Gaston Vergara

Association of Left Atrial Fibrosis Detected by Delayed-Enhancement Magnetic Resonance Imaging and the Risk of Stroke in Patients With Atrial Fibrillation

OBJECTIVES This study tried to determine the association between left atrial (LA) fibrosis, detected using delayed-enhanced magnetic resonance imaging (DE-MRI), and the CHADS(2) score (point system based on individual clinical risk factors including congestive heart failure, hypertension, age, diabetes, and prior stroke) variables, specifically stroke. BACKGROUND In patients with atrial fibrillation (AF), conventional markers for the risk of stroke base their higher predictive effect on clinical features, particularly previous stroke history, and not individual LA pathophysiological properties. We aimed to determine the association between LA fibrosis, detected using DE-MRI, and the CHADS(2) score variables, specifically stroke. METHODS Patients with AF who presented to the AF clinic and received a DE-MRI of the LA were evaluated. Their risk factor profiles, including a CHADS(2) score, were catalogued. The degree of LA fibrosis was determined as a percentage of the LA area. Any history of previous strokes, warfarin use, or cerebrovascular disease was recorded. RESULTS A total of 387 patients, having a mean age of 65 ± 12 years, 36.8% female, were included in this study. A history of previous stroke was present in 36 (9.3%) patients. Those patients with previous strokes had a significantly higher percentage of LA fibrosis (24.4 ± 12.4% vs. 16.2 ± 9.9%, p < 0.01). A larger amount of LA fibrosis was also seen in those patients with a higher CHADS(2) score (≥ 2: 18.7 ± 11.4 vs. <2: 14.7 ± 9.2, p < 0.01). A logistic regression analysis of all variables except strokes (CHAD score) demonstrated that LA fibrosis independently predicted cerebrovascular events (p = 0.002) and significantly increased the predictive performance of the score (area under the curve = 0.77). CONCLUSIONS Our preliminary, multicenter results suggest DE-MRI-based detection of LA fibrosis is independently associated with prior history of strokes. We propose that the amount of DE-MRI-determined LA fibrosis could represent a marker for stroke and a possible therapeutic target with potential applicability for clinical treatment for patients with AF.

Evaluation of left atrial lesions after initial and repeat atrial fibrillation ablation: lessons learned from delayed-enhancement MRI in repeat ablation procedures.

