Mapping of a Left Lateral Accessory Pathway with a High-Density Multipolar Mapping Catheter

Case Description

A 53-year-old female who was a long-time smoker and had a history of surgical repaired aortic aneurysm and recurrent supraventricular tachycardia (SVT) underwent catheter ablation of a concealed left lateral pathway at another hospital. She continued to have palpitations shortly after, and presented two months later to the emergency department with an episode of short RP supraventricular tachycardia, which required administration of 12 mg of adenosine (Figure 1). Her medical regimen at that time included metoprolol 25 mg bid and flecainide 50 mg bid. After a discussion on the risks and benefits of a second procedure, she was scheduled for repeat ablation.

Under conscious sedation in the postabsorptive state, three standard quadripolar catheters were placed in the high right atrium, AV junction, and right ventricular apex. A 10-electrode decapolar catheter was placed in the coronary sinus. The procedure was done with zero fluoroscopy guided by electroanatomical mapping with the EnSite Precision Cardiac Mapping System (Abbott). Baseline intracardiac intervals were as follows: AH = 94 ms, and HV = 55 msec. 

SVT with a cycle length of 280 msec was easily induced during programmed ventricular pacing (Figure 2). Careful observation of coronary sinus activation revealed discontinuous activation; the earliest atrial signal at the distal bipoles was 1-2 followed by pair 3-4 and then the CS 9-10 electrodes. Differential diagnosis included atrial tachycardia, atypical AVNRT with a left-sided AV nodal extension, and orthodromic SVT. A premature ventricular beat, delivered when the His bundle was already depolarized,  terminated the tachycardia; there was an accessory pathway present that participated in this arrhythmia. After transseptal puncture guided by intracardiac echo, an Advisor HD Grid Mapping Catheter, Sensor Enabled (Abbott) was introduced in the left atrium to map the atrial insertion of this pathway. A total of 2420 points were collected in 8 minutes. The bandpass filter was set at 30 to 200 Hz. Mapping points were automatically acquired using the following criteria: cycle length stability, catheter position stability, and point density. The interior projection was set at 4 mm and color interpolation at 7 mm. Field scaling was applied to the map. Careful handling of the catheter to avoid ectopy was ensured. Recording from the Advisor HD Grid showed areas of fractionated signals at the mitral isthmus (Figure 3) where prior ablations were delivered. The earliest atrial site was recorded on the Advisor HD Grid at bipoles A1-A2. The activation and propagation maps showed mitral isthmus conduction block and counterclockwise left atrial activation, accounting for the discontinuation of atrial activation within the coronary sinus. Mitral isthmus conduction block was likely the result of prior ablation.  

A 4 mm tip irrigated ablation catheter (FlexAbility, Abbott) was placed at the earliest site using a deflectable sheath (Agilis, Abbott). The atrial electrogram preceded the P waves by 42 msec (Figure 4). There was a possible pathway potential at this site. The generator was set at 30 watts to a temperature of 40^oC for 60 seconds, and one application of radiofrequency energy at the lateral mitral annulus eliminated conduction through this pathway in 3.2 seconds.

At 6-month follow-up, the patient has not had any more arrhythmias. 

Discussion

Mapping of cardiac arrhythmias has been done traditionally with large size electrodes (3.5-4.0 mm). The availability of multipolar catheters with smaller electrodes (including the Advisor HD Grid, Abbott; CARTO PENTARAY, Biosense Webster, Inc., a Johnson & Johnson company; and INTELLAMAP ORION, Boston Scientific) has changed the way that electrophysiologists approach complex arrhythmias. These new catheters can provide very rapid and reliable acquisition of points, providing the operator with detailed arrhythmia substrate mapping to treat poorly tolerated and complex cardiac arrhythmias.

In addition to the benefits of high-density mapping, there is also no substitute for basic EP maneuvers when dealing with cardiac arrhythmias. A common pitfall while ablating left-sided pathways is to target the earliest atrial electrogram within the coronary sinus without carefully mapping the mitral annulus and analyzing the intracardiac electrograms. Pacing from different ventricular sites may expose a pathway potential, the real target for ablation of accessory pathways. In this case, extensive and unnecessary ablation was performed around the mitral isthmus and coronary sinus, which led to significant disruption of the left atrial activation, as shown in Figure 5. Paradoxically,  conduction through this pathway was still intact and the patient underwent a second procedure. 

Summary

Mapping cardiac arrhythmias with a multipolar electrode catheter has improved the ability to identify critical areas of interest when ablating complex arrhythmias. Detailed mapping and application of the basic principles of electrophysiology are also still required to successfully ablate conventional accessory pathways with a limited number of energy applications and avoid collateral damage. 

Disclosures: Dr. Navarrete has no conflicts of interest to report regarding the content herein. Outside the submitted work, he reports personal fees as a consultant and for education for Abbott.