Intrinsic Contrast for Characterization of Acute Radiofrequency Ablation Lesions

Abstract

Cardiac arrhythmias reflect abnormal electric activity in the heart. Radiofrequency ablation (RFA) is used to treat different arrhythmias by thermally damaging tissue regions and eliminating irregular action potential propagation paths. To ensure a permanent electric block, RFA must create a continuous line of transmural lesions.1 Notwithstanding extensive efforts, the success rates of the RFA operations are still low, 2 likely because of the lack of tools to validate the lesion extent. Current ablation methods rely on suboptimal fluoroscopy and electrophysiology electroanatomic systems; fluoroscopy has poor soft tissue contrast, and even with electroanatomic systems locating and characterizing the ablation lesions are challenging. More importantly, it is difficult to predict which of the lesions that yield a conduction block in the acute setting will maintain a block in the chronic setting. Clinical Perspective on p 727MRI is a powerful tool to detect ablation lesions because of its high soft tissue contrast. Double inversion fast spin echo (DIR) sequence demonstrates intrinsic T 2 -weighted contrast and quickly detect lesions, but DIR images lack specificity and provide poor border visibility. 3,4 Late gadolinium enhancement (LGE) methods provide high contrast between healthy myocardium and the ablation lesions. 3,[5][6][7] However, acute lesion appearance on the LGE image varies with the time between the Gd-DTPA injection and image acquisition because of the wash-in/wash-out kinetics, 7 particularly in areas associated with microvascular obstruction. Shortly after Gd-DTPA injection, the lesion contains hypoenhanced regions in typical LGE acquisitions. Then Gd-DTPA starts to enter the lesion, and a bright rim becomes visible. As the bright rim expands toward the center of the lesion over the ensuing minutes, wash-out mechanisms also begin to diminish the contrast at the outer border of the lesion. The lesion severity can also affect the wash-in/wash-out kinetics. As a second consideration, a recent study reported that the scar size measured 3 months after ablation with LGE images is <50% of that measured acutely. 6 One of the possible reasons for this © 2014 American Heart Association, Inc. Original ArticleBackground-Both intrinsic contrast (T 1 and T 2 relaxation and the equilibrium magnetization) and contrast agent (gadolinium)-enhanced MRI are used to visualize and evaluate acute radiofrequency ablation lesions. However, current methods are imprecise in delineating lesion extent shortly after the ablation. Methods and Results-Fifteen lesions were created in the endocardium of 13 pigs. A multicontrast inversion recovery steady state free precession imaging method was used to delineate the acute ablation lesions, exploiting T 1 -weighted contrast. T 2 and M o * maps were also created from fast spin echo data in a subset of pigs (n=5) to help characterize the change in intrinsic contrast in the lesions. Gross pathology was used as reference for the lesion size comparison, and the lesion structures were confirm...

Irrigated Needle Ablation Creates Larger and More Transmural Ventricular Lesions Compared With Standard Unipolar Ablation in an Ovine Model

“…13 Finally, MRI characterization was only used in the needle ablation group, given the limited availability of MRI, prolonged scanning times (>120 hours), and the fact that previous studies have reported on MRI imaging after conventional ablation, we focused our imaging on the needle group. [19][20][21] The description of conventional ablation lesions on MRI has already been reported, and the sizing of these lesions from gross pathology measurements was shown to be similar and feasible. 21 …”

“…[19][20][21] The description of conventional ablation lesions on MRI has already been reported, and the sizing of these lesions from gross pathology measurements was shown to be similar and feasible. 21 …”

“…The ability of MRI to assess acute ablation lesions is consistent with prior reports using conventional ablation in humans and to a recent animal study. [19][20][21] In this study, we also performed ex vivo MRI on explanted hearts using a high field strength MRI system (9.4T). The rationale to add ex vivo MRI data was to provide structural information on ablation lesions with high spatial resolution and with minimal organ deformation.…”

Cardiac Electrophysiology Under MRI Guidance: an Emerging Technology

“…57 Celik et al performed a detailed study of the characterisation of acute RF lesions using native contrast, performing imaging of left ventricular lesions within 60 min of ablation in 13 pigs. 23 They concluded that it was the higher ferric iron concentration in lesion core that caused a shortening of T 1 -relaxation time, and that this was best exploited using an inversion recovery SSFP sequence. Implementation and clinical validation in humans remains to be established.…”

Impact of Contact Force Technology on Atrial Fibrillation Ablation: A Meta-Analysis

“…4,[7][8][9] Many advances have been introduced to enhance the quality of ablation applications in pulmonary vein isolation such as the use of irrigated and circular diagnostic catheters, 10 3-dimensional tracking systems, robotics, 11 testing with adenosine to reveal dormant conductions, 12 and cardiac magnetic resonance imaging to assess the quality of lesions. 13 Contact force (CF) is a fairly new technology that allows real-time contact feedback between the catheter tip and the targeted cardiac tissue. Theoretically, this approach improves the quality of the lesions and enhances safety outcomes.…”