Michael Cooklin

Acute pulmonary vein isolation is achieved by a combination of reversible and irreversible atrial injury after catheter ablation: evidence from magnetic resonance imaging.

Background— Pulmonary vein reconnection after pulmonary vein isolation is common and is usually associated with recurrences of atrial fibrillation. We used cardiac magnetic resonance imaging after radiofrequency ablation to investigate the hypothesis that acute pulmonary vein isolation results from a combination of irreversible and reversible atrial injury. Methods and Results— Delayed enhancement (DE; representing areas of acute tissue injury/necrosis) and T2-weighted (representing tissue water content, including edema) cardiac magnetic resonance scans were performed before, immediately after (acute), and later than 3 months (late) after pulmonary vein isolation in 25 patients with paroxysmal atrial fibrillation undergoing wide-area circumferential ablation. Images were analyzed as pairs of pulmonary veins to quantify the percentage of circumferential antral encirclement composed of DE, T2, and combined DE+T2 signal. Fourteen of 25 patients were atrial fibrillation free at 11-month follow-up (interquartile range, 8–16 months). These patients had higher DE (71±6.0%) and lower T2 signal (72±7.8%) encirclement on the acute scans compared with recurrences (DE, 55±9.1%; T2, 85±6.3%; P<0.05). Patients maintaining sinus rhythm had a lesser decline in DE between acute and chronic scans compared with recurrences (71±6.0% and 60±5.8% versus 55±9.1% and 34±7.3%, respectively). The percentage of encirclement by a combination of DE+T2 was almost similar in both groups on the acute scans (atrial fibrillation free, 89±5.4%; recurrences, 92±4.8%) but different on the chronic scans (60±5.7% versus 34±7.3%). Conclusions— The higher T2 signal on acute scans and greater decline in DE on chronic imaging in patients with recurrences suggest that they have more reversible tissue injury, providing a potential mechanism for pulmonary vein reconnection, resulting in arrhythmia recurrence.

3-D Visualization of Acute RF Ablation Lesions Using MRI for the Simultaneous Determination of the Patterns of Necrosis and Edema

Catheter ablation using RF energy is a common treatment for atrial arrhythmias. Although this treatment provides a potential cure, currently, there remains a high proportion of patients returning for repeat ablations. Electrophysiologists have little information to verify that a lesion has been created in the myocardium. Temporary electrical block can be created from edema, which will subside. MRI can visualize acute and chronic ablation lesions using delayed-enhancement techniques. However, the ablation patterns cannot be determined from 2-D images alone. Using the combination of T2-weighted and delayed-enhancement MRI, ablation lesions can be characterized in terms of necrosis and edema. A novel 3-D visualization technique is presented that projects the image intensity due the lesions onto a 3-D cardiac surface, allowing the complete, simultaneous visualization of the delayed-enhancement and T2 -weighted ablation patterns. Results show successful visualization of ablation patterns in 18 patients, and an application of this technique is presented in which electroanatomical mapping systems can be validated by overlaying the acquired ablation points onto the cardiac surfaces and assessing the correlation with the lesion maps.

A subject-specific technique for respiratory motion correction in image-guided cardiac catheterisation procedures

We describe a system for respiratory motion correction of MRI-derived roadmaps for use in X-ray guided cardiac catheterisation procedures. The technique uses a subject-specific affine motion model that is quickly constructed from a short pre-procedure MRI scan. We test a dynamic MRI sequence that acquires a small number of high resolution slices, rather than a single low resolution volume. Additionally, we use prior knowledge of the nature of cardiac respiratory motion by constraining the model to use only the dominant modes of motion. During the procedure the motion of the diaphragm is tracked in X-ray fluoroscopy images, allowing the roadmap to be updated using the motion model. X-ray image acquisition is cardiac gated. Validation is performed on four volunteer datasets and three patient datasets. The accuracy of the model in 3D was within 5mm in 97.6% of volunteer validations. For the patients, 2D accuracy was improved from 5 to 13mm before applying the model to 2-4mm afterwards. For the dynamic MRI sequence comparison, the highest errors were found when using the low resolution volume sequence with an unconstrained model.

