How to Perform Pulmonary Vein Isolation Using Laser Catheter Ablation

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How to Perform Pulmonary Vein Isolation Using Laser Catheter Ablation


Edward P. Gerstenfeld, MD


Background


Catheter-based PVI has advanced significantly since it was initially described in 1999.1 However, the problem of PV reconnection after ablation2 remains the Achilles heel of the procedure and is likely responsible for most late AF recurrences.3,4 Use of a focal catheter for isolation of the PVs in a connect-the-dots approach is the major limitation of our current approach to PVI. Although use of irrigated contact force catheters, electroanatomic mapping systems with image integration, and general anesthesia to promote greater catheter stability have improved the speed and safety of acute PVI, late recurrences continue to occur. Given the variable LA topology, thickness, variation in PV anatomy, and adjacent extracardiac structures such as the esophagus and lung, it is not surprising that contiguous full-thickness lesions over a wide area are difficult to achieve with consistency using a focal ablation catheter.


Balloon ablation technology offers a different approach to PVI. Rather than adapting catheters designed for focal ablation to wide-area encircling lesions, balloon catheters allow an approach adapted specifically to the PVs. This offers enhanced catheter stability and lesion delivery. Balloons typically use alternative energy sources that may be more suited to circumferential ablation compared to radiofrequency energy. Thus far, balloon energy sources have included ultrasound,58 cryoablation,9,10 and now laser ablation.11,12


The endoscopic laser balloon (Heartlight; Cardiofocus, Marlborough, MA) has gone through several design iterations (Figure 18.1). The original concept was to deliver a 360-circumferential beam that would allow complete PVI with one energy delivery. However, it was soon appreciated that the PVs are oval structures with variable branching and that no single circumferential pattern was suitable to PV anatomy. The second-generation balloon was a fixed-diameter balloon that came in 20-, 25-, and 30-mm diameter sizes. An endoscopic fiber allowed direct visualization of the LA endocardium in contact with the balloon, directing a 90° arc of laser energy around the PV periphery. It was felt that compared to the 360° laser, a 90° arc would allow a more directed delivery of energy in a pattern that could be “stitched” together to create complete isolation. While such an approach was successful in preclinical animal and initial human studies, the noncompliant balloon and 90° arc made the ablation procedures challenging.



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Figure 18.1 Evolution of the laser balloon concept from the original 360°-circumferential design to the 90° noncompliant balloon to the current compliant balloon with 30° laser arc.


The current-generation endoscopic laser ablation system has 3 components, an outer compliant balloon, a lesion generator, and the endoscope (Figure 18.2). The balloon is made of a compliant material that has an adjustable size depending on the inflation pressure, with diameter that varies from 25 to 32 mm, with internal inflation pressures varying from 1 to 5 PSI. The catheter shaft contains the lesion generator and endoscope. The laser is designed to ablate cardiac tissue using light energy in the infrared spectrum. The lesion generator produces a 30° arc of light energy and is powered by a 980-nm diode laser. The 980-nm wavelength was chosen because it is optimal for absorption by H2O, which allows tissue heating (Figure 18.3); it is poorly absorbed by deuterium oxide (D2O, “heavy water”), which is an inert medium that can be used to inflate the balloon and provide a “loss-free” path for the projection of laser energy. The balloon is inflated with a mixture of sterile D2O and sodium diatrizoate. The diode laser requires minimal power for energy generation (5.5–14 W). The endoscope has a 115° field of view and allows direct visualization of the area of the balloon in contact with the LA endocardium; tissue appears white and blood appears dark red; visualization cannot occur through moving blood. One must be careful not to ablate with the laser in areas of stagnant blood, or coagulum (thrombus) can occur. The catheter and lesion generator are disposable; the endoscope can be resterilized and reused during subsequent procedures.



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Figure 18.2 Schematic of the compliant laser balloon, which includes the central catheter shaft, compliant balloon, and catheter lumen that incorporates the lesion generator and endoscope. (Courtesy of Cardiofocus.)



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Figure 18.3 Absorption spectrum of water (H2O) and deuterium oxide (D2O) showing the difference in laser energy absorption at 980 nm for water compared to deuterium oxide. (Used with permission.)


