July 01, 2011
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New modality offers noninvasive look into arrhythmias

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Noninvasive imaging of the electrophysiological activity of the heart has been an elusive quest in cardiology because no standard clinical imaging modality exists to noninvasively map the heart’s electrical activation.

Currently, cardiac electrical function is typically determined using an electrocardiogram or catheter-based mapping system, whereas assessing cardiac function is generally performed using ultrasound and magnetic resonance techniques. Each of these techniques has its shortcomings, however, as modalities that measure electrical activity typically ignore cardiac function, whereas those that measure function are not usually fast enough to detect the speed at which electrical impulses conduct throughout.

Now, however, researchers at Columbia University have developed a noninvasive approach called electromechanical wave imaging (EWI) that may someday simplify the process by offering one modality that can perform both measurements while capturing the electromechanical activity of heart, a phenomenon that happens within just a few milliseconds. EWI is an entirely ultrasound-based imaging technology that, in a feasibility study, was able to map the electromechanics of all four chambers of the heart. The images generated from this modality, according to the study, captured high temporal and spatial resolution images with a precision previously unobtainable in a full cardiac view in both animals and humans. With a frame rate of 500 frames per second, EWI features a speed that is five times faster than standard echocardiography while not sacrificing the large field of view.

Elisa E. Konofagou, PhD, associate professor of biomedical engineering and radiology at Columbia and principal investigator in the study, told Cardiology Today that with EWI, the two worlds of cardiology — the electrical and the mechanical, which have before now never really converged — are brought together.

“This is important because physicians need to know where the arrhythmia origins are, and currently, they don’t know,” Konofagou said. “That is what we are trying to provide with EWI.”

Experiences in humans

In the feasibility study, Konofagou and colleagues were able to use EWI to successfully depict normal electromechanical activation sequence of both atria and ventricles in two healthy participants, one male and one female and both 23 years of age. According to Konofagou, additional research performed by the group has also shown the usefulness of EWI for depicting atrial fibrillation and atrial flutter, as well as Wolff-Parkinson-White syndrome.

“We were able to pick up [Wolff-Parkinson-White syndrome] in all humans, and now, we’re putting it together in a clinical paper,” she said. “Acquisition-wise, it’s exactly like what you would do for an ultrasound, so there is nothing additional to it.”

In addition, the researchers have tested EWI during CRT, “so we were able to activate the right ventricle separately from the left ventricle and then do biventricular pacing, and our images actually show when the two ventricles are activated rather than each one separately,” Konofagou said, adding that these findings are currently in press.

Konofagou and colleagues plan to further improve and refine the EWI modality, which will make it more useful to physicians by making images available in real time.

“Right now, we have the luxury of taking the data and going to the lab and processing it, but a physician wants to know right away whether a patient should be rushed to surgery or interventional treatment,” she said. “So we want to implement this in real time and also optimize it.”

Peer appraisal

James Thomas, MD
James Thomas

For James Thomas, MD, the Charles and Lorraine Moore Chair of Cardiovascular Imaging at the Cleveland Clinic and president-elect of the American Society of Echocardiography, this new modality could potentially one day play a role in finding the focus of where ventricular tachycardia is, as well as tracking dyssynchrony more precisely.

“There are ways to do some of this with conventional imaging, however,” Thomas said. “You can use tissue Doppler and get almost to the same frame rates as they are describing (around 200 per second). So, it’s addressing a problem that is important but may not be keeping us awake at night. What they describe here is evolutionary, not revolutionary, but it’s definitely a real technological improvement, particularly how they can derive high-resolution strain images from the radio frequency ultrasound signal. What remains to be seen is if this can be packaged into something that can be delivered clinically or if it is something that will be kept in the laboratory.”

On the arrhythmia side, Henry Halperin, MD, professor of medicine, biomedical engineering and radiology at Johns Hopkins University and an avid researcher in the field of electrophysiology, said the findings of the feasibility study are exciting and show potential usefulness for the field of electrophysiology, adding, however, that he has a couple of concerns with this technique that could be problematic when trying to get an accurate assessment of the heart.

Henry Halperin, MD
Henry Halperin

“The main problem that these kinds of techniques have is that it assumes the mechanical activity of the heart is going to reflect the electrical activity of the heart, and that has to be shown for many different types of heart disease,” Halperin said in an interview. “So the fact that it works in normal hearts doesn’t mean it’s going to necessarily work in diseased hearts. There may be some situations where the mechanical activity doesn’t reflect the electrical activity; for instance, if there are scars in the heart tissue, the electrical activity may not follow the mechanical activity or vice versa.”

There are also certain shortcomings inherent with echocardiography that are important to keep in mind, he said. “Echo has a lot of limitations because, in many patients, you cannot get a good echo because the acoustic windows are limited. For instance, echo cannot image through ribs, it has to go between ribs, so the question is how do you get adequate acoustic windows on the chest that give you an adequate view of the heart, which may be limited in many patients. Also, in some patients, the lungs are inflated more than they should be, like those with lung disease, which can cause scatter on the ultrasound.

“My bottom line on this is: It’s exciting research, and I’m anxiously awaiting to see how it comes out,” Halperin said. “It holds promise, but it requires a lot of studies to validate it and determine what it could be used for.” – by Brian Ellis

For more information:

  • Provost J. Proc Natl Acad Sci U S A. 2011;108:8565-8570.

Disclosures: Drs. Halperin, Konofagou and Thomas report no relevant financial disclosures.


PERSPECTIVE

W. Gregory Hundley, MD
W. Gregory Hundley

Understanding the relationship between electromechanical activation and cardiac diastolic and systolic function is very important to the practice of medicine. We don’t currently have accurate methods to do this. The potential of EWI in the future is that not only does it look accurate, but because it’s ultrasound-based, it could be widely available and rapidly disseminated worldwide. So you’re doing something that could be inexpensive, widely available and taught universally throughout all the CV training programs easily. If successful, this modality could rapidly translate to the practice of CV medicine.

– W. Gregory Hundley, MD

Cardiology Today Section Editor

Disclosure: Dr. Hundley reports no relevant financial disclosures.


PERSPECTIVE

Bruce Wilkoff, MD
Bruce Wilkoff

This appears to be a technique for imaging the heart with very high time resolution. This permits a more close correspondence to the electrical activity of the heart, but not an electrical mapping of the heart. Usually, mapping is about the progression of electrical activity, as this represents the sequence of the activation. However, this is more of the response to that rapid electrical impulse but in very high resolution. This could be interesting in the evaluation of dyssynchrony as in the evaluation for cardiac resynchronization therapy or the response after application of this therapy. Obviously, this is a new tool, and it is not certain what the best application will entail as more studies are required.

– Bruce Wilkoff, MD

Cardiology Today Editorial Board member

Disclosure: Dr. Wilkoff reports no relevant financial disclosures.