Update on the SMART-AF Trial: Utilizing Force Sensing Capabilities for the Treatment of AF

In this article, Dr. Natale provides a brief discussion on his use of an investigative contact force sensing catheter for the treatment of drug-refractory symptomatic paroxysmal atrial fibrillation (AF), as part of the SMART-AF clinical trial.

On July 6, 2011, we performed the first AF ablation using the ThermoCool^® SmartTouch^™ Contact Force Sensing Catheter (Biosense Webster, Inc., a Johnson & Johnson company, Diamond Bar, CA). This procedure was part of the SMART-AF Investigational Device Exemption (IDE) study, and was the first use of the technology in the United States. The ThermoCool^® SmartTouch^™ Contact Force Sensing Catheter has not yet received approval by the U.S. Food and Drug Administration.

We also utilized this catheter during a clinical trial in Prague in February 2010 — the first human case in the world — along with professor Josef Kautzner, MD, PhD, FESC, head of the department of cardiology at the Institute for Clinical and Experimental Medicine, Cardiology, and Hiroshi Nakagawa, MD, PhD, of the Heart Rhythm Institute at the University of Oklahoma Health Sciences Center. During this trial, we treated approximately 20 patients in an effort to carefully examine the possible benefits of this catheter. The objective of this study was to compare current technologies and procedures using this new catheter — including the examination of contact pressure.

The purpose of the study in the United States, however, is to examine the safety and effectiveness of this technology in the treatment of AF. For this study, we will enroll nearly 200 patients from several leading facilities, including the Texas Cardiac Arrhythmia Institute (TCAI) at St. David’s Medical Center. The study will run for approximately 18 months to two years.

About the Contact Force Sensing Technology

During cardiac ablation, the SmartTouch catheter enables the measurement of catheter tip contact force and direction inside the heart. The force and contact information are graphically displayed on the Carto^® 3 Mapping and Navigation System with the Carto^® 3 SmartTouch^™ Software Module (Biosense Webster, Inc., a Johnson & Johnson company), creating a fully integrated solution that combines contact force with three-dimensional mapping and navigation capabilities. The joining of these technologies allows the physician to display detailed images, generate a map of the contact pressure achieved during the procedure — possibly reducing the chance that a patient will need an additional follow-up ablation procedure — as well as increase patient safety.

One of the key issues with current ablation catheters is that they can provide limited tactile feedback. During catheter ablation, it is difficult for EPs to determine whether or not they are maintaining good contact with the tissue. Maintaining close contact with the tissue and knowing how much pressure the operator is applying can result in the creation of better lesions, which ultimately means better outcomes for patients. Catheter contact pressure can critically affect the efficacy of a lesion.

The primary benefit of the SmartTouch catheter is that it gives the operator reliable information on the catheter contact pressure with the cardiac tissue. This greatly enhances a physician’s ability to create consistent, high-quality lesions during ablation. Recent data suggests that catheter contact pressure during ablation is the most critical factor in predicting the long-term quality of a lesion. We know that if the operator has adequate contact pressure, the chances of disconnecting the pathway of abnormal rhythm is high; however, if contact is not adequate, there is a greater chance that the targeted tissue will recover. Specifically, if the contact pressure is less than 5 grams, it is almost certain the lesion will not be adequate, likely resulting in the failure of a therapy. This can result in an additional hospitalization to repair the AF.

On the other hand, in the hands of a less-experienced physician, current ablation catheters can puncture the heart if too much pressure is used. An excessive amount of contact pressure and power can cause a “steam pop,” a risk during ablation procedures. During a steam pop, the vaporization of the deepest tissue layer causes a local explosion (the operator can often feel the explosion through the catheter), which can disrupt the cardiac wall enough to cause perforation.

Since this new catheter allows physicians the ability to measure pressure during ablation, it can help prevent complications and lessen the likelihood of damage to a patient’s heart.

Summary

As ablation becomes more prevalent as a technique to treat heart rhythm problems, it is critically important that we do everything we can to maximize the success and safety of these procedures. As we continue to study the use of this catheter, we hope to be able to find that it provides an objective measure of contact between the catheter and heart muscle.