Tissue characterization of acute lesions during cardiac magnetic resonance-guided ablation of cavo-tricuspid isthmus-dependent atrial flutter: a feasibility study

AIMS

To characterize acute lesions during cardiac magnetic resonance (CMR)-guided radiofrequency (RF) ablation of cavo-tricuspid isthmus (CTI)-dependent atrial flutter by combining T2-weighted imaging (T2WI), T1 mapping, first-pass perfusion, and late gadolinium enhancement (LGE) imaging. CMR-guided catheter ablation offers a unique opportunity to investigate acute ablation lesions. Until present, studies only used T2WI and LGE CMR to assess acute lesions.

METHODS AND RESULTS

Fifteen patients with CTI-dependent atrial flutter scheduled for CMR-guided RF ablation were prospectively enrolled. Directly after achieving bidirectional block of the CTI line, CMR imaging was performed using: T2WI (n = 15), T1 mapping (n = 10), first-pass perfusion (n = 12), and LGE (n = 12) imaging. In case of acute reconnection, additional RF ablation was performed. In all patients, T2WI demonstrated oedema in the ablation region. Right atrial T1 mapping was feasible and could be analysed with a high inter-observer agreement (r = 0.931, ICC 0.921). The increase in T1 values post-ablation was significantly lower in regions showing acute reconnection compared with regions without reconnection [37 ± 90 ms vs. 115 ± 69 ms (P = 0.014), and 3.9 ± 9.0% vs. 11.1 ± 6.8% (P = 0.022)]. Perfusion defects were present in 12/12 patients. The LGE images demonstrated hyper-enhancement with a central area of hypo-enhancement in 12/12 patients.

CONCLUSION

Tissue characterization of acute lesions during CMR-guided CTI-dependent atrial flutter ablation demonstrates oedema, perfusion defects, and necrosis with a core of microvascular damage. Right atrial T1 mapping is feasible, and may identify regions of acute reconnection that require additional RF ablation.

Fetal MRI of the heart and brain in congenital heart disease

Antenatal assessment of congenital heart disease and associated anomalies by ultrasound has improved perinatal care. Fetal cardiovascular MRI and fetal brain MRI are rapidly evolving for fetal diagnostic testing of congenital heart disease. We give an overview on the use of fetal cardiovascular MRI and fetal brain MRI in congenital heart disease, focusing on the current applications and diagnostic yield of structural and functional imaging during pregnancy. Fetal cardiovascular MRI in congenital heart disease is a promising supplementary imaging method to echocardiography for the diagnosis of antenatal congenital heart disease in weeks 30-40 of pregnancy. Concomitant fetal brain MRI is superior to brain ultrasound to show the complex relationship between fetal haemodynamics in congenital heart disease and brain development.

The use of novel 3D dark-blood late gadolinium enhancement MRI to determine the optimal threshold for atrial scar after pulmonary vein isolation ablation

Background

Dark-blood late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) is proved to be superior to bright-blood LGE MRI in localising subtle subendocardial scar in the ventricles, because of improved contrast between myocardial scar and blood. However, dark-blood LGE MRI has not yet been applied to identify atrial scar in the left atrium (LA) and therefore its threshold to determine scar is unknown.

Purpose

To determine the optimal intensity threshold for 3D dark-blood LGE MRI for atrial ablation scar after pulmonary vein isolation (PVI)

Methods

Twelve re-do PVI patients with symptomatic atrial fibrillation (AF) who underwent pre-procedural 3D dark-blood LGE MRI were included. The image intensity ratio (IIR = myocardial intensity normalized to the blood pool) from the LGE MRI were calculated using ADAS-AF. High-density bipolar voltages (BiV) maps were recorded during sinus rhythm prior to ablation. All BiV locations ≤5 mm from the ADAS LA anatomy were compared with the corresponding IIR, using custom-made software in MATLAB. To achieve an equal ratio between scar (BiV ≤0.15 mV) and non-scar (BiV >0.15 mV) for each patient, non-scar pairs were randomly resampled to the same number as scar pairs. This was repeated 10 times and for every random selection, receiver operating characteristics (ROC) analysis was performed to determine the optimal IIR threshold (provided by the Youden's index) for scar defined as BiV <0.15 mV (Figure 1). All IIR thresholds and areas under the curve were averaged to determine the overall performance and optimal IIR threshold.

