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Sensing systems with multiple sensors and operating modes warrant active management techniques to balance estimation quality and measurement costs. Existing literature shows that in the joint sensor-scheduling and state-estimation problem for HMMs, estimator optimization can be done independently of the scheduler at each time step. We investigate the special case when a MAP estimator is used, and show how the joint problem can be converted to a standard Partially Observable MarkovDecision Process (POMDP), which in turn enables us to use POMDP solvers. As this approach is highly redundant, we derive a direct solution, which exploits the separability property while still utilizing standard solvers. When compared to standard techniques, the direct algorithm provides savings by a factor of the state-space dimension. Numerical results are given for an example motivated by wildlife monitoring.

Many applications involve sparse signals with unknown, continuous parameters; a common example is a signal consisting of several sinusoids of unknown frequency. Applying compressed sensing techniques to these signals requires a highly oversampled dictionary for good approximation, but these dictionaries violate the RIP conditions and produce inconsistent results. We consider recovering both a sparse vector and parameter perturbations from an initial set of parameters. Joint recovery allows for accurate reconstructions without highly oversampled dictionaries. Our algorithm for sparse recovery solves a series of linearized subproblems. Recovery error for noiseless simulated measurements is near zero for coarse dictionaries, but increases with the oversampling. This technique is also used to reconstruct Radio Frequency data. The algorithm estimates sharp peaks and transmitter frequencies, demonstrating the potential practical use of the algorithm on real data.

In many detection applications with battery powered or energy-harvesting sensors, energy constraints preclude the use of the optimal detector all the time. Optimal energy-performance trade-off is therefore needed in such situations. In many applications, the signal and noise power may vary greatly over time, and this can be exploited to constrain energy consumption while maintaining the best possible performance. A detector scheduling algorithm based on the signal and noise power information is developed in this work. The resulting algorithm is simple due to its threshold-test structure and can be easily implemented with almost no overhead. A detection system with two detectors using the proposed scheduling scheme is estimated to greatly reduce the energy consumption for a wildlife monitoring application.

Transcatheter aortic valve implantation (TAVI) is a minimally invasive alternative to conventional aortic valve replacement for severe aortic stenosis in high-risk patients in which a stent-based bioprosthetic valve is delivered into the heart via a catheter. TAVI relies largely on single-plane fluoroscopy for intraoperative navigation and guidance, which provides only gross imaging of anatomical structures. Inadequate imaging leading to suboptimal valve positioning contributes to many of the early complications experienced by TAVI patients, including valve embolism, coronary ostia obstruction, paravalvular leak, heart block, and secondary nephrotoxicity from excessive contrast use. Improved visualization can be provided using intraoperative registration of a CT-derived surface to transesophageal echo (TEE) images. In this study, the accuracy and robustness of a surface-based registration method suitable for intraoperative use are evaluated, and the performances of different TEE surface extraction methods are compared. The use of cross-plane TEE contours demonstrated the best accuracy, with registration errors of less than 5 mm. This guidance system uses minimal intraoperative interaction and workflow modification, does not require tool calibration or additional intraoperative hardware, and can be implemented at all cardiac centers at extremely low cost.

Direct catheter ablation for atrial fibrillation does not yield reproducible permanent control as for other atrial arrhythmias. Therefore, there is a need for an alternative intervention, i.e., left atrial exclusion, based on elective ablation of the interatrial connecting bundles. We describe the “operative anatomy” of the three major interatrial connections: the Bachmann bundle, the coronary sinus bundle, and the left atrial-atrioventricular node connection, based on macroscopic dissections of human and porcine hearts and our previous experience. We identified the three right atrial attachments, with the coronary sinus (CS) and left atrial (LA)–atrioventricular (AV) nodal connection being most problematic for safe ablation. To obtain a complete isolation of the left from the right atrium, all three connections must be ablated. The CS connection must be ablated distal to the ostium. If present, the LA–AV nodal connection can be safely ablated from the left atrium.

Author(s): Whitehouse, Harvey; Swann, William; Ingram, Gordon; Prochownik, Karolina; Lanman, Jonathan; Waring, Timothy M; Frost, Karl; Jones, Douglas; Reeve, Zoey; Johnson, Dominic | Abstract: A special feature at the Social Evolution Forum

Autonomic tone may contribute to cardiac arrhythmogenesis and influence the efficacy of implantable defibrillators. Fifty-two anesthetized pigs were randomized to: (1) methacholine (n = 12); (2) nitroprusside (n = 12); (3) phenylephrine (n = 12); (4) carbachol (n = 8); and (5) saline (n = 8). Ventricular fibrillation threshold (VFT) and triplicate defibrillation thresholds (DFT) were obtained before and during each intervention. Mean (+/- SE) VFT was increased with: methacholine (76 +/- 10.6 V vs 39 +/- 7.1 V, P < 0.001); phenylephrine (68 +/- 10.5 V vs 38 +/- 6.2 V, P < 0.001); and carbachol (106 +/- 11.5 V vs 30 +/- 6.5 V, P < 0.0001). Nitroprusside and saline failed to alter VFT. Mean (+/- SE) DFT was decreased with: methacholine (7.7 +/- 0.8) vs 9.7 +/- 0.8 J, P < 0.001); phenylephrine (9.8 +/- 0.9 J vs 11.3 +/- 1.0 J, P < 0.05); and carbachol (9.2 +/- 0.7 J vs 12.2 +/- 0.8 J, P < 0.0001), remaining unchanged following nitroprusside and saline infusion. Thus, modulation of autonomic tone modified arrhythmia susceptibility and the energy necessary for defibrillation, increased parasympathetic tone, increased VFT, and decreased DFT. Evaluation of autonomic balance, particularly parasympathetic tone, may be useful with the implantation of automatic defibrillators.

Fundamental to the theory of joint signal representations is the idea of associating a variable, such as time or frequency, with an operator, a concept borrowed from quantum mechanics. Each variable can be associated with a Hermitian operator, or equivalently and consistently, as we show, with a parameterized unitary operator. It is well known that the eigenfunctions of the unitary operator define a signal representation which is invariant to the effect of the unitary operator on the signal, and is hence useful when such changes in the signal are to be ignored. However, for detection or estimation of such changes, a signal representation covariant to them is needed. Using well-known results in functional analysis, we show that there always exists a translationally covariant representation; that is, an application of the operator produces a corresponding translation in the representation. This is a generalization of a recent result in which a transform covariant to dilations is presented. Using Stone's theorem, the "covariant" transform naturally leads to the definition of another, unique, dual parameterized unitary operator. This notion of duality, which we make precise, has important implications for joint distributions of arbitrary variables and their interpretation. In particular, joint distributions of dual variables are structurally equivalent to Cohen's class of time-frequency representations, and our development shows that, for two variables, the Hermitian and unitary operator correspondences can be used consistently and interchangeably if and only if the variables are dual.

