Image: ECGI mapping the heart (Photo courtesy of Washington University, St. Louis).

Electrocardiographic Imaging (ECGI), a novel noninvasive functional imaging technology, can locate the source of ventricular tachycardia (VT) in just one second, according to a new study.

The technique, developed in Washington University (WUSTL; St. Louis, MO, USA) combines computerized tomography (CT) with around 250 electrocardiograms (ECGs)--recorded by electrodes placed on a vest across a patient's torso--to map the source and pattern of VT in the heart and determine the kind of VT irregularity. Using a special algorithm, ECGI can then generate a graphic representation of the distinctive VT excitation waves from recordings of multiple heartbeats. While much information can be deduced from the ECGI analysis of just one heartbeat, multiple heartbeats are often imaged to reveal even more about the nature of the arrhythmia.

The researchers conducted a systematic study of 25 cardiology patients with VT scheduled to undergo catheter ablation to correct their electrical defects, but who first underwent ECGI. The imaging correctly found the VT origin and categorized the two VT mechanisms; the first is a focal mechanism, comprising a mass of abnormal cells generating a wave similar to pebble tossed into a pool. The second mechanism is labeled re-entry, in which excitation waves become circular, forming a closed loop similar to a tornado. In each mechanism, the heart's pacemaker activity is seized from its natural, normal site in the sinus node. The researchers showed that the abnormal excitation patterns of VT often began in scar tissues that were telltale signs of previous heart attacks. The study was published in the August 31, 2011, issue of Science Translational Medicine.

“ECG measures the reflection of the heart's electrical activity far away from the heart on the torso surface. In the process, resolution is lost,” said lead author, Prof. Yoram Rudy, PhD, director of the cardiac bioelectricity and arrhythmia center (CBAC) at WUSTL. “ECGI gets far closer. Imagine a car coming toward you at night from far away. You see only one light. But as it gets closer and closer, you start to resolve the two headlights and their location in space. It's similar here.”

“ECGI is a treasure for basic medical research. It is a tool that opens the door to study the electrical functioning of the heart and arrhythmia mechanisms in people with various hereditary and nonhereditary cardiac disorders,” added Professor Rudy. “Clinically, it is promising as a diagnostic tool that could guide therapy of cardiac arrhythmias, and because it is noninvasive, it could also be used as a follow-up tool to evaluate progression of the disorder and the results of therapy.”

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