A method for x-ray image-guided robotic instrument positioning is reported and evaluated in preclinical studies of spinal pedicle screw placement with the aim of improving delivery of transpedicle K-wires and screws. The known-component (KC) registration algorithm was used to register the three-dimensional patient CT and drill guide surface model to intraoperative two-dimensional radiographs. Resulting transformations, combined with offline hand-eye calibration, drive the robotically held drill guide to target trajectories defined in the preoperative CT. The method was assessed in comparison with a more conventional tracker-based approach, and robustness to clinically realistic errors was tested in phantom and cadaver. Deviations from planned trajectories were analyzed in terms of target registration error (TRE) at the tooltip (mm) and approach angle (deg). In phantom studies, the KC approach resulted in [Formula: see text] and [Formula: see text], comparable with accuracy in tracker-based approach. In cadaver studies with realistic anatomical deformation, the KC approach yielded [Formula: see text] and [Formula: see text], with statistically significant improvement versus tracker ([Formula: see text] and [Formula: see text]). Robustness to deformation is attributed to relatively local rigidity of anatomy in radiographic views. X-ray guidance offered accurate robotic positioning and could fit naturally within clinical workflow of fluoroscopically guided procedures.

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Caveolin-3 (Cav-3) is an essential scaffolding protein for formation of caveolae in muscle cells. Cav-3 is part of a macromolecular complex including several ion channels. Mutations in Cav-3 have been associated with the inherited long QT syndrome as well as a variety of skeletal myopathies. To investigate the role of Cav-3 in heart and whether loss of function of Cav-3 explains the long QT phenotype, we generated cardiac-specific, inducible Cre-lox Cav-3 knockout mice. 8 week old mice were treated with tamoxifen in the chow to induce cardiac-specific recombination. Western blot analysis and transmitted electron microscopy demonstrated a graded loss of Cav-3 and caveolae in Cav-3 KO heterozygous mice (Cav-3-/+), Cav-3 KO homozygous mice (Cav-3-/-) relative to the littermate controls mice (WT). Echocardiography revealed no significant difference in %EF, %FS, LV chamber dimensions, and LV wall thickness between the different genotypes. Histopathological examination demonstrated no significant difference in HW/BW ratio, cardiac structure or fibrosis comparing Cav-3-/- and WT mice. Telemetry ECG recordings revealed a significant increase in QTc interval Cav-3-/- (68.5±7 ms) compared to WT (54.83±6 ms). Whole cell patch clamp analysis from isolated ventricular myocytes indicated a progressive increase in action potential duration (APD) with loss of Cav-3: WT (APD50: 4.7 ± 1ms; APD90: 28.0±3 ms; n=9); Cav-3-/+(APD50: 10.3±2 ms; APD90: 42.4±3 ms; n=13), Cav-3-/- (APD50: 32.4±6ms; APD90: 97.4±7ms; n=12). Whole cell voltage clamp measurements from Cav-3-/- revealed increased late INa, decrease in ICa,L, Ito,Iss current density without altering peak INa compared to WT cells, and these current changes were adequate to explain the increased APD based on computational representation using the Morotti et al. mouse ventricular cell model. Intracardiac programmed electrical stimulation (ventricular burst pacing) induced VT/Vfib in 8 out of 9 Cav3-/- but none of WT mice (0/5). Our results demonstrate that loss of Cav-3 and caveolae in adult mice does not alter cardiac structure or contractile function but leads to prolonged APD, an increased in QTc, and increased susceptibility to ventricular arrhythmias.

Caveolin proteins are involved in establishing membrane microstructure, lipid raft organization, and cell signaling. In the heart, caveolin-3 (Cav3) predominates. Inherited or disease-induced Cav3 loss increases risk of sudden cardiac death (SCD). We aimed to explore connections between Cav3 loss and arrhythmogenic changes in the ventricular action potential (AP) by investigating the Cav3 dependence of ionic currents. Drugs commonly used to disrupt or remove Cav3 in cultured cells exclude any compensatory process likely to occur in vivo. This motivated us to engineer a novel conditional Cav3 knockout (Cav3-/-) mouse that survives to adulthood. We isolated ventricular cells for electrophysiological experimentation. AP duration (APD90) was prolonged from 2454 ms in WT to 9659 ms in Cav3-/-, and several currents were affected. Reduced peak: L-type Ca 2þ current (ICaL), 21%; slow K þ current, 81%; transient outward K þ current, 57%; steady state outward K þ current (Iss), 43%. Late Na þ current was enhanced~10-fold. These changes were partially offsetting -preventing a simple account for the APD90 increase. To relate changes in currents to changes in the AP, we developed a computational representation of Cav3-/-based on the Morotti et al. mouse ventricular cell model and defined by fractional change in currents. Unexpectedly, the relatively small change in relatively small Iss caused 33% of total simulated AP prolongation. Though Iss conductance was reduced, peak Iss actually increased in the dynamic setting of the simulated AP. Early in the AP, lower Iss indirectly enhanced inward currents (importantly late ICaL) by extending the plateau phase, which in turn allowed Iss to more fully activate. This Iss/ ICaL process largely accounted for the pro-arrhythmic APD90 increase following Cav3 loss and is therefore a candidate target for normalizing SCD risk. Diabetes mellitus is associated with sinoatrial node dysfunction, as evidenced by an increased risk of atrial fibrillation, pacemaker implantation due to bradycardia and cardiac death in diabetic patients. While sinoatrial node myocytes (SAMs) generate the spontaneous action potentials (APs) that initiate each heartbeat, little is known about how diabetes affects SAMs directly. In this study, we used streptozoticin (STZ) -treated mice as a model of diabetic hyperglycemia. Four weeks after STZ injections, we found that both intrinsic heart rate (measured during autonomic blockade) and maximum heart rate (measured during restraint stress) were reduced in diabetic animals compared to pretreatment values. Current-clamp recordings from acutely isolated SAMs from diabetic animals revealed corresponding reductions in spontaneous AP firing rates. AP waveform analysis showed that the reduced firing rates in diabetic cells resulted from a prolongation of the AP duration and a slowing of the rate of repolarization. Accordingly, we observed significant decreases in steady state and transient outward K þ current densities in whole-cell voltage-clamp recordings from SAMs from diabet...

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