CARTO is a brand-name medical system produced by Biosense-Webster, a subsidiary Johnson&Johnson.
CARTO is a brand-name medical system produced by Biosense-Webster, a subsidiary Johnson&Johnson.
The CARTO XP EP navigation system is designed to visualise the real-time calculated position and orientation of a specialised RF ablation catheter within the patient’s heart. The goal of this technology is to minimise radiation exposure during fluoroscopy, increase the accuracy of targeted RF ablation and reacquisition of pacing sites for re-ablation.[1][2]
The CARTO navigation system calculates the position and orientation of the catheter tip, using three known magnetic sources as references.[3] The CARTO system uses static magnetic fields that are calibrated and computer controlled. Due to the nature of magnetic fields, the orientation may also be calculated while the tip is stationary. By calculating the strength and orientation of the magnetic fields at a given location, the x,y,z position may be calculated along with the roll, pitch, yaw orientation.
The system is typically described anecdotally as ‘similar to the GPS unit in a car’, indeed it operates on several of the same principles. The GPS satellite network operates by transmitting the location and reference time on each satellite via an radio signal, allowing the user’s GPS device to triangulate its position from multiple satellites. A limitation inherent is that a GPS unit can not determine the orientation unless the user is moving (change in position over time).
The CARTO system may be described as four ‘Black Box’ devices.
A ring with three fixed, computer controlled, magnets is positioned beneath the patient. The magnets are calibrated to be of different strengths and at fixed positions. As the strength and position of each of the magnets is both known and fixed, this provides suitable point of origin references for the magnetic fields in the surrounding space.
The Positioning Sensor detects the characteristics of the magnetic fields at a given point in space, this signal is in turn transmitted to the decoding unit where it is used to calculate the position and orientation. A Position Sensor is located in the Catheter tip and a second sensor is in a patch affixed to the patient’s back. By having the second Position Sensor as a reference, the relative position of the Catheter tip may be calculated. This offers improved accuracy within the magnetic fields along with detection of any patient movement. The relative position is important as it allows the location data to be referenced to patient anatomy.
The signals received from the assortment of sensors are converted and calculated to provide comprehensible information. The position, orientation, temperature and ECG values are determined for the catheter tip. These steps require specialised processing hardware.
The data from the decoder unit is interpreted by the Workstation. The user selects calculated points that are then projected onto a pre-acquired CT and a map is extrapolated. The displayed position and orientation, along with ECG information is offered to the surgeon as a roadmap. This is to assist in targeting specific locations, monitoring catheter tip behaviour and reacquiring previous points for additional ablation.
The CARTO workstation is typically used to display two generated windows with different points-of-view, this is to allow the operating physician an x,y,z and pitch,roll,yaw position of the catheter.
Points within the cardiac structures are logged and used to generate a 3D map, these points may be correlated to a CT scan. Once a suitable fit has been established, the CT will afford a great degree of detail with regard to the cardiac structures. The real-time projection of the catheter onto the CT image is an incredibly powerful tool during AF ablation procedures.
As the catheter tip has an ECG pickup, recordings may be taken and correlated to a 12-lead ECG, pacing wire, Lasso catheter and/or pentarray catheter (ECG catheter featuring 4 leads on each of the 5 armatures). Through tracking and plotting the local ECG characteristics against the cardiac cycle, a map of the conduction velocity can be generated as a colour-code on the CT or point-generated CARTO map. This information is of great value in identifying the location of high-velocity pathways, micro-circuits or errant pacing nodes.
This technology allows the operator to determine catheter placement relative to previously observed physical features. This is particularly useful when ablating sites along the ridges surrounding Pulmonary Veins [4], which are otherwise difficult to acquire. This device also allows for continuous catheter monitoring without exposing the patient and the theatre staff to additional radiation.
The CARTO user interface is controlled by a technician, providing two separate points-of-view images of the catheter to the surgeon. Usability of the visual information is dependant on technician skill and communication with the physician. The closeness of fit of the previously acquired CT image is manipulated by a series of points established by the physician along cardiac structures. This is also determined by the physician-technician relationship as well as the anatomical knowledge of the technician. While the basic usability of the CARTO system may be performed with minimal training, a good result requires time, knowledge and training.
The CARTO system is capable of accuracy and specificity down to <2mm. This is entirely dependant on fitting the registered endocardial points to the previously acquired CT. Anatomical knowledge and skill on the part of the technician, along with a good working relationship and communication with the physician or surgeon is key to the usability of this system. Due to movement during the cardiac cycle, the probe position is gaited against the cardiac cycle via the ECG trace. It must be noted that, during arrhythmia, the contraction characteristics of the heart changes. This can result in a shift of cardiac features by 10-20mm within the chest. Operator skill is required to disregard this movement, along with judging shift during the respiratory cycle.
As the technician acquires points on the inside of the heart, a theoretical model is constructed. A point on this model is then flagged and correlated with a similar point on the CT image. The software automatically adjusts the CT to a best fit with the registered points and may then be updated with future points. A false sense of faith in the technology may result in misleading information being extrapolated and delivered to the technician and physician. Physician training and skill will quickly identify an incorrect fit, resulting in acquiring new points to generate an accurate fit.
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