Optimization of late gadolinium enhancement cardiovascular magnetic resonance imaging of post-ablation atrial scar: a cross-over study

Abstract

Background: Cardiovascular magnetic resonance (CMR) imaging may be used to visualize post-ablation atrial scar (PAAS), and three-dimensional late gadolinium enhancement (3D LGE) is the most widely employed technique for imaging of chronic scar. Detection of PAAS provides a unique non-invasive insight into the effects of the ablation and may help guide further ablation procedures. However, there is evidence that PAAS is often not detected by CMR, implying a significant sensitivity problem, and imaging parameters vary between leading centres. Therefore, there is a need to establish the optimal imaging parameters to detect PAAS.

Methods: Forty subjects undergoing their first pulmonary vein isolation procedure for AF had detailed CMR assessment of atrial scar: one scan pre-ablation, and two scans post-ablation at 3 months (separated by 48 h). Each scan session included ECG- and respiratory-navigated 3D LGE acquisition at 10, 20 and 30 min post injection of a gadolinium-based contrast agent (GBCA). The first post-procedural scan was performed on a 1.5 T scanner with standard acquisition parameters, including double dose (0.2 mmol/kg) Gadovist and 4 mm slice thickness. Ten patients subsequently underwent identical scan as controls, and the other 30 underwent imaging with a reduced, single, dose GBCA (n = 10), half slice thickness (n = 10) or on a 3 T scanner (n = 10). Apparent signal-to-noise (aSNR), contrast-to-noise (aCNR) and imaging quality (Likert Scale, 3 independent observers) were assessed. PAAS location and area (%PAAS scar) were assessed following manual segmentation. Atrial shells with standardised %PAAS at each timepoint were then compared to ablation lesion locations to assess quality of scar delineation.

Results: A total of 271 3D acquisitions (out of maximum 280, 96.7%) were acquired. Likert scale of imaging quality had high interobserver and intraobserver intraclass correlation coefficients (0.89 and 0.96 respectively), and showed lower overall imaging quality on 3 T and at half-slice thickness. aCNR, and quality of scar delineation increased significantly with time. aCNR was higher with reduced, single, dose of GBCA (p = 0.005).

Conclusion: 3D LGE CMR atrial scar imaging, as assessed qualitatively and quantitatively, improves with time from GBCA administration, with some indices continuing to improve from 20 to 30 min. Imaging should be performed at least 20 min post-GBCA injection, and a single dose of contrast should be considered.

Trial registration: Trial registry- United Kingdom National Research Ethics Service 08/H0802/68 - 30th September 2008.

Keywords: Atrial fibrillation; Atrium; Cardiovascular magnetic resonance imaging; Catheter ablation; Late gadolinium enhancement; Optimization.

Conflict of interest statement

Authors’ information

No third parties were involved in the authorship of review of the manuscript.

Ethics approval and consent to participate

Forty subjects provided written and informed consent and the study was approved by the National Research Ethics Service (South London Research Ethics Committee reference 08/H0802/68)- 30th September 2008.

Consent for publication

Patient information sheet and consent form included provision for consent for publication (08/H0802/68). All data presented in this article is non-identifiable.

Competing interests

The authors declare that they have no competing interests.

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Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures

Fig. 1

Flowchart demonstrating subject allocation and number of scan acquisitions achieved

Fig. 2

Typical imaging results with identical CMR scan protocol for scan 1 and 2. Note clearly enhanced regions in imaging performed at 30 min post gadolinium-based contrast agent administration, representing post-ablation atrial scar. Slight variations between scan sessions were common at 10 min, where contrast was changing most rapidly, but stabilised by 30 min

Fig. 3

Typical imaging with reduced, single, gadolinium dose for Scan 2

Fig. 4

Typical imaging with half slice thickness for Scan 2

Fig. 5

Typical CMR imaging with Scan 2 performed at 3 T

Fig. 6

Summary of Likert Scores for each set of imaging acquisition parameters See above for full details of imaging parameters. The blue, green and red columns indicate imaging performed at 10 min, 20 min and 30 min post GBCA injection respectively. P-values for two-way ANOVA

Fig. 7

Relationship of acquisition timing post GBCA administration and signal/contrast-to-noise ratios. (Top left) apparent blood pool signal-to-noise ratio (SNR), (top right) apparent scar SNR, (bottom left) apparent scar to blood pool contrast-to-noise ratio, and (bottom right) LA scar area as a percentage of left atrium, thresholded at 3.3 standard deviations above blood pool mean. Values presented are for standard acquisition parameters only (n = 49 at each time point). For each plot, 3 p-values are presented: the top is p-value for Friedman test, assessing overall impact of time, and the bottom two are the p-values for Wilcoxon matched-pairs signed rank test

Fig. 8

Impact of acquisition timing upon PAAS thresholding and quality of scar imaging. Charts (upper panels) show the change in threshold required for the acquisitions at 10 min and 30 min in order to achieve the same total %PAAS as that observed at 20 min at 3.3standard deviations (SD) above the blood pool (BP) mean (left- red line at 3.3) and BP image intensity ratio (IIR) 1.32 (right- red line at 1.32). Lower panels show the impact of changing time and threshold on scar location for a typical subject, with identical scar burden for all acquisitions. The true ablation lesion locations are shown in yellow on left, with thresholded scar in three subsequent panels to the right. Note clearest delineation of scar at 30 min. LUPV: left upper pulmonary vein (PV), RUPV: right upper PV, LLPV: left lower PV, RLPV: right lower PV, TSP: trans-septal puncture site

Fig. 9

Impact of scan parameters on apparent scar to blood pool contrast-to-noise ratio. Paired acquisitions at 10, 20 and 30 min post GBCA injection, for control subjects (top left), reduced, single, GBCA dose (top right), half slice thickness (bottom left) and 3 T scanner (bottom right). Scan 1 (standard acquisition, circle) and scan 2 (experimental acquisition, square) are linked for each subject. P-values are for two-way repeated measures ANOVA: at the bottom of each plot is the p-value for variance with time, and to the right is the p-value for variance with acquisition parameter. Unpaired acquisitions are shown as unlinked circle or square and were not included in statistical analyses