DE-MRI of left atrial wall scarring predicts a-fib ablation success
Three-dimensional delayed-enhancement MR imaging (DE-MRI) of the left atrial wall is a powerful tool to evaluate injury resulting from radiofrequency ablation for atrial fibrillation. In addition, injury on MRI seems to reflect tissue scarring, and the degree of scarring correlates with procedural outcomes, according to a study in the Oct. 7 issue of the Journal of the American College of Cardiology.
Atrial fibrillation (AF) is a growing clinical problem with enormous impact on both short-term quality of life and long-term survival. Radiofrequency (RF) ablation targeting the pulmonary veins’ ostia and antra has been proven to be effective in managing patients with AF, according to the study.
Researchers also acknowledged that DE-MRI is an established clinical method for characterizing tissue in a variety of cardiac disease processes, including after MI and injury due to myocarditis. However, the data are lacking regarding the use of this technique to determine AF ablation procedural success, particularly in humans.
With this background, investigators evaluated DE-MRI to detect and quantify left atrial wall injury after pulmonary vein antrum isolation (PVAI) in patients with AF. They used a 3D FLASH sequence, along with parallel imaging, on a 1.5T Avanto scanner (Siemens Medical Solutions), pre- and post-contrast administration (Multihance, Bracco Diagnostic).
Christopher J. McGann, MD, and colleagues at the University of Utah School of Medicine in Salt Lake City said that RF ablation to achieve PVAI is a promising approach to curing AF. Controlled lesion delivery and scar formation within the left atrium are indicators of procedural success, but the assessment of these factors is currently limited to invasive methods.
“Noninvasive evaluation of left atrium wall injury to assess permanent tissue injury may be an important step in improving procedural success,” McGann said.
The investigators preformed imaging of the left atrium wall with a cardiac 3D DE-MRI sequence before and three months after ablation in 46 patients undergoing PVAI for AF. They said their 3D respiratory-navigated MRI sequence using parallel imaging resulted in excellent spatial resolution with imaging times ranging from eight to 12 minutes.
McGann and colleagues found that RF ablation “resulted in hyper-enhancement of the left atrium wall in all patients post-PVAI” and the MRI data “seems to represent tissue scarring.” New methods of reconstructing the left atrium in 3D allowed quantification of left atrium scarring using automated methods.
They also found that arrhythmia recurrence at three months correlated with the degree of wall enhancement with greater than 13 percent injury predicting freedom from AF. In patients who responded to ablation, the average left atrium wall injury was 19 percent, whereas in those who did not respond, the average left atrium wall injury was 12 percent.
After controlling for age, gender, ablation time and type of AF, researchers found that large scar areas strongly predicted the absence of recurrences.
In acknowledging the study’s limitations, the researchers said that although the outcomes data in the study were statistically significant, the sample size was relatively small. In addition, 3D MRI in the study was performed on a 1.5T scanner. They wrote that “significant improvements in left atrium wall imaging with greater spatial resolution, signal-to-noise ratio and contrast-to-noise ratio is expected at higher magnetic field (3T).”
Senior author Nassir F. Marrouche, MD, told Cardiovascular Business News that this study paved the way for MRI to be a routine part of managing the AF ablation patient.
“We track the success and safety of the procedure with MRI. We look for patency of lesions, and collateral damage that can develop overtime. I do recommend an MRI scan acutely after every AF ablation at follow-up,” he said.
Future role of MRI
A commentary by Halperin and Nazarian in the same issue of JACC suggested that a future application would be to import DE-MRI scar images into electroanatomical systems, which has the “potential to reduce mapping time and to improve the efficacy of initial and follow-up ablation procedures.”
They also said that the technique may become available for real-time MRI guidance of electrophysiology procedures, enabling real-time visualization of myocardial scar for guidance of mapping and real-time feedback for titration of radiofrequency lesion application.
