Ventricular Intramyocardial Navigation for Tachycardia Ablation Guided by Electrograms (VINTAGE): Deep Ablation in Inaccessible Targets.

BACKGROUND: Deep intramural ventricular tachycardia substrate targets are difficult to access, map, and ablate from endocardial and epicardial surfaces, resulting in high recurrence rates. OBJECTIVES: In this study, the authors introduce a novel approach called ventricular intramyocardial navigation for tachycardia ablation guided by electrograms (VINTAGE) to access and ablate anatomically challenging ventricular tachycardia from within the myocardium. METHODS: Guidewire/microcatheter combinations were navigated deep throughout the extravascular myocardium, accessed directly from the right ventricle cavity, in Yorkshire swine (6 naive, 1 infarcted). Devices were steered to various intramyocardial targets including the left ventricle summit, guided by fluoroscopy, unipolar electrograms, and/or electroanatomic mapping. Radiofrequency ablations were performed to characterize ablation parameters and reproducibility. Intramyocardial saline irrigation began 1 minute before ablation and continued throughout. Lesions were analyzed on cardiac magnetic resonance and necropsy. RESULTS: VINTAGE was feasible in all animals within naive and infarcted myocardium. Forty-three lesions were created, using various guidewires and power settings. Forty-one (95%) lesions were detected on cardiac magnetic resonance and 38 (88%) on necropsy; all undetected lesions resulted from intentionally subtherapeutic ablation energy (10 W). Larger-diameter guidewires yielded larger size lesions. Lesion volumes on necropsy were significantly larger at 20 W than 10 W (178 mm3 [Q1-Q3: 104-382 mm3] vs 49 mm3 [Q1-Q3: 35-93 mm3]; P = 0.02). Higher power (30 W) did not create larger lesions. Median impedance dropped with preablation irrigation by 12 Ω (Q1-Q3: 8-17 Ω), followed by a further 15-Ω (Q1-Q3: 11-19 Ω) drop during ablation. Intramyocardial navigation, ablation, and irrigation were not associated with any complications. CONCLUSIONS: VINTAGE was safe and effective at creating intramural ablation lesions in targets traditionally considered inaccessible from the endocardium and epicardium, both naive and infarcted. Intramyocardial guidewire irrigation and ablation at 20 W creates reproducibly large intramural lesions.

Evaluation of 12-lead electrocardiogram at 0.55T for improved cardiac monitoring in magnetic resonance imaging.

BACKGROUND: The 12-lead electrocardiogram (ECG) is a standard diagnostic tool for monitoring cardiac ischemia and heart rhythm during cardiac interventional procedures and stress testing. These procedures can benefit from magnetic resonance imaging (MRI) information; however, the MRI scanner magnetic field leads to ECG distortion that limits ECG interpretation. This study evaluated the potential for improved ECG interpretation in a "low field" 0.55T MRI scanner. METHODS: The 12-lead ECGs were recorded inside 0.55T, 1.5T, and 3T MRI scanners, as well as at scanner table "home" position in the fringe field and outside the scanner room (seven pigs). To assess interpretation of ischemic ECG changes in a 0.55T MRI scanner, ECGs were recorded before and after coronary artery occlusion (seven pigs). ECGs was also recorded for five healthy human volunteers in the 0.55T scanner. ECG error and variation were assessed over 2-minute recordings for ECG features relevant to clinical interpretation: the PR interval, QRS interval, J point, and ST segment. RESULTS: ECG error was lower at 0.55T compared to higher field scanners. Only at 0.55T table home position, did the error approach the guideline recommended 0.025 mV ceiling for ECG distortion (median 0.03 mV). At scanner isocenter, only in the 0.55T scanner did J point error fall within the 0.1 mV threshold for detecting myocardial ischemia (median 0.03 mV in pigs and 0.06 mV in healthy volunteers). Correlation of J point deviation inside versus outside the 0.55T scanner following coronary artery occlusion was excellent at scanner table home position (r2 = 0.97), and strong at scanner isocenter (r2 = 0.92). CONCLUSION: ECG distortion is improved in 0.55T compared to 1.5T and 3T MRI scanners. At scanner home position, ECG distortion at 0.55T is low enough that clinical interpretation appears feasible without need for more cumbersome patient repositioning. At 0.55T scanner isocenter, ST segment changes during coronary artery occlusion appear detectable but distortion is enough to obscure subtle ST segment changes that could be clinically relevant. Reduced ECG distortion in 0.55T scanners may simplify the problem of suppressing residual distortion by ECG cable positioning, averaging, and filtering and could reduce current restrictions on ECG monitoring during interventional MRI procedures.

