Microfidelity (MIFI) Ablation Technology Versus Standard Ablation Catheter for Atrioventricular Nodal Ablation

Introduction In some elderly patients with atrial fibrillation (AF), especially in combination with heart failure, a rate control strategy may be preferred. When pharmacological therapy is ineffective or not tolerated, it is reasonable to perform atrioventricular (AV) node ablation with ventricular pacing as a class IIA indication per current guidelines.

Usually, the procedure is simple and straightforward and complete heart block can be achieved without any difficulty. However, this "simple" procedure can sometimes prove to be a most difficult case. The most common reason for failure to achieve complete heart block is the inability to localize the compact AV node using the His signal with standard intracardiac electrograms. As these patients come to the laboratory in AF, the His signal may be obscured by AF waves. In some patients with a deeper intramyocardial location of the His bundle and compact AV node it becomes necessary to produce deeper ablation lesions using an irrigated catheter to achieve block.

In patients with AF, the target of ablation for the "ablate and pace" approach is the compact AV node, located at the apex of the triangle of Koch. Ideally, ablation is performed at the most proximal penetrating part of the His bundle in order to maintain a proximal automatic junctional rhythm and avoid pacemaker dependence.

Para Hisian pacing is most commonly used to reveal the presence of a septal accessory pathway.

The His bundle is a deep insulated structure and it is difficult to capture it at usual energy outputs. Using a high- output pacing (usually 20 mA at 2 msec) it is possible to directly capture the deeply situated His bundle, which is confirmed by a narrower QRS complex on the paced electrograms. Thus, high-output pacing can be utilized to map the His bundle area in difficult situations.

By applying this electrophysiologic principle of differential tissue capture to help identify the location of the compact AV node, which is in close proximity to the His bundle. Ventricular pacing was performed initially at high output to capture both the basal right ventricular myocardium and the His bundle and the output was gradually lowered to lose His bundle capture. The QRS duration is relatively narrow with high output pacing and increases when the pacing output is lowered, representing ventricular myocardial capture alone. Finally, loss of ventricular capture is seen with further reduction of pacing output. This maneuver has been shown to aid in determining the proximity of the ablation catheter to compact AV node as was validated by successful ablation at this site. Parahisian pacing in conjunction with av nodal ablation has recently been described in the literature.

A novel catheter with three mini electrodes within the ablation tip (IntellaTip MiFi, Boston Scientific, Boston, MA) may enhance the available data for such a signal dependent technique. In this catheter, bipolar signals can be recorded between the three 0.8-mm-wide electrodes that are arranged radially 1.3 mm from the end of the catheter alongside the standard distal and proximal bipolar recordings. Animal studies have already demonstrated that the mini electrodes in this novel catheter are more accurate in identifying conducting gaps in linear ablations than conventional electrode recordings.

Study Aims:

The aim of our study is to investigate the comparative efficacy of high fidelity multi electrode ablation catheters vs the standard bipolar configuration in success of AV nodal ablation This study will provide insights on the use of new technology where application may increase efficacy, promote patient and physician safety and decrease costs.

Primary and secondary objectives Primary endpoints

1. Acute success of ablation identified by a junctional rhythm or complete heart block
2. Time from application of radiofrequency energy to acute success

Secondary endpoints include

1. Procedure time
2. Radiation time
3. Frequency of ablation application
4. Duration of ablation application