Background—We evaluated scar lesions after initial and repeat catheter ablation of atrial fibrillation (AF) and correlated these regions to low-voltage tissue on repeat electroanatomic mapping. We also identified gaps in lesion sets that could be targeted and closed during repeat procedures. Methods and Results—One hundred forty-four patients underwent AF ablation and received a delayed-enhancement MRI at 3 months after ablation. The number of pulmonary veins (PV) with circumferential lesions were assessed and correlated with procedural outcome. Eighteen patients with AF recurrence underwent repeat ablation. MRI scar regions were compared with electroanatomic maps during the repeat procedure. Regions of incomplete scar around the PVs were then identified and targeted during repeat ablation to ensure complete circumferential lesions. After the initial procedure, complete circumferential scarring of all 4 PV antrum (PVA) was achieved in only 7% of patients, with the majority of patients (69%) having <2 completely scarred PVA. After the first procedure, the number of PVs with complete circumferential scarring and total left atrial wall (LA) scar burden was associated with better clinical outcome. Patients with successful AF termination had higher average total left atrial wall scar of 16.4%±9.8 (P=0.004) and percent PVA scar of 66.2±25.4 (P=0.01) compared with patients with AF recurrence who had an average total LA wall scar 11.3%±8.1 and PVA percent scar 50.0±24.7. In patients who underwent repeat ablation, the PVA scar percentage was 56.1%±21.4 after the first procedure compared with 77.2%±19.5 after the second procedure. The average total LA scar after the first ablation was 11.0%±4.1, whereas the average total LA scar after second ablation was 21.2%±7.4. All patients had an increased number of completely scarred pulmonary vein antra after the second procedure. MRI scar after the first procedure and low-voltage regions on electroanatomic mapping obtained during repeat ablation demonstrated a positive quantitative correlation of R2=0.57. Conclusions—Complete circumferential PV scarring difficult to achieve but is associated with better clinical outcome. Delayed-enhancement MRI can accurately define scar lesions after AF ablation and can be used to target breaks in lesion sets during repeat ablation.Background— We evaluated scar lesions after initial and repeat catheter ablation of atrial fibrillation (AF) and correlated these regions to low-voltage tissue on repeat electroanatomic mapping. We also identified gaps in lesion sets that could be targeted and closed during repeat procedures. Methods and Results— One hundred forty-four patients underwent AF ablation and received a delayed-enhancement MRI at 3 months after ablation. The number of pulmonary veins (PV) with circumferential lesions were assessed and correlated with procedural outcome. Eighteen patients with AF recurrence underwent repeat ablation. MRI scar regions were compared with electroanatomic maps during the repeat procedure. Regions of incomplete scar around the PVs were then identified and targeted during repeat ablation to ensure complete circumferential lesions. After the initial procedure, complete circumferential scarring of all 4 PV antrum (PVA) was achieved in only 7% of patients, with the majority of patients (69%) having <2 completely scarred PVA. After the first procedure, the number of PVs with complete circumferential scarring and total left atrial wall (LA) scar burden was associated with better clinical outcome. Patients with successful AF termination had higher average total left atrial wall scar of 16.4%±9.8 ( P =0.004) and percent PVA scar of 66.2±25.4 ( P =0.01) compared with patients with AF recurrence who had an average total LA wall scar 11.3%±8.1 and PVA percent scar 50.0±24.7. In patients who underwent repeat ablation, the PVA scar percentage was 56.1%±21.4 after the first procedure compared with 77.2%±19.5 after the second procedure. The average total LA scar after the first ablation was 11.0%±4.1, whereas the average total LA scar after second ablation was 21.2%±7.4. All patients had an increased number of completely scarred pulmonary vein antra after the second procedure. MRI scar after the first procedure and low-voltage regions on electroanatomic mapping obtained during repeat ablation demonstrated a positive quantitative correlation of R 2=0.57. Conclusions— Complete circumferential PV scarring difficult to achieve but is associated with better clinical outcome. Delayed-enhancement MRI can accurately define scar lesions after AF ablation and can be used to target breaks in lesion sets during repeat ablation.

Real-time magnetic resonance imaging–guided radiofrequency atrial ablation and visualization of lesion formation at 3 Tesla

BACKGROUND Magnetic resonance imaging (MRI) allows visualization of location and extent of radiofrequency (RF) ablation lesion, myocardial scar formation, and real-time (RT) assessment of lesion formation. In this study, we report a novel 3-Tesla RT -RI based porcine RF ablation model and visualization of lesion formation in the atrium during RF energy delivery. OBJECTIVE The purpose of this study was to develop a 3-Tesla RT MRI-based catheter ablation and lesion visualization system. METHODS RF energy was delivered to six pigs under RT MRI guidance. A novel MRI-compatible mapping and ablation catheter was used. Under RT MRI, this catheter was safely guided and positioned within either the left or right atrium. Unipolar and bipolar electrograms were recorded. The catheter tip-tissue interface was visualized with a T1-weighted gradient echo sequence. RF energy was then delivered in a power-controlled fashion. Myocardial changes and lesion formation were visualized with a T2-weighted (T2W) half Fourier acquisition with single-shot turbo spin echo (HASTE) sequence during ablation. RESULTS RT visualization of lesion formation was achieved in 30% of the ablations performed. In the other cases, either the lesion was formed outside the imaged region (25%) or the lesion was not created (45%) presumably due to poor tissue-catheter tip contact. The presence of lesions was confirmed by late gadolinium enhancement MRI and macroscopic tissue examination. CONCLUSION MRI-compatible catheters can be navigated and RF energy safely delivered under 3-Tesla RT MRI guidance. Recording electrograms during RT imaging also is feasible. RT visualization of lesion as it forms during RF energy delivery is possible and was demonstrated using T2W HASTE imaging.

