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Cardiac electrical alternans have been associated with spontaneous ventricular arrhythmias during myocardial ischemia. The study aims were to use a new algorithm to measure depolarization and repolarization alternans from epicardial electrograms in an ischemia model and to evaluate which features are predictive of ventricular fibrillation (VF). The left anterior descending coronary artery was occluded in 21 dogs, of which 6 developed spontaneous VF. Four seconds of unipolar epicardial electrograms was recorded before and 5 min after occlusion from an 8 x 14-electrode plaque placed on the anterior left ventricle. Alternans amplitudes were estimated with a triangular wave-fitting algorithm and for each unipolar electrogram for various measurements of the QRS and ST-T wave amplitude. The root mean square error was computed for each fit. Receiver-operator characteristic curves were used to determine whether prevalence of alternans having estimated alternans amplitude-to-error ratio (A/E) above a given threshold could distinguish the dogs who had and did not have spontaneous VF. The prevalence of alternans after ischemia was highly predictive of VF when measured both during depolarization (sensitivity of 83% and specificity of 87%) and during repolarization (sensitivity of 100% and specificity of 73%). The optimal alternans A/E ranged from 1 to 4. There were no differences in the level of discordance or alternans amplitude between dogs who developed VF versus dogs who did not. The prevalence of alternans in the ventricles may be the key risk factor for developing VF during myocardial ischemia when short-term recordings are used.

Background: Reverse high-contrast (white-onblack) visual acuity has been shown to improve visual acuity in older patients and patients with pathology under photopic testing. In this study, we investigated whether reverse contrast results in improved visual acuity at mesopic light levels. Methods: Monocular visual acuities (logMAR) were assessed at four different light levels (1 photopic {94 cd/m2} and 3 mesopic {3 cd/m2, 0.75 cd/m2, and 0.38 cd/m2}) in 47 visually normal subjects (27.4±9.3 years). Visual acuity was assessed using an E-ETDRS algorithm, in standard and reverse contrast, at 3 m. Repeated measures ANOVA with post-hoc Tukey testing was used to analyze the data across the light levels. Results: The mean standard contrast visual acuity was -0.07±0.06 under the photopic condition, 0.06±0.08 at 3 cd/m2, 0.17±0.08 at 0.75 cd/m2, and 0.28±0.09 at 0.38 cd/m2. For reverse contrast, it was -0.08±0.06 under the photopic condition, 0.01±0.07 at 3 cd/m2, 0.12±0.08 at 0.75 cd/m2, and 0.22±0.09 at 0.38 cd/m2. There was a significant improvement in visual acuity using reverse contrast under all mesopic light levels (p<0.001), but not under photopic conditions (p=0.15). Conclusions: At mesopic light levels, there were significant differences between standard and reverse contrast. The use of mesopic reverse-contrast visual acuity could be another way to detect subtle changes in visual acuity. Reversecontrast presentations under low lighting conditions may be advantageous for a patient's visual acuity. [ABSTRACT FROM AUTHOR]

Dofetilide Effect on f Waves in AF Introduction The electrocardiogram (ECG) fibrillatory (f) wave characteristics in atrial fibrillation (AF) could provide important information regarding the efficacy of antiarrhythmic drug therapy. Methods and Results To measure the effects of dofetilide on the surface ECG f wave characteristics in patients with persistent AF, baseline and post-drug (2 hours after first dose and after multiple doses) ECGs in 31 patients with persistent AF admitted for dofetilide loading were evaluated. A QRST template subtraction algorithm was used to yield an atrial ECG. Fast Fourier transform analysis was performed to evaluate the maximum organizational index (OI), the dominant frequency (DF) in the lead with max OI, the median DF for all leads, and the vector magnitude f wave amplitude. Dofetilide reduced DF in the lead with the max OI (6.32 ± 0.98 Hz at baseline vs. 4.83 ± 0.63 Hz after final dose, P < 0.0001) and median DF (6.46 ± 0.87 Hz vs. 4.92 ± 0.62 Hz, P < 0.0001). Dofetilide also increased the maximum OI from 0.52 ± 0.11 at baseline to 0.59 ± 0.11 after final dose (P = 0.02). Of the 29 patients with long-term follow-up, the 22 (76%) with recurrent AF on dofetilide had a lower baseline DF in the lead with the max OI (6.01 ± 1.08 vs. 6.89 ± 0.46; P = 0.05). The change in DF after dofetilide did not correlate with the change in QTc interval. Conclusions The standard ECG can be used to assess atrial rate in AF. This may be useful to assess antiarrhythmic drug effects for treatment of AF. [ABSTRACT FROM AUTHOR]

Teleradiology applications and universal availability of patient records using web-based technology are rapidly gaining importance. Consequently, digital medical image security has become an important issue when images and their pertinent patient information are transmitted across public networks, such as the Internet. Health mandates such as the Health Insurance Portability and Accountability Act require healthcare providers to adhere to security measures in order to protect sensitive patient information. This paper presents a fully reversible, dual-layer watermarking scheme with tamper detection capability for medical images. The scheme utilizes concepts of public-key cryptography and reversible data-hiding technique. The scheme was tested using medical images in DICOM format. The results show that the scheme is able to ensure image authenticity and integrity, and to locate tampered regions in the images. [ABSTRACT FROM AUTHOR]