CathRx was founded in Australia over 10 years ago with the goal of designing better medical devices. With a strong background in the pacing/defibrillator industry, its initial focus has been on electrophysiology catheters. These devices have been used for over 40 years, with little change in their fundamental design and construction. Considering the tremendous advances in understanding and treatment within the electrophysiology arena, it was apparent there was an opportunity for CathRx devices to improve outcomes.
This article describes the design philosophy behind the catheters, product features and resulting benefits for users. It also describes the current range of CathRx devices and explores the future of electrophysiology catheter technology, including catheter reprocessing and the treatment of atrial fibrillation.
Design Goals
The company’s design goals are to incorporate features in its devices that lead to improved outcomes for patients and clinicians and reduce costs for healthcare providers. These goals focus on:
- Safety – this is of the utmost importance. CathRx has analysed ways of achieving safer procedures.
- Steering/handling – this involves torque, pushability and being able to position the catheter where it is needed.
- Clinical versatility – increased functionality for each catheter, so one catheter can do the job of several.
- Size – smaller catheters are more comfortable for patients and potentially enable deeper access into cardiac structures.
- Signal quality – high-quality signals are essential for good diagnosis.
- Cost – with hospital budgets constantly shrinking, the goal was to provide a superior product with lower overall cost to the centre via catheters designed for multiple uses and reprocessing.
Technology
The resulting patented catheter construction method revolves around separation of the steering mechanism from the electrode sheath. This leads to a number of benefits for users including technical advantages, such as improved versatility and safety, as well as cost and environmental benefits through reusability.
In these catheters, the conducting wires are coiled around a central lumen (see Figure 1). This ordered packing of conducting wires allows the creation of smaller catheters with more electrodes, providing room for enhanced functionality. The central lumen is used to house the steering mechanism, which is typically made of high-quality, super-elastic nitinol. Nitinol provides increased deflection response, durability and consistency.
Diagnostic Catheters
The current range of CathRx diagnostic catheters now available in Europe through Pioneer Medical Devices as the Master2cout range is ‘modular’. In these catheters the electrode sheath can accept a range of different steering mechanisms or stylets. The catheter is 5 French (Fr) in size and available with up to 20 electrodes, with various electrode spacings. The handle uses a push–pull controller to cause deflection.
The stylets are available with a fixed or deflectable curve. The fixed or ‘formable’ stylet has a nitinol shaft with a stainless steel distal end that may be formed into various shapes multiple times to access specific anatomies. The deflectable stylet is constructed from laser-cut nitinol and is available in a range of sizes – from small enough to access tight spaces to large enough to map entire chambers.
Exchange of these stylets may be achieved in vivo with the electrode sheath left in position. This removes the need for an extra catheter, along with the associated difficulties and X-ray exposure needed to feed the replacement catheter into the body. Alternatively, the stylet may be partially or completely retracted, which makes the distal end more flexible and further reduces the chance of perforation.
The modular catheter has a feature that allows the sweep of the catheter to be changed and provides a method for projecting the tip of the catheter. The front knob of the catheter handle is pushed forward, which advances the tip of the catheter over the stylet. This projection feature may be useful to actively contact a surface, access an ostium or simply change the sweep of the curve (see Figure 2).
The deflectable stylets are approved for re-use, further reducing the cost per procedure. This has allowed more expensive materials and construction methods to be used and a more versatile steering mechanism to be developed.
The steerable multipolar catheters have been clinically tested in a case mix of patients to assess the usefulness of their peculiar characteristics. Interestingly, their reduced diameter, associated with steerability, allowed easy positioning in the coronary sinus by a left or right cephalic or basilic vein approach in more than 90% of cases, as shown in Figure 3. This is particularly useful when an aggressive anticoagulation strategy is used, such as for atrial fibrillation ablation. In fact, in this case the access through a brachial vein (which can be directly compressed at the end of the procedure) is associated with minimal complications. On the other hand, subclavian, jugular or femoral cannulation may be associated with bleeding complications/haematoma, possibly leading to severe complications. Due to the catheter peculiarities, namely the small diameter of the catheter shaft, steerability and possibility of withdrawing the stylet from the distal part, the catheter can be safely advanced more distally into the coronary sinus. This is the case even when a patient has unfavourable anatomy (see Figure 4). This results in an optimal catheter stability without the need for repositioning during the procedure, high-quality recorded signals and a very low pacing threshold. A pacing threshold of 0.5mV was observed in about 50% of the sites tested when the catheter was positioned in the coronary sinus.
Finally, the option of having a proximal 6Fr catheter shaft in this series of multipolar diagnostic catheters enhances torquability. This can be particularly useful when the inferior vena cava approach is used to cannulate the coronary sinus, as shown in Figure 5. Using this approach, a precise clockwise torsion is required to direct the catheter inserted via the inferior vena cava towards the coronary sinus ostium. Afterwards, the abovementioned unique characteristics of the catheter facilitate stable positioning in the coronary sinus.
Other sites clinically tested for positioning of multipolar steerable catheters during an electrophysiological procedure are the Hisbundle area and the crista terminalis. The latter is the place where a multipolar catheter is routinely positioned during the ablation of a cavo-tricuspid isthmus-dependent atrial flutter. As shown in Figure 6, an extra-large curve of the stylet, associated with catheter steerability, renders the positioning of the catheter in this area very easy. The small diameter of the catheter favours adherence to the atrial wall, with no risk of perforation. This results in safe and stable positioning, both during sinus rhythm and atrial flutter.
