Electroanatomic mapping of the left ventricle in a porcine model of chronic myocardial infarction with magnetic resonance-based catheter tracking.

BACKGROUND: X-ray fluoroscopy constitutes the fundamental imaging modality for catheter visualization during interventional electrophysiology procedures. The minimal tissue discriminative capability of fluoroscopy is mitigated in part by the use of electroanatomic mapping systems and enhanced by the integration of preacquired 3-dimensional imaging of the heart with computed tomographic or magnetic resonance (MR) imaging. A more ideal paradigm might be to use intraprocedural MR imaging to directly image and guide catheter mapping procedures. METHODS AND RESULTS: An MR imaging-based electroanatomic mapping system was designed to assess the feasibility of navigating catheters to the left ventricle in vivo using MR tracking of microcoils incorporated into the catheters, measuring intracardiac ventricular electrograms, and integrating this information with 3-dimensional MR angiography and myocardial delayed enhancement images to allow ventricular substrate mapping. In all animals (4 normal, and 10 chronically infarcted swine), after transseptal puncture under fluoroscopic guidance, catheters were successfully navigated to the left ventricle with MR tracking (13 to 15 frames per second) by both transseptal and retrograde aortic approaches. Electrogram artifacts related to the MR imaging gradient pulses were successfully removed with analog and digital signal processing. In all animals, it was possible to map the entire left ventricle and to project electrogram voltage amplitude maps to identify the scarred myocardium. CONCLUSIONS: It is possible to use MR tracking to navigate catheters to the left ventricle, to measure electrogram activity, and to render accurate 3-dimensional voltage maps in a porcine model of chronic myocardial infarction, completely in the MR imaging environment. Myocardial delayed enhancement guidance provided dense sampling of the proximity of the infarct and accurate localization of complex infarcts.

View-synchronized robotic image-guided therapy for atrial fibrillation ablation: experimental validation and clinical feasibility.

BACKGROUND: A robotic catheter navigation system has been developed that provides a significant degree of freedom of catheter movement. This study examines the feasibility of synchronizing this robotic navigation system with electroanatomic mapping and 3-dimensional computed tomography imaging to perform view-synchronized left atrial (LA) ablation. METHODS AND RESULTS: This study consisted of a porcine experimental validation phase (9 animals) and a clinical feasibility phase (9 atrial fibrillation patients). Preprocedural computed tomography images were reconstructed to provide 3-dimensional surface models of the LA pulmonary veins and aorta. Aortic electroanatomic mapping was performed manually, followed by registration with the corresponding computed tomography aorta image using custom software. The mapping catheter was remotely manipulated with the robotic navigation system within the registered computed tomography image of the LA pulmonary veins. The point-to-surface error between the LA electroanatomic mapping data and the computed tomography image was 2.1+/-0.7 and 1.6+/-0.1 mm in the preclinical and clinical studies, respectively. The catheter was remotely navigated into all pulmonary veins, the LA appendage, and circumferentially along the mitral valve annulus. In 7 of 9 animals, circumferential radiofrequency ablation lesions were applied periostially to ablate 11 pulmonary veins. In patients, all of the pulmonary veins were remotely electrically isolated in an extraostial fashion. Adjunctive ablation included superior vena cava isolation in 6 patients, cavotricuspid isthmus ablation in 5 patients, and ablation of sites of complex fractionated activity and atypical LA flutters in 3 patients. CONCLUSIONS: This study demonstrates the safety and feasibility of an emerging paradigm for atrial fibrillation ablation involving the confluence of 3 technologies: 3-dimensional imaging, electroanatomic mapping, and remote robotic navigation.

Impedance and temperature monitoring improve the safety of closed-loop irrigated-tip radiofrequency ablation.

INTRODUCTION: Irrigated-tip catheter ablation allows larger ablation lesions to be created, but also decreases catheter temperature monitoring accuracy. It is unclear which parameters should be monitored to optimize efficacy and safety during irrigated-tip ablation. METHODS AND RESULTS: Freshly excised hearts from eight male pigs were perfused and superfused using oxygenated swine blood in an ex vivo model. Ablations were performed for 1 minute using one of five different ablation protocols: (1) Temperature Control (42 degrees C 40 W), (2) Fixed Power 20 W, (3) Fixed Power 30 W, (4) Impedance Control (target 10 ohm impedance drop), and (5) Impedance Control (target 20 ohm drop). All ablations were performed with a perpendicular orientation of the catheter to the endocardial surface. Ablation lesions depth was significantly lower in the temperature control group (5.0 +/- 1.7 mm) compared with the fixed power ablation groups (6.5 +/- 1.0 mm for Power 20 W, 6.6 +/- 1.2 mm for Power 30 W). Impedance-controlled ablation created lesions intermediate in depth between fixed power and temperature controlled (6.0 +/- 1.6 for Impedance 10 ohms and 6.2 +/- 1.4 mm for Impedance 20 ohms groups). There was a significantly greater incidence of pops and thrombus formation in the Power 20 W (9/14), Power 30 W (10/14), and Impedance 20 ohms (10/16) groups than the Temperature Control (1/16) and Impedance control 10 ohms (2/16) groups. CONCLUSION: Temperature control improved the safety profile during irrigated-tip ablation in comparison with fixed-power ablations, but resulted in significantly smaller lesions. Impedance-controlled ablation lesions (target 10 ohm drop) created lesions of comparable size to fixed-power ablations with a significantly better safety profile.

