Methods

Steerable catheters with 8 mm distal electrodes, some of them irrigated, were used for mapping and RF ablation [4]. The temperature-controlled catheters were manufactured by Medtronic Cardiorhythm (San Jose, CA), Biosense Webster (Baldwin Park, CA), and by Boston Scientific EPT (San Jose, CA).

The generators used for RF ablation were Medtronic Stockert and the EPT 1000XP generators. Each of these generators incorporated a micro-computer with the appropriate software for impedance and temperature monitoring. The return radiofre-quency electrode was located on patients, back adjacent to the indifferent electrode used for fulguration or defibrillation.

The fulgurator was a Fulgucor (Odam, Wissem-bourg, France) delivering a monophasic damped sine wave of 8ms duration at 10% of the baseline. In the fulguration sessions, bursts of two consecutive cathodal shocks were programmed at 160J [5].

During the procedures, the fluoroscopic events were recorded on videodisc and the ECG and endocardial signals were recorded using a Cardiolab System (GE Marquette Medical Systems, Houston, TX).

Mapping was performed with the Carto system (Biosense Webster, Baldwin Park, CA) or the LocaLisa Medtronic system.

Radial blood pressure was monitored continuously during the procedure. A SvO2 Swan-Ganz catheter was inserted in the pulmonary artery to monitor cardiac output and RV ejection fraction. A second SvO2 Swan-Ganz catheter was positioned in the coronary sinus to monitor myocardial oxygen consumption during VT. This parameter was found to be a reliable marker for procedure tolerance [6]. Intravenous heparin was given to patients with marked right ventricular dilatation according to well-established protocols. Monitoring of coagulation was performed during the procedure by APTT He-mochrom, Bard, US.

Before ablation, class I antiarrhythmic drugs were discontinued for at least 5 half-lives. Amiodarone was continued. Only monomorphic or multiple monomorphic sustained ventricular tachycardias, either clinical or induced during the ablation session, were considered for attempted ablation. The procedure was performed under general anesthesia in order to have continuous assessment of myocardial function and in critical cases to monitor thrombogenicity by transesophageal echocardiography. Ventricular tachycardia was induced by programmed pacing. In some cases pacing and iso-prenaline injection were required to induce VT. Dobutamine was used in case of significant hypotension.

The classical approach of VT mapping was to record the earliest potentials before the QRS complex was seen on the surface tracing during ventricular tachycardia. This coupling interval was usually longer than 30 ms in patients with structural heart disease. Pacemapping was also used with the aim of reproducing the morphology of QRS complexes during spontaneous VT in all twelve leads. Pacemap-ping was achieved by slight overdrive pacing during VT using the same catheter used to deliver electrical energy for ablation. In addition, VT should be present after interruption of pacing. Special attention was paid to treat the area of slow conduction that was frequently represented by fragmented high frequency potentials located between two ventricular QRS complexes. There are additional features which facilitate the identification of the zone of slow conduction that is a necessary link for the perpetuation of arrhythmia [7-11].

During the study period, RF was used first for all ablation attempts. When it was ineffective or if there was an impedance rise or lack of increase of temperature after multiple attempts of RV ablation, one or several F were delivered through the same catheter during the same session.

When the F technique was used, the DC ablation signal of voltage and current was displayed on the screen of a two-channel digital Tektronix 5116 oscilloscope. This enabled to assess that the energy of each shock was correctly delivered, and that there was no damage to the catheter permitting its use for the next shock if necessary.

25 3D 35 10 45 SO 55 60 65 70 75 Left Ventricular Ejection Fraction

The In-Hospital Follow-Up Period

Postoperative hemodynamic surveillance consisted of monitoring the radial artery blood pressure for 24h. After each ablation session, the surface ECG was monitored continuously by computerized telemetry (GE Marquette).

Control of VT was always assessed before hospital discharge by 3 days of telemonitoring.

Definition of terms

The following definitions of the ablation results have been simplified from those used in the previous report [1]. If ventricular tachycardia identical or similar to the previous attacks in rate as well as in morphology on the twelve-lead ECG occurred spontaneously or was inducible by the same previously defined protocols, the case was considered a "failure". Any favorable change in the behavior of VT as compared to the features observed before ablation including decrease in the rate of VT (>10 bpm), number of VT morphologies, sustained VT becoming nonsustained or effectiveness of antiarrhythmic drugs, was classified as a "partial success" because the ablation had prevented or clinically modified the arrhythmias by some alteration of the arrhythmogenic substrate. Effectiveness of drug treatment was assessed by EPS in case of rapid hemodynamically unstable VTs or by monitoring in slower, well-tolerated VT episodes.

The case was classified as "success" when drugs were no longer needed and when patients were non-inducible after ablation. However, antiarrhythmic drugs were continued in the vast majority of cases for safety reasons (multiple episodes of rapid VT or VF documented prior to ablation or induced during the procedure,or to treat ventricular or supraventricular extrasystoles after ablation). The final clinical assessment of VT control was represented by the sum of "success," and "partial success."

A repeat ablation session was always performed in patients in whom a session and previously defined drug therapy failed.

Follow-Up

After hospital discharge, follow-up was systematically assessed by a computer-based system consisting of discussion with the referring physician or the referring hospital, as well as by direct telephone calls to the patient or family members. Follow-up was based on the time interval between the first ablation procedure and the latest information obtained for each patient.

Statistical Analysis

Statistical analysis and graphs have been performed with Statistica v6.0 (Statsoft, Tulsa, OK). The t-test was used for all statistical computations. A p value <0.05 was considered significant.

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