the following sections, we will describe our protocol as well as that of other experienced operators with the use of a cryoballoon ablation catheter for the treatment of patients with AF.


Preprocedure Planning


Most patients undergoing cryoballoon catheter ablation have symptomatic AF refractory to one or more antiarrhythmic agents. There are two competing major approaches to discontinuation of antiarrhythmic drugs that can be considered depending on the patient’s arrhythmia status: (1) all antiarrhythmic agents except amiodarone are stopped at least five half-lives before the procedure, or (2) antiarrhythmic drug therapy may be continued (particularly in patients with persistent or long-standing atrial fibrillation).


Also, there are a number of anticoagulation strategies that may be used, and the ablation can be either performed on or off therapeutic anticoagulation. In addition, the choice of anticoagulation may include warfarin or a non-vitamin K–dependent anticoagulant. In some cases, patients with a CHADS2 score of 2 or more will receive anticoagulation with warfarin for at least 1 month before the procedure and warfarin will be stopped 5 days prior to the procedure with a low-molecular-weight heparin bridge. All patients will receive a transthoracic echocardiogram as part of the outpatient cardiovascular assessment. The use of other preprocedural imaging such as MRI or CT is variable, with some operators routinely performing them to assess LA and PV anatomy and others using these examinations only selectively. The use of transesophageal echocardiography is performed routinely on patients with persistent AF. For paroxysmal AF, some operators perform transesophageal echocardiography routinely while others use it only in selected cases (e.g., a patient history of prior stroke). Anesthesia care is variable, with some operators using general anesthesia and others using conscious sedation.


Procedure


Venous sheaths are usually placed in the right femoral vein for transseptal access, and in the left femoral vein, another venous sheath is placed if intracardiac echocardiography (ICE) is used. Other sheaths may be used for a coronary sinus catheter and/or the pacing catheter used for diaphragmatic pacing (see below). The initial 8-Fr right femoral vein access should have a shallow angle of entry to ease the eventual exchange for the Flexcath Advance Sheath. Full anticoagulation with IV heparin bolus may be given before initial transseptal access or immediately after puncture, with the target activated clotting time set between 350 to 400 seconds. Standard transseptal puncture can be performed; however, a low and anterior transseptal puncture approach that is near or on the limbus of the septum provides some mechanical advantages (Figure 17.1). Transseptal puncture through the thicker portion of the septum at the inferior limbus may also provide a reduction of iatragenic atrial septal defect from the large sheath access.1617 A variety of transseptal sheaths may be used but the SR0 or SL1 are popular because they provide ease of insertion into the left superior pulmonary vein (LSPV). A long guidewire (typically an extra stiff wire) is then inserted into the LSPV for safe exchange for the Flexcath Advance™. Prior to insertion of the Flexcath Advance into the right femoral vein, a 10- or 11-Fr dilator may be used. A gentle but firm twisting motion may facilitate the insertion of the Flexcath Advance. The Flexcath Advance is advanced across the interatrial septum with steady pressure and the dilator is given a counter clockwise quarter turn to disengage the dilator from the sheath prior to advancement of the sheath itself across the septum. When the interatrial septum is difficult to cross, placing the guidewire in the right superior pulmonary vein (RSPV) will allow a straight push upwards across the septum and toward the RSPV. After the dilator is removed, the sheath should be carefully flushed by tapping the handle to release trapped air and connect it to a low-flow drip saline bag at 1–3 cc/min.



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Figure 17.1 Transseptal puncture site that is more anterior with ICE view with mitral valve (MV) in view, as well as more inferior. Change in the incident angle is noted in graph.4. (Stanford University, Stanford, California, USA.)


After preparing the balloon and balloon sleeve in heparinized saline, the balloon is inserted. With the Achieve™ leading the advancement out of the sheath, the cryoballoon is advanced and guided by looking at the cryoballoon shaft markers—the first band is the balloon tip at the end of the sheath, and the second white band indicates the cryoballoon is out of the sheath and ready for full inflation.


To reduce complication and improve outcome, several maneuvers and rules can be utilized. An antral level of isolation should improve the success of the cryoballoon PVI, and it may reduce complications. Imaging using ICE to visualize the PV antrum, sheath, Achieve, and balloon is also very helpful in minimizing fluoroscopy. The inflation pressure of the cryoballoon is low pressure and is unlikely to cause mechanical trauma. However, inadvertent inflation inside the PV should still be avoided.


When ablating the lower PVs, anchoring the tip of the balloon at the lower PV branch often provide the best angle for balloon engagement. The angle of the sheath should be aligned with the vector of the targeted PV. With the balloon at the target PV, the Achieve can provide additional support for the cryoballoon, but the main control of the balloon-PV engagement is via the deflectable sheath. Optimal balloon-to-PV antrum contact will result in successful isolation of the respective vein. The best contact can be assessed by color Doppler on ICE or by contrast venography. After the initial venogram demonstrates complete occlusion, prior to ablation the cryoballoon should be withdrawn slightly to allow a slight contrast leak around the PV-balloon interface to confirm the location of the PV ostium. This maneuver may reveal that the balloon is actually well inside the PV, and repositioning of the cryoballoon needs to be done to avoid complications. Ablation then should be initiated, and allow 2 to 3 seconds prior to the advancement of the cryoballoon back into the best occlusion/contact position. This technique is often denoted as the “proximal-seal” technique. This technique also lessens the risk for phrenic nerve injury at the right superior PV (Figure 17.2). If a leak is detected during the venogram, small adjustments with additional pressure toward the side of the leak will often secure occlusion at an optimal location.16 If complete occlusion is not possible due the PV antrum being more ovoid, then separate application of ablation with cryoballoon deflected toward superior aspect of the vein should be performed. A second application of ablation should then be performed with the cryoballoon deflected toward the inferior aspect of the vein so that the lesions have overlapped.



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Figure 17.2 Pull back method to assess the location of PV antrum (Panels A–D). Panel A: Contrast venogram revealing good cryoballoon occlusion of the PV. However, ablation at this point will yield a deeper lesion than intended. Panel B: Cryoballoon is pulled back to observe for contrast leak or leak observed on Intracardiac ultrasound to identify the PV antrum. Ablation should then be initiated for 2–3 seconds to increase the cryoballoon pressure prior to reengaging the balloon at the antrum at the ostium.

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Aug 27, 2018 | Posted by in CARDIOLOGY | Comments Off on How to Use Balloon Cryoablation for Ablation of Atrial Fibrillation
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