Tailored Management of Atrial Fibrillation Using a LGE-MRI Based Model: From the Clinic to the Electrophysiology Laboratory

Tailored Management of Atrial Fibrillation with LGE‐MRI. Ablation provides a good therapeutic alternative for atrial fibrillation (AF) management; however, its effectiveness relies in adequate patient selection. Late gadolinium enhancement‐magnetic resonance imaging (LGE‐MRI) allows for atrial arrhythmic substrate, as well as postablation scarring visualization. In this article, we describe a new staging system for AF based on the amount of left atrial enhancement on LGE‐MRI (Utah I ≤ 5%, Utah II >5–20%, Utah III > 20–35%, and Utah IV > 35%). On the basis of patient stage, a more tailored approach to AF management can be taken. This includes triaging appropriate candidates for ablation (Utah stages I–III), as well as anticoagulation management based on an increase on the predictive statistics of the CHADS2. LGE‐MRI also allows for ablation lesion characterization. Acute edema, defined as enhancement on T2‐weighted MRI images immediately post‐AF ablation correlates with low voltage areas but not with LGE‐MRI‐defined scar. Post‐AF ablation LGE‐MRI scans show significant heterogeneity in the atrial wall on portions subject to radiofrequency (RF). We have postulated that some of these areas correspond to no‐reflow type phenomenon. Postablation LGE‐MRI can also help identify breaks in lesion sets and its correlation with conduction recovery has been used successfully to guide redo procedures. Real‐time MRI‐based ablation system has the potential advantage of tissue lesion visualization during RF delivery. To that end, we have developed a 3‐Tesla‐based real‐time MRI ablation system. We demonstrated the feasibility to safely navigate, pace, and record intracardiac EGMs in the atrial chambers, as well as applying RF energy while directly visualizing lesion formation in real time. (J Cardiovasc Electrophysiol, Vol. 22, pp. 481‐487)

80×80 VPD PbSe: the first uncooled MWIR FPA monolithically integrated with a Si-CMOS ROIC

In this work a breakthrough in the field of low cost uncooled infrared detectors is presented: an 80x80 MWIR VPD PbSe detector monolithically integrated with the corresponding Si-CMOS circuitry. Fast speed of response and high frame rates are, until date, non existing performances in the domain of low cost uncooled IR imagers. The new detector presented fills the gap. The device is capable to provide MWIR images to rates as high as 2 KHz, full frame, in real uncooled operation which converts it in an excellent solution for being used in applications where short events and fast transients dominate the system dynamics to be studied or detected. VPD PbSe technology is unique because combines all the main requirements demanded for a volume ready technology: 1. Simple processing 2. Good reproducibility and homogeneity 3. Processing compatible with big areas substrates 4. Si-CMOS compatible (no hybridation needed) 5. Low cost optics and packagin The new FPA represents a milestone in the road towards affordable uncooled MWIR imagers and it is the demonstration of VPD PbSe technology has reached industrial maturity. The device presented in the work was processed on 8-inch Si wafers with excellent results in terms of manufacturing yield and repeatability. The technology opens the MWIR band to SWaP concept.

Compact high-speed MWIR spectrometer applied to monitor CO2 exhaust dynamics from a turbojet engine

Dfgfdg Due to international environmental regulations, aircraft turbojet manufacturers are required to analyze the gases exhausted during engine operation (CO, CO2, NOx, particles, unburned hydrocarbons (aka UHC), among others).Standard procedures, which involve sampling the gases from the exhaust plume and the analysis of the emissions, are usually complex and expensive, making a real need for techniques that allow a more frequent and reliable emissions measurements, and a desire to move from the traditional gas sampling-based methods to real time and non-intrusive gas exhaust analysis, usually spectroscopic. It is expected that the development of more precise and faster optical methods will provide better solutions in terms of performance/cost ratio. In this work the analysis of high-speed infrared emission spectroscopy measurements of plume exhaust are presented. The data was collected during the test trials of commercial engines carried out at Turbojet Testing Center-INTA. The results demonstrate the reliability of the technique for studying and monitoring the dynamics of the exhausted CO2 by the observation of the infrared emission of hot gases. A compact (no moving parts), high-speed, uncooled MWIR spectrometer was used for the data collection. This device is capable to register more than 5000 spectra per second in the infrared band ranging between 3.0 and 4.6 microns. Each spectrum is comprised by 128 spectral subbands with aband width of 60 nm. The spectrometer operated in a passive stand-off mode and the results from the measurements provided information of both the dynamics and the concentration of the CO2 during engine operation.

