Ventricular cycle length characteristics estimative of prolonged RR interval during atrial fibrillation

BACKGROUND

When atrial fibrillation (AF) is incessant, imaging during a prolonged ventricular RR interval may improve image quality. It was hypothesized that long RR intervals could be predicted from preceding RR values.

METHODS

From the PhysioNet database, electrocardiogram RR intervals were obtained from 74 persistent AF patients. An RR interval lengthened by at least 250 ms beyond the immediately preceding RR interval (termed T0 and T1, respectively) was considered prolonged. A two-parameter scatterplot was used to predict the occurrence of a prolonged interval T0. The scatterplot parameters were: (1) RR variability (RRv) estimated as the average second derivative from 10 previous pairs of RR differences, T13-T2, and (2) Tm-T1, the difference between Tm, the mean from T13 to T2, and T1. For each patient, scatterplots were constructed using preliminary data from the first hour. The ranges of parameters 1 and 2 were adjusted to maximize the proportion of prolonged RR intervals within range. These constraints were used for prediction of prolonged RR in test data collected during the second hour.

RESULTS

The mean prolonged event was 1.0 seconds in duration. Actual prolonged events were identified with a mean positive predictive value (PPV) of 80% in the test set. PPV was >80% in 36 of 74 patients. An average of 10.8 prolonged RR intervals per 60 minutes was correctly identified.

CONCLUSIONS

A method was developed to predict prolonged RR intervals using two parameters and prior statistical sampling for each patient. This or similar methodology may help improve cardiac imaging in many longstanding persistent AF patients.

Use of shape-from-shading to estimate three-dimensional architecture in the small intestinal lumen of celiac and control patients

BACKGROUND

As measured from videocapsule endoscopy images, the small intestinal mucosa of untreated celiac patients has significantly greater and more varied texture compared to normal patients. Three-dimensional modeling using shape-from-shading principles may further increase classification accuracy.

METHODS

A sequence of 200 consecutive videocapsule images acquired at a 2s(-1) frame rate and 576×576 pixel dimension, were obtained at four locations in the small intestinal lumen of ten patients with biopsy-proven celiac disease and ten control patients. Each two-dimensional image was converted to a three-dimensional architectural approximation by considering the 256 grayscale level to be linearly representative of image depth. From the resulting three-dimensional architecture, distinct luminal protrusions, representative of the macro-architecture, were automatically identified by computer algorithm. The range and number of protrusions per image, and their width and height, were determined for celiacs versus controls and tabulated as mean±SD.

RESULTS

The mean number of villous protrusions per image was 402.2±15.0 in celiacs versus 420.8±24.0 in controls (p<0.001). The average protrusion width was 14.7 pixels in celiacs versus 13.9 pixels in controls (p=0.01). The mean protrusion height was 3.10±2.34 grayscale levels for celiacs versus 2.70±0.43 grayscale levels for controls (p<0.001). Thus celiac patients had significantly fewer protrusions on the luminal surface of the small intestine as compared with controls, and these protrusions had greater dimensions, suggesting they are indicative of a mosaic (cobblestone) macro-architectural pattern which is common in celiacs.

CONCLUSIONS

Shape-from-shading modeling is useful to explore luminal macro-architecture and to detect significant differences in luminal morphology in celiac versus normal patients, which can increase the usefulness of videocapsule studies.

Ibutilide increases the variability and complexity of atrial fibrillation electrograms: antiarrhythmic insights using signal analyses

INTRODUCTION

Intravenous ibutilide is used to convert atrial fibrillation (AF) to sinus rhythm (SR) due to its Class III antiarrhythmic mechanisms. However, the effects of ibutilide on local electrograms (EGMs) during AF have not been elucidated.

METHODS AND RESULTS

We used EGM analysis techniques to characterize how ibutilide administration changes the frequency, morphology, and repeatability of AF EGM signals, thereby providing insight into ibutilide's antiarrhythmic mechanism of action. AF recordings were collected from 21 patients with AF, both before and after ibutilide administration. The effects of ibutilide on the following AF EGM parameters were assessed: (1) dominant frequency (DF), (2) variations in EGM amplitude and overall morphology, (3) repetition of EGM patterns, and (4) complexity of the AF frequency spectra. When comparing pre- versus post-ibutilide administration EGMs, DF decreased from 5.45 Hz to 4.02 Hz (P < 0.0001). There was an increase in the variability of both AF EGM amplitudes (P = 0.003) and overall AF EGM morphologies (P = 0.003). AF EGM pattern repetitiveness decreased (P = 0.01), and the AF frequency spectral profile manifested greater complexity (P = 0.02).

CONCLUSIONS

Novel EGM signal analysis techniques reveal that ibutilide administration causes increased complexity in the atrial electrical activation pattern with decreasing rate. These findings may be explained by the progressive destabilization of higher frequency, more homogeneous primary drivers of AF over the course of ibutilide administration, and/or less uniform propagation of atrial activation, until AF maintenance becomes more difficult and either transforms to atrial tachycardia or terminates to SR.