MR-Safe Cartesian Platform for Active Cardiac Shimming: Preliminary Validation.

OBJECTIVE: Implanted Cardioverter Defibrillators (ICDs) induce a large (100 parts per million) inhomogeneous magnetic field in the magnetic resonance imaging (MRI) scanner which cannot be corrected by the scanner's built-in shim coils, leading to significant image artifacts that can make portions of the heart unreadable. To compensate for the field inhomogeneity, an active shim coil capable of countering the field deviation in user-defined regions was designed that must be optimally placed at patient-specific locations. We aim to develop and evaluate an MR-safe robotic solution for automated shim coil positioning. METHODS: We designed and fabricated an MR-safe Cartesian platform that holds the shim coil inside the scanner. The platform consists of three lead screw stages actuated by pneumatic motors, achieving decoupled translations of 140 mm in each direction. The platform is made of plastics and fiberglass with the control electronics placed outside the scanner room, ensuring MR safety. Mechanical modeling was derived to provide design specifications. RESULTS: Experiments show that the platform achieves less than 2 mm average motion error and 0.5 mm repeatability in all directions, and reduces the adjustment time from 5 min to a few seconds. Phantom and animal trials were conducted, showing that the proposed system is able to position a heavy shim coil ( kg) for improved ICD artifact suppression. CONCLUSION: This robotic platform provides an effective method for reliable shim coil positioning inside the scanner. SIGNIFICANCE: This work contributes to improving cardiac MRI quality that could facilitate accurate diagnosis and treatment planning for patients with implanted ICDs.

Balanced-force shim system for correcting magnetic-field inhomogeneities in the heart due to implanted cardioverter defibrillators.

Background: In the US, 1.4 million people have implanted ICDs for reducing the risk of sudden death due to ventricular arrhythmias. Cardiac MRI (cMR) is of particular interest in the ICD patient population as cMR is the optimal imaging modality for distinguishing cardiac conditions that predispose to sudden death, and it is the best method to plan and guide therapy. However, all ICDs contain a ferromagnetic transformer which imposes a large inhomogeneous magnetic field in sections of the heart, creating large image voids that can mask important pathology. A shim system was devised to resolve these ICD issues. A shim coil system (CSS) that corrects ICD artifacts over a user-selected Region-of-Interest (ROI), was constructed and validated. Methods: A shim coil was constructed that can project a large magnetic field for distances of ~15 cm. The shim-coil can be positioned safely anywhere within the scanner bore. The CSS includes a cantilevered beam to hold the shim coil. Remotely controlled MR-conditional motors allow 2 mm-accuracy three-dimensional shim-coil position. The shim coil is located above the subjects and the imaging surface-coils. Interaction of the shim coil with the scanner's gradients was eliminated with an amplifier that is in a constant current mode. Coupling with the scanners' radio-frequency (rf) coils, was reduced with shielding, low-pass filters, and cable shield traps. Software, which utilizes magnetic field (B0) mapping of the ICD inhomogeneity, computes the optimal location for the shim coil and its corrective current. ECG gated single- and multiple-cardiac-phase 2D GRE and SSFP sequences, as well as 3D ECG-gated respiratory-navigated IR-GRE (LGE) sequences were tested in phantoms and N = 3 swine with overlaid ICDs. Results: With all cMR sequences, the system reduced artifacts from >100 ppm to <25 ppm inhomogeneity, which permitted imaging of the entire left ventricle in swine with ICD-related voids. Continuously acquired Gradient recalled echo or Steady State Free Precession images were used to interactively adjust the shim current and coil location. Conclusion: The shim system reduced large field inhomogeneities due to implanted ICDs and corrected most ICD-related image distortions. Externally-controlled motorized translation of the shim coil simplified its utilization, supporting an efficient cardiac MRI workflow.

Interventional cardiovascular magnetic resonance: state-of-the-art.

