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

Abstract

Background: Cardiovascular magnetic resonance (CMR) imaging has been used to visualise post-ablation atrial scar (PAAS), generally employing a three-dimensional (3D) late gadolinium enhancement (LGE) technique. However the reproducibility of PAAS imaging has not been determined. This cross-over study is the first to investigate the reproducibility of the technique, crucial for both future research design and clinical implementation.

Methods: Forty subjects undergoing first time ablation for atrial fibrillation (AF) had detailed CMR assessment of PAAS. Following baseline pre-ablation scan, two scans (separated by 48 h) were performed at three months post-ablation. Each scan session included 3D LGE acquisition at 10, 20 and 30 min post administration of gadolinium-based contrast agent (GBCA). Subjects were allocated at second scan post-ablation to identical imaging parameters ('Repro', n = 10), 3 T scanner ('3 T', n = 10), half-slice thickness ('Half-slice', n = 10) or half GBCA dose ('Half-gad', n = 10). PAAS was compared to baseline scar and then reproducibility was assessed for two measures of thresholded scar (% left atrial (LA) occupied by PAAS (%LA PAAS) and Pulmonary Vein Encirclement (PVE)), and then four measures of non-thresholded scar (point-by-point assessment of PAAS, four normalisation methods). Thresholded measures of PAAS were evaluated against procedural outcome (AF recurrence).

Results: A total of 271 3D acquisitions (out of maximum 280, 96.7%) were acquired. At 20 and 30 min, inter-scan reproducibility was good to excellent (coefficient of variation at 20 min and 30 min: %LA PAAS 0.41 and 0.20; PVE 0.13 and 0.04 respectively for 'Repro' group). Changes in imaging parameters, especially reduced GBCA dose, reduced inter-scan reproducibility, but for most measures remained good to excellent (ICC for %LA PAAS 0.454-0.825, PVE 0.618-0.809 at 30 min). For non-thresholded scar, highest reproducibility was observed using blood pool z-score normalisation technique: inter-scan ICC 0.759 (absolute agreement, 'Repro' group). There was no significant relationship between indices of PAAS and AF recurrence.

Conclusion: PAAS imaging is a reproducible finding. Imaging should be performed at least 20 min post-GBCA injection, and a blood pool z-score should be considered for normalisation of signal intensities. The clinical implications of these findings remain to be established in the absence of a simple correlation with arrhythmia outcome.

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

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

Conflict of interest statement

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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Figures

Fig. 1

Flowchart demonstrating subject allocation and number of scan acquisitions achieved

Fig. 2

Illustration of derivation of pulmonary vein encirclement (PVE) measurement. The left atrial shell is thresholded at 3.3 standard deviations above the blood pool mean, with scar shown in red and healthy atrial myocardium in blue. a antero-superior view and b postero-lateral view of left atrium. The computed route of the pulmonary vein (PV) encirclement is shown in yellow dashed line, whilst detected gaps in the ablation line are shown in white. For this acquisition, the PV encirclement (PVE) for the right sided veins was 98.5%, and for the left was 81.5%. (LAA: left atrial appendage, LSPV: left superior PV, LIPV: left inferior PV, RSPV: right superior PV, RIPV: right inferior PV)

Fig. 3

Examples of raw images and corresponding scar shells for a single subject. Scans 1 and 2 were performed using identical (standard) acquisition parameters, with acquisitions performed at 10 min, 20 min and 30 min post injection of gadolinium. Scan 2 was performed 2 days after Scan 1. Upper six panels show single representative slices of the 3D late gadolinium enhancement (LGE) dataset, at the level of the aortic root. The six panels below show corresponding scar shells, normalised according to blood pool z-score. Note the relatively poor reproducibility for acquisitions at 10 min, particularly Scan 1. The bottom two panels show the baseline scan, performed 20 min after gadolinium based contrast agent (GBCA) administration one month prior to ablation. Acq: acquisition. LSPV: left superior pulmonary vein, LIPV: left inferior pulmonary vein, RSPV: right superior pulmonary vein, RIPV: right inferior pulmonary vein, LAA: left atrial appendage, SD: standard deviation

Fig. 4

Bland-Altman plots demonstrating the reproducibility of the proportion of the LA shell occupied by post ablation atrial scar (PAAS), comparing scan acquisitions performed at the same time points post gadolinium administration. The top left chart shows the comparison for acquisitions performed with identical imaging parameters (‘Repro’). The other three charts show the reproducibility for those performed with differing imaging protocols, as previously detailed. Crosses show data points for comparison of acquisitions at 10 min post gadolinium (C1,4), open circles for comparison of acquisitions at 20 min post gadolinium (C2,5), and closed circles for comparison of acquisitions at 30 min post gadolinium (C3,6). Red lines show mean bias ±95% confidence interval

Fig. 5

Impact of time from GBCA administration upon pulmonary vein encirclement (PVE)

Fig. 6

Reproducibility of pulmonary vein encirclement (PVE) measurements. Bland-Altman plots demonstrate reproducibility of measurements performed at 20 min post GBCA (C2,5 (open squares)) and 30 min post GBCA (C3,6 (closed squares)). Red lines show mean bias ±95% confidence interval

Fig. 7

Relationship between percentage PVE and electrical reconnection. Electrical reconnection was assessed at repeat procedure in patients who had a sustained recurrence of arrhythmia (n = 11), and analysed as vein pairs (left and right, as indicated on charts). Closed circles indicate PVE at scan 1, open circles PVE at scan 2, and PVE scores are shown only for acquisitions at 20 min (Acq2 and Acq5) and 30 min (Acq3 and Acq6) post gadolinium