Collaborating Investigators:

• John Triedman, MD, Children's Hospital Boston
• Matt Jolley, MD, Stanford University
• Natalia Trayanova, John's Hopkins University
• Tom Pilcher, University of Utah

The CIBC has a longstanding collaboration with Drs. Triedman, Jolley, Trayanova, and Pilcher to improve the design and efficacy of implantable cardioverter-defibrillators (ICDs) through improved computational modeling and new simulation tools. ICDs are now a standard tool of modern interventional cardiology, providing an effective, lifesaving technology. Over 110,000 devices were implanted in patients in the U.S in 2004 alone.¹ However, the growing size and diversity of the population with ICDs have exposed some of the limitations of this technology. To minimize the risk of fatal events, ICDs are usually designed and implanted with standardized safety factors, with little tailoring to an individual subject. ICDs are designed to provide electrical shocks higher than many patients need in order to accommodate the 17-24% of patients who require more energetic shocks. Additionally, current ICD design is suboptimal for many patients, specifically children, patients of small body size, and patients with congenital heart disease, resulting in unnecessary pain, unsuccessful shock, and diminished quality of life.²

Unique difficulties exist for these groups, including high rates of lead failure^3,4,5, frequently inappropriate therapy⁶, mismatch of lead device and lead size to the patient's body, and the effects of somatic growth and long life expectancy. Lead failure, in particular, can result in substantial risks. These data indicate that tuning ICD parameters to patient-specific factors is critical to further developing ICD technology. The potential for adverse effects coupled with the increasing use of these devices has spurred renewed interest in reexamining the standard design approaches.

In previous studies with Drs. Triedman and Jolley, the CIBC created a series of detailed torso models, which form the basis of the simulations, as well as interactive software tools to place the ICD device and electrodes at any locations within the torso model. We have used SCIRun software to generate a database of over 400 different electrode lead configurations placed inside four different computational anatomical models. We continue to develop and improve these models, using a suite of tools including SCIRun, ImageVis3D, Seg3D and BioMesh3D.

Expanding the scope of the research occurs on several fronts. We have begun clinical validation of the simulation models through a collaboration with physicians at the Primary Childrens' Hospital at the University of Utah. In these experiments, we create patient specific models of a cohort of children and young adults with congenital heart abnormalities who require ICD implants. During the implant surgery, which includes testing the ICD in situ, we record body surface ECGs from up to 32 sites placed at specific locations on the thorax. By capturing the electrical signals during the testing of the device, we obtain patient specific torso surface potentials from the shock, which we then compare to simulations of the same shock using the torso geometry and actual device location.

A second new direction of the research seeks to use detailed simulations of fibrillation and defibrillation in high resolution models of human hearts. For this collaboration with Dr. Natalia Trayanova, we perform MRI scans of explanted or autopsied human hearts using the small animal MRI facilities at the University of Utah. These scans include diffusion weighted MRI, which yields information on local fiber structure of the heart as scales well below 1 mm. Such detailed, realistic models of the heart will provide the substrate necessary to address fundamental questions about the role of heart anatomy and fiber structure on the propensity of the heart for fibrillation as well as the mechanisms of successful and unsuccessful defibrillation shock. We will then combine findings from the heart simulations with the torso models and develop complete, whole body models of fibrillation and defibrillation.

[1] Hall MJ, LJ Kozak, and CJ DeFrances. National hospital discharge survey: 2004 annual summary with detailed diagnosis and procedure data. National Center for Health Statistics. Vital Health Stat., 13(162), 2006.

[2] J. P. Daubert, W. Zareba, D. S. Cannom, S. McNitt, S. Z. Rosero, P. Wang, C. Schuger, J. S. Steinberg, S. L. Higgins, D. J. Wilber, H. Klein, M. L. Andrews, W. J. Hall, and A. J. Moss. Inappropriate implantable cardioverter-defibrillator shocks in MADIT II: frequency, mechanisms, predictors, and survival impact. J. Am. Coll. Cardiol., 51(14):1357–65, 2008.

[3] T. Korte, W. Jung, S. Spehl, C. Wolpert, R. Moosdorf, M. Manz, and B. Luderitz. Incidence of icd lead related complications during long-term follow-up: comparison of epicardial and endocardial electrode systems. Pacing Clin Electrophysiol., 18(11):2053–2061, Nov 1995.

[4] J. Kron, J. Herre, E. G. Renfroe, C. Rizo-Patron, M. Raitt, B. Halperin, M. Gold, B. Goldner, M. Wathen, B. Wilkoff, A. Olarte, and Q. Yao. Lead- and device-related complications in the antiarrhythmics versus implantable defibrillators trial. American Heart Journal, 141(1):92–8, 2001.

[5] R.G. Hauser nd L.M. Kallinen, A.K. Almquist, C.C. Gornick, and W.T. Katsiyiannis. Early failure of a small-diameter high-voltage implantable cardioverter-defibrillator lead. Heart Rhythm, 4(7):892–896, July 2007.

[6] M. E. Alexander, F. Cecchin, E. P. Walsh, J. K. Triedman, L. M. Bevilacqua, and C. I. Berul. Implications of implantable cardioverter defibrillator therapy in congenital heart disease and pediatrics. J. Cardiovasc. Electrophysiol., 15(1):72, 2004.