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Mark Schwartz

Publications and source records attributed to Mark Schwartz.

6 recordsLinked to original sources
PubMed2006

Performance of a new single-chamber ICD algorithm: discrimination of supraventricular and ventricular tachycardia based on vector timing and correlation.

AIMS: Interval- and morphology-based algorithms have been used in modern implantable cardioverter defibrillators (ICDs) to discriminate supraventricular tachycardia (SVT) from other rhythms. A newly developed ICD discrimination algorithm, Rhythm ID (Guidant Corporation, St Paul, MN, USA), uses both interval-based metrics and an electrogram vector timing and correlation (VTC) algorithm in a dual-chamber ICD. In a single-chamber ICD, Rhythm ID contains only the VTC component. This study conducted a retrospective analysis of the performance of Rhythm ID for the detection of induced and spontaneous rhythms in a single-chamber ICD. METHODS AND RESULTS: This study gathered the data from a prospective, multicentre clinical trial. Ninety-six patients were implanted with a dual-chamber ICD. For this study, each episode was analysed to determine the performance of the single-chamber ICD Rhythm ID algorithm. The mean age of the patients implanted with the device was 67+/-11 years. Seventy-eight patients were male. The primary cardiovascular disease was coronary artery disease and the primary tachyarrhythmia was monomorphic ventricular tachycardia (VT). The mean follow-up time was 11.4 months. A total of 369 induced and spontaneous ventricular arrhythmias was analysed. The algorithm detected 100% of ventricular arrhythmias. Four hundred and forty-two SVT episodes were analysed, including 145 induced and 297 spontaneous. The SVTs were atrial fibrillation (n=199), atrial flutter (n=135), and 1:1 SVT (n=108). The single-chamber ICD Rhythm ID algorithm successfully discriminated 403 SVT episodes and achieved a specificity of 91%. CONCLUSION: The single-chamber version of Rhythm ID demonstrated high specificity without compromising sensitivity.

Aged↗
PubMed2006

Measurement of protection afforded by ultraviolet-absorbing window film using an in vitro model of photodamage.

BACKGROUND AND OBJECTIVES: The effects of chronic sun damage including telangiectasias, solar lentigos, rhytides, enlarged pores, sagging skin, and pre-cancerous and cancerous growths are among the most common presenting complaints in a dermatologist's office. These changes are often worse on the driver's side of the face, emphasizing the role of UVA exposure received while driving in producing these changes. This study was undertaken to measure the ability of car window glass alone and in combination with ultraviolet (UV)-absorbing film to reduce UV-damage as measured using an established in vitro model of photoprotection. STUDY DESIGN MATERIALS AND METHODS: Using the 3T3 neutral red uptake photoprotection assay with solar simulating radiation (SSR) administered by a xenon arc solar simulator, we measured the photoprotection ability of auto glass, window film that filters UV radiation, and the combination of window film and auto glass. RESULTS: As measured by the 3T3 neutral red uptake photoprotection assay, auto glass reduced cell death from SSR by 29%, while window film reduced it 90%, and the combination of auto glass and film reduced cell death by 93%, when compared to unfiltered SSR. CONCLUSIONS: Window film that filters UV radiation results in dramatic reductions in cytotoxicity when measured by the neutral red uptake photoprotection assay. Widespread use of window film provides an ever-present barrier to ultraviolet A (UVA) exposure and could potentially reduce the detrimental effects of UVA, including photoaging, skin cancer, and ocular damage, such as cataracts. In addition, such film is essential for patients suffering from conditions sensitive to UV radiation, such as lupus erythematosis.

Animals↗
PubMed2006

Clinical experience with tiered atrial therapies and atrial arrhythmia prevention algorithms in a dual chamber cardioverter defibrillator.

INTRODUCTION: The acceptance of atrial arrhythmia features in implantable cardioverter defibrillators (ICDs) will depend on their ability to appropriately discriminate atrial tachyarrhythmias/atrial fibrillation (AT/AF). This study tested the effectiveness of an atrial/ventricular ICD with advanced atrial detection and new algorithms designed to prevent atrial arrhythmias. METHODS AND RESULTS: Ninety-five patients were implanted with a dual chamber ICD (Model 1900, Guidant Corporation, MN, USA) at 25 US centers. Ten patients received a coronary sinus (CS) lead allowing a defibrillation vector for AT/AF cardioversion. Follow-up was 12.2 months. The addition of new atrial features designed for detection, discrimination, and prevention of AT/AF had no adverse effect upon detection of induced ventricular fibrillation (VF) (mean detection time with new features ON was 2.22 seconds vs 2.19 seconds with features OFF). A total of 100% of the induced and spontaneous ventricular and atrial arrhythmias receiving shock therapy were reviewed as appropriate detection. Atrial shock conversion efficacy for spontaneous and induced AT/AF episodes was 83% and 96%, respectively (144 spontaneous, 162 induced episodes). A 3-month randomized crossover trial of atrial preventative pacing features did not result in adverse effects, but there was no clinical efficacy for prevention of AT/AF. CONCLUSION: Enhanced atrial detection and discrimination features combined with tiered atrial therapies did not adversely impact the ability of the ICD (Model 1900) to appropriately detect and treat ventricular tachyarrhythmias.