MRI/CCT Fusion into Fluoroscopic Imaging

The combination of an EAM system and a CCT/cMRI is able to provide real-time information with regard to catheter position; however, this approach requires registration of two different models with different appearance. Furthermore, EAM systems are dedicated, expensive, and require operator familiarity with its function and display modalities. Registration of CCT/cMRI with fluoroscopy-based systems has several benefits. Advantages related to fluoroscopy-based systems are its widespread use and the familiarity of its images to most electrophysiologists. Some of the disadvantages are related to the low soft-tissue resolution, images that are 2D projections, and high exposure to ionizing radiation from X-rays. CCT and cMRI have the capability to provide very high quality and resolution imaging which can be processed to generate 3D renderings or models of the cardiac chamber selected in great detail. Disadvantages are related to the use of contrast to delineate the endocardial surface of the cardiac chambers, the inability to reliably image patients with implantable cardiac defibrillators (cMRI), and exposure to ionizing radiation (CCT), among others. Potential pitfalls related to this newer methodology are related to difficulty performing an accurate registration and potentially double exposure to ionizing radiation (if CCT is used).

Magnetic Resonance Imaging: Description of Technology and Protocols

Since its introduction in the late 1970s, catheter-based radiofrequency ablation has evolved from a primitive and experimental procedure to the mainstay for arrhythmia management it is today. Initial intracardiac catheter navigation was fluoroscopy based, and therefore subject to x-ray limitations and side effects. However, accurate catheter location within the cardiac chambers has required electrophysiologic confirmation of catheter positioning. This led to the development of conventional cardiac mapping techniques. The limitations of fluoroscopy and conventional mapping techniques led to the development of electro-anatomical mapping systems (EAM), in which information regarding catheter position in a 3D space is combined with electrophysiological information in real time to provide an accurate localization of the catheter tip while, at the same time, data regarding electrophysiological properties of the underlying myocardial substrate. Eventually, the mechanisms of more complex arrhythmias, such as atrial fibrillation and scar-based monomorphic ventricular tachycardia, started to be elucidated. This was followed by more difficult ablation procedures that required more accurate mapping systems able to provide real-time information. The introduction of EAM combined with Cardiac Computerized Tomography (CCT), cardiac Magnetic Resonance Imaging (cMRI), and real-time intracardiac echocardiography (ICE) allows for more precise mapping with significant improvement in cure rates for ablation procedures. However, most of these techniques are essentially x-ray based and expose the patient and the operator to the noxious effects of ionizing radiation.

USING REAL TIME MRI TO VISUALIZE AND ABLATE GAPS IN RADIOFREQUENCY ABLATION LESION SETS IN THE ATRIUM

Methods: A pig model was used for this study (n=3). Two ablation lesions were made in the right atrium in the electrophysiology (EP) lab using fluoroscopy. Animal was transferred to the Magnetic Resonance Imaging (MRI) scanner. Gadolinium delayed enhancement image was acquired to identify the ablation lesions and visualize the gap between them. While in the MRI scanner the gap area was ablated using MRI compatible catheters and real time catheter guidance. Delayed enhancement image was repeated to confirm the ablation of the gap area.

REAL-TIME MRI EVALUATION OF ACUTE LEFT ATRIAL INJURY PROGRESSION DURING RADIOFREQUENCY ABLATION OF ATRIAL FIBRILLATION

Methods: 5 animal models were utilized. A single RF lesion was placed at the interatrial septum. A T2w DIR-FSE sequence was performed immediately after lesion placement and repeated 10 minutes later. Sequence parameters were: TE = 83 ms, TR = 2RR, ETL = 21, fat suppression using SPAIR, in-plane resolution of 1.25 x 1.25 mm, slice thickness of 4 mm, 20 slices, GRAPPA with R = 2 and 42 reference lines. Typical scan time was 6 minutes.