We propose to develop and evaluate a multimodal imaging system for guiding cardiac ablation therapy. Cardiac ablation has become the standard of therapy for most forms of atrial tachyarrhythmia in the United States. Hundreds of ablation procedures are performed daily for atrial flutter, atrial fibrillation, AV nodal reentrant tachycardia and Wolff-Parkinson-White syndrome. While ablation for all of these arrhythmias is common, AFl and AF ablations are the most complex and present the greatest challenges.
          Sophisticat ed electroanatomical mapping tools have been developed and are now c ommonly used to map the spread of electrical activation and to guide the physician in placing the catheter tip f or ablation. Intracardiac ultrasound has been developed to guide trans-septal punctures for left atrial procedures and to assure ablation tip contact. Yet many AFl and AF procedures still require many hours (mean 3.5 hours) to complete and frequently (10%-20%) require repeat procedures1, 2. One of the major reasons for lengthy procedures and repeat ablations is the inability to directly visualize ablation lesions.
          Acoustic Radiation Force Impulse (ARFI ) imaging is a relatively new technique for assessing tissue viscoelastic properties. ARFI has been shown to differentiate normal from ablated tissue in the heart, liver and kidney. ARFI was developed and currently is implemented f or hand held transducers. Our initial studies have demonstrated the in vivo capabilities of intracardiac ARFI imaging at distinguishing ablated from normal tissue. We propose to integrate a custom-built 128 element ultrasound probes into our system, develop improved
beam sequencing and signal processing methods for ARFI imaging and construct a real-time ICE based ARFI and B-mode imaging system. We will evaluate ARFI imaging’s ability to guide and assess ablations under clinically realistic conditions.
          Electroanatomical mapping tools use catheter mount ed location sensors operating in electromagnetic fields to guide catheters within the heart chambers and facilitate placement of lesions. These t ools, however, do not image and can not be registered with other imaging systems. We will work in concert with Siemens Medical and J ohnson & Johnson, using a new AcuNav ™ catheter with a CARTO™ magnetic sensor (see letter of support from Siemens Medical) to enable registration of ARFI images to the electroanatomical maps made by the CARTO™ system. This multimodal system will enable rapid evaluation and repair of incomplete lesions greatly enhancing the clinicians ability to perform these procedures.
          This image guided ablation system will enable the physician to outline a cardiac chamber using the position sensing system and to create a cartoon image of the chamber and superimpose electrical maps of conduction measured from the catheters (existing technology). The clinician will be able to position the catheter guided by the cartoon, create lesions, and catalog their locations (existing technology). They will be able to steer the ICE catheter image plane to the lesion location, and image the lesion (new technology). They will be able to use ARFI imaging to visualiz e lesion creation in real time, to assess lesion transmurality and continuity, and to guide the catheter to imaged lesions found to be in need of repair (new technology). Using this integrated system, interventional electrophysiologists will, for the first time, have a multimodal system capabl e of imaging lesions directly that will work in concert with the existing suite of tools for ablation therapy of tachyarr hythmias. The successful implementation of the proposed methods will result in shortened car diac ablation procedure times, a reduction in the number of repeat procedures, and a minimization of collateral tissue damage and its associated morbidity.
          Our collaborative team includes Dr. Patrick Wolf a mapping, ablation and position sensing technology expert, Dr. Gregg Trahey, the co-developer of ARFI technology and recognized leader in ultrasound research, and Dr. Tristram Bahns on a clinical ablation expert and Director of Arrhythmia Ablation Services and the AF Clinic at Duke University Medical Center. This team, supported by Siemens Medical Syst ems, is uniquely qualified to implement this important advance in image guided therapy.
          Over the next three years we will bring this integrated system to the brink of clinical use by meeting the following milestones which will resolve remaining technical issues, characterize the performance of the system, and confirm its ability to guide these ablation procedures.