Aged↗
PubMed2002

Advanced rhythm discrimination for implantable cardioverter defibrillators using electrogram vector timing and correlation.

INTRODUCTION: Discrimination of ventricular and supraventricular arrhythmias remains one of the major challenges for appropriate implantable defibrillator (ICD) therapy delivery. The electrogram vector timing and correlation (VTC) algorithm was developed for such rhythm discrimination. The VTC algorithm differentiates normally conducted supraventricular beats from abnormally conducted ventricular beats by comparing the timing and correlation of rate and shock channel electrograms. METHODS AND RESULTS: Rate and shock channel electrograms of sinus rhythm and induced arrhythmias were collected from 93 patients during ICD placement. The algorithm was developed using data from 50 patients and prospectively tested in a software model with the remaining 43 patients. A sinus rhythm reference was formed by averaging complexes of the shock channel signal aligned by the peak amplitude of the rate channel. Eight features measuring the amplitude and timing of shock channel signal characteristics were extracted from the reference for comparison. When a high-rate rhythm was detected, the VTC algorithm computed the correlation of the arrhythmia complex features with the reference. Rhythms with a sufficient number of uncorrelated beats were classified as ventricular tachycardia (VT). In a dual-chamber implementation, the VTC algorithm is integrated with ventricular and atrial rate comparison (V>A) and stability above an atrial fibrillation rate threshold. The test set consisted of 117 arrhythmias. Dual-chamber sensitivity was 100% (81/81 VT) and specificity was 97% (35/36 supraventricular tachycardia). Single-chamber analysis demonstrated 99% sensitivity and 97% specificity. CONCLUSION: The VTC algorithm demonstrated high sensitivity and specificity in discriminating between ventricular and supraventricular arrhythmias.

Aged↗
PubMed2002

Open reduction and internal fixation of humeral nonunions : a biomechanical and clinical study.

BACKGROUND: Several studies have compared different methods for fixation of the midpart of the humeral shaft, but there are only scattered data regarding which type of plate construct provides the best fixation for humeral nonunion. The objectives of this study were (1) to obtain objective data on the performance of four different plate constructs used for fixation of humeral nonunion, and (2) to report our clinical experience with plate fixation of thirty-seven nonunions of the midpart of the humeral shaft. METHODS: In the first part of the study, four plate constructs were compared in a Sawbones model. The groups consisted of (1) a posterior limited-contact dynamic compression plate alone; (2) a posterior limited-contact dynamic compression plate and an interfragmentary screw; (3) a posterior limited-contact dynamic compression plate, a lateral 3.5-mm reconstruction plate, and an interfragmentary screw; and (4) a posterior limited-contact dynamic compression plate and a lateral 3.5-mm reconstruction plate. Tests were performed with use of an MTS Bionix machine in anterior-posterior four-point bending, medial-lateral four-point bending, and external rotation torque. In the second part of the study, the charts of thirty-seven consecutive patients in whom a nonunion of the midpart of the humeral shaft had been treated with plate fixation were reviewed retrospectively. The average age of the patients was forty-eight years (range, thirteen to seventy-eight years). Nineteen patients were treated with a single posterior plate, and eighteen were treated with a two-plate construct with the plates parallel and lying at 90 degrees to each other. All of the nonunions were treated with bone-grafting, and an interfragmentary screw was used in thirty-six of the thirty-seven patients. Radiographs and the clinical status were evaluated at an average of thirteen months postoperatively. RESULTS: The biomechanical testing showed that the two-plate constructs were significantly stiffer than the single-plate constructs in all test modes (p < 0.05). In the clinical part of the study, thirty-four (92%) of the nonunions healed without complications at an average of 4.8 months. Two nonunions treated with the two-plate construct and one treated with one plate failed to heal. CONCLUSIONS: No significant difference in the healing rate was found between the two clinical groups (p = 0.4, beta = 0.9), and the overall healing rate was 92%. However, a two-plate construct with the plates at right angles is mechanically stiffer than a single-plate construct, which might be helpful if rigid stabilization of the humerus at the midshaft level is needed.

Adolescent↗