3D electrocardiographic imaging boosts EP ablation accuracy
Yoram Rudy, PhD, and colleagues at Washington University in St. Louis have successfully used 3D electrocardiographic imaging (ECGI), for the first time to ablate an atrioventricular accessory pathway in a patient with Ebstein anomaly, according to a study in the June issue of Heart Rhythm Journal.

ECGI can noninvasively image cardiac activity on the epicardial surface of the heart from body-surface potentials measured with 250 electrodes, overlaid with anatomic data from an ECG-gated thoracic CT scan. ECGI can complement the routine ECG in certain cases by providing more detailed and quantitative information about regional ventricular activation.

Right anterior oblique (RAO) and left lateral views of ECGI imaged activation (isochrone) map before (A and B) and after (C and D) ablation. Pre-ablation: Earliest activation occurs at a right posterolateral area around the tricuspid valve annulus (A, red region; earliest site marked by asterisk). Post-ablation: Late activation occurs at the pre-ablation region of earliest activation (C, blue, ‘+’). Earliest activation of RV (C, yellow *) is delayed compared to LV activation. Source: Yoram Rudy, Washington University in St. Louis, Mo., and the Heart Rhythm Journal.
ECGI data are processed on a standard laptop and do not require a special computing environment, Rudy told Cardiovascular Business News. “Most parts of ECGI reconstruction are automated, but some still require operator manual intervention. Greater automation can be achieved with farther development,” he said, adding that technologists require special training to reconstruct the images.

Rudy and colleagues have used ECGI so far for the following purposes:
  • To image electrophysiologic responses to pacing in heart failure patients undergoing cardiac resynchronization therapy (pacing sites were localized with an accuracy better than 10 mm);
  • To guide catheter ablation of focal ventricular and atrial tachycardias;
  • To image typical atrial flutter prior to catheter ablation and atypical atrial flutter prior to a surgical Cox-Maze procedure, and
  • To help guide catheter ablation in a pediatric patient with a univentricular heart and Wolff-Parkinson-White syndrome.
In current study, researchers used ECGI on a 16-year-old girl referred for palpitations. An echocardiography revealed mild inferior displacement of the septal leaflet of the tricuspid valve consistent with mild Ebstein anomaly and mild tricuspid regurgitation with normal ventricular systolic function.

The abnormal development of the tricuspid valve in Ebstein often is associated with several conduction abnormalities, including delayed intra-atrial conduction, right bundle branch block and ventricular pre-excitation.

The 250 electrodes were arranged in strips covering the front and back of the patient’s torso. Skin markers were adhered to her torso to mark the layout of the strips for future application at the same locations. The use of skin markers allows researchers to avoid a repeat CT scan to coregister post-ablation ECGI.

Researchers also performed invasive three-dimensional electroanatomical mapping (CARTO, Biosense Webster) to localize the accessory pathway. The ECGI prediction agreed with electroanatomical mapping. 

The earliest activation was found to occur at the posterolateral area of the annular plane, approximately at the 7 o’clock position around the tricuspid annulus (see images). Researchers found no evidence of a second accessory pathway or atrioventricular nodal reentry.

They used a cryoablation system because of the close proximity of the ablation target to the right coronary artery. They also applied four more lesions within the vicinity for insurance.

Although ECGI in conjunction with invasive electroanatomical mapping guided the ablation procedure, the follow-up ECGI images showed for the first time how the activation sequence changes after ablation of an accessory pathway in a heart with Ebstein anomaly, the authors wrote.

Researchers noted that several ECG-based algorithms with high sensitivity and specificity have diminished accuracy in children and patients with congenital heart disease. In the present case, ECGI proved to be more accurate than 12-lead ECG, they said.

In a commentary about ECGI in the August 2007 HRJ, David J. Wilber, MD, from Loyola University Medical Center, Maywood, Ill., said that ECGI could potentially supplant much of the information currently acquired via point-by-point mapping or intracavitary noncontact arrays.

“The capacity for repeated imaging to identify focal sources of activation, macroreentrant circuits and regional changes in activation frequency and gaps in ablation lines would be of considerable utility,” he wrote.

Regarding cost-effectiveness, the use of ECGI will add the cost of a thoracic CT scan and a “modest” operational cost to the ECGI procedure, Rudy said. “However, using ECGI will likely shorten significantly the very expensive EP procedure—and even replace it in certain cases,” resulting in less radiation exposure from fluoroscopy.

Currently, the tool is being used for research. But two of Rudy’s former doctoral students have formed CardioInsight Technologies in Cleveland to develop and commercialize ECGI for routine clinical use, according to Rudy.