Using the Wigner distribution, we derive and analyze a matrix formulation for the chirplet transform, a signal analysis tool that generalizes the wavelet and short-time Fourier transforms. The formulation expresses the translations, scalings, and shears of the chirplet transform in terms of affine matrix transformations on the time-frequency plane. Our approach leads naturally to several new signal transforms, which we derive, analyze, and extend.

Time-frequency analysis has significant advances in two main directions: statistically optimized methods that extend the scope of time-frequency-based techniques from merely exploratory data analysis to more quantitative application and generalized joint signal representations that extend time-frequency-based methods to a richer class of nonstationary signals. This paper fuses the two advances by developing optimal detection and estimation techniques based on generalized joint signal representations. By generalizing the statistical methods developed for time-frequency representations to arbitrary joint signal representations, this paper develops a unified theory applicable to a wide variety of problems in nonstationary statistical signal processing.

Joint signal representations (JSRs) of arbitrary variables generalize time-frequency representations (TFRs) to a much broader class of nonstationary signal characteristics. Two main distributional approaches to JSRs of arbitrary variables have been proposed by Cohen (see Time-Frequency Analysis, Englewood Cliffs, NJ, Prentice Hall, 1995 and Proc. SPIE 1566, San Diego, 1991) and Baraniuk (see Proc. IEEE Int. Conf. Acoust., Speech Signal Processing, ICASSP'94, vol.3, p.357-60, 1994). Cohen's method is a direct extension of his original formulation of TFRs, and Baraniuk's approach is based on a group theoretic formulation; both use the powerful concept of associating variables with operators. One of the main results of the paper is that despite their apparent differences, the two approaches to generalized JSRs are completely equivalent. Remarkably, the JSRs of the two methods are simply related via axis warping transformations, with the broad implication that JSRs with radically different covariance properties can be generated efficiently from JSRs of Cohen's method via simple pre- and post-processing. The development in this paper, which is illustrated with examples, also illuminates other related issues in the theory of generalized JSRs. In particular, we derive an explicit relationship between the Hermitian operators in Cohen's method and the unitary operators in Baraniuk's approach, thereby establishing the relationship between the two types of operator correspondences.

Environmental noise has become a major problem in large cities, increasing health risks for the urban population. Current methods are overly expensive for city-wide noise-monitoring as they generally require dense deployment of fixed microphones for noise-level measurements. We present here alternative sparse tomographic acoustic imaging techniques using arrays with relatively few number of microphones for large-region acoustic noise mapping. We first demonstrate that the locations and sound pressure levels of fixed noise sources sparsely located in a large field are recovered by collecting acoustic data at multiple locations with a portable microphone array for tomographic reconstruction. We then introduce a nonstationary tomographic imaging approach using fixed microphone arrays, which can also capture the intermittent changes in the acoustic field due to transient and/or moving noise sources. We test both the sparse static and dynamic imaging models with acoustic measurements collected with a circular ...

Presents a technique to adaptively optimize the performance of the cone-kernel distribution (CKD) by varying the cone length in response to changing signal properties. The result is an adaptive CKD that preserves the outer hull of signal time support, yields excellent results on real signals, outperforms fixed-length CKDs, and requires only slightly more computation than a fixed-kernel distribution. >

A method to determine the shape of a patient by placing radiopaque wires and chains on the skin and taking two isocentric X-ray films is described. The wire locations are reconstructed by X-ray stereo photogrammetry, and a beam's eye view of the wire frame structure can be obtained with reference to the original setup of the “stereo-pair” films. An algorithm for paving between the wires with triangular plates is described which allows the calculation of the tissue deficit distance and compensator thickness. The depth and distance to points on the spinal cord are calculated, and the dose rate is calculated using a standard irregular field computation program. The limit for spinal cord tolerance is specified in terms of the maximum daily dose based on an equivalent dose formula. The additional thickness of compensator, required for the posterior field compensator to satisfy the tolerance limit, is calculated. The technique readily accommodates the kyphotic and scoliotic spine and has been in routine clinical use for seven years.

Background Despite the clinical importance of atrial fibrillation (AF), the development of chronic nonvalvular AF models has been difficult. Animal models of sustained AF have been developed primarily in the short-term setting. Recently, models of chronic ventricular myopathy and fibrillation have been developed after several weeks of continuous rapid ventricular pacing. We hypothesized that chronic rapid atrial pacing would lead to atrial myopathy, yielding a reproducible model of sustained AF. Methods and Results Twenty-two halothane-anesthetized mongrel dogs underwent insertion of a transvenous lead at the right atrial appendage that was continuously paced at 400 beats per minute for 6 weeks. Two-dimensional echocardiography was performed in 11 dogs to assess the effects of rapid atrial pacing on atrial size. Atrial vulnerability was defined as the ability to induce sustained repetitive atrial responses during programmed electrical stimulation and was assessed by extrastimulus and burst-pacing techniques. Effective refractory period (ERP) was measured at two endocardial sites in the right atrium. Sustained AF was defined as AF ≥15 minutes. In animals with sustained AF, 10 quadripolar epicardial electrodes were surgically attached to the right and left atria. The local atrial fibrillatory cycle length (AFCL) was measured in a 20-second window, and the mean AFCL was measured at each site. Marked biatrial enlargement was documented; after 6 weeks of continuous rapid atrial pacing, the left atrium was 7.8±1 cm 2 at baseline versus 11.3±1 cm 2 after pacing, and the right atrium was 4.3±0.7 cm 2 at baseline versus 7.2±1.3 cm 2 after pacing. An increase in atrial area of at least 40% was necessary to induce sustained AF and was strongly correlated with the inducibility of AF ( r =.87). Electron microscopy of atrial tissue demonstrated structural changes that were characterized by an increase in mitochondrial size and number and by disruption of the sarcoplasmic reticulum. After 6 weeks of continuous rapid atrial pacing, sustained AF was induced in 18 dogs (82%) and nonsustained AF was induced in 2 dogs (9%). AF occurred spontaneously in 4 dogs (18%). Right atrial ERP, measured at cycle lengths of 400 and 300 milliseconds at baseline, was significantly shortened after pacing, from 150±8 to 127±10 milliseconds and from 147±11 to 123±12 milliseconds, respectively ( P R 2 =.93). Mean AFCL was significantly shorter in the left atrium (81±8 milliseconds) compared with the right atrium 94±9 milliseconds ( P Conclusions Sustained AF was readily inducible in most dogs (82%) after rapid atrial pacing. This model was consistently associated with biatrial myopathy and marked changes in atrial vulnerability. An area in the posterior left atrium was uniformly shown to have the shortest AFCL. The results of restoration of sinus rhythm and prevention of inducibility of AF after cryoablation of this area of the left atrium suggest that this area may be critical in the maintenance of AF in this model.