Transcatheter cardiovascular interventions increasingly rely on advanced imaging. X-ray fluoroscopy provides excellent visualization of catheters and devices, but poor visualization of anatomy. In contrast, magnetic resonance imaging (MRI) provides excellent visualization of anatomy and can generate real-time imaging with frame rates similar to X-ray fluoroscopy. Realization of MRI as a primary imaging modality for cardiovascular interventions has been slow, largely because existing guidewires, catheters and other devices create imaging artifacts and can heat dangerously. Nonetheless, numerous clinical centers have started interventional cardiovascular magnetic resonance (iCMR) programs for invasive hemodynamic studies or electrophysiology procedures to leverage the clear advantages of MRI tissue characterization, to quantify cardiac chamber function and flow, and to avoid ionizing radiation exposure. Clinical implementation of more complex cardiovascular interventions has been challenging because catheters and other tools require re-engineering for safety and conspicuity in the iCMR environment. However, recent innovations in scanner and interventional device technology, in particular availability of high performance low-field MRI scanners could be the inflection point, enabling a new generation of iCMR procedures. In this review we review these technical considerations, summarize contemporary clinical iCMR experience, and consider potential future applications.

EDEN (Electrocardiographic Radial Depth Navigation): A Novel Approach to Navigate Inside Heart Muscle.

BACKGROUND: Intramyocardial guidewire navigation is a novel technique that allows free transcatheter movement within ventricular muscle. Guidewire radial depth, between endocardial and epicardial surfaces, is ambiguous by x-ray and echocardiography. OBJECTIVES: The aim of this study was to develop a simple tool, EDEN (Electrocardiographic Radial Depth Navigation), to indicate radial depth during intramyocardial guidewire navigation. Combined with routine imaging, EDEN facilitates a new family of intramyocardial catheter procedures to slice, reshape, pace, and ablate the heart. METHODS: We mapped intramyocardial electrograms of left and right ventricular walls and septum during open- and closed-chest swine procedures (N = 53), including MIRTH (Myocardial Intramural Remodeling by Transvenous Tether) ventriculoplasty. We identified radial depth-dependent features on unipolar electrograms. We developed a machine learning-based classifier to indicate categorical position, and modeled the findings in silico to test understanding of the physiology. RESULTS: EDEN signatures distinguished 5 depth zones throughout left and right ventricular free walls and interventricular septum. Relative ST-segment elevation magnitude best discriminated position and was maximum (40.1 ± 6.5 mV) in the midmyocardium. Subendocardial positions exhibited dominant Q waves with lower-amplitude ST segments (16.8 ± 5.8 mV), whereas subepicardial positions exhibited dominant R waves with lower-amplitude ST segments (15.7 ± 4.8 mV). EDEN was unaffected by pacing-induced left bundle branch block. ST-segment elevation declined over minutes and reappeared after submillimeter guidewire manipulation. Modeling recapitulated EDEN features. The machine learning-based classifier was 97% accurate. EDEN successfully guided MIRTH ventriculoplasty. CONCLUSIONS: EDEN provides a simple and reproducible real-time reflection of categorical guidewire-tip radial depth during intramyocardial guidewire navigation. Used in tandem with x-ray, EDEN enables novel, transcatheter, intramyocardial therapies such as MIRTH, SESAME (Septal Surfing Along Midline Endocardium), and cerclage ventriculoplasty.

Growth Differentiation Factor-15 Predicts Mortality and Heart Failure Exacerbation But Not Ventricular Arrhythmias in Patients With Cardiomyopathy.

Background Heart failure (HF) has been increasing in prevalence, and a need exists for biomarkers with improved predictive and prognostic ability. GDF-15 (growth differentiation factor-15) is a novel biomarker associated with HF mortality, but no serial studies of GDF-15 have been conducted. This study aimed to investigate the association between GDF-15 levels over time and the occurrence of ventricular arrhythmias, HF hospitalizations, and all-cause mortality. Methods and Results We used a retrospective case-control design to analyze 148 patients with ischemic and nonischemic cardiomyopathies and primary prevention implantable cardioverter-defibrillator (ICD) from the PROSe-ICD (Prospective Observational Study of the ICD in Sudden Cardiac Death Prevention) cohort. Patients had blood drawn every 6 months and after each appropriate ICD therapy and were followed for a median follow-up of 4.6 years, between 2005 to 2019. We compared serum GDF-15 levels within ±90 days of an event among those with a ventricular tachycardia/fibrillation event requiring ICD therapies and those hospitalized for decompensated HF. A comparator/control group comprised patients with GDF-15 levels available during 2-year follow-up periods without events. Median follow-up was 4.6 years in the 148 patients studied (mean age 58±12, 27% women). The HF cohort had greater median GDF-15 values within 90 days (1797 pg/mL) and 30 days (2039 pg/mL) compared with the control group (1062 pg/mL, both P<0.0001). No difference was found between the ventricular tachycardia/fibrillation subgroup within 90 days (1173 pg/mL, P=0.60) or 30 days (1173 pg/mL, P=0.78) and the control group. GDF-15 was also significantly predictive of mortality (hazard ratio, 3.17 [95% CI, 2.33-4.30]). Conclusions GDF-15 levels are associated with HF hospitalization and mortality but not ventricular arrhythmic events.

