13th International Congress
THE "NEW FRONTIERS"
OF ARRHYTHMIAS 1998

January 24-31, 1998
Marilleva, Trento, Italy

S-23

Clinical impact of electroanatomically guided catheter compartmentation of human atria in the treatment of paroxysmal atrial fibrillation

Carlo Pappone, Giuseppe Oreto*, Francesco Furlanello, Maria Luisa Loricchio, Gabriele Vicedomini, Stefano Bianchi, Shlomo Shpun**, Cristoforo D'Ascia, Maria Pia Calabro*, Cosimo Dicandia, Shlomo A. Ben-Haim**, Tiziana Russo, Sergio Chierchia.
Cardiology Department, Hospital S. Raffaele, Milan, *Cardiology Department, University of Messina, Messina, Italy, **Cardiovascular System Laboratory, Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel

The electroanatomically guided catheter approach.
Personal experience

Patients

We treated 14 patients with symptomatic, recurrent, drug-refractory paroxysmal AF lasting for at least 1 year. There were 10 males and 4 females, with a mean age of 45.8 ± 11.6 years (range 27 to 67 years). Only 2 patients had structural heart disease, 1 with hypertrophic cardiomyopathy and 1 with mitral valve prolapse with mild mitral and tricuspid regurgitation. Correctable causes of AF, such as thyroid disease, had been excluded in all patients, and all patients had proved to be nonresponders to antiarrhythmic drugs (average 3.6 ± 1.5 drugs per patient). Every patient underwent complete clinical evaluation, including history, physical examination, ECG, blood tests, chest x-ray, and transthoracic and transesophageal echocardiogram. Prior to inclusion in the protocol, each patient underwent extensive observation throughout 1 month. Two 24-hour Holter recordings were performed, to obtain documentation of episodes of AF and to demonstrate the correspondence of the arrhythmia with reliable symptoms. Patients were also provided with an event report, to record every episode of AF with particular regard to its duration. Inclusion in the study required, over 3 weeks, a minimum of three episodes per week, with a duration exceeding 1 hour and spontaneous termination in < 24 hours. No patient had persistent (> 24 hours) or chronic AF.

Electrophysiologic study

The study protocol was approved by the ethic committee of the Hospital; patients were informed about the experimental nature of the procedure and its related risks, and gave written informed consent. Antiarrhythmic drugs were discontinued for at least 5 half-lives; no patient was on amiodarone at the time of the enrollment. The electrophysiologic study was performed in accordance with the standard technique: catheters were inserted through the femoral and left subclavian vein and through the right or left femoral artery. Quadripolar 6F catheters were placed in the coronary sinus (CS) and in the right ventricular apex. A 6F pigtail catheter was placed in the ascending aorta to obtain continuous arterial pressure monitoring and as a reference for atrial septal puncture. A reference catheter (REF-STAR, Cordis-Webster) was placed on the back of the patient, and a deflectable-tip catheter (NAVI-STAR, Cordis-Webster) was used for mapping and ablation. Left atrial (LA) catheterization was obtained by a transseptal route, using a standard Brockenbrough needle and a long sheath.

Mapping system

The nonfluoroscopic navigation and mapping system²⁴ are composed of a miniature passive magnetic field sensor incorporated into a standard electrophysiologic catheter, an external ultralow magnetic field emitter (location pad), and a processing unit (CARTO, Biosense). Ultralow magnetic fields are emitted from the location pad, placed under the operating table. The spatial and temporal characteristics of the sensed magnetic fields contain the information needed to solve a set of overdetermined algebraic equations yielding the location (x, y, and z) and orientation (roll, yaw, and pitch) of the catheter tip. The resolution of the location capabilities of the system was quantified previously and shown to be < 1 mm for both in vitro and in vivo studies²⁵. This information enables tracking of the tip of the mapping catheter while it is deployed within the heart.