Loop Catheters
One complication with loop catheters is entanglement of the loop in the mitral valve, chordae tendineae or other cardiac structures. Estimated to occur in 0.9% of procedures (95% confidence interval [CI] 0.2–2.5%),1 in most serious cases this has resulted in open heart surgery to remove the loop fragment or to replace the valve. The CathRx loop catheter has a patented feature to help reduce this complication. The loop itself can be simply unravelled in vivo, which reduces the entanglement force by approximately half. This is achieved by unclipping the loop stylet and partially withdrawing it. This removes the rigid loop shape from the end of the catheter and makes disentanglement easier (see Figure 7).
This device is currently available in Europe as the Master2cout loop catheter. It has 10 electrodes and comes in three different sizes: 15, 20 and 25mm in diameter. The catheter has a bidirectional curve that allows it to achieve true straightness for easy access to the left superior vein. It also has a tight 25mm curve diameter for easy access to the right inferior vein. The handle uses the familiar push–pull mechanism to achieve deflection. Future loop catheter products will include variants with more electrodes, variable diameter loops and spiral shapes.
The development of a 5Fr loop catheter with bidirectional variable curve and variable diameter will allow easy and safe positioning, being able to adapt to the highly variable anatomy of the pulmonary veins. A small deflection curve would be suitable to enter the superior pulmonary vein, whereas a longer curve will facilitate catheter insertion into the inferior pulmonary veins. The latter will enable the use of a steerable trans-septal sheath (which can be impractical, imply added costs and cause vascular and septal damage, being of large diameter) to be avoided.
Ablation Catheters
The first of the CathRx range of ablation catheters, the irrigated tip version was pilot trialled in Australia and New Zealand. The catheter has a feature that allows the user to select the size of the deflection curve. Rather than change the stylet, as with the modular diagnostic catheter, the ablation catheter has a slider that selects the distal curve diameter (see Figure 8). Curve diameter varies from as small as 25 to 55mm diameter. Early results for treating patients with atrial flutter with the new irrigated ablation catheter with variable deflection are promising. The versatility provided by the ability to change the deflection curve size and reach of the catheter seem to be beneficial.
The initial range of irrigated tip catheters are awaiting regulatory approval in Europe and will be available through Pioneer Medical Devices. The tip is 4mm long with a 7Fr diameter and six holes for irrigation. For deflection, the handle uses a screw-type controller for enhanced control and precision. The first catheter will be compatible with the common Stockert generator with CoolFlow pump. Future developments may include the addition of location sensors, tissue-proximity sensing and alternate tip types.
Reprocessing of Electrophysiology Catheters
Single-use medical devices create large amounts of waste that need to be disposed of. Therefore, re-use of a medical device reduces the amount of waste generated per procedure, improving environmental outcomes. Healthcare budgets around the world are under pressure and reprocessing is one avenue by which a centre can reduce costs. The procedure cost of a device that may be used a number of times is significantly less than a device that is used once. Experience in countries with regulated device reprocessing, such as the US and Germany, shows that safe reprocessing of electrophysiology catheters is not only possible but practical. Millions of dollars have been saved by hospitals and thousands of tons of environmental waste have been avoided.
CathRx has allied with Pioneer Medical Devices in Europe to provide clinicians with a complete catheter solution. Pioneer Medical Devices exclusively specialises in the development, manufacturing and reprocessing of innovative medical devices of limited reprocessability. Initially Pioneer Medical Devices will provide reprocessing services to a hospital, maximising the utility of the current Master2cout modular diagnostic catheter range. Each catheter will be loaded with the desired stylet for each individual clinician. These will be provided for their use and then collected for reprocessing at the end of the procedure. Development is now under way on a range of multi-use catheters that are purpose-built for reprocessing by specialist reprocessors.
Atrial Fibrillation
Atrial fibrillation is the most common arrhythmia. It has a large, poorly treated population. Catheter ablation is now second-line therapy and continues to show great promise. Radiofrequency energy is undoubtedly the preferred energy source and CathRx is working on a range of catheters and generators to improve patient outcomes.
The most common deficiency in the treatment of atrial fibrillation is the creation of deep, long lesions. Most ablation procedures involve the creation of a linear barrier of lesions to prevent the passage of electrical signals. Typically, these lines are created point-to-point by conventional ablation catheters. This procedure is long and prone to gaps that may recur and result in the need for a follow-up procedure.
CathRx is developing a catheter/generator system to potentially address this matter. A single linear lesion catheter may be used to create a continuous line of lesions, ensuring that there are no gaps through which electrical signals can pass. Irrigation may also be incorporated into this device. A radiofrequency generator with a patented waveform can also be used to create deep lesions.
Summary
CathRx has a number of exciting catheter families based on a new method of manufacturing. These include the range of modular diagnostic catheters with reusable stylets, the loop catheter with enhanced safety, and the ablation catheter with a selectable deflection. Partnering in Europe with Pioneer Medical Devices, the diagnostic catheters are available as the Master2cout range.
CathRx is constantly looking to improve its catheters with clinical feedback and new catheters are being developed utilising such information. The company continues to put emphasis on reprocessing and the creation of products to help improve outcomes in atrial fibrillation.