Atrial fibrillation is the most prevalent cardiac rhythm disorder today, affecting more than 6 million people worldwide. Patients with AF experience irregular heartbeats due to abnormal electrical activity in the upper chambers of the heart (see Figure 1, below). This can cause shortness of breath, fatigue, dizziness and potential stroke or heart failure.
Conventional treatment options include drugs, which in addition to poor long-term effectiveness, can result in significant side effects or invasive surgery. In the latter case, lesions are created in the heart wall to eliminate the abnormal electrical activity.
A new form of therapy called catheter ablation is less invasive, but until now has the disadvantage of being complex while giving unpredictable results. During the procedure, the physician threads an ablation catheter — a thin flexible tube — up through a vein in the patient’s groin area to the upper chambers of the heart and, through radio frequency waves, creates targeted lesions along the beating heart wall. Outside “guidance” is provided by fluoroscopy, 3-D mapping technologies and ultrasound. Until now, there has been no means by which the physician can realistically assess the level of contact force required to create the lesions.
If the contact force is too slight, the treatment may be ineffective; if too great, the catheter may perforate the heart wall (see Figure 2, below).
First Force-Sensing Ablation Catheter
Endosense, based in Geneva, Switzerland, has developed the first force-sensing ablation catheter to give physicians real time objective measure of the contact force during the catheter ablation procedure. Through it, physicians can be assured they are using the correct force for creating lesions. Called the TactiCath™, it is a high-end 2.33-mm (0.092-inch) irrigated steerable ablation catheter that integrates the company’s Touch™ fiber-optic sensor technology in the catheter tip. This technology is widely employed in civil engineering and telecommunications’ applications. It permits physicians to achieve accurate force measurements with a sensitivity of 1 gm.
System components shown in Figure 3 (see below) include the catheter and tip, the monitor, the larger blue base station and the smaller blue TactiCath™ Splitter, all developed and assembled by Endosense.
The splitter serves as the interface between the catheter on one side and the pieces of equipment required for the procedure (the base station and the RF generator) on the other. It serves as a sophisticated Y-connector separating the optical cables from the electrical and irrigation cables running through the catheter shaft to the catheter itself. The splitter measures optical information coming from the catheter sensors, reads the temperature information measured by the sensor thermocouples and computed inside the splitter, then computes and displays the force information on the monitor. The base station software incorporates various algorithms to acquire the raw data from the catheter’s force sensor.
The flexible catheter shaft (see Figure 4, below) is made of medical-grade Pebax,® which is a block copolymer offering the widest range of performances (mechanical, chemical, processing) among the thermoplastic elastomers (TPE). Electrodes and the tip are made of platinum-iridium.
Figure 5 (below) shows the open irrigated catheter tip and the three Fiber Bragg Grating (FBG) fiber-optic strain sensors that provide real time accurate force and angle measurements between the catheter and the heart wall. This is the essence of the Endosense innovation as it completely overcomes the potential problems of using other forms of catheter ablation. Measurements at the tip (see Figure 6, below) with sensitivity of 1 gm are conducted at 100 ms intervals and are displayed on the monitor (see Figure 1, below).
The system is designed to be compatible with RF generators currently on the market. Energy at the tip is delivered by specific electrical wires and can deliver a power between 0 and 70W. The holes at the distal tip of the catheter distribute a saline solution pumped through the catheter tube to focus and control temperature at the tip, a common procedure in catheter ablation. Solution flow is then absorbed by the blood stream.
The main design challenge faced by Endosense was fitting a triaxial force sensor into a 2.33-mm (0.092-inch) diameter catheter, along with other components used in conventional ablation catheters and without degrading the catheter performance. According to Endosense representatives, this required several development iterations where different materials and configurations were tested and refined in order to reach the optimal solution. Adding to the challenge was that as a medical device, catheter materials and glues have to be biocompatible.
The length of the catheter tube, matched by the length of the fiber-optics, RF and saline solution delivery systems, called for innovations in equipment used during catheter fabrication, which is done under a microscope in a clean room environment. As well, all components are sterilized with ethylene oxide to further meet design validation criteria.
TactiCath™ has undergone extensive pre-clinical testing in the U.S. and Europe. Initial data indicates real time contact force measurements with TactiCath™ potentially have a major positive impact on the safety and efficacy of the catheter ablation procedure, while improving physician decision making and shortening procedure time. Endosense’s growing body of study data on TactiCath™ has been the subject of nine abstracts presented at annual meetings of the Heart Rhythm Society, American College of Cardiology and American Heart Assn.
Human trials are now underway in Europe with CE Mark approval expected in 2009. The U.S. Food and Drug Administration currently limits the TactiCath™ to investigational use.