An RF Ablation System for the Treatment of SVT: An Alternative with Promise

We report the initial results from the clinical trial of the IBI RF ablation system. The system is composed of: 1) a 4-mm tip ablation catheter utilizing a unique thermocouple to enhance tip temperature control; and 2) a computer-controlled radiofrequency (RF) delivery system which incorporates built-in closed loop target temperature regulation and an impedance based safety shut-off. Our initial results suggest that the IBI system is comparable to published performance data. It sports new technological enhancements in a user-friendly interface, and can easily assume the role of being the primary RF ablation system in a laboratory such as ours. The electrophysiology lab at St. Mary's Medical Center is a busy center which does over 1,600 EP procedures annually. Apart for the routine procedures done in major regional referral lab, St Mary's lab also does atrial fibrillation ablations using 3-dimensional electroanatomic mapping and laser lead extractions. In addition, St. Mary's has a successful biventricular device implant program. Dr. Mahmud started the program in 1995 after leaving an academic career at East Carolina University. He attributes the success of the lab to the extremely knowledgeable and efficient RN staff that is always looking for new technologies to conquer. The following is an overview of the IBI Ablation System, our early results, and the imminence of other IBI technologies to treat cardiac arrhythmias. The proxysmal nature of supraventricular tachycardia was recognized as early as 1909. Radiofrequency electrosurgery has been performed since the 1920s, and is a modality that has been used successfully in neurosurgery and oncology. Cardiac applications for the treatment of recurrent symptomatic arrhythmias have only recently been introduced within the past 10-15 years. Non-surgical cure of many supraventricular arrhythmias is now common with radiofrequency ablation. Supraventricular tachycardia (SVT) refers to a rapid heartbeat that originates from cardiac tissues above the ventricles of the heart. The term SVT is a generic in nature and includes the following, which are being investigated in this study: atrioventricular nodal reentry tachycardia (AVNRT), proxysmal supraventricular tachycardia (PSVT), atrial fibrillation (AF) with fast ventricular response, atrial tachycardia with RVR, and WPW Syndrome. SVT can cause palpitations, lightheadedness, shortness of breath, sweating, and chest pain. Medications are often effective in managing these associated symptoms and can often reduce the frequency and severity of the SVT. However, the introduction of electrothermal treatment, namely radiofrequency, offers the potential for a permanent cure for SVT. In this article, we report our experience with the Irvine Biomedical Inc. (IBI) RF ablation system. IBI is a world leader in manufacturing innovative diagnostic and therapeutic products distributed worldwide. Irvine Biomedical s mission is to provide high quality, cost-effective products for current and future electrophysiology needs. The IBI Therapy line of temperature ablation catheters currently under clinical trial investigation represents a novel entry into the SVT ablation practice.

Catheter

The catheter has a 4 mm ablation electrode with a temperature sensor. The catheter also has three diagnostic electrodes equivalent to the existing legally marketed Inquiry catheters. The catheter has accurate rotational control (torqueability), compliant distal ends with smooth transitions, and flush electrodes for obstruction-free insertion and positioning. The connector part of the catheter is a special quick-attachment system. The catheter body is constructed of a braided Pebax® polyether block amide thermoplastic elastomer. The electrodes are comprised of 90% platinum and 10% iridium.

Generator

The generator is a microprocessor-controlled device that produces a continuous unmodulated radiofrequency output at 500 kHz. A front panel displays power output, tissue impedance, and temperature. The desired tissue temperature is user selectable by the physician. The generator has built-in safety features, which include automatic shut-off if the measured tissue impedance falls below 25 ohms or exceeds 300 ohms and if the system exceeds maximum voltage and current limits.

Principles of Operation

The radiofrequency energy delivery is temperature regulated. A high performance microprocessor and special software algorithm regulates the RF-output depending on the difference between the target temperature and the actual measured temperature at the ablation electrode. The target temperature will be reached quickly and then maintained. The generator has an independent channel for monitoring the tissue temperature through using a thermocouple sensor mounted on the ablating electrode. The desired tissue temperature is user selectable. Based on a special RF-filter technique, the intracardiac electrograms can be recorded directly from the ablation electrode not only during mapping, but also during RF energy delivery.

Procedure

The procedure entails locating the abnormal electrical pathways in the heart and then burning (i.e. dessicating) the localized tissue causing the disruption to the electrical transmission. Through the curative nature of the treatment, abnormal areas can be eliminated and normal heart rhythm can resume.

