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CLINICAL RESEARCH: CARDIAC RHYTHM DISORDER

Characterization of Radiofrequency Ablation Lesions With Gadolinium-Enhanced Cardiovascular Magnetic Resonance Imaging

Division of Cardiology, Department of Radiology, Johns Hopkins School of Medicine, and the Division of Cardiology, University of Maryland, Baltimore, Maryland

Manuscript received November 16, 2004; revised manuscript received June 14, 2005, accepted July 26, 2005.

^_* Reprint requests and correspondence: Dr. Timm Dickfeld, University of Maryland, School of Medicine, Division of Cardiology, 22 South Greene Street, Room N3W77, Baltimore, Maryland 21201. (Email: tdickfel{at}medicine.umaryland.edu).

OBJECTIVES: This study was designed to evaluate the characteristics of gadolinium-enhanced imaging of radiofrequency ablations.

BACKGROUND: Gadolinium-enhanced magnetic resonance imaging (MRI) has been used successfully to evaluate tissue necrosis after myocardial infarction. In electrophysiology, radiofrequency energy is used to create a targeted myocardial necrosis for the treatment of various arrhythmias.

METHODS: Using a power-controlled, cooled-tip 7-F catheter system, radiofrequency lesions (10 to 40 W for 30 s) were created on the epicardium of the right ventricle in eight mongrel dogs. After injection of 0.225 mmol/kg gadolinium, T1-weighted fast gradient echo images were obtained during a follow-up of 10 h using an intrathoracic high-resolution coil. Radiofrequency ablations were analyzed on the MR images and compared with gross anatomy and histopathology.

RESULTS: Four distinct phases of signal enhancement were observed. After gadolinium injection, radiofrequency lesions were delineated clearly as contrast-free areas of low signal intensity (contrast-to-noise ratio [CNR] = –21.1 ± 19.8). Signal enhancement in the lesion periphery started 4.0 ± 1.8 min after injection and progressively extended toward the lesion center at a rate of 0.02 mm/min. Full delayed enhancement was observed after 98 ± 21 min (CNR = +17.8 ± 9.0). During the follow-up period, CNR started to decrease, but the lesions were detectable for as long as 10 h of follow-up. During the first three phases of enhancement, MRI correlated well with the pathological findings (r = 0.88, r = 0.88, and r = 0.86 [p < 0.001], respectively).

CONCLUSIONS: Radiofrequency ablation can be evaluated accurately by using gadolinium-enhanced MRI, which may allow the noninvasive assessment of procedural success. The dissimilar wash-in and wash-out kinetics compared with myocardial infarction suggest a different pathophysiological process with complete loss of microvasculature.

Abbreviations and Acronyms   ANOVA = analysis of variance   CNR = contrast-to-noise ratio   GEE = generalized estimating equation   MRI = magnetic resonance imaging   RFA = radiofrequency ablation   SI = signal intensity   SNR = signal-to-noise ratio

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