Measurement of electrical coupling between cardiac ablation catheters and tissue.

Managing cardiac arrhythmias with catheter ablation requires positioning electrodes in contact with myocardial tissue. Objective measures to assess contact and effective coupling of ablation energy are sought. An electrical coupling index (ECI) was devised using complex impedance at 20 kHz to perform in the presence of RF ablation and deliver information about electrical interactions between the tip electrode and its adjacent environment. ECI was derived and compared with clinical judgment, pacing threshold, electrogram amplitude, and ablation lesion depth and transmurality in a porcine model. ECI was also compared with force and displacement using ex vivo bovine myocardial muscle. Mean noncontact ECI was 97.2 ± 14.3 and increased to 145.2 ± 33.6 (p <; 0.001) in clinician assessed (CLIN) moderate contact. ECI significantly improved CLIN's prediction of the variance in pacing threshold from 48.7% to 56.8% ( ). ECI was indicative of contact force under conditions of smooth myocardium. Transmural lesions were associated with higher pre-RF (109 ± 17 versus 149 ± 25, ) and during-RF (82 ± 9 versus 101 ± 17, ) ECI levels. ECI is a tip specific, robust, correlate with contact and ablation efficacy, and can potentially add to clinical interpretation of electrical coupling during electrophysiology procedures.

Endotoxin exposure during late pregnancy alters ovine offspring febrile and hypothalamic-pituitary-adrenal axis responsiveness later in life.

A growing number of studies indicate that maternal infection during pregnancy is associated with adverse fetal development and neonatal health. In this study, late gestating sheep (day 135) were challenged systemically with saline (0.9%) or Escherichia coli lipopolysaccharide endotoxin (400 ng/kg x 3 consecutive days, or 1.2 microg/kg x 1 day) in order to assess the impact of maternal endotoxemia on the developing fetal neuroendocrine-immune system. During adulthood, cortisol secretion and febrile responses of female offspring and the cortisol response of the male offspring to endotoxin (400 ng/kg), as well as the female cortisol response to adrenocorticotropic hormone (ACTH) challenge, were measured to assess neuroendocrine-immune function. These studies revealed that maternal endotoxin treatment during late gestation altered the female febrile and male and female cortisol response to endotoxin exposure later in life; however, the response was dependent on the endotoxin treatment regime that the pregnant sheep received. The follow-up ACTH challenge suggests that programing of the adrenal gland may be altered in the female fetus during maternal endotoxemia. The long-term health implications of these changes warrant further investigation.

First in human validation of impedance-based catheter tip-to-tissue contact assessment in the left atrium.

BACKGROUND: In this study, a new method of contact assessment based on the measurement of the local electrical properties at the catheter tip-to-tissue interface was validated in a blinded fashion in vivo in the human left atrium. METHODS: Using a 3-terminal circuit model, local resistance and reactance between catheter tip and tissue surface were measured and combined in an electrical coupling index (ECI). Twelve patients undergoing atrial fibrillation (AF) catheter ablation were included in this study. The catheter was placed in the left atrium at various levels of contact. Blinded to the physician, measurements of electrogram amplitudes, pacing thresholds, and impedances at the catheter tip-to-tissue interface were performed. RESULTS: As the catheter went from noncontact to contact, ECI increased from 118 +/- 15 to 145 +/- 24 (P < 0.0001), electrogram amplitudes increased from 0.14 +/- 0.16 to 2.0 +/- 1.9 mV (P < 0.0001), and pacing thresholds decreased from 13.9 +/- 3.1 to 3.1 +/- 2.0 mA (P < 0.0001). ECI was significantly higher in vascular tissue as compared with trabeculated and smooth myocardium. Patch orientation, operator, body mass index, or clinical type of AF had no influence on ECI values. On a patient-by-patient analysis, true contact/noncontact locations showed a mean ECI difference of 32.7 +/- 11.6 units (95% CI 25.8-39.6). A cut-off value of 5 ECI units was able to separate contact from noncontact with 97% sensitivity and 95% specificity. CONCLUSION: Measurement of local impedances between catheter tip and tissue is feasible to reproducibly describe electrical catheter contact within the left atrium in a clinical setting of AF catheter ablation.