Results

Of the 12 included patients, 8 had prior cryo PVI, 2 radiofrequency PVI, and 2 surgical/hybrid AF ablation. ROC curve analysis estimated the average optimal threshold for predicting BiV <0.15 mV to be an IIR of 1.106, with a mean area under the curve (AUC) of 0.73 (Figure 1). Figure 2 shows two examples of the IIR map (A), BiV map (B), and the correspondence map (C) providing information on spatial agreement between IIR and BiV. This individual qualitative assessment provides insight into the spatial variation between techniques and may facilitate future studies on the pathophysiological understanding of atrial ablation scarring.

Conclusion

This is the first study to use the novel 3D dark-blood whole heart LGE MRI to evaluate LA ablation scar after PVI. Based on the ROC analyses, an IIR of 1.106 is the optimal threshold for atrial ablation scar, defined as high density bipolar voltage <0.15 mV.

Funding Acknowledgement

Type of funding sources: None.

Direct pre- and post-ablation cardiac magnetic resonance imaging of tissue characteristics in patients with typical atrial flutter

Funding Acknowledgements

Type of funding sources: None.

Background

Real-time cardiac magnetic resonance (CMR) imaging as guidance in electrophysiology (EP) procedures enables a detailed overview of the anatomy of the heart and surrounding structures, active and passive catheter tracking, and real-time visualisation of ablation lesions throughout the ablation procedure, without using fluoroscopy.

Purpose

To evaluate ablation induced changes in tissue characteristics of the cavotricuspid isthmus (CTI), directly following typical atrial flutter ablation in an interventional cardiac magnetic resonance (iCMR) suite.

Methods

Nine patients with symptomatic typical atrial flutter were referred for CTI ablation in an iCMR suite. Procedures were performed using a 1.5T MRI scanner. Pre-ablation imaging included T2-weighted edema imaging in the right anterior oblique (RAO) and transversal view. During the ablation procedure, CMR imaging facilitated active tracking and real-time navigation of both diagnostic and ablation catheters, as well as visualisation of the ablated tissue. Post-ablation imaging to evaluate the target tissue again included T2-weighted edema imaging as well as dark-blood late gadolinium enhancement (LGE) imaging. Data regarding post-ablation imaging findings, ablation outcome, and complications were collected for all patients. All patients provided written informed consent.

Results

In eight of the nine patients, T2-weighted imaging was successfully performed pre- and post-ablation, which identified myocardial edema at the CTI ablation line in all patients (Figure 1A-B). Due to time restraints, post-ablation LGE imaging was performed in five patients, which showed pathological signal intensity at the level of the CTI in all five patients (Figure 1C). Bidirectional block of the CTI was confirmed by differential pacing in eight patients. No complications occurred during or immediately after the procedures. In one patient, the registration of intracardiac electrograms was not possible due to technical problems and the patient was transferred to a conventional EP lab to complete the ablation following our predefined bailout procedure.

Conclusion

Real-time CMR guided CTI ablation in patients with typical atrial flutter is safe and successful. CMR enables accurate visualisation of the CTI line and provides immediate post-ablation evaluation of tissue characteristics at the ablation target location.

Figure 1. T2-weighted edema cardiac magnetic resonance (CMR) imaging in the right anterior oblique (RAO) view acquired pre- (A) and post-ablation (B) during interventional CMR ablation therapy. Late gadolinium enhancement (LGE) CMR in the RAO view post-ablation (C) of the same patient. The blue arrowheads indicate the cavotricuspid isthmus (CTI) line. High signal intensity at the level of CTI is observed post-ablation on both T2-weighted (indicating edema) and LGE (indicating cell membrane rupture) images.

First clinical experience with cardiac magnetic resonance guided typical atrial flutter ablation with the integration of active catheter tracking and electro-anatomical mapping

Funding Acknowledgements

Type of funding sources: None.

Background

In our university hospital, we previously implemented cardiac magnetic resonance (CMR) guided typical atrial flutter ablation in a pre-existing MRI suite which was transformed into an interventional cardiac MRI (iCMR) suite.