Time-frequency representations with fixed windows or kernels figure prominently in many applications, but perform well only for limited classes of signals. Representations with signal-dependent kernels can overcome this limitation. However, while they often perform well, most existing schemes are block-oriented techniques unsuitable for on-line implementation or for tracking signal components with characteristics that change with time. The time-frequency representation developed in the present paper, based on a signal-dependent radially Gaussian kernel that adapts over time, surmounts these difficulties. The method employs a short-time ambiguity function both for kernel optimization and as an intermediate step in computing constant-time slices of the representation. Careful algorithm design provides reasonably efficient computation and allows on-line implementation. Certain enhancements, such as cone-kernel constraints and approximate retention of marginals, are easily incorporated with little additional computation. While somewhat more expensive than fixed kernel representations, this new technique often provides much better performance. Several examples illustrate its behavior on synthetic and real-world signals. >

Unitary similarity transformations furnish a powerful vehicle for generating infinite generic classes of signal analysis and processing tools based on concepts different from time, frequency, and scale. Implementation of these new tools involves simply preprocessing the signal by a unitary transformation, performing standard processing on the transformed signal, and then (in some cases) transforming the resulting output. The resulting unitarily equivalent systems can focus on the critical signal characteristics in large classes of signals and, hence, prove useful for representing and processing signals that are not well matched by current techniques. As specific examples of this procedure, we generalize linear time-invariant systems, orthonormal basis and frame decompositions, and joint time-frequency and time-scale distributions. These applications illustrate the utility of the unitary equivalence concept for uniting seemingly disparate approaches proposed in the literature. >

Bilinear time-frequency representations (TFRs) and time-scale representations (TSRs) are potentially very useful for detecting a nonstationary signal in the presence of nonstationary noise or interference. As quadratic signal representations, they are promising for situations in which the optimal detector is a quadratic function of the observations. All existing time-frequency formulations of quadratic detection either implement classical optimal detectors equivalently in the time-frequency domain, without fully exploiting the structure of the TFR, or attempt to exploit the nonstationary structure of the signal in an ad hoc manner. We identify several important nonstationary composite hypothesis testing scenarios for which TFR/TSR-based detectors provide a "natural" framework; that is, in which TFR/TSR-based detectors are both optimal and exploit the many degrees of freedom available in the TFR/TSR. We also derive explicit expressions for the corresponding optimal TFR/TSR kernels. As practical examples, we show that the proposed TFR/TSR detectors are directly applicable to many important radar/sonar detection problems. Finally, we also derive optimal TFR/TSR-based detectors which exploit only partial information available about the nonstationary structure of the signal.

Current theories of a time-varying spectrum of a nonstationary process all involve, either by definition or by difficulties in estimation, an assumption that the signal statistics vary slowly over time. This restrictive quasistationarity assumption limits the use of existing estimation techniques to a small class of nonstationary processes. We overcome this limitation by deriving a statistically optimal kernel, within Cohen's (1989) class of time-frequency representations (TFR's), for estimating the Wigner-Ville spectrum of a nonstationary process. We also solve the related problem of minimum mean-squared error estimation of an arbitrary bilinear TFR of a realization of a process from a correlated observation. Both optimal time-frequency invariant and time-frequency varying kernels are derived. It is shown that in the presence of any additive independent noise, optimal performance requires a nontrivial kernel and that optimal estimation may require smoothing filters that are very different from those based on a quasistationarity assumption. Examples confirm that the optimal estimators often yield tremendous improvements in performance over existing methods. In particular, the ability of the optimal kernel to suppress interference is quite remarkable, thus making the proposed framework potentially useful for interference suppression via time-frequency filtering. >

A recently proposed time-frequency filtering technique has shown promising results for the enhancement of signal-averaged electrocardiograms. This method weights the short-time Fourier transform of the ensemble-averaged signal, analogous to the spectral domain Wiener filtering of stationary signals. In effect, it is a self-designing, time-varying Wiener filter applied to the high-resolution electrocardiogram (HRECG). In this study, the authors empirically show that the performance of the proposed technique is about 2-3 dB lower over the critical late-potential portion of the HRECG than the optimal fixed-window, time-frequency filter based on ideal a priori knowledge of statistics. Although this ideal knowledge and performance is unattainable in practice, these results suggest that there remains potential for modest improvement. To narrow this gap in performance, improvements based on alternative structures for the time-frequency filter, including time-varying short-time Fourier transform windows, are proposed. Simulation results show that an improved fixed-window technique can potentially yield an improvement of about 1-1.5 dB. By using properly chosen time-varying windows, the performance could potentially be improved of about 1-1.5 dB. By using properly chosen time-varying windows, the performance could potentially be improved even further. Thus, the improved techniques could produce an HRECG using fewer averages than the existing method, or that could tolerate a lower initial signal-to-noise ratio.

In this paper, we present a fast-converging adaptive frequency-domain minimum-variance-distortionlessresponse (MVDR) beamformer (FMV) for speech enhancement. The well-known FMV solution is optimum in the microphone array processing. However, the direct computation of the optimum FMV solution is often undesirable due to the the inversion of the spatio-spectral correlation matrix which is often unstable and is expensive for large arrays. To avoid the matrix inversion, we develop a fast-converging conjugate gradient (CG) algorithm for iteratively computing the FMV solution. Compared to the existing steepest descent (SD) algorithm, the CG algorithm can dramatically improve the convergence speed for the case of multiple interfering signals in speech enhancement. Therefore, the computational load and processing time can be significantly reduced. The speech enhancement experiments using a four-channel acousticvector-sensor (AVS) microphone array are demonstrated for the target speech signal corrupted by two and five interfering speech signals and superior performance are achieved.