Initial experience with a novel remote-guided magnetic catheter navigation system for left ventricular scar mapping and ablation in a porcine model of healed myocardial infarction.

OBJECTIVE: This study examined the feasibility of using a remote magnetic catheter navigation system (MNS) in concert with an EAM system to perform detailed left ventricular scar mapping and ablation in a porcine model of healed myocardial infarction. BACKGROUND: Substrate-based catheter ablation of ventricular tachycardia (VT) involves detailed electroanatomical mapping (EAM) of the ventricles. While a safe and effective procedure, VT ablation is nonetheless uncommonly performed, due in part to the technical challenges related to ventricular mapping. METHODS: Using a prototype EAM system (CARTO-RMT), seven chronically infarcted swine were mapped using either: (i) a standard manually manipulated catheter or (ii) a magnetic remotely manipulated (Niobe) catheter. A total of 191 +/- 54 and 221 +/- 64 points were acquired to map the chamber either manually or remotely, respectively. RESULTS: Procedure times were longer remotely (94 +/- 22 vs. 59 +/- 19 minute, P = 0.004; and 27 +/- 8 vs. 18 +/- 3 sec/point, P = 0.04), but this became less apparent with increased operator experience. However, the fluoroscopy time was significantly shorter with remote mapping (56 +/- 56 vs. 244 +/- 67 sec/map, P = 0.03). The calculated scar size was comparable between the two methods (16.3 +/- 4.9 vs. 16.4 +/- 4.8 cm2, P = 0.37). Pathologic examination confirmed that the MNS was able to precisely deliver radiofrequency lesions to the scar borders. Using the MNS, the error to reach an evenly distributed set of endocardial targets was 6.6 +/- 3.6 mm and 4.6 +/- 2.0 mm, using transseptal and retrograde approaches, respectively. CONCLUSIONS: Ventricular mapping using this remote navigation paradigm is technically possible and requires minimal fluoroscopy exposure, potentially facilitating ventricular substrate mapping and ablation.

Epidural fever and its implications for mothers and neonates: taking the heat.

Epidural fever is a maternal temperature elevation seen in women who use epidural analgesia during labor. It occurs in a subset of laboring women after epidural administration and is noninfectious in origin. Epidural fever is not associated with neonatal sepsis, but it often is difficult to distinguish from chorioamnionitis, a condition that can cause neonatal sepsis. Because of this, neonates born to mothers who experience fever during labor are often evaluated for sepsis. Potential solutions to this problem include establishing better methods to distinguish between epidural fever and chorioamnionitis and making alternative methods of pain relief available to laboring women.

Testosterone cannot activate an adult-like stress response in prepubertal male rats.

The pubertal maturation of the hypothalamic-pituitary-adrenal (HPA) axis has received relatively little experimental attention. The present set of experiments sought to extend our understanding of the pubertal stress response by measuring corticotropin (ACTH), corticosterone, and testosterone levels in prepubertal and adult male rats exposed to a single 30-min session of restraint stress. We show that ACTH and corticosterone levels in prepubertal males take significantly longer to return to baseline after termination of the stressor compared to adults. These data indicate that prepubertal males demonstrate a more prolonged stress response compared to adults after a single acute stressor with both psychogenic and neurogenic components. As testosterone has been shown to reduce the stress response in adulthood, we next investigated whether the relatively low levels of circulating testosterone in prepubertal males mediated their protracted stress response. Data collected from additional experiments revealed that prepubertal males treated with adult-like physiological levels of testosterone still exhibited an extended stress response compared to similarly treated adults. These results indicate that the stress response demonstrated by adult males cannot be mimicked or activated in prepubertal males by mere supplementation of testosterone. Thus, we conclude that the HPA neuroendocrine axis is further shaped during pubertal development to allow for the emergence of a more tightly regulated stress response in adulthood.