Detection of Leak From Left Atrial Appendage Occlusion Using Dielectric Imaging.

BACKGROUND: Peri-device leak (PDL) following left atrial appendage occlusion (LAAO) may lead to an increased risk of thrombosis. However, current modalities for PDL detection, such as trans-esophageal echo (TEE) and cardiac CT do not provide quantitative measures of PDL. OBJECTIVE: to use dielectric imaging (DI) to measure PDL from a Watchman (WM) LAAO device. METHODS: A conductivity contrast agent is injected into the left atrium (LA) through the WM delivery system, while making DI measurements. Recordings are analyzed with a two-compartment model and the flow from the left atrial appendage (LAA) characterized by a "% clearance / beat" (CPB) parameter. With ethics approval, four dogs (26 ± 1.8  kg) were anesthetized and ventilated. Body-surface electrodes were placed and impedance data continuously acquired. WM devices (0-35% oversized) were introduced and placed into the LAA. During the study, the WM was either fully or partial deployed. At each deployment level, 10 mL of conductivity contrast was injected through the WM delivery sheath. At twenty-two deployment conditions, Doppler-flow TEE measurements were made, and compared to the DI-based value. RESULTS: In all cases, CPB values correctly predicted the TEE-based assessment of PDL (100% sensitivity/specificity). The TEE leak size also corresponded to CPB values with a correlation of r = 0.914 (p 0.001). CONCLUSION: Using DI signals, the leak flow from the WM LAAO can be measured and yields comparative results to TEE for detection of PDL. The DI method requires no other imaging modality or ionizing radiation and iodine contrast agent injection.

Visual detection of time-varying signals: Opposing biases and their timescales.

Human visual perception is a complex, dynamic and fluctuating process. In addition to the incoming visual stimulus, it is affected by many other factors including temporal context, both external and internal to the observer. In this study we investigate the dynamic properties of psychophysical responses to a continuous stream of visual near-threshold detection tasks. We manipulate the incoming signals to have temporal structures with various characteristic timescales. Responses of human observers to these signals are analyzed using tools that highlight their dynamical features as well. Our experiments show two opposing biases that shape perceptual decision making simultaneously: positive recency, biasing towards repeated response; and adaptation, entailing an increased probability of changed response. While both these effects have been reported in previous work, our results shed new light on the timescales involved in these effects, and on their interplay with varying inputs. We find that positive recency is a short-term bias, inversely correlated with response time, suggesting it can be compensated by afterthought. Adaptation, in contrast, reflects trends over longer times possibly including multiple previous trials. Our entire dataset, which includes different input signal temporal structures, is consistent with a simple model with the two biases characterized by a fixed parameter set. These results suggest that perceptual biases are inherent features which are not flexible to tune to input signals.

Plasticity compartments in basal dendrites of neocortical pyramidal neurons.

Synaptic plasticity rules widely determine how cortical networks develop and store information. Using confocal imaging and dual site focal synaptic stimulation, we show that basal dendrites, which receive the majority of synapses innervating neocortical pyramidal neurons, contain two compartments with respect to plasticity rules. Synapses innervating the proximal basal tree are easily modified when paired with the global activity of the neuron. In contrast, synapses innervating the distal basal tree fail to change in response to global suprathreshold activity or local dendritic spikes. These synapses can undergo long-term potentiation under unusual conditions when local NMDA spikes, which evoke large calcium transients, are paired with a "gating molecule," BDNF. Moreover, these synapses use a new temporal plasticity rule, which is an order of magnitude longer than spike timing dependent plasticity and prefers reversed presynaptic/postsynaptic activation order. The newly described plasticity compartmentalization of basal dendrites expands the networks plasticity rules and may support different learning and developmental functions.