We report the first use of a new platform, the Guiraudon Universal Cardiac Introducer (GUCI), in humans for accessing the left atrium for catheter-based ablations in patients with resistant atrial arrhythmias after total cavopulmonary derivation. The GUCI was originally designed for intracardiac access for closed, beating instrumental intracardiac surgery. The patient was a 29-year-old man with problematic atrial arrhythmias resistant to antiarrhythmic drugs because of severe uncontrolled bradycardia and because his pacemaker was explanted for infection. The GUCI was attached to the left atrial appendage via an anterior left thoracotomy. The GUCI was modified to accommodate introduction and manipulation of multiple catheters. This allowed electrophysiologists to perform catheter-based exploration and ablation. A DDD pacemaker was implanted, with an atrial endocardial lead introduced via the GUCI cuff and a ventricular epicardial lead. Postoperative atrial arrhythmias were controlled using amiodarone and atrial pacing. At the 12-month follow-up, the patient was arrhythmia- and drug-free and returned to full employment. This new access offers an additional new alternative atrial access to treat resistant arrhythmia after total cavopulmonary derivation. The current state-of-the-art makes patient selection difficult and uncomfortable for the surgeons because of incomplete preoperative electrophysiological data, such as a return to the beginning of surgery for arrhythmia; however, more cumulative experience with intraoperative electrophysiological data and new mapping technologies should address these limitations.

Objective We report our experience with ultrasound augmented reality (US-AR) guidance for mitral valve prosthesis (MVP) implantation in the pig using off-pump, closed, beating intracardiac access through the Guiraudon Universal Cardiac Introducer attached to the left atrial appendage. Methods Before testing US-AR guidance, a feasibility pilot study on nine pigs was performed using US alone. US-AR guidance, tested on a heart phantom, was subsequently used in three pigs (~65 kg) using a tracked transesophageal echocardiography probe, augmented with registration of a 3D computed tomography scan, and virtual representation of the MVP and clip-delivering tool (Clipper); three pigs were used to test feature-based registration. Results Navigation of the MVP was facilitated by the 3D anatomic display. AR displayed the MVP and the Clipper within the Atamai Viewer, with excellent accuracy for tool placement. Positioning the Clipper was hampered by the design of the MVP holder and Clipper. These limitations were well displayed by AR, which provided guidance for improved design of tools. Conclusions US-AR provided informative image guidance. It documented the flaws of the current implantation technology. This information could not be obtained by any other method of evaluation. These evaluations provided guidance for designing an integrated tool: combining an unobtrusive valve holder that allows the MVP to function properly as soon as positioned, and an anchoring system, with clips that can be released one at a time, and retracted if necessary, for optimal results. The portability of Real-time US-AR may prove to be the ideal practical image guidance system for all closed intracardiac interventions.

Optimal atrial septal defect (ASD) closure should combine off-pump techniques with the effectiveness and versatility of open-heart techniques. We report our experience with off-pump ASD closure using the Universal Cardiac Introducer (UCI) in a porcine model. The goal was to create an ASD over the fossa ovale (FO) and position a patch over the ASD under ultrasound (US) imaging and augmented virtual reality guidance.: An US probe (tracked with a magnetic tracking system) was positioned into the esophagus (transesophageal echocardiographic probe) for real-time image-guidance. The right atrium (RA) of six pigs was exposed via a right lateral thoracotomy or medial sternotomy. The UCI was attached to the RA wall. A punching tool was introduced via the UCI, navigated and positioned, under US guidance, to create an ASD into the FO. A patch with its holder and a stapling device were introduced into the RA via the UCI. The patch was positioned on the ASD. Occlusion of the ASD was determined using US and Doppler imaging.: The FO membrane was excised successfully in all animals. US image-guidance provided excellent visualization. The patch was positioned in all cases with complete occlusion of the ASD. The stapling device proved too bulky, impeding circumferential positioning.: Using the UCI, ASD closure was safe and feasible. US imaging, combined with virtual and augmented reality provided accurate navigating and positioning. This study also provided valuable information on the future design of anchoring devices for intracardiac procedures.

Real-time detection of intermittent events requires continual monitoring and processing of sensor data. A battery-powered device that supports multiple sensing modalities and processing algorithms has the potential to save energy by using expensive sensors and algorithms only when the event of interest is most likely to occur. To develop a policy for sensing and processing management, we adopt maximum sequential information gain as an objective criterion for such energy-limited systems, which can be solved via dynamic programming. For binary hypothesis testing with two sensing options, the optimal management policy is a simple two-threshold test on the posterior belief. Detection of bird presence/absence in a wildlife monitoring application shows up to a 37% reduction in error rate over standard constant-duty-cycle sensing.

Applications such as long-term environmental monitoring and large-scale surveillance demand reliable performance from sensor nodes while operating within strict energy constraints. There is often not enough power for sensors to make measurements all of the time. In these cases, one must decide when to run each sensor. To this end, we develop a one-step optimal sensor-scheduling algorithm based on expected-utility maximization. “Utility” is an application-specific measure of the benefit from a given sensor measurement. In sensing environments that can be modeled using a hidden Markov model, selecting the appropriate combination of sensors at each time instant enables maximization of the expected utility while operating within an energy budget. For some budgets, the utility-based algorithm shows more than 300% utility gains over a constant duty-cycle scheme designed to consume the same amount of energy. These benefits are dependent on the energy budget.

Existing techniques utilizing bio-inspired robotic whisker sensory systems generally address object feature extraction with artificial whiskers as a mechanical problem. We present an alternative signal-processing approach that formulates the object shape recognition as a 2-D tactile imaging problem. Observing that the whisker position at the very initial contact is similar to a ‘ray path’ in X-ray computed tomography; the 2-D cross-sectional image of the object can be tomographically reconstructed by measuring only the angle at the whisker base and the whisker-base location at the initial contact for each viewing angle. This approach has the important practical advantage of eliminating the need for the calibration of the force/moment measurements. Experimental results demonstrate the promising potential for bio-inspired systems using arrays of vibrissal sensors for object shape recognition.

