Endocardial Ablation of Hemodynamically Unstable VT: A Strategy Targeting Late Potentials Using a Closed- Irrigated Catheter

   Ablation of ventricular tachycardia (VT) is one of the most challenging procedures in electrophysiology. Patients with scar-mediated reentrantVT have systolic dysfunction and frequently have multiple co-morbidities and end-organ dysfunction. Additionally, multiple morphologies are often inducible from a single substrate and the majority of VTs are hemodynamically unstable. These characteristics lead to long procedure times and variable success rates. We report a case of endocardial ablation of hemodynamically unstable VT and our strategy for targeting late potentials by using a closed-irrigated catheter.

Case History

   A 70-year-old man presented with a history of anteroseptal infarction and ejection fraction of 25%. The patient underwent dual ICD implantation in 2003. He was referred for ablation of VT after receiving multiple ICD discharges despite amiodarone and mexiletine. A prior EP study performed at an outside hospital demonstrated multiple induced morphologies, and an apical thrombus was noted on echocardiography and confirmed on cardiac CT. Global hypokinesis with thinning of the anteroseptal wall with apical akinesis was seen on both modalities. For these reasons, the procedure was deferred for one month of anti-coagulation prior to elective ablation.

Procedure

   A decapolar diagnostic coronary sinus catheter was placed from the right internal jugular vein to serve as an internal reference for electroanatomic mapping. Quadripolar diagnostic catheters were placed from the right femoral vein into the His region and right ventricular apex. The patient was placed under general anesthesia and VT was induced with programmed stimulation. Overdrive pacing was required to restore sinus rhythm due to hypotension. The tachycardia had a cycle length (CL) of 445 ms with right bundle branch block (RBBB) morphology with superior axis. An abrupt loss of R wave in the precordium at V3 is shown in Figure 1. An electroanatomic map was created (EnSite, NavXTM, St. Jude Medical, St. Paul, MN), revealing anteroapical and inferior scar. Multiple areas with late potentials were seen within the extensive infarct (Figure 2). The 12-lead EKG of the first targeted VT suggested an inferoapical exit site, and pacemapping was performed at this border in the scar. A perfect pacemap was seen with long stimulus latency. This suggested a site in the proximal part of the circuit. Interestingly, during pacemapping, a different morphology with left bundle branch block (LBBB) configuration was seen on the first two beats with short stimulus-QRS interval, indicating a second exit site from the site of stimulation indicating a common conducting channel (Figure 3).    Ablation was performed in this area where a perfect pacemap was seen with the Chilli II® internally irrigated tip catheter (Model M00490310, Standard Curve, Boston Scientific, Natick, MA). The standard curve was selected because the left ventricle was not markedly dilated (LV end diastolic dimension 63 mm) and the apical LV was to be targeted. Ablation parameters were set at 40W with temperature limit of 45° C.    Repeat programmed stimulation was performed and a second untoleratedVT was induced with CL of 410 ms with RBBB morphology, inferior axis, with gradual tran- sition at V4. This exit from the surface lead analysis suggested a site more anterior and superior in the scar compared to the firstVT, and mapping was performed in this area (Figure 4). Late potentials were mapped and a pacemap from this site demonstrated a good but not perfect match. Ablation was performed and all late potentials in the region were abolished (Figure 5).    Repeat programmed stimulation was performed and a third untolerated VT was induced with CL of 390 ms with RBBB morphology, superior axis, with transition at V4. This was notable for more notching in the complex, and a good pacemap was found during this VT as well. After additional ablation in this area, a fourth untolerated VT was seen during pacemapping with CL of 345 ms with similar axis and configuration, but without notching. A perfect pacemap was found (Figure 6), and additional ablation was performed in this area targeting late potentials and the scar border. After ablation, only a rapid untolerated sine wave tachycardia with CL of 270 ms was induced with triple extrastimulus testing. The patient has not received any ICD therapies six months after ablation.

Role of Closed-Irrigated Catheter During VT Ablation

   Irrigated catheters create larger ablation lesions by allowing for higher power to be delivered into the myocardium. By the convective cooling of the catheter-tissue interface, boiling and coagulum formation is less likely, and resultant increases in impedance that can limit power delivery are minimized. Due to these reasons, irrigated technology is invaluable for complex ablations requiring larger lesions and extensive substrate modification. The closed loop system of the Chilli II ablation catheter has the advantage over opened systems in that saline is not infused into the body. Avoiding a volume load in patients with systolic dysfunction and cardiorenal syndrome is preferable. In addition, the Chilli II ablation catheter is a bidirectional catheter, which allows for greater degrees of freedom when maneuvering within the left ventricle.

Conclusion

A strategy of late potential ablation that is characterized by pacemapping is effective for ablation of unmappable VT. Abolition of late potentials is targeted at eliminating channels of slow conduction that are critical for reentry and homogenization of scar has been proposed as a new ablation endpoint. Ablation of targeted VT with faster VTs seen afterward is commonly seen and can serve as an acute endpoint for success. The closed-loop cooled catheter technology in the Chilli II cooled ablation catheter is uniquely suited for this application because of the larger lesion size created without fluid administration, and the bidirectional steering allows for enhanced maneuverability. Case Study Disclosure: This case involves use of the Chilli II^® Ablation Catheter in a single case. Use in other cases may vary. *Conflict of Interest Disclosure: Boston Scientific pro- vided compensation to the author for preparation of this article and reviewed and edited the content of this article.