Quality assessment of cardiac magnetic resonance myocardial scar imaging prior to ventricular arrhythmia ablation.

High-resolution scar characterization using late gadolinium enhancement cardiac magnetic resonance imaging (LGE-CMR) is useful for guiding ventricular arrhythmia (VA) treatment. However, imaging study quality may be degraded by breath-holding difficulties, arrhythmias, and implantable cardioverter-defibrillators (ICDs). We evaluated the effect of image quality on left ventricle (LV) base to apex scar interpretation in pre-VA ablation LGE-CMR. 43 consecutive patients referred for VA ablation underwent gradient-recalled-echo LGE-CMR. In ICD patients (n = 24), wide-bandwidth inversion-recovery suppressed ICD artifacts. In non-ICD patients, single-shot steady-state free-precession LGE-CMR could also be performed to reduce respiratory motion/arrhythmia artifacts. Study quality was assessed for adequate/limited scar interpretation due to cardiac/respiratory motion artifacts, ICD-related artifacts, and image contrast. 28% of non-ICD patients had studies where image quality limited scar interpretation in at least one image compared to 71% of ICD patient studies (p = 0.012). A median of five image slices had limited quality per ICD patient study, compared to 0 images per non-ICD patient study. Poorer quality in ICD patients was largely due to motion-related artifacts (54% ICD vs 6% non-ICD studies, p = 0.001) as well as ICD-related image artifacts (25% of studies). In VA ablation patients with ICDs, conventional CMR protocols frequently have image slices with limited scar interpretation, which can limit whole-heart scar assessment. Motion artifacts contribute to suboptimal image quality, particularly in ICD patients. Improved methods for motion and ICD artifact suppression may better delineate high-resolution LGE scar features of interest for guiding VA ablation.

The Association of Clustered Ventricular Arrhythmia and Cycle Length With Scar Burden in Cardiomyopathy.

BACKGROUND: Patients with ≥2 ventricular arrhythmia (VA) events within 3 months (clustered VA) have increased risk for mortality. OBJECTIVES: The aim of this study was to examine the association of risk factors including scar characteristics on cardiovascular magnetic resonance imaging with clustered VA and VA cycle length in nonischemic cardiomyopathy (NICM) and ischemic cardiomyopathy (ICM). METHODS: Data from 329 primary prevention implantable cardioverter-defibrillator recipients (mean age 57 years, 26% women) were analyzed from the Left Ventricular Structural Predictors of Sudden Cardiac Death study. RESULTS: Twenty-one patients developed clustered VA (median time 2.7 years after implantable cardioverter-defibrillator placement). Men had the greatest risk for recurrent VA. Patients with NICM and scar had the highest incidence rate of clustered VA. In patients with NICM, each 1-g increase in core scar correlated with greater clustered VA risk (HR: 1.19; 95% CI: 1.07-1.32). Gray scar was similar among subgroups. Patients with NICM with clustered VA had the longest mean VA cycle length (297 ± 40 milliseconds). Higher core scar burden correlated with longer VA cycle length in patients with NICM (P = 0.002), and higher body mass index correlated with shorter VA cycle length in those with ICM (P = 0.02). Type of VA was similar between cardiomyopathy subgroups, and no scar pattern predominated. CONCLUSIONS: Clustered VA was most common in patients with NICM and scar, with greatest risk among those with larger core scar. Core scar correlated with slower VA in patients with NICM, and higher body mass index correlated with faster VA in those with ICM. Type of VA was similar by cardiomyopathy etiology, and no dominant scar pattern was associated with clustered VA.

Intracardiac MR imaging (ICMRI) guiding-sheath with amplified expandable-tip imaging and MR-tracking for navigation and arrythmia ablation monitoring: Swine testing at 1.5 and 3T.