Conventional mitral valve replacement requires a median sternotomy and cardio-pulmonary bypass with aortic crossclamping and is associated with significant mortality and morbidity which could be reduced by performing the procedure off-pump. Replacing the mitral valve in the closed, off-pump, beating heart requires extensive development and validation of surgical and imaging techniques. Image guidance systems and surgical access for off-pump mitral valve replacement have been previously developed, allowing the prosthetic valve to be safely introduced into the left atrium and inserted into the mitral annulus. The major remaining challenge is to design a method of securely anchoring the prosthetic valve inside the beating heart. The development of anchoring techniques has been hampered by the expense and difficulty in conducting large animal studies. In this paper, we demonstrate how prosthetic valve anchoring may be evaluated in a dynamic phantom. The phantom provides a consistent testing environment where pressure measurements and Doppler ultrasound can be used to monitor and assess the valve anchoring procedures, detecting pararvalvular leak when valve anchoring is inadequate. Minimally invasive anchoring techniques may be directly compared to the current gold standard of valves sutured under direct vision, providing a useful tool for the validation of new surgical instruments. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE)., SPIE Medical Imaging, February 5-7, 2012, San Diego, CA, USA, Series: Proceedings of SPIE; no. 8316

The role of autonomic balance during upright tilt in patients with neurally mediated syncope is unclear. To assess the characteristics of autonomic tone during orthostatic stress, 15 patients (mean age 32 years) with recurrent episodes of syncope (≥2) and a positive response to a 30-minute 60 ° upright tilt were compared with the following control groups: (1) 15 patients (mean age 33.5 years) with ≥2 episodes of recurrent syncope and a negative tilt response, and (2) 15 age-and sex-matched healthy volunteers (mean age 34 years) with no previous history of presyncope or syncope. Time domain measurements assessed were mean RR interval, standard deviation of normal RR intervals, and percentage of normal consecutive RR intervals differing by >50 ms. Frequency domain measurements of the lowfrequency (LF) and high-frequency (HF) bands were obtained, and the LF HF ratio was also calculated. All variables were calculated in the supine position and during the first 5 minutes of upright tilt. No significant difference was observed in the time and frequency domain variables in the supine position between control groups with a negative head-up tilt response and the group with a positive response. The percentage of normal consecutive RR intervals differing by >50 ms during the first 5 minutes of head-up tilt was significantly higher in the group with positive tilt tests than in the controls (25 ± 12% vs 7 ± 4%, p 2 / Hz) compared with the control group (1.1 ± 0.5 beats/min 2 /Hz, p LF HF ratio ≤6 during the first 5 minutes of tilt was highly predictive of syncope occurrence, subsequently noted at 15 ± 6 minutes of tilt (sensitivity 88%, specificity and positive predictive value 100%). Sympathovagal balance during the first 5 minutes of head-up tilt was markedly abnormal in patients with neurally mediated syncope and a positive head-up tilt response. Failure to withdraw parasympathetic tone during upright tilt may play a role in determining susceptibility to recurrent neurally mediated syncope.

BACKGROUND Patients with ischemic heart disease may require antianginal and/or antiarrhythmic regimes. These patients may also be candidates for implantable defibrillators. The effects of antiarrhythmics, such as bretylium, or calcium antagonists, such as verapamil, nifedipine, or diltiazem on internal defibrillation efficacy have been inconsistent or are unknown. METHODS AND RESULTS The effects of bretylium and verapamil on the energy requirements for ventricular defibrillation threshold (DFT) were determined in 92 open-chest anesthetized pigs. Triplicate DFTs were determined before and after intravenous administration of saline or one of four doses of verapamil, or saline or one of three doses of bretylium, in a balanced random order. Bretylium elicited a dose dependent reduction of DFT (F = 2.72 at 3 degrees and 36 degrees of freedom). DFT was significantly reduced with the highest dose of bretylium, (from 5.9 +/- 0.6 J to 4.7 +/- 0.6 J, mean +/- S.E.M.; P < 0.01). However, cardiac massage was sometimes needed at this dose due to low blood pressure immediately after defibrillation. In contrast, there was a positive correlation between DFT and serum verapamil concentration (r = 0.54, P < 0.001). The highest dose of verapamil significantly increased DFT (from 6.3 +/- 0.6 J to 8.2 +/- 1.1 J; P < 0.05), at a serum verapamil concentration of 86.6 +/- 6.8 ng/mL. CONCLUSIONS These data indicate that bretylium decreases while verapamil increases the minimum energy requirement for internal defibrillation. Caution is warranted in patients who may be hemodynamically comprised and may be candidates for bretylium therapy or in patients who have marginal DFT value who might be candidates for verapamil therapy.

A time-frequency representation based on an optimal, signal-dependent kernel has been previously been proposed in an attempt to overcome one of the primary limitations of bilinear time-frequency distributions: that the best kernel and distribution depend on the signal to be analyzed. The optimization formulation for the signal-dependent kernel results in a linear program with a unique feature: a tree structure that summarizes a set of constraints on the kernel. The authors present a fast algorithm based on sorting to solve a special class of linear programs that includes the problem of interest. For a kernel with Q variables, the running time of the algorithm is O(Q log Q), which is several orders of magnitude less than any other known method for solving this class of linear program. This efficiency enables the computation of the signal-dependent, optimal-kernel time-frequency representation at a cost that is on the same order as a fixed-kernel distribution. An important property of the optimal kernel is that it takes on essentially only the values of 1 and 0. >

This study considers the problem of representing high-resolution ECG (HRECG) signals in the time-frequency plane using spectrotemporal mapping (STM). High-resolution ECG signal components overlap in both time and frequency. The central issue with STM techniques is whether sufficient time-frequency resolution exists to discriminate normal and abnormal QRS signals. The trade-off between signal resolution in time and in frequency must be made without a priori knowledge of the HRECG's time-frequency structure. A simulation experiment was performed to examine the time-frequency distribution of normal, abnormal low-level (late potentials), and bundle branch block components of the QRS. Results suggest that discrimination of these signals with STM is problematic. Signals and noise within the HRECG ensemble can, however, be easily distinguished. This observation forms the basis of a new optimally filtered ensemble averaging technique for signal-to-noise ratio enhancement.