Mapping process

The mapping and ablation procedure was performed during continuous CS pacing at a rate of 100 beats/min; it was a prerequisite that patients were in sinus rhythm at the beginning of the electrophysiologic study, in order to obtain atrial capture. The mapping catheter was introduced into the atria under fluoroscopic guidance, and its location was recorded relative to the location of the fixed reference catheter, compensating for patient motion and heart movements. Determination of the location of the mapping catheter was gated to the pacing artifact. By moving the catheter inside the heart, the mapping system continuously analyzed its location and orientation and presented it to the user on the monitor of a graphic workstation, thereby enabling navigation without the use of fluoroscopy.

The mapping procedure was based on dragging the catheter over the endocardium and sequentially acquiring the location of its tip together with its electrogram while in contact with the endocardium. Three-dimensional (3D) chamber geometry was then reconstructed in real time, using the set of location points sampled from the endocardium. The local activation time (LAT) at each site was determined as the time interval between the pacing artifact and the steepest negative intrinsic deflection in the unipolar electrogram (filtered at 0.5 to 400 Hz) recorded from the catheter tip.

Based on the various LATs, a map was constructed showing the activation sequence resulting from the time of activation of different zones in a cardiac chamber. The activation map was color-coded (red indicating the earliest and purple the latest activation) and superimposed on the 3D chamber geometry (Fig. 1). The icon showing 3D location and orientation of the catheter was continuously shown on the graphic workstation, superimposed on the electroanatomic map, thus allowing accurate navigation of the catheter to desired areas for the acquisition of additional data points or for delivery of RF energy to predefined sites.

slika

Fig. 1: Left atrial electroanatomic map during distal coronary sinus pacing. Left atrium anteroposterior view (panel A) and posteroanterior view (panel B) showing the mitral annulus (red ring) and the 4 pulmonary veins protruding from the posterior left atrial wall. Note the catheter icon during the maping procedure (panel B); the catheter tip (dark green ellipsoid) is pointing down. The color coding of electroanatomic maps represents activation times (red represents earliest activation time and purple represents the latest activation time).

RF application

All lesions were performed using the NAVI-STAR catheter. RF energy was delivered in unipolar fashion to a cutaneous ground patch via the distal electrode. RF power was titrated to achieve a thermocouple temperature of 65° C in the RA or 55° C in the LA; alternatively, power of up to 60 W was used for 60 to 120 seconds, with the target of consistently reducing the amplitude of the local electrogram. Breakdown of the local potential (unipolar and bipolar recordings) was considered satisfactory in the presence of amplitude reduction > 75% of the initial value. Any linear lesion was composed of a series of standard focal temperature-controlled lesions. The location of each focal lesion was tagged on the electroanatomic map of the atria.

In the RA, the following three linear lesions were designed: (1) posterior intercaval, between the SVC and IVC; (2) medial isthmus, between the IVC and the tricuspid annulus; and (3) septal, between the superior aspect of the intercaval line and the posteroseptal tricuspid annulus. In the LA, one long lesion was generated, encircling the PVs and connecting the line to the mitral annulus on two sides. A complete series of linear lesions deployed in the LA is shown in figure 2 in the anterior (A) and posterior (B) views.

Fig. 2: Left atrium electroanatomic map after ablation. Red spheres indicate sites were RF energy was deployed. Anteroposterior (panel A) and posteroanterior (panel B) views of the ablation line; encircling the superior pulmonary veins. The line then continues to connect the encircled pulmonary veins to the mitral annulus at two sites, one on the posterior wall between the septal and lateral pulmonary veins (panel B) and the second along the lateral wall (panel A and B).

After creating the planned lines of block, the atria were re-mapped, and the postablation activation map was compared with the preablation one. The result was defined as satisfactory whenever there was no impulse propagation across the line of block, but the depolarization wave front reached the region beyond the block over a different route. An incomplete block was revealed by impulse propagation through the line of block, shown by an identical color in points lying at the same level on the two sides of the line; in such a case, further RF pulses were given to complete the line of block.