PURPOSE: Develop a deflectable intracardiac MR imaging (ICMRI) guiding-sheath to accelerate imaging during MR-guided electrophysiological (EP) interventions for radiofrequency (500 kHz) ablation (RFA) of arrythmia. Requirements include imaging at three to five times surface-coil SNR in cardiac chambers, vascular insertion, steerable-active-navigation into cardiac chambers, operation with ablation catheters, and safe levels of MR-induced heating. METHODS: ICMRI's 6 mm outer-diameter (OD) metallic-braided shaft had a 2.6 mm OD internal lumen for ablation-catheter insertion. Miniature-Baluns (MBaluns) on ICMRI's 1 m shaft reduced body-coil-induced heating. Distal section was a folded "star"-shaped imaging-coil mounted on an expandable frame, with an integrated miniature low-noise-amplifier overcoming cable losses. A handle-activated movable-shaft expanded imaging-coil to 35 mm OD for imaging within cardiac-chambers. Four MR-tracking micro-coils enabled navigation and motion-compensation, assuming a tetrahedron-shape when expanded. A second handle-lever enabled distal-tip deflection. ICMRI with a protruding deflectable EP catheter were used for MR-tracked navigation and RFA using a dedicated 3D-slicer user-interface. ICMRI was tested at 3T and 1.5T in swine to evaluate (a) heating, (b) cardiac-chamber access, (c) imaging field-of-view and SNR, and (d) intraprocedural RFA lesion monitoring. RESULTS: The 3T and 1.5T imaging SNR demonstrated >400% SNR boost over a 4 × 4 × 4 cm3 FOV in the heart, relative to body and spine arrays. ICMRI with MBaluns met ASTM/IEC heating limits during navigation. Tip-deflection allowed navigating ICMRI and EP catheter into atria and ventricles. Acute-lesion long-inversion-time-T1-weighted 3D-imaging (TWILITE) ablation-monitoring using ICMRI required 5:30 min, half the time needed with surface arrays alone. CONCLUSION: ICMRI assisted EP-catheter navigation to difficult targets and accelerated RFA monitoring.

Native contrast visualization and tissue characterization of myocardial radiofrequency ablation and acetic acid chemoablation lesions at 0.55 T.

PURPOSE: Low-field (0.55 T) high-performance cardiovascular magnetic resonance (CMR) is an attractive platform for CMR-guided intervention as device heating is reduced around 7.5-fold compared to 1.5 T. This work determines the feasibility of visualizing cardiac radiofrequency (RF) ablation lesions at low field CMR and explores a novel alternative method for targeted tissue destruction: acetic acid chemoablation. METHODS: N = 10 swine underwent X-ray fluoroscopy-guided RF ablation (6-7 lesions) and acetic acid chemoablation (2-3 lesions) of the left ventricle. Animals were imaged at 0.55 T with native contrast 3D-navigator gated T1-weighted T1w) CMR for lesion visualization, gated single-shot imaging to determine potential for real-time visualization of lesion formation, and T1 mapping to measure change in T1 in response to ablation. Seven animals were euthanized on ablation day and hearts imaged ex vivo. The remaining animals were imaged again in vivo at 21 days post ablation to observe lesion evolution. RESULTS: Chemoablation lesions could be visualized and displayed much higher contrast than necrotic RF ablation lesions with T1w imaging. On the day of ablation, in vivo myocardial T1 dropped by 19 ± 7% in RF ablation lesion cores, and by 40 ± 7% in chemoablation lesion cores (p < 4e-5). In high resolution ex vivo imaging, with reduced partial volume effects, lesion core T1 dropped by 18 ± 3% and 42 ± 6% for RF and chemoablation, respectively. Mean, median, and peak lesion signal-to-noise ratio (SNR) were all at least 75% higher with chemoablation. Lesion core to myocardium contrast-to-noise (CNR) was 3.8 × higher for chemoablation. Correlation between in vivo and ex vivo CMR and histology indicated that the periphery of RF ablation lesions do not exhibit changes in T1 while the entire extent of chemoablation exhibits T1 changes. Correlation of T1w enhancing lesion volumes indicated in vivo estimates of lesion volume are accurate for chemoablation but underestimate extent of necrosis for RF ablation. CONCLUSION: The visualization of coagulation necrosis from cardiac ablation is feasible using low-field high-performance CMR. Chemoablation produced a more pronounced change in lesion T1 than RF ablation, increasing SNR and CNR and thereby making it easier to visualize in both 3D navigator-gated and real-time CMR and more suitable for low-field imaging.

