Distal end of the atrioventricular nodal artery predicts the risk of atrioventricular block during slow pathway catheter ablation of atrioventricular nodal re-entrant tachycardia

OBJECTIVE—To search for a reliable anatomical landmark within Koch's triangle to predict the risk of atrioventricular (AV) block during radiofrequency slow pathway catheter ablation of AV nodal re-entrant tachycardia (AVNRT).
PATIENTS AND METHODS—To test the hypothesis that the distal end of the AV nodal artery represents the anatomical location of the AV node, and thus could be a useful landmark for predicting the risk of AV block, 128 consecutive patients with AVNRT receiving slow pathway catheter ablation were prospectively studied in two phases. In phase I (77 patients), angiographic demonstration of the AV nodal artery and its ending was performed at the end of the ablation procedure, whereas in the subsequent phase II study (51 patients), the angiography was performed immediately before catheter ablation to assess the value of identifying this new landmark in reducing the risk of AV block. Multiple electrophysiologic and anatomical parameters were analysed. The former included the atrial activation sequence between the His bundle recording site (HBE) and the coronary sinus orifice or the catheter ablation site, either during AVNRT or during sinus rhythm. The latter included the spatial distances between the distal end of the AV nodal artery and the HBE and the final catheter ablation site, and the distance between the HBE and the tricuspid border at the coronary sinus orifice floor.
RESULTS—In phase I, nine of the 77 patients had complications of transient (seven patients) or permanent (two patients) complete AV block during stepwise, anatomy guided slow pathway catheter ablation. These nine patients had a wider distance between the HBE and the distal end of the AV nodal artery, and a closer approximation of the catheter ablation site to the distal end of the AV nodal artery, which independently predicted the risk of AV block. In contrast, none of the available electrophysiologic parameters were shown to be reliable. When the distance between the distal end of the AV nodal artery and the ablation target site was more than 2 mm, the complication of AV block virtually never occurred. In phase II, all 51 patients had successful elimination of the slow pathways without complication when the ablation procedure was guided by preceding angiography with identification of the distal end of the AV nodal artery.
CONCLUSIONS—The distal end of the AV nodal artery shown by angiography serves as a useful landmark for the prediction of the risk of AV block during slow pathway catheter ablation of AVNRT.


Keywords: atrioventricular nodal artery; atrioventricular nodal re-entrant tachycardia; catheter ablation; heart block.     

Abundant mitochondrial DNA variation and world-wide population structure in humpback whales.

Hunting during the last 200 years reduced many populations of mysticete whales to near extinction. To evaluate potential genetic bottlenecks in these exploited populations, we examined mitochondrial DNA control region sequences from 90 individual humpback whales (Megaptera novaeangliae) representing six subpopulations in three ocean basins. Comparisons of relative nucleotide and nucleotype diversity reveal an abundance of genetic variation in all but one of the oceanic subpopulations. Phylogenetic reconstruction of nucleotypes and analysis of maternal gene flow show that current genetic variation is not due to postexploitation migration between oceans but is a relic of past population variability. Calibration of the rate of control region evolution across three families of whales suggests that existing humpback whale lineages are of ancient origin. Preservation of preexploitation variation in humpback whales may be attributed to their long life-span and overlapping generations and to an effective, though perhaps not timely, international prohibition against hunting.     

Cell distributions and functions of Toll-like receptor 4 studied by fluorescent gene constructs

