Characterization of radiofrequency ablation lesions with gadolinium-enhanced cardiovascular magnetic resonance imaging

Abstract

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.

Figures

Figure 1

Gadolinium enhancement of a radiofrequency ablation lesion. The time-course (1 to 600 min) after injection of 0.225 mmol/kg gadolinium demonstrates four characteristic phases of enhancement: (A) Schematic of magnetic resonance (MR) images (30-W radiofrequency [RF] and 40-W RF = 30- and 40-W RF ablation lesions; Myo = right ventricular myocardial wall; EP = epicardial side; EN = endocardial side; RV-C = right ventricular cavity). (B) Phase 1 with a contrast void. (C and D) Phase 2 displaying an increasing peripheral enhancement (white arrows). (E) Phase 3 showing “very” delayed enhancement with high signal intensity throughout the ablation lesion. (F) Phase 4 displaying loss of enhancement with decreasing signal intensity and lesion size. (G) Corresponding pathological specimen.

Figure 2

Contrast-to-noise-ratio during the four phases of gadolinium-enhanced imaging between the radiofrequency lesion and the adjacent myocardium (A). Signal-to-noise ratio of radiofrequency lesions during the four phases of gadolinium enhancement in lesion center, lesion periphery, and adjacent myocardium (B).

Figure 3

Correlation of radiofrequency lesion size and peripheral enhancement. Shown is the lesion size assessed in the pathological specimen compared with the lesion size assessed by magnetic resonance imaging (MRI) during the Phase 1 of contrast void (A), Phase 2 of peripheral enhancement (B), and Phase 3 of “very” delayed enhancement (C). Increasing thickness of peripheral enhancement over time observed as a rim of high signal intensity surrounding a center of low signal after the injection of 0.225 mmol/kg of gadolinium (D).

Figure 4

Evaluation of discontinuous ablation line. Gap (dotted arrow) observed in ablation line between two ablation lesions (solid arrows). Pathological specimen after chloraldehyde preparation (left panel) and with gadolinium-enhanced magnetic resonance imaging (right panel).

Figure 5

Radiofrequency ablation lesion. Masson’s trichrome stain. (A) AM = adjacent myocardium; CAN = coagulation necrosis; CBN = contraction band necrosis. (B) Blue center core with severe coagulation necrosis, necrotic cavity, and complete loss of cellular structure. (C) Light purple periphery demonstrating contraction band necrosis with erythrocytes and cell debris in vasculature. (D) Adjacent viable myocardium. Calibration bars are presented in millimeters (mm).