Purpose

To describe our first clinical experience with integration of active catheter tracking and dedicated electro-anatomical mapping (EAM) system for the treatment of typical atrial flutter in a transformed pre-existing MRI suite.

Methods

Between February 2021 and December 2021, all consecutive patients planned for CMR guided typical atrial flutter ablation were included in this analysis. The procedure was performed under general anaesthesia. Feasibility and safety of active catheter tracking and the integration with a dedicated EAM was evaluated. All patients provided written informed consent.

Results

In total, nine patients underwent CMR guided atrial flutter ablation. Procedural characteristics are presented in Table 1. In all patients, both active catheter tracking and the integration with EAM were performed successfully. Bidirectional cavo-tricuspid isthmus block was achieved in eight out of nine patients and confirmed by differential pacing using intracardiac electrograms and EAM. In one of these eight patients, the registration of intracardiac electrograms was not possible due to technical problems and the patient was transferred to a conventional electrophysiology lab to complete the ablation following our predefined bailout procedure. Seven out of nine patients were in sinus rhythm at the start of the procedure, one in nodal rhythm with atrial bigeminy, one patient required electrical cardioversion for atrial fibrillation prior to the procedure. No periprocedural complications occurred.

Conclusion

CMR guided typical atrial flutter ablation in a transformed pre-existing MRI suite using active catheter tracking and a dedicated EAM system is feasible and safe based on this small population. It allows for detailed visualisation of catheters and individual patients anatomy. Further studies in larger patient populations are required to evaluate whether iCMR is cost effective and can improve clinical outcome of typical atrial flutter ablation and other arrhythmias.

Development and validation of a fully automatic algorithm to align 3D MRI and electro-anatomical mapping anatomies of the left atrium

Funding Acknowledgements

Type of funding sources: None.

Background

The role of pre-procedural cardiac imaging in the guidance and planning of ablation procedures is becoming increasingly important. Emerging non-invasive techniques such as late gadolinium enhancement magnetic resonance imaging (LGE MRI) and electrocardiographic imaging (ECGi) can potentially help to locate ablation targets prior to the ablation procedure. To be able to integrate LGE MRI and ECGi information into targeted ablation procedures, a reliable alignment between cardiac imaging and electro-anatomical mapping (EAM) is required.

Purpose

To develop and evaluate a fully automatic technique to align pre-procedural MRI anatomies with EAM anatomies of the left atrium (LA).

Methods

Twenty-one patients scheduled for a (re-do) pulmonary vein (PV) isolation with a 3D pre-procedural LGE MRI were enrolled in this study. LA anatomy was segmented from the MRI dataset using ADAS-AF. During the ablation procedure LA anatomy was recorded with an HD-grid (Ensite) or Pentaray catheter (CARTO). The MRI segmentation and EAM were performed by different cardiologists blinded for each other’s results. Anatomies of both MRI and EAM were aligned using an iterative closest point-to-plane algorithm in custom-made software in Matlab 2021a. With this algorithm, the distance between MRI anatomy voxels (=points) and the surface of the EAM anatomy (=plane) is minimized by translating and rotating the MRI anatomy until the total residual distance is minimized. The result of the alignment is quantified by calculating the Euclidian distance between the aligned anatomies after excluding PVs and the mitral anulus.

Results

The algorithm was successfully applied in 18/21 patients (n=11 CARTO, n=7 Ensite). In the remaining 3 patients, the algorithm could not align the anatomies because of a large difference in LA volume or PV anatomy between the two techniques. In the analysed patients, the average distance between anatomies was 2.7±0.77mm. The top of Figure 1 shows the alignment of the anatomies with the smallest (patient A) and the largest (patient B) residual distances as well as the distances between these anatomies for both patients (right) with purple ≤2.5mm and red ≥5.0mm. The distributions of distances (bottom left) show that, after alignment most of the MRI anatomy is closer than 5mm from the EAM anatomy in every patient. On average, 87.6±10.4% of the atrial surfaces showed distances below 5.0mm between the two anatomies and 55.1±13.2% of the surfaces was within 2.5mm from each other. Results did not differ between Ensite and CARTO anatomies.

Conclusion

LA anatomy obtained from 3D LGE MRI can automatically and reliably be aligned with LA anatomy recorded during an ablation procedure with an EAM system using an iterative closest point-to-plane algorithm.