Case Study: Ablation of Left Ventricular Tachycardia

The AcuNav ICE catheter (Siemens Medical Solutions, Malvern, PA) is our choice for intracardiac echocardiography, because of its greater maneuverability and increased functionality over other ICE systems. We routinely use the AcuNav catheter (Siemens) for atrial fibrillation ablation, as it helps guide transseptal puncture, locate the ostia of the pulmonary veins in relation to the ablation catheter, discover potential thrombi on the transseptal sheath or mapping catheter, and allows early discovery of a pericardial effusion, should it develop. The recent introduction of the CartoSound software (Biosense Webster, Inc., a Johnson & Johnson company, Diamond Bar, CA) has further increased functionality. CartoSound (Biosense Webster, Inc., a Johnson & Johnson company) allows construction of a real-time virtual “shell’ of the left atrium, appendage, and veins without entering the left atrium, thereby obviating the need for a preliminary left atrial CT scan or left atrial point mapping with the ablation catheter. We report on the use of CartoSound (Biosense Webster, Inc., a Johnson & Johnson company) for a case of left ventricular tachycardia (LV VT).

Case Description

Ventricular tachycardia ablation was contemplated in a 74-year-old male patient with ischemic cardiomyopathy and a LVEF 28%, who experienced repetitive ICD shocks in response to hemodynamically unstable monomorphic VT despite amiodarone use. During the EP study, two distinct monomorphic VTs were induced, both hemodynamically unstable. The AcuNav SoundStar catheter was introduced into the right ventricle (RV) under fluoroscopic guidance, and positioned in the long axis of the RV with the tip close to the RV apex, and reference mark pointing superiorly. The catheter shaft was then rotated counterclockwise through approximately 60 degrees, and a near-long axis view of the LV chamber was obtained. Rotating the SoundStar (Biosense Webster, Inc., a Johnson & Johnson company) counterclockwise in minute gradations, allowed construction of a real-time virtual shell of the LV. (Figure 1) The SoundStar (Biosense Webster, Inc., a Johnson & Johnson company) was then withdrawn, until the tip lay in the mid chamber of the RV. Counterclockwise rotation allowed acquisition of the shell at the level of the papillary muscles. Due to the ability of the SoundStar catheter (Biosense Webster, Inc., a Johnson & Johnson company) to flex by 60 degrees in all four directions, catheter introduction and shell acquisition was completed within approximately five minutes. Using the retrograde aortic route, an 8 Fr ThermoCool catheter (Biosense Webster, Inc., a Johnson & Johnson company) was introduced into the LV. Point mapping was then performed. The presence of the shell allowed us to direct the catheter to each portion of the LV endocardium with confidence. The best orientation was a cutaway of the shell through the plane of the mitral valve, viewed from the left posterior aspect. (Figure 2) Contact mapping was then performed. Since the patient was known to have an anterior and septal scar, high density contact mapping was performed in this area, and lower density mapping was performed over the lateral wall and remaining areas of the LV endocardium. This materially shortened the duration of contact mapping. The ensuing voltage maps are seen in the RAO and LAO views in Figures 3 and 4. Note how the contact map in Figure 3 corresponds closely to the ultrasound shell created in Figure 1, even though they are in different views. Attention was then directed to the antero-septal scar. The anterior and septal scars were separated by a zone of viable tissue. By ICE, we were able to confirm that this zone corresponded to the middle and distal portions of the anterior papillary muscle. Consequently, our original plan, which was to connect the two scars by a line of lesions, was abandoned (ablation of the papillary muscle may have engendered mitral regurgitation). Instead, VT ablation was performed guided by pacemapping and location of fractionated electrograms, as well as mid diastolic potentials during VT. (With isoproterenol infusion, non-sustained runs of VT occurred frequently, and sometimes sustained, but were terminated by overdrive pacing.) The ablation lesions were concentrated in two areas, as noted on the map. Following a total of 42 lesions at 35-40 watts, VT did not occur spontaneously with isoprotrenol infusion. Programmed stimulation did not elicit the two original “clinical” VTs, although ventricular flutter, CL 200, was induced with aggressive protocols. This was considered an appropriate endpoint for terminating the procedure.

Discussion

The AcuNav CartoSound system allowed construction of a virtual real-time shell of the left ventricle in less than five minutes; this allowed us to shorten the duration of point mapping by concentrating on the area of interest. Being able to visualize the entire shell in three dimensions (best done through the aperture of the mitral valve annulus, Figure 2) allowed us to rapidly locate the catheter tip within the LV cavity, and manipulate it to contact the desired segment of the endocardium. Locating the anterior papillary muscle by AcuNav and marking its location on the voltage map led us to change our approach to ventricular tachycardia ablation with success (Figure 5). Since we were able to visualize the catheter tip in contact with the LV wall, we felt confident that any thrombus formation or pericardial effusion would have been detected early. This allowed us to deliver lesions at high-energy settings, which are generally required for successful ablation in the thick-walled LV.