Experts discuss cardiac issues as Forum reconvenes

The CIMIT Forum re-opened for learning and networking on Sept. 11 following an August hiatus with a discussion of issues relating to cardiac care.

After the session, CIMIT staff and guests adjourned for a reception to toast the 10th anniversary of the Forum.

One presenter was Patrick O’Gara, MD, vice chairman, clinical affairs, Department of Medicine at Brigham and Women’s Hospital. His session was moderated by Ahmed Tawakol, MD, co-director, Cardiac MR-PET-CT Program, and associate director, nuclear cardiology, Massachusetts General Hospital; and co-leader of the CIMIT Cardiovascular Disease Program.

Also presenting were Matthew Jolley, MD, of Children’s Hospital Boston, and Jeroen Stinstra, PhD, of the SCI Institute Utah. Moderator was Ron Kikinis, MD, director, Surgical Planning Laboratory of the Department of Radiology, BWH and Harvard Medical School, and professor of radiology, Harvard Medical School; and co-leader of the CIMIT Image Guided Therapy Program.

The title of Dr. O’Gara’s presentation was “Application of cardiac non-invasive imaging in clinical decision-making.”

He said challenges to the institutionalization of cardiovascular imaging include cost, safety (in relation to doses of radiation), quality of images, competence and appropriateness.

Dr. O’Gara said that clinicians have been challenged to understand the appropriate application in cardiovascular imaging, and to collaborate more effectively with imaging experts. Training programs have been developed but much work remains.

“Advances in CV imaging have been nothing short of fantastic,” Dr. O’Gara said. “In many ways they have preceded our ability to know how to use the technologies appropriately and cost-effectively. Issues about safety (radiation/contrast exposure) are still present. There are many more advances to come, particularly in the area of molecular imaging. But how will these impact treatment decisions and outcomes?”

Dr. Jolley spoke on the topic of “Modeling of optimal ICD electrode placement in children and adults.” He said that implantable defibrillators have become standard practice in large adults, but there is a reluctance to place them in the bodies of growing children. He stated that studies must continue to determine when and how such devices can be placed inside a youngster - or adults who would not normally be considered candidates for such technology.

Dr. Jolley is developing data with Dr. Stinstra, a software specialist who is based in Utah. Dr. Jolley credited CIMIT Fast Forward grants with providing the two (and their laboratories) with the resources (including financial support for transportation) to continue their work even though separated by many miles.

 

The number of cases in which cardiac defibrillators are implanted in children is increasing, but the procedure is still performed in a largely ad hoc manner.  Compared to similar procedures in octogenarians, implanting defibrillators in kids is difficult.  Children are small and will grow over time, and their cardiac anatomy differs from that of adults.  Hoping to improve the efficacy of implanted defibrillators in children, Matthew Jolley, MD, and Jeroen Stinstra, PhD, have created a modeling system capable of mapping an individual’s chest and then determining the optimal position for an implanted cardiac defibrillator. 

To model an individual’s thorax, the software uses pre-existing surgical planning applications such as 3Dslicer and SCIRun.  It segments images from CT and MRI scans and creates a meshwork model that is good for visualization.

Jolley and Stinstra’s software uses myocardial voltage gradients to predict the likelihood of successful defibrillation.  According to the critical mass hypothesis, defibrillation is effective – rendering the heart temporarily inexcitable – if it produces a threshold voltage gradient in a large fraction of the myocardial mass.  Usually, a gradient of three to five volts per centimeter is needed in 95 % of the heart.  Voltage gradients of over 60 V/cm can damage tissue.  When modeling different defibrillator placements, Jolley and Stinstra sought to obtain safe voltage gradients above the defibrillation threshold.  Their model suggests that small changes in defibrillator electrode position and length have large effects on voltage gradients in the heart. 

To test their software, Jolley and Stinstra compared its predictions to defibrillation metrics obtained in a catheterization lab.  They found a good, albeit not perfect, correlation between the model’s predictions and the data. 

Additional challenges must be overcome if their modeling system is to be used clinically.  First, the CT and MRI scans needed to model a patient’s chest are difficult and slightly dangerous to obtain.  These scans are usually taken only of patients who have cancer or who have suffered serious trauma.  From an engineering perspective, the user interface of the software needs to be improved, and the software must be adapted to run on PC’s. 

Despite these challenges, the modeling system developed by Jolley and Stinstra promises to help guide the placement of implanted defibrillators in children, and it nicely illustrates the uses to which computer modeling may be put.

   

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