Cardiac magnetic resonance and electroanatomical mapping of acute and chronic atrial ablation injury: a histological validation study

AIMS To provide a comprehensive histopathological validation of cardiac magnetic resonance (CMR) and endocardial voltage mapping of acute and chronic atrial ablation injury. METHODS AND RESULTS 16 pigs underwent pre-ablation T2-weighted (T2W) and late gadolinium enhancement (LGE) CMR and high-density voltage mapping of the right atrium (RA) and both were repeated after intercaval linear radiofrequency ablation. Eight pigs were sacrificed following the procedure for pathological examination. A further eight pigs were recovered for 8 weeks, before chronic CMR, repeat RA voltage mapping and pathological examination. Signal intensity (SI) thresholds from 0 to 15 SD above a reference SI were used to segment the RA in CMR images and segmentations compared with real lesion volumes. The SI thresholds that best approximated histological volumes were 2.3 SD for LGE post-ablation, 14.5 SD for T2W post-ablation and 3.3 SD for LGE chronically. T2-weighted chronically always underestimated lesion volume. Acute histology showed transmural injury with coagulative necrosis. Chronic histology showed transmural fibrous scar. The mean voltage at the centre of the ablation line was 3.3 mV pre-ablation, 0.6 mV immediately post-ablation, and 0.3 mV chronically. CONCLUSION This study presents the first histopathological validation of CMR and endocardial voltage mapping to define acute and chronic atrial ablation injury, including SI thresholds that best match histological lesion volumes. An understanding of these thresholds may allow a more informed assessment of the underlying atrial substrate immediately after ablation and before repeat catheter ablation for atrial arrhythmias.

Repeat Left Atrial Catheter Ablation: Cardiac Magnetic Resonance Prediction of Endocardial Voltage and Gaps in Ablation Lesion Sets

Background—Studies have reported an inverse relationship between late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR) signal intensity and left atrial (LA) endocardial voltage after LA ablation. However, there is controversy regarding the reproducibility of atrial LGE CMR and its ability to identify gaps in ablation lesions. Using systematic and objective techniques, this study examines the correlation between atrial CMR and endocardial voltage. Methods and Results—Twenty patients who had previous ablation for atrial fibrillation and represented with paroxysmal atrial fibrillation or atrial tachycardia underwent preablation LGE CMR. During the ablation procedure, high-density point-by-point Carto voltage maps were acquired. Three-dimensional CMR reconstructions were registered with the Carto anatomies to allow comparison of voltage and LGE signal intensity. Signal intensities around the left and right pulmonary vein antra and along the LA roof and mitral lines on the CMR-segmented LA shells were extracted to examine differences between electrically isolated and reconnected lesions. There were a total of 6767 data points across the 20 patients. Only 119 (1.8%) of the points were ⩽0.05 mV. There was only a weak inverse correlation between either unipolar (r=−0.18) or bipolar (r=−0.17) voltage and LGE CMR signal intensities with low voltage occurring across a large range of signal intensities. Signal intensities were not statistically different for electrically isolated and reconnected lesions. Conclusions—This study demonstrates that there is only a weak point-by-point relationship between LGE CMR and endocardial voltage in patients undergoing repeat LA ablation. Using an objective method of assessing gaps in ablation lesions, LGE CMR is unable to reliably predict sites of electrical conduction.

Myocardial tissue characterization by cardiac magnetic resonance imaging using T1 mapping predicts ventricular arrhythmia in ischemic and non-ischemic cardiomyopathy patients with implantable cardioverter-defibrillators

BACKGROUND Diffuse myocardial fibrosis may provide a substrate for the initiation and maintenance of ventricular arrhythmia. T1 mapping overcomes the limitations of the conventional delayed contrast-enhanced cardiac magnetic resonance (CE-CMR) imaging technique by allowing quantification of diffuse fibrosis. OBJECTIVE The purpose of this study was to assess whether myocardial tissue characterization using T1 mapping would predict ventricular arrhythmia in ischemic and non-ischemic cardiomyopathies. METHODS This was a prospective longitudinal study of consecutive patients receiving implantable cardioverter-defibrillators in a tertiary cardiac center. Participants underwent CMR myocardial tissue characterization using T1 mapping and conventional CE-CMR scar assessment before device implantation. The primary end point was an appropriate implantable cardioverter-defibrillator therapy or documented sustained ventricular arrhythmia. RESULTS One hundred thirty patients (71 ischemic and 59 non-ischemic) were included with a mean follow-up period of 430 ± 185 days (median 425 days; interquartile range 293 days). At follow-up, 23 patients (18%) experienced the primary end point. In multivariable-adjusted analyses, the following factors showed a significant association with the primary end point: secondary prevention (hazard ratio [HR] 1.70; 95% confidence interval [95% CI] 1.01-1.91), noncontrast T1(_native) for every 10-ms increment in value (HR 1.10; CI 1.04-1.16; 90-ms difference between the end point-positive and end point-negative groups), and Grayzone(_2sd-3sd) for every 1% left ventricular increment in value (HR 1.36; CI 1.15-1.61; 4% difference between the end point-positive and end point-negative groups). Other CE-CMR indices including Scar(_2sd), Scar(_FWHM), and Grayzone(_2sd-FWHM) were also significantly, even though less strongly, associated with the primary end point as compared with Grayzone(_2sd-3sd). CONCLUSION Quantitative myocardial tissue assessment using T1 mapping is an independent predictor of ventricular arrhythmia in both ischemic and non-ischemic cardiomyopathies.