MRI Conditional Actively Tracked Metallic Electrophysiology Catheters and Guidewires With Miniature Tethered Radio-Frequency Traps: Theory, Design, and Validation.

OBJECTIVE: Cardiovascular interventional devices typically have long metallic braids or backbones to aid in steerability and pushability. However, electromagnetic coupling of metallic-based cardiovascular interventional devices with the radiofrequency (RF) fields present during Magnetic Resonance Imaging (MRI) can make a device unsafe for use in an MRI scanner. We aimed to develop MRI conditional actively-tracked cardiovascular interventional devices by sufficiently attenuating induced currents on the metallic braid/tube and internal-cabling using miniaturized resonant floating RF traps (MBaluns). METHOD: MBaluns were designed for placement at multiple locations along a conducting cardiovascular device to prevent the establishment of standing waves and to dissipate RF-induced energy. The MBaluns were constructed with loosely-wound solenoids to be sensitive to transverse magnetic fields created by both surface currents on the device's metallic backbone and common-mode currents on internal cables. Electromagnetic simulations were used to optimize MBalun parameters. Following optimization, two different MBalun designs were applied to MR-actively-tracked metallic guidewires and metallic-braided electrophysiology ablation catheters. Control-devices were constructed without MBaluns. MBalun performance was validated using network-analyzer quantification of current attenuation, electromagnetic Specific-Absorption-Rate (SAR) analysis, thermal tests during high SAR pulse sequences, and MRI-guided cardiovascular navigation in swine. RESULTS: Electromagnetic SAR simulations resulted in ≈20 dB attenuation at the tip of the wire using six successive MBaluns. Network-analyzer tests confirmed ∼17 dB/MBalun surface-current attenuation. Thermal tests indicated temperature decreases of 5.9 °C in the MBalun-equipped guidewire tip. Both devices allowed rapid vascular navigation resulting from good torquability and MR-Tracking visibility. CONCLUSION: MBaluns increased device diameter by 20%, relative to conventional devices, providing a spatially-efficient means to prevent heating during MRI. SIGNIFICANCE: MBaluns allow use of long metallic components, which improves mechanical performance in active MR-guided interventional devices.

Acute enhancement of necrotic radio-frequency ablation lesions in left atrium and pulmonary vein ostia in swine model with non-contrast-enhanced T1 -weighted MRI.

PURPOSE: To evaluate non-contrast-enhanced MRI of acute radio-frequency ablation (RFA) lesions in the left atrium (LA) and pulmonary vein (PV) ostia. The goal is to provide a method for discrimination between necrotic (permanent) lesions and reversible injury, which is associated with recurrence after treatment of atrial fibrillation. METHODS: Fifteen normal swine underwent RFA around the right-superior PV ostia. Electrical pulmonary vein isolation (PVI) was verified by electro-anatomic mapping (EAM) and pacing. MRI was carried out using a 3D respiratory-gated T1 -weighted long inversion time (TWILITE) sequence without contrast agent. Key settings were: inversion time 700 ms, triggering over 2 cardiac cycles, pixel size 1.1 mm3 . Contrast-enhanced imaging and T2 -weighted imaging were carried out for comparison. Six animals were sacrificed on ablation day for TTC-stained gross pathology, 9 animals were sacrificed after 2-3 mo after repeat EAM and MRI. Image intensity ratio (IIR) was used to measure lesion enhancement, and gross pathology was used to validate image enhancement patterns and compare lesion widths. RESULTS: RFA lesions exhibited unambiguous enhancement in acute TWILITE imaging (IIR = 2.34 ± 0.49 at 1.5T), and the enhancement patterns corresponded well with gross pathology. Lesion widths in MRI correlated well with gross pathology (R2 = 0.84), with slight underestimation by 0.9 ± 0.5 mm. Lesion enhancement subsided chronically. CONCLUSION: TWILITE imaging allowed acute detection of permanent RFA lesions in swine LA and PV ostia, without the need for contrast agent. Lesion enhancement pattern showed good correspondence to gross pathology and was well visualized by volume rendering. This method may provide valuable intra- or post-procedural assessment of RFA treatment.

Computationally guided personalized targeted ablation of persistent atrial fibrillation.