Left Atrium Access and Balloon Deployment


One should perform some type of LA imaging to identify the PV anatomy, typically either computed tomography or magnetic resonance angiography, prior to the procedure. The maximum balloon diameter is 32 mm, so isolation cannot be performed on a single PV with an average of major and minor axes > 32 mm diameter. Most left common PVs can still be isolated more distally as individual PVs, but the trade-off of a more distal PVI should be considered. Finally, PVs with multiple proximal branches (Figure 18.4) may be difficult to isolate with balloon techniques, and a more standard catheter approach might be considered. However, it should be noted that in clinical trials with the laser balloon, 99% of PVs attempted were successfully isolated. This is one of the strengths of the compliant balloon technology.



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Figure 18.4 Left panel: CT angiogram of the LA demonstrating an early proximal posterior branch of the RSPV. Right panel: The endoscopic view through the laser balloon shows the posterior PV branch (arrow), which is compressed by the balloon with little clearance for ablation (aiming beam in green) on the posterior edge.


The laser ablation system is deployed using a custom 12-Fr-inner-diameter, 16-Fr-outer-diameter 180° deflectable sheath. The sheath comes with a soft-tipped dilator and has a distal fluoroscopic marker. The sheath should be flushed with heparinized saline under pressure throughout the procedure. If one is using ICE to guide transseptal access, full heparinization to an ACT > 300 seconds can be performed prior to transseptal access. For those not comfortable with this approach, a heparin bolus should be given as soon as possible after LA access is obtained to prevent thrombus from forming on the transseptal sheath. LA access is first gained with a standard transseptal sheath; this sheath is then exchanged over a long wire for the custom laser ablation sheath. A low and anterior transseptal puncture (compared to the typical posterior punctures for catheter-based PVI) will facilitate balloon introduction into the RIPV, which often can be the most challenging approach for balloon catheters. A stiff long wire (Amplatz 240 cm extra stiff, 0.35” or smaller) is then introduced to the LA via the transseptal sheath and advanced out the left superior (or inferior) PVs. Securing the wire distally out one of the PVs before sheath exchange is important; the 16-Fr guiding sheath could otherwise injure the posterior LA wall during the exchange. The standard sheath is withdrawn over the wire and the 16-Fr laser sheath is advanced over the wire to the LA. One should be careful to withdraw blood and flush the 16-Fr sheath after any catheter exchange to avoid entraining air into the LA. We typically perform a second transseptal puncture to allow simultaneous LA access and PV mapping with a circular mapping catheter; however, others may perform a single transseptal puncture and exchange the balloon catheter for a circular mapping catheter sequentially.


Preparation of the balloon catheter can be performed simultaneously with LA access. The catheter tubing is connected to the console and the balloon and tubing are purged with D2O. The console provides continuous circulation of fluid while the balloon is inflated to the desired pressure/size and maintains the catheter at a constant temperature. The endoscope needs to be advanced into place through the tubing and central catheter lumen to rest distally inside the balloon. The balloon is then deflated, immersed in saline, covered with the introducing tool, and advanced into the sheath. The sheath is typically kept in the mid-atrial cavity with the distal end oriented toward the PV of interest. Radio-opaque markers are present on the tip and distal end of the catheter to aid with fluoroscopic visualization. One should not advance the sheath out a PV as is often done for PV angiography. If one prefers to perform PV angiography, this should be done with a standard sheath before the exchange. Injecting contrast into the laser sheath should also be avoided. The deflated balloon is then advanced to the PV ostium under fluoroscopic and echocardiographic guidance and inflated. Although there is a soft tip on the balloon catheter, one should avoid advancing the balloon too far out of a PV. The sheath can then be withdrawn to the proximal “Z” marker on the balloon catheter to allow balloon inflation (Figure 18.5). The “Z” marker can be used to identify the balloon rotational orientation under fluoroscopy in order to ensure that the endoscopic image will be displayed in an anatomic view. We typically find phased-array intracardiac ultrasound extremely also helpful for guiding and confirming balloon position.



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Figure 18.5 Left panel: Fluoroscopic right anterior oblique views demonstrating the laser balloon in the LSPV (top) and LIPV (bottom) with the circular catheter in the other ipsilateral vein. Right panel: Endoscopic view of the LSPV (top) and LIPV (bottom). In the top panel, the LSPV, carina, and superior portion of the LIPV can be seen. In the bottom panel, the laser aiming beam (green) is shown on the anterior ridge between the LIPV and LAA.

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Aug 27, 2018 | Posted by in CARDIOLOGY | Comments Off on How to Perform Pulmonary Vein Isolation Using Laser Catheter Ablation
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