We present a 256-tap PN code acquisition filter in an 180nm CMOS process employing statistical system-level error compensation. Under voltage overscaling (VOS), near constant detection probability (P det ) above 90% with 5.8× reduction in energy is achieved at a supply voltage 27% below the point of first failure (PoFF) with an error rate (p e ) of 0.868. This is an improvement of 5.8× in energy-efficiency over conventional error free designs and 3.79× in energy-efficiency and 2170× in error tolerance over existing error tolerant designs.

Off-pump, intracardiac, beating heart surgery has the potential to improve patient outcomes by eliminating the need for cardiopulmonary bypass and aortic cross clamping but it requires extensive image guidance as well as the development of specialized instrumentation. Previously, developments in image guidance and instrumentation were validated on either a static phantom or in vivo through porcine models. This paper describes the design and development of a surgical phantom for simulating off-pump mitral valve replacement inside the closed beating heart. The phantom allows surgical access to the mitral annulus while mimicking the pressure inside the beating heart. An image guidance system using tracked ultrasound, magnetic instrument tracking and preoperative models previously developed for off-pump mitral valve replacement is applied to the phantom. Pressure measurements and ultrasound images confirm the phantom closely mimics conditions inside the beating heart. © 2011 SPIE., SPIE Medical Imaging, February 13-15, 2011, Lake Buena Vista, Florida, USA, Series: Proceedings of SPIE; no. 7964

Surgical procedures often have the unfortunate side-effect of causing the patient significant trauma while accessing the target site. Indeed, in some cases the trauma inflicted on the patient during access to the target greatly exceeds that caused by performing the therapy. Heart disease has traditionally been treated surgically using open chest techniques with the patient being placed "on pump" - i.e. their circulation being maintained by a cardio-pulmonary bypass or "heart-lung" machine. Recently, techniques have been developed for performing minimally invasive interventions on the heart, obviating the formerly invasive procedures. These new approaches rely on pre-operative images, combined with real-time images acquired during the procedure. Our approach is to register intra-operative images to the patient, and use a navigation system that combines intra-operative ultrasound with virtual models of instrumentation that has been introduced into the chamber through the heart wall. This paper illustrates the problems associated with traditional ultrasound guidance, and reviews the state of the art in real-time 3D cardiac ultrasound technology. In addition, it discusses the implementation of an image-guided intervention platform that integrates real-time ultrasound with a virtual reality environment, bringing together the pre-operative anatomy derived from MRI or CT, representations of tracked instrumentation inside the heart chamber, and the intra-operatively acquired ultrasound images.

This study assesses the accuracy of a new transesophageal (TEE) ultrasound (US) fluoroscopy registration technique designed to guide percutaneous aortic valve replacement. In this minimally invasive procedure, a valve is inserted into the aortic annulus via a catheter. Navigation and positioning of the valve is guided primarily by intra-operative fluoroscopy. Poor anatomical visualization of the aortic root region can result in incorrect positioning, leading to heart valve embolization, obstruction of the coronary ostia and acute kidney injury. The use of TEE US images to augment intra-operative fluoroscopy provides significant improvements to image-guidance. Registration is achieved using an image-based TEE probe tracking technique and US calibration. TEE probe tracking is accomplished using a single-perspective pose estimation algorithm. Pose estimation from a single image allows registration to be achieved using only images collected in standard OR workflow. Accuracy of this registration technique is assessed using three models: a point target phantom, a cadaveric porcine heart with implanted fiducials, and in-vivo porcine images. Results demonstrate that registration can be achieved with an RMS error of less than 1.5mm, which is within the clinical accuracy requirements of 5mm. US-fluoroscopy registration based on single-perspective pose estimation demonstrates promise as a method for providing guidance to percutaneous aortic valve replacement procedures. Future work will focus on real-time implementation and a visualization system that can be used in the operating room.

Atrial fibrillation (AF), the most common cardiac arrhythmia seen in general practice, can be promoted by conduction slowing. Cardiac impulse conduction depends on gap junction channels, which are composed of connexins (Cxs). While atrial Cx40 and Cx43 are equally expressed, AF studies have primarily focused on Cx40 reductions. The G60S Cx43 mutant (Cx43G60S/+) mouse model of Oculodentodigital dysplasia has a 60% reduction in Cx43 in the atria. Cx43G60S/+ mice were compared with Cx40-deficient (Cx40−/−) mice to determine the role of Cxs in atrial tachycardia/fibrillation (AT/F). Intracardiac electrophysiological studies were done in 6-mo-old male C57BL/6 Cx43G60S/+ mutant, littermate (Cx43+/+), Cx40−/−, and C57BL/6 wild-type (WT) mice. AT/F induction used an extra stimulus during sinus rhythm, programmed electrical stimulation, or burst pacing (1-ms pulses, 50-Hz, 400-ms train) in the absence and presence of carbachol (CCh). Atrial effective refractory periods did not differ between strains. Cx43G60S/+ mice were more susceptible to induction of sustained AT/F (duration >2 min, 9 of 12; maximum >35 min) compared with Cx43+/+ mice (3 of 11; χ2 = 5.24; P = 0.02). CCh enhanced sustained AT/F susceptibility in WT (from 1 of 12 without, to 7 of 10 with CCh; χ2 = 8.98; P < 0.01) but not in Cx40−/− mice (1 of 13 without vs. 2 of 9 with CCh; χ2 = 0.95; P = NS). The pattern of epicardial recordings during AT/F in Cx43G60S/+ mice was left preceding right, with left atrial fractionated activation patterns consistent with clinical observations of AF. In conclusions, while Cx43G60S/+ mice had severe AT/F, Cx40−/− mice were resistant to CCh-induced AT/F.

Most fish have the capability of sensing flows and nearby movements even in dark or murky conditions by using the lateral line organs. This enables them to perform a variety of underwater activities, such as localizing prey, avoiding predators, navigating in narrow spaces, and schooling. To emulate this capability for Autonomous Underwater Vehicles, we developed an artificial lateral line using an array of Micro-Electro-Mechanical-Systems (MEMS) flow sensors. The signals collected via the artificial lateral line are then processed by an adaptive beamforming algorithm developed from Capon's method. The system produces 3D images of source locations for different hydrodynamic activities, including the vibration of a dipole source and the movement of a tailflicking crayfish. A self-calibration algorithm provides the capability of self-adaptation to different environments. Lastly, we give a Cramer-Rao bound on the theoretical performance limit which is consistent with experimental results.