Atrial fibrillation (AF)-the most common arrhythmia-significantly increases the risk of stroke and heart failure. Although catheter ablation can restore normal heart rhythms, patients with persistent AF who develop atrial fibrosis often undergo multiple failed ablations, and thus increased procedural risks. Here, we present personalized computational modelling for the reliable predetermination of ablation targets, which are then used to guide the ablation procedure in patients with persistent AF and atrial fibrosis. First, we show that a computational model of the atria of patients identifies fibrotic tissue that, if ablated, will not sustain AF. Then, we report the results of integrating the target ablation sites in a clinical mapping system and testing its feasibility in ten patients with persistent AF. The computational prediction of ablation targets avoids lengthy electrical mapping and could improve the accuracy and efficacy of targeted AF ablation in patients while eliminating the need for repeat procedures.

Ablation Lesion Characterization in Scarred Substrate Assessed Using Cardiac Magnetic Resonance.

OBJECTIVES: This study examined radiofrequency catheter ablation (RFCA) lesions within and around scar by cardiac magnetic resonance (CMR) imaging and histology. BACKGROUND: Substrate modification by RFCA is the cornerstone therapy for ventricular arrhythmias. RFCA in scarred myocardium, however, is not well understood. METHODS: We performed electroanatomic mapping and RFCA in the left ventricles of 8 swine with myocardial infarction. Non-contrast-enhanced T1-weighted (T1w) and contrast-enhanced CMR after RFCA were compared with gross pathology and histology. RESULTS: Of 59 lesions, 17 were in normal myocardium (voltage >1.5 mV), 21 in border zone (0.5 to 1.5 mV), and 21 in scar (<0.5 mV). All RFCA lesions were enhanced in T1w CMR, whereas scar was hypointense, allowing discrimination among normal myocardium, scar, and RFCA lesions. With contrast-enhancement, lesions and scar were similarly enhanced and not distinguishable. Lesion width and depth in T1w CMR correlated with necrosis in pathology (both; r2 = 0.94, p < 0.001). CMR lesion volume was significantly different in normal myocardium, border zone, and scar (median: 397 [interquartile range (IQR): 301 to 474] mm3, 121 [IQR: 87 to 201] mm3, 66 [IQR: 33 to 123] mm3, respectively). RFCA force-time integral, impedance, and voltage changes did not correlate with lesion volume in border zone or scar. Histology showed that ablation necrosis extended into fibrotic tissue in 26 lesions and beyond in 14 lesions. In 7 lesions, necrosis expansion was blocked and redirected by fat. CONCLUSIONS: T1w CMR can selectively enhance necrotic tissue in and around scar and may allow determination of the completeness of ablation intra- and post-procedure. Lesion formation in scar is affected by tissue characteristics, with fibrosis and fat acting as thermal insulators.

Effect of high flow transnasal dry air on core body temperature in intubated human subjects.

PURPOSE: Early initiation of hypothermia is recommended in the setting of cardiac arrest. Current hypothermia methods are invasive and expensive and not applicable in ambulatory settings. We investigated the evaporative cooling effect of high flow transnasal dry air on core esophageal temperature in human volunteers. METHODS & RESULTS: A total of 32 subjects (mean age 53.2 ± 9.3 yrs., mean weight 90 ± 17 kg) presenting for elective electrophysiological procedures were enrolled for the study. Half of the subjects were men. Following general anesthesia induction, high flow (30 LPM) medical grade ambient dry air with a relative humidity ∼20% was administered through a nasal mask for 60 min. Core temperature was monitored at the distal esophagus. Half of the subjects (16/32) were subject to high flow air and the remainder served as controls. Over a 1-h period, mean esophageal temperature decreased from 36.1 ± 0.3 °C to 35.5 ± 0.1 °C in the test subjects (p < 0.05). No significant change in temperature was observed in the control subjects (36.3 ± 0.3 °C to 36.2 ± 0.2 °C, p = NS). No adverse events occurred. CONCLUSION: Transnasal high flow dry air through the nasopharynx reduces core body temperature. This mechanism can be harnessed to induce hypothermia in patients where clinically indicated without any deleteriouseffects in a short time exposure.

Segmented radial cardiac MRI during arrhythmia using retrospective electrocardiogram and respiratory gating.

