"Until now, there has not been an accurate, non-invasive way to assess LA scar formation," said lead author Dr Nassir F Marrouche, assistant professor of internal medicine in the University of Utah School of Medicine and director of its Atrial-Fibrillation Program. "We have developed a novel MRI-based method to detect and measure the extent of LA wall scarring and, potentially, predict the success of RF ablation in patients with atrial fibrillation."
In this study, Marrouche and his University of Utah colleagues developed a technique for using a non-invasive method called delayed-enhancement cardiovascular MRI (DE-CMRI) to create 3D images of the left atrium both before and after RF ablation in patients with atrial fibrillation. They processed and analysed these images using custom software tools and then used computer algorithms to calculate the extent of LA wall injury.
Marrouche and his colleagues found that all patients who underwent RF ablation showed evidence of left atrium wall injury on MRI three months after the procedure. The pattern of tissue injury correlated with the areas where the radiofrequency energy was applied during RF ablation, and thus, was presumed to reflect tissue scarring. Marrouche and his colleagues also found patients with a higher percentage of LA wall injury were more likely to be free of arrhythmia than patients with lower percentages, suggesting the degree of scarring is linked to the likelihood of success in the RF ablation procedure.
"DE-CMRI is an established method for evaluating the tissues of the heart after a heart attack," said Marrouche. "But performing DE-CMRI to detect left atrium wall injury is challenging because the wall of the left atrium is so thin."
The 3D technique used by Marrouche and his colleagues achieves a much greater imaging resolution than the two-dimensional technique typically used to evaluate the extent of tissue damage after a heart attack or in other cardiac disease processes. Marrouche and his colleagues also developed methods of processing the MRI images in order to visualise the entire volume of left atrium wall injury in 3D.
The novel visualisation technique and analysis developed by Marrouche and his colleagues potentially could help doctors improve planning for RF ablation procedures by making it easier to identify the heart muscle cells that need to be destroyed. Improved localisation and isolation of these heart muscle cells would likely lead to a reduction in the recurrence rate of AF.
"The benefit of 3D MRI is that it visualises the entire LA wall," said Marrouche. "And, it is safe and non-invasive, so it can be repeated without significant risk to the patient."