Study Design

The study is being conducted under an Investigational Device Exemption (IDE). Patients are enrolled as they present with SVT symptoms and meet the inclusion/exclusion criteria. The study is approved for 170 subjects contributed by nearly 20 investigators at 10 institutions. At St. Mary's Hospital, located in Saginaw, Michigan, we have enrolled 20 subjects. The first case was enrolled in May 2002, and we continue to enroll today. There are 12 females and 8 males; the mean age is 61.7 ± 13.1 years. The majority of the cases manifested symptoms of AVNRT (55%) or atrial fibrillation with fast ventricular response (20%). Symptom frequency averaged 1-2 per month and the duration of symptoms ranged from 2 months to 40 years. Acute success is defined as tachycardia that can no longer be induced, either baseline or by isoproterenol infusion. The acute success rate following the last burn was 92% (18/20). The median number of ablations required to complete the procedure was three. However, eight subjects required only 1 burn to achieve success. Nineteen patients have been followed out to 1-month post-ablation, and 12 subjects have been seen for the 3-month follow-up at the time of this writing. Over 94% (18/19) of the subjects at 1 month and 92% (1/12) of the subjects at 3 months post-ablation were free of arrhythmia. Three subjects reported an adverse response at 1 month following the procedure. The events included sepsis and pneumonia for one subject, hypertension for another, and chest pain with non-sustained fluttering for the third. Four subjects reported events at 3 months. They included premature ventricular complexes, persistent AF requiring a pacemaker, congestive heart failure (CHF), and palpitations. Catheter ablation of the slow pathway by radiofrequency energy is the preferred initial approach toward curative treatment and is rapidly becoming the therapy of first choice. Without corrective ablation, most patients with arrhythmias would require life-long drug treatment. Although still investigational, the preliminary results of this study at one study center would seem to provide support for the conclusion that the IBI Radiofrequency ablation catheter is comparable to published performance of available ablation products, is a viable alternative for the treatment of SVT, and offers several unique features. This Therapy frontline product incorporates many advanced features that makes it unique and cost effective. One unique feature of this catheter is an embedded thermocouple within a 4 mm distal electrode for quick response time and accurate temperature readings. The 7 French catheter shaft offers braided wire reinforcement combined with PEBAX to create superior torqueability, excellent stability, and enhanced pushability. The platinum-iridium electrodes, gold-plated connectors, and copper conductor wires assure high-fidelity recordings. The Quick-Connect cables provide rapid connections. One IBI catheter cable can be used with this and other IBI catheters (currently under clinical trial investigation) to simplify cable identification and reduce multiple cable needs. This Therapy catheter comes in Thermistor or Thermocouple for easy use with all other commercially available RF generator (s). The features mentioned above, as well as the fact that IBI has a complete range of diagnostic and therapeutic catheters, make this system a contender for the role of the primary radiofrequency ablation system for an electrophysiology lab. Another IBI ablation catheter is the Super 4. This ablation catheter is designed for treatment of atrial flutter. The Super 4 features four electrodes that are 4 mm wide and 4 mm Bandwidth. Using the IBI 1500T6 150-watt capable RF generator, ablation can be performed sequentially or simultaneously through the four electrodes (the thermocouples are positioned on the concave side of the curve.) This therapy ablation catheter is still investigational and not available for commercial distribution. IBI s Dual 8 catheters feature an 8 mm tip electrode that is dual-sensor temperature controlled. With the Dual 8 sensors, the temperature provides more effective heating and control of the power for less incidence of an impedance rise. The Dual 8, like other IBI ablation catheters, has a 7 French shaft made of PEBAX material. Curves are medium through Far Reach. This catheter is currently used with the 100 watt IBI 1500T6 RF generator. This therapy ablation catheter is still investigational and not available for commercial distribution. IBI s Cooled-Tip (irrigational) catheter with its multiple open irrigational ducts is another catheter designed for atrial flutter and is now being used in several countries, internationally. Along with the Therapy line of catheters, IBI has come out with the Triflex line, which has a softer distal tip. Triflex features the same curves as Therapy. Looking toward the future, the need for effective tools for the treatment of atrial fibrillation are being addressed. Catheters in the IBI design process will feature alternate energy sources for ablation. IBI has recently designed several catheters targeting the pulmonary vein as one of its main areas of focus.