A frameless method for stereotactic multiple arc radiotherapy (SMART) is described. Three short gold wires are implanted in the scalp approximately 100 mm apart. These are localized in a computed tomographic or angiographic study along with the target. Subsequently the gold markers are localized on beam films and the target position calculated using a computer program ISOLOC. This program provides the couch movements required to move the target to the isocentre and a micropositioner attached to the couch is used to make the adjustment. Beam films are repeated until the movements required are less than 1 mm in any direction. It is shown that the simple procedures of implanting the markers subcutaneously do not provide a stable reference system in about 25% of patients and the markers are now screwed into the cranium. The precision of the method is evaluated by phantom studies and measurements taken during several hundred treatments.

Objectives. To understand the mechanisms of postdefibrillation arrhythmias and failed defibrillation, we studied the cellular effects of high voltage shocks on different cardiomyocytes in the dog. Background. The causes of postdefibrillation arrhythmias and unsuccessful defibrillation are not clear. Methods. High voltage shocks with voltage differentials of 9.3 to 97.6 V/cm were delivered to isolated canine papillary muscles with attached Purkinje fibers. Transmembrane potentials were recorded simultaneously from the Purkinje fiber and the ventricular muscle using standard microelectrode techniques. Results. After delivery of high voltage shocks, significant depolarization and rapid firing were observed in Purkinje fibers. The maximal rate of the rapid firing in the Purkinje fibers correlated with shock intensity (r = 0.69, p < 0.05). In contrast, in ventricular muscle, only slight depolarization and a transient refractory state were observed after the shock. The incidence of the refractory state was correlated with both the shock intensity and the rate of the rapid firing in the Purkinje fiber (r = 0.89 and 0.74, p < 0.01 and 0.05, respectively). Propranolol at a concentration sufficient for complete beta-blockade (1 mg/liter) did not change the tissue response to shocks but suppressed or abolished the shock-induced rapid firing of Purkinje fibers at a higher concentration (3 mg/liter). Blockade of the slow calcium channel with verapamil (400 μg/dl) did not alter the responsiveness of the preparation to shocks. Conclusion. These results indicate that high voltage shocks induce different responses in Purkinje fibers and ventricular muscle. The shock-induced rapid firing in the Purkinje fiber may contribute to postshock arrhythmias and possibly refibrillation in some cases. The shock-induced transient refractory state in the ventricular muscle may prevent the ventricle from responding to the rapid firing and thus may decrease the incidence of postshock arrhythmias.

Time-frequency distributions are two-dimensional functions that indicate the time-varying frequency content of one-dimensional signals. Each bilinear time-frequency distribution corresponds to a kernel function that controls its cross-component suppression properties. Current distributions rely on fixed kernels, which limit the class of signals for which a given distribution performs well. In this paper, we propose a signal-dependent kernel that changes shape for each signal to offer improved time-frequency representation for a large class of signals. The kernel design procedure is based on quantitative optimization criteria and two-dimensional functions that are Gaussian along radial profiles. We develop an efficient scheme based on Newton's algorithm for finding the optimal kernel; the cost of computing the signal-dependent time-frequency distribution is close to that of fixed-kernel methods. Examples using both synthetic and real-world multi-component signals demonstrate the effectiveness of the signal-dependent approach-even in the presence of substantial additive noise. An attractive feature of this technique is the ease with which application-specific knowledge can be incorporated into the kernel design procedure.

A new time-frequency distribution (TFD) that adapts to each signal and so offers a good performance for a large class of signals is introduced. The design of the signal-dependent TFD is formulated in Cohen's class as an optimization problem and results in a special linear program. Given a signal to be analyzed, the solution to the linear program yields the optimal kernel and, hence, the optimal time-frequency mapping for that signal. A fast algorithm has been developed for solving the linear program, allowing the computation of the signal-dependent TFD with a time complexity on the same order as a fixed-kernel distribution. Besides this computational efficiency, an attractive feature of the optimization-based approach is the ease with which the formulation can be customized to incorporate application-specific knowledge into the design process. >

Two techniques for efficient computation of filters that support time-varying coefficients are developed. These methods are forms of distributed arithmetic that encode the data, rather than the filter coefficients. The first approach efficiently computes scalar-vector products, with which a digital filter is easily implemented in a transpose-form structure. This method, based on digital coding, supports time-varying coefficients with no additional overhead. Alternatively, distributed-arithmetic schemes that encode the data stream in sliding blocks support efficient direct-form filter computation with time-varying coefficients. A combination of both of these techniques greatly reduces the computation required to implement LMS adaptive filters. >

It has been demonstrated recently that both biphasic and sequential pulse defibrillation shocks are superior to monophasic defibrillation shocks in animals and humans. There is little information directly comparing these two waveforms when pulse characteristics, subjects, and total electrode surface areas are kept constant. We determined the defibrillation threshold intraoperatively in 12 patients undergoing arrhythmia surgery, with the use of two or three patch electrodes (Medtronic 6891 and 6892), while keeping the electrode surface area constant. Patients were randomized in a crossover design for determinations of defibrillation threshold by means of biphasic and sequential pulse shocks. Leading-edge delivered current and delivered energy were significantly lower with sequential pulse shocks than with biphasic shocks (delivered energy means +/- SEM 3.6 +/- 0.7 joules vs 5.5 +/- 0.9 joules, respectively). We conclude that sequential pulse defibrillation with three defibrillating electrodes provides an important current delivery system not matched by biphasic shocks with two electrodes when subjects, waveform characteristics, and total electrode surface areas are kept constant.