Bacterial lipopolysaccharide (LPS) is recognized in mammals by a receptor complex composed of CD14, Toll-like receptor 4 (TLR4), and MD-2. The detailed mechanisms of how TLR4 transmits the signal from the outside to the inside of the cell remain to be elucidated. One way of studying TLR4 signaling mechanisms is to construct chimeras of TLR molecules C-terminally fused to fluorescent proteins and stably express these constructs in cells. Such constructs are functional when transfected into HEK293 epithelial cells. Confocal microscopy of TLR4 expression in live cells demonstrated pronounced expression on the plasma membrane as well in the Golgi apparatus. Studies were performed to clarify whether expression of TLR4 in the Golgi was necessary for LPS stimulation. Rapid recycling of TLR4/CD14/MD-2 complexes between the Golgi and the plasma membrane was a prominent phenomenon. In agreement with other types of plasma membrane receptors, aggregation of TLR4 by immobilized TLR4 antibodies was sufficient to induce signaling. Also, pharmacological disruption of the Golgi did not inhibit LPS induced NF-kappaB activation. Furthermore, LPS stimulation recruited the adapter molecule, MyD88, to the inside of the plasma membrane. Thus, LPS signaling commences on the plasma membrane and is independent of trafficking to the Golgi.     

Caffeine alters resting‐state functional connectivity measured by blood oxygenation level‐dependent MRI

This study aimed to investigate the pharmacological effect of caffeine on functional connectivity measured by resting‐state blood oxygenation level‐dependent (BOLD) MRI in the motor cortex, visual cortex and default mode network (DMN). The protocols and procedures of the study were reviewed and approved by the Institutional Review Board of our institution. On a 3‐T clinical MR system, 20 healthy volunteers underwent imaging before and after oral ingestion of a 200‐mg over‐the‐counter caffeine pill (data from three individuals were excluded from further analysis because of excessive motion). The demographics of the remaining participants were as follows: female/male, 8/9; age, 21–35 years; non‐habitual caffeine consumers over the past 6 months. Functional connectivity was calculated using the general linear model, assessed in terms of connected area (voxels) and statistical significance (Student t‐values), and correlated with changes in regional cerebral blood flow as measured by arterial spin labeling MRI. Per‐subject data analysis showed that caffeine decreased functional connectivity in the motor/visual cortices, but its effects on DMN varied among subjects. Correlation analysis of the changes in functional connectivity and regional blood flow suggested that the effect of caffeine on BOLD functional connectivity was predominantly neural (motor/visual cortices) and partly vascular (DMN). Group analysis showed that, after caffeine ingestion, DMN involved more attentional networks, and more extrastriate areas were integrated into the functional connectivity of the visual cortex, which may be associated with the known pharmacological effect of caffeine in elevating alertness. Caffeine consumption should thus be considered in the experimental design and data interpretation of functional connectivity studies using resting‐state BOLD MRI. © 2014 The Authors. NMR in Biomedicine published by John Wiley & Sons, Ltd.     

Branched-chain amino acid levels are associated with improvement in insulin resistance with weight loss

Aims/hypothesis

Insulin resistance (IR) improves with weight loss, but this response is heterogeneous. We hypothesised that metabolomic profiling would identify biomarkers predicting changes in IR with weight loss.

Methods

Targeted mass spectrometry-based profiling of 60 metabolites, plus biochemical assays of NEFA, ??-hydroxybutyrate, ketones, insulin and glucose were performed in baseline and 6?month plasma samples from 500 participants who had lost ??4?kg during Phase I of the Weight Loss Maintenance (WLM) trial. Homeostatic model assessment of insulin resistance (HOMA-IR) and change in HOMA-IR with weight loss (?HOMA-IR) were calculated. Principal components analysis (PCA) and mixed models adjusted for race, sex, baseline weight, and amount of weight loss were used; findings were validated in an independent cohort of patients (n?=?22).

Results

Mean weight loss was 8.67?±?4.28?kg; mean ?HOMA-IR was ?0.80?±?1.73, range ?28.9 to 4.82). Baseline PCA-derived factor 3 (branched chain amino acids [BCAAs] and associated catabolites) correlated with baseline HOMA-IR (r?=?0.50, p?p?r?=?0.24). These findings were validated in the independent cohort, with a factor composed of BCAAs and related metabolites predicting ?HOMA-IR (p?=?0.007).

Conclusions/interpretation

A cluster of metabolites comprising BCAAs and related analytes predicts improvement in HOMA-IR independent of the amount of weight lost. These results may help identify individuals most likely to benefit from moderate weight loss and elucidate novel mechanisms of IR in obesity.