Buckner Leads Team in Development of Robotic Catheter for Cardiac Procedures
By Shaphan Jernigan
May 12, 2008

For the past two years, a research team led by Dr. Gregory Buckner has been developing a shape-memory-alloy (SMA) actuated cardiac catheter for use in minimally invasive surgery and catheterization. Cardiac catheters are commonly used in the diagnosis and treatment of cardiovascular disorders to perform procedures such as diagnoses, angioplasties, stent placement, and pacemaker lead placement. Most catheters use manual pull-wire systems to deflect the catheter tip, a fundamental feature used to navigate catheters within the body. Dr. Buckner believes that using electronically controlled SMAs to deflect the catheter tip and body could greatly increase the catheter's functionality. The crystalline structure of SMAs allows them to recover up to 6% strain when heated, a behavior similar to that of biological muscles. This heating can be achieved simply by routing an electrical current through the SMA (Joule heating). With the SMA-embedded catheter developed at NC State, all the actuation occurs within the catheter itself. Other computer-controlled catheter systems under development rely on large external magnets or mechanical drives to control the catheter tip. These systems not only occupy valuable operating room space above the patient, but also require extensive capital (>$500,000).

Two-camera measurement system for 3-D tracking of catheter tip position.

Dr. Buckner and his research team—consisting of MAE students and personnel, surgeons and electro-physiologists, and an industrial collaborator—have developed a working prototype with one actuated segment. The device uses dual cameras and an electroanatomical mapping system to measure the position of the catheter tip. Position sensing allows Dr. Buckner's research team to closely study and record the behavior of the catheter system. It also enables closed-loop control of the catheter tip. The current prototype can be controlled by joystick or computer-controlled to track previously-logged points.

Future research will be focused on more efficient closed-loop (feedback) control systems (algorithms) to provide precise, intuitive positioning of the catheter tip by the operator. This work will require mathematical modeling of the entire system and the selection of an optimal control strategy. The team has already employed an accurate model for SMAs, which are challenging to control due to their nonlinear, hysteretic behavior.

Response of the catheter to joystick commands. Commanded positions are indicated in blue, measured positions in red.

Results showing computer-controlled positioning of the catheter tip.

The team also plans to build a highly functional two-segment prototype. The ability to control two segments should allow the catheter to navigate easily in open spaces, such as the heart chambers or thoracic cavity. For example, a two-segment prototype could form an “S” shape to avoid anatomical obstacles within the chest cavity. Current catheters lack the ability to navigate in open spaces as they require blood vessels for guidance.

Once refinements have been made, the prototypes will be tested on animal models at NC State's College of Veterinary Medicine. Dr. Buckner has years of experience in medical device research and a long working relationship with the vet school's research personnel. The device will first be tested for its ability to place pacemaker leads on porcine models.

The near-term goal of the research is to build a catheter that can place epicardial pacing leads without spreading the sternum or ribs. It is estimated that up to 30% of patients with heart failure may benefit from Cardiac Resynchronization Therapy, which requires pacing of both the left and right ventricles. While the preferred method of lead placement is through the blood vessels, many patients require that the lead be placed on the outside surface of the heart (epicardially). Currently, epicardial lead placement requires opening the sternum (sternotomy) or rib cage (thoracotomy). The NC State team hypothesizes that the SMA-actuated catheter will enable physicians to place epicardial pacing leads via an incision below the sternum (subxiphoid incision) rather than the conventional invasive methods.

Future applications of the technology are vast and could include highly precise atrial ablation, bronchoscopy, colonoscopy, inspection of hazardous materials, and other medical and non-medical functions.