Alcohol ingestion has been associated with cardiac arrhythmias and may initiate fibrillation in patients with automatic defibrillators. The effect of alcohol on defibrillation efficacy is unknown. To assess the acute effects of alcohol on defibrillation efficacy, triplicate defibrillation thresholds (DFTs) were determined before and after intravenous administration of 25% ethanol. Fifty-two pigs were randomized into four groups: (1) control, 6 mL/kg of saline over 10 minutes (n = 12); (2) low dose, 6 mL/kg of 25% ethanol over 10 minutes (n = 12); (3) mid dose, 0.45 mL/kg per minute for 30 minutes followed by 0.045 mL/kg per minute for 45 minutes (n = 12); and (4) high dose, 0.6 mL/kg per minute for 30 minutes followed by 0.06 mL/kg per minute for 45 minutes (n = 16). Three coil defibrillating electrodes (Medtronic 6888) were sutured to the epicardium of the right and left ventricles for defibrillation shocks. Ventricular fibrillation was induced using alternating current and after 10 seconds of fibrillation, the minimum energy for defibrillation was established using sequential pulse defibrillation. Triplicate determinations were obtained before and after saline or ethanol infusion. Alcohol elevated DFT in a dose related manner. Control and low dose groups thresholds were unchanged, but the mid dose approached statistical significance (6.8 +/- 0.7 vs 7.6 +/- 0.9 J, 0.05 < P < 0.1) and the high dose was significantly elevated (8.5 +/- 0.7 vs 11.2 +/- 1.1 J, P < 0.01). Ventricular effective refractory periods and cycle lengths between fibrillatory waves did not differ before and after the high dose ethanol.(ABSTRACT TRUNCATED AT 250 WORDS)

The proportional-bandwidth and constant-bandwidth time-frequency signal decompositions of the wavelet, Gabor, and Wilson orthonormal bases have attracted substantial interest for representing nonstationary signals. However, these representations are limited in that they are based on rectangular tessellations of the time-frequency plane. While much effort has gone into methods for designing nice wavelet and window functions for these frameworks, little consideration has been given to methods for constructing orthonormal bases employing nonrectangular time-frequency tilings. The authors take a first step in this direction by deriving two new families of orthonormal bases and frames employing elements that shear, or chirp, in the time-frequency plane, in addition to translate and scale. The new scale-shear fan bases and shift-shear chevron bases are obtained by operating on an existing: wavelet, Gabor (1946), or Wilson basis set with two special unitary warping transformations. In addition to the theoretical benefit of broadening the class of valid time-frequency plane tilings, these new bases could possibly also be useful for representing certain types of signals, such as chirping and dispersed signals. >

This position paper is the result of discussions between the Associate Editors and Editors of the Canadian Journal of Physiology and Pharmacology, which took place over the summer of 2013 in response to the need to have some guidelines regarding publishing research findings that involved compounds or extracts of natural products that have not yet been fully characterized. Some journals have adopted the policy that they will not publish such studies. In the instruction for authors for the journal Basic & Clinical Pharmacology & Toxicology it states as follows: “For all compounds used in the studies, the chemical constitution and composition should be known, also for natural compounds” (http://onlinelibrary.wiley.com/journal/10.1111/%28ISSN%291742–7843/ homepage/ForAuthors.html). However, I will argue that to do so is not only a form of censorship, but it also ignores the need for disclosure of information that may be critical to the evaluation of the neutral, beneficial, or detrimental properties of such compounds. Failure to expose these studies to full scientific scrutiny abandons the primary tenant of science: to dispassionately examine all of the facts. Further, failure to do somay put individuals at undue risk, and thus is ethically questionable. Although it is much easier to evaluate the potential when there is a “defined chemical”, and certainly easier to find reviewers, extracts of native species may not have reached that level of purity. Indeed, the American College of Cardiology ACCF Complementary Medicine Experts Consensus publication on complementary andalternativemedicines concluded that “FewU.S. products benefit from rigorous characterization and standardization necessary for clinical study” (Vogel et al. 2005). Nevertheless, 40% to 50% of Americans are using complementary medicines together with prescription drugs (Vogel et al. 2005). Thus, to ignore the potential interactions of nonprescription usage is putting a very high proportion of the population at risk (Zipes 2001; Tachjian et al. 2010). To restrict CJPP publication to only fully chemically characterized compounds, removes from scientific scrutiny some early and potentially important discoveries. For example, there is the classical description in 1785 by William Withering, an English botanist, chemist, geologist, and physician, of the benefits of extracts from the foxglove (Digitalis purpurea) (Goldthorp 2009). Withering's description has been described as the beginning of modern therapeutics. Subsequently, there was the determination of the active compound digitalis, which is still in common clinical use today. Another example is a naturally occurring biological product, the long term search for the elusive endothelium-derived relaxation factor “EDRF”. It took decades to identify this as the gas nitric oxide (NO) (Moncada 2006). There also is the example provided by my colleague Dr. Ed Lui, (pers. comm.) of the purification of rosy periwinkle (Cathanthus roseus) extract. The best knownmedical agents from rosy periwinkle arose from investigation into the plant's use in Jamaican folk medicine. Known as periwinkle tea in Jamaica, the well-known folk-use of rosy periwinkle led researchers to delve into its natural chemical properties in the 1950s. Scientific analysis of rosy periwinkle led to the discovery of 2 previously unknown compounds, vincristine and vinblastine, which have been subsequently developed into potent medicines to save lives from leukemia (Bucur et al. 2013) and Hodgkin's lymphoma (Skoetz et al. 2013), respectively. One final example is the recent publication by Cheng (Yale University, New Haven, Connecticut, USA), of a nonpurified product based on a traditional Chinese formula, and its ability to reduce chemotherapy-induced gastrointestinal toxicity (Lam et al. 2010). Of course not all studies show beneficial responses: toxicity is equally important to document. A neutral response is also important as the sale of “natural products” in North America has been stated as reaching 30 billion dollars in 2001 (Vogel et al. 2005). CJPP is not considering an open door policy for undisciplined science. Rather, it is proposing a set of guidelines to assist in maintaining an ethical and scientifically rigorous approach to publishing articles that use natural products. The approach in this set of guidelines attempts to reduce potential misinformation; however, at the same time, following the guidelines would permit some early exploratory descriptions and knowledge of/alert to potentially beneficial/harmful compounds being assessed. Two keys to the publication of the results include (i) clear and detailed descriptions of the methods used, and (ii), to completely as possible describe the way in which the product was obtained. It would be necessary to have these “keys” in the Instructions to Authors, and it would be important for the journal to screen articles for compliance prior to sending to the Associate Editors for review assignment. In conclusion, exclusion from publication simply because a study uses a natural product is not only a form of censorship, but it removes the important disclosure of information that may be critical to the evaluation of the neutral, beneficial, or detrimental properties of such compounds. It removes these studies from rigorous scientific scrutiny of all the facts. A lack of rigorous scientific scrutiny may put individuals at undue risk and thus, in my opinion, is ethically questionable.