Advanced image fusion to overlay coronary sinus anatomy with real-time fluoroscopy to facilitate left ventricular lead implantation in CRT.

Background: Failure rate for left ventricular (LV) lead implantation in cardiac resynchronization therapy (CRT) is up to 12%. The use of segmentation tools, advanced image registration software, and high‐fidelity images from computerized tomography (CT) and cardiac magnetic resonance (CMR) of the coronary sinus (CS) can guide LV lead implantation. We evaluated the feasibility of advanced image registration onto live fluoroscopic images to allow successful LV lead placement.

Trends, indications and outcomes of cardiac implantable device system extraction: a single UK centre experience over the last decade

Background:  The rising number of device implantation has seen a parallel in the rising numbers of lead extraction. Herein we have analysed our experience in cardiac device and lead extraction in a single tertiary centre over the last decade.

Real‐time x‐ray fluoroscopy‐based catheter detection and tracking for cardiac electrophysiology interventions

PURPOSE X-ray fluoroscopically guided cardiac electrophysiology (EP) procedures are commonly carried out to treat patients with arrhythmias. X-ray images have poor soft tissue contrast and, for this reason, overlay of a three-dimensional (3D) roadmap derived from preprocedural volumetric images can be used to add anatomical information. It is useful to know the position of the catheter electrodes relative to the cardiac anatomy, for example, to record ablation therapy locations during atrial fibrillation therapy. Also, the electrode positions of the coronary sinus (CS) catheter or lasso catheter can be used for road map motion correction. METHODS In this paper, the authors present a novel unified computational framework for image-based catheter detection and tracking without any user interaction. The proposed framework includes fast blob detection, shape-constrained searching and model-based detection. In addition, catheter tracking methods were designed based on the customized catheter models input from the detection method. Three real-time detection and tracking methods are derived from the computational framework to detect or track the three most common types of catheters in EP procedures: the ablation catheter, the CS catheter, and the lasso catheter. Since the proposed methods use the same blob detection method to extract key information from x-ray images, the ablation, CS, and lasso catheters can be detected and tracked simultaneously in real-time. RESULTS The catheter detection methods were tested on 105 different clinical fluoroscopy sequences taken from 31 clinical procedures. Two-dimensional (2D) detection errors of 0.50 ± 0.29, 0.92 ± 0.61, and 0.63 ± 0.45 mm as well as success rates of 99.4%, 97.2%, and 88.9% were achieved for the CS catheter, ablation catheter, and lasso catheter, respectively. With the tracking method, accuracies were increased to 0.45 ± 0.28, 0.64 ± 0.37, and 0.53 ± 0.38 mm and success rates increased to 100%, 99.2%, and 96.5% for the CS, ablation, and lasso catheters, respectively. Subjective clinical evaluation by three experienced electrophysiologists showed that the detection and tracking results were clinically acceptable. CONCLUSIONS The proposed detection and tracking methods are automatic and can detect and track CS, ablation, and lasso catheters simultaneously and in real-time. The accuracy of the proposed methods is sub-mm and the methods are robust toward low-dose x-ray fluoroscopic images, which are mainly used during EP procedures to maintain low radiation dose.

Laser lead extraction to facilitate cardiac implantable electronic device upgrade and revision in the presence of central venous obstruction

Aims The number of procedures involving upgrade or revision of cardiac implantable electronic devices (CIEDs) is increasing and the risks of adding additional leads are significant. Central venous occlusion in patients with pre-existing devices is often asymptomatic and optimal management of such patients in need of device revision/upgrade is not clear. We sought to assess our use of laser lead extraction in overcoming venous obstruction. Methods and results Patients in need of device upgrade/revision underwent pre-procedure venography to assess venous patency. In patients with venous occlusion or stenosis severe enough to preclude passage of a hydrophilic guide wire, laser lead extraction with retention of the outer sheath in the vasculature was performed with the aim of maintaining a patent channel through which new leads could be implanted. Data were recorded on a dedicated database and patient outcomes were assessed. Between July 2004 and April 2012, laser lead extractions were performed in 71 patients scheduled for device upgrade/revision who had occluded or functionally obstructed venous anatomy. New leads were successfully implanted across the obstruction in 67 (94%) cases. There were two major complications (infection) and four minor complications with no peri-procedural mortality. Device follow-up was satisfactory in 65 (92%) cases with mean follow-up up to 26 ± 19 months. Conclusion Laser lead extraction is a safe and effective option when managing patients with central venous obstruction in need of CIED revision or upgrade.