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| Overlay Images of Left Atrium Wall Injury – Panels 1A to 1D are four examples of left atrium slices from 3D DE-MRI that show close correlation of left atrium injury as determined by automated methods using a 3-SD cutoff value (blue transparency) overlaying MRI. Right panels show 3D overlay of full data set (3D PA [posterior-anterior] and RL [right-left]). Left atrium injury mask (blue) determined by automated methods should match and overlay hyperenhanced areas (white) of true injury on DE-MRI. Although the left pulmonary veins are white on MRI, this enhancement is attributable to navigator interference, not injured tissue, as the navigator is positioned over the right hemidiaphragm. The pulmonary veins are shown here only to help with anatomical orientation and are excluded from raw data used to produce injury mask by automated methods. Source: Nassir F. Marrouche, MD |
Researchers also acknowledged that DE-MRI is an established clinical method for characterizing tissue in a variety of cardiac disease processes, including after MI and injury due to myocarditis. However, the data are lacking regarding the use of this technique to determine AF ablation procedural success, particularly in humans.
With this background, investigators evaluated DE-MRI to detect and quantify left atrial wall injury after pulmonary vein antrum isolation (PVAI) in patients with AF. They used a 3D FLASH sequence, along with parallel imaging, on a 1.5T Avanto scanner (Siemens Medical Solutions), pre- and post-contrast administration (Multihance, Bracco Diagnostic).
Christopher J. McGann, MD, and colleagues at the University of Utah School of Medicine in Salt Lake City said that RF ablation to achieve PVAI is a promising approach to curing AF. Controlled lesion delivery and scar formation within the left atrium are indicators of procedural success, but the assessment of these factors is currently limited to invasive methods.
“Noninvasive evaluation of left atrium wall injury to assess permanent tissue injury may be an important step in improving procedural success,” McGann said.
The investigators preformed imaging of the left atrium wall with a cardiac 3D DE-MRI sequence before and three months after ablation in 46 patients undergoing PVAI for AF. They said their 3D respiratory-navigated MRI sequence using parallel imaging resulted in excellent spatial resolution with imaging times ranging from eight to 12 minutes.
McGann and colleagues found that RF ablation “resulted in hyper-enhancement of the left atrium wall in all patients post-PVAI” and the MRI data “seems to represent tissue scarring.” New methods of reconstructing the left atrium in 3D allowed quantification of left atrium scarring using automated methods.
They also found that arrhythmia recurrence at three months correlated with the degree of wall enhancement with greater than 13 percent injury predicting freedom from AF. In patients who responded to ablation, the average left atrium wall injury was 19 percent, whereas in those who did not respond, the average left atrium wall injury was 12 percent.
After controlling for age, gender, ablation time and type of AF, researchers found that large scar areas strongly predicted the absence of recurrences.
In acknowledging the study’s limitations, the researchers said that although the outcomes data in the study were statistically significant, the sample size was relatively small. In addition, 3D MRI in the study was performed on a 1.5T scanner. They wrote that “significant improvements in left atrium wall imaging with greater spatial resolution, signal-to-noise ratio and contrast-to-noise ratio is expected at higher magnetic field (3T).”
Senior author Nassir F. Marrouche, MD, told Cardiovascular Business News that this study paved the way for MRI to be a routine part of managing the AF ablation patient.
“We track the success and safety of the procedure with MRI. We look for patency of lesions, and collateral damage that can develop overtime. I do recommend an MRI scan acutely after every AF ablation at follow-up,” he said.
Future role of MRI
A commentary by Halperin and Nazarian in the same issue of JACC suggested that a future application would be to import DE-MRI scar images into electroanatomical systems, which has the “potential to reduce mapping time and to improve the efficacy of initial and follow-up ablation procedures.”
They also said that the technique may become available for real-time MRI guidance of electrophysiology procedures, enabling real-time visualization of myocardial scar for guidance of mapping and real-time feedback for titration of radiofrequency lesion application.