PURPOSE: To improve segmented cardiac MRI image quality during arrhythmia. METHODS: Electrocardiogram (ECG) and respiratory waveforms were recorded during imaging. Imaging readouts were retrospectively classified into heartbeat-types based on the RR interval of the current and preceding beats, QRS morphology, and respiratory phase. Image data were sorted by these classifiers to generate separate cine images of different heartbeat-types during sinus rhythm and arrhythmia. A simulation study evaluated the efficiency of K-space sampling over a range of heart rhythms, heart rates, and respiratory rates. In vivo imaging was performed in volunteers with sinus rhythm, swine with arrhythmia simulated by pacing, and a human subject with spontaneous premature beats. RESULTS: K-space sampling uniformity and image quality incrementally improve with additional occurrences of the desired normal sinus or arrhythmia heartbeat-type. To approach the image quality of breath-hold imaging, sufficiently restrictive gating parameters are required. Compared with real-time imaging, retrospective gated images had reduced noise and improved sharpness while maintaining desired cine temporal resolution. Variations of cardiac function between arrhythmia heartbeats could be observed in arrhythmia imaging cases that are not captured by conventional segmented imaging. CONCLUSION: Retrospective ECG and respiratory gating permits imaging of various heartbeats during arrhythmia with fewer resolution restrictions compared to real-time imaging. For a fixed imaging time, imaging quality depends on frequency of the imaged heartbeat-type. Imaging additional heartbeats permits incremental improvement in image quality.

Efficacy and Safety of Transnasal CoolStat Cooling Device to Induce and Maintain Hypothermia.

Targeted temperature management (TTM) is recommended as a standard of care for postcardiac arrest patients. Current TTM methods have significant limitations to be used in an ambulatory setting. We investigated the efficacy and safety of a novel noninvasive transnasal evaporative cooling device (CoolStat™). Eleven Yorkshire pigs underwent hypothermia therapy using the CoolStat device. CoolStat induces evaporative cooling by blowing dehumidified ambient air over the nasal turbinates in a unidirectional fashion. CoolStat's efficacy and safety were assessed by applying different cooling strategies (groups A, B and C). In group A (efficacy study; n = 5, TTM for 8 hours), time to achieve brain target temperature (2°C reduction from baseline), and the percentage of time in which the temperature ranged within ±0.5°C after reaching the target temperature were investigated. In the safety assessment (groups B and C), two worst-case therapy situations were reproduced: in group B (n = 3), continuous maximum air flow (65 L/min) was applied without temperature control and, in group C (n = 3), subjects underwent 24-hour TTM (prolonged therapy). Hemodynamic and respiratory parameters, nasal mucosa integrity (endoscopic assessment), and other therapy-related adverse effects were evaluated. Efficacy study: CoolStat cooling therapy successfully induced and sustained managed hypothermia in all subjects. Brain target temperature was achieved in 0.5 ± 0.6 hours and kept within a ±0.5°C range for the therapy duration (99.9% ± 0.1%). All animals completed the safety studies. Maximum air flow (group B) and 24-hour (group C) therapies were well tolerated and no significant damage was observed on nasal mucosa for neither of the groups. CoolStat was able to efficiently induce and maintain hypothermia using unidirectional high flow of dry air into the nostrils of porcine models. CoolStat therapy was well tolerated and no damage to nasal mucosa was observed under either maximum air flow or prolonged therapy.

Initial validation of a novel ECGI system for localization of premature ventricular contractions and ventricular tachycardia in structurally normal and abnormal hearts.

BACKGROUND: View into Ventricular Onset (VIVO) is a novel ECGI system that uses 3D body surface imaging, myocardial CT/MRI, and 12­lead ECG to localize earliest ventricular activation through analysis of simulated and clinical vector cardiograms. OBJECTIVE: To evaluate the accuracy of VIVO for the localization of ventricular arrhythmias (VA). METHODS: In twenty patients presenting for catheter ablation of VT [8] or PVC [12], VIVO was used to predict the site earliest activation using 12­lead ECG of the VA. Results were compared to invasive electroanatomic mapping (EAM). RESULTS: A total of 22 PVC/VT morphologies were analyzed using VIVO. VIVO accurately predicted the location of the VA in 11/13 PVC cases and 8/9 VT cases. VIVO correctly predicted right vs left ventricular foci in 20/22 cases. CONCLUSION: View into Ventricular Onset (VIVO) can accurately predict earliest activation of VA, which could aid in catheter ablation, and should be studied further.