Implementation of a polling protocol for predicting celiac disease in videocapsule analysis

AIM: To investigate the presence of small intestinal villous atrophy in celiac disease patients from quantitative analysis of videocapsule image sequences.

METHODS: Nine celiac patient data with biopsy-proven villous atrophy and seven control patient data lacking villous atrophy were used for analysis. Celiacs had biopsy-proven disease with scores of Marsh II-IIIC except in the case of one hemophiliac patient. At four small intestinal levels (duodenal bulb, distal duodenum, jejunum, and ileum), video clips of length 200 frames (100 s) were analyzed. Twenty-four measurements were used for image characterization. These measurements were determined by quantitatively processing the videocapsule images via techniques for texture analysis, motility estimation, volumetric reconstruction using shape-from-shading principles, and image transformation. Each automated measurement method, or automaton, was polled as to whether or not villous atrophy was present in the small intestine, indicating celiac disease. Each automaton’s vote was determined based upon an optimized parameter threshold level, with the threshold levels being determined from prior data. A prediction of villous atrophy was made if it received the majority of votes (≥ 13), while no prediction was made for tie votes (12-12). Thus each set of images was classified as being from either a celiac disease patient or from a control patient.

RESULTS: Separated by intestinal level, the overall sensitivity of automata polling for predicting villous atrophy and hence celiac disease was 83.9%, while the specificity was 92.9%, and the overall accuracy of automata-based polling was 88.1%. The method of image transformation yielded the highest sensitivity at 93.8%, while the method of texture analysis using subbands had the highest specificity at 76.0%. Similar results of prediction were observed at all four small intestinal locations, but there were more tie votes at location 4 (ileum). Incorrect prediction which reduced sensitivity occurred for two celiac patients with Marsh type II pattern, which is characterized by crypt hyperplasia, but normal villous architecture. Pooled from all levels, there was a mean of 14.31 ± 3.28 automaton votes for celiac vs 9.67 ± 3.31 automaton votes for control when celiac patient data was analyzed (P < 0.001). Pooled from all levels, there was a mean of 9.71 ± 2.8128 automaton votes for celiac vs 14.32 ± 2.7931 automaton votes for control when control patient data was analyzed (P < 0.001).

CONCLUSION: Automata-based polling may be useful to indicate presence of mucosal atrophy, indicative of celiac disease, across the entire small bowel, though this must be confirmed in a larger patient set. Since the method is quantitative and automated, it can potentially eliminate observer bias and enable the detection of subtle abnormality in patients lacking a clear diagnosis. Our paradigm was found to be more efficacious at proximal small intestinal locations, which may suggest a greater presence and severity of villous atrophy at proximal as compared with distal locations.

Comparison of spectral estimators for characterizing fractionated atrial electrograms

Background

Complex fractionated atrial electrograms (CFAE) acquired during atrial fibrillation (AF) are commonly assessed using the discrete Fourier transform (DFT), but this can lead to inaccuracy. In this study, spectral estimators derived by averaging the autocorrelation function at lags were compared to the DFT.

Method

Bipolar CFAE of at least 16 s duration were obtained from pulmonary vein ostia and left atrial free wall sites (9 paroxysmal and 10 persistent AF patients). Power spectra were computed using the DFT and three other methods: 1. a novel spectral estimator based on signal averaging (NSE), 2. the NSE with harmonic removal (NSH), and 3. the autocorrelation function average at lags (AFA). Three spectral parameters were calculated: 1. the largest fundamental spectral peak, known as the dominant frequency (DF), 2. the DF amplitude (DA), and 3. the mean spectral profile (MP), which quantifies noise floor level. For each spectral estimator and parameter, the significance of the difference between paroxysmal and persistent AF was determined.

Results

For all estimators, mean DA and mean DF values were higher in persistent AF, while the mean MP value was higher in paroxysmal AF. The differences in means between paroxysmals and persistents were highly significant for 3/3 NSE and NSH measurements and for 2/3 DFT and AFA measurements (p<0.001). For all estimators, the standard deviation in DA and MP values were higher in persistent AF, while the standard deviation in DF value was higher in paroxysmal AF. Differences in standard deviations between paroxysmals and persistents were highly significant in 2/3 NSE and NSH measurements, in 1/3 AFA measurements, and in 0/3 DFT measurements.

Conclusions

Measurements made from all four spectral estimators were in agreement as to whether the means and standard deviations in three spectral parameters were greater in CFAEs acquired from paroxysmal or in persistent AF patients. Since the measurements were consistent, use of two or more of these estimators for power spectral analysis can be assistive to evaluate CFAE more objectively and accurately, which may lead to improved clinical outcome. Since the most significant differences overall were achieved using the NSE and NSH estimators, parameters measured from their spectra will likely be the most useful for detecting and discerning electrophysiologic differences in the AF substrate based upon frequency analysis of CFAE.

Celiac Disease in Patients With Type 1 Diabetes

Objective

The purpose of this study was to investigate screening practices for celiac disease in patients with type 1 diabetes across North America. The research question investigated was whether diabetes centers screen for celiac disease in type 1 diabetes more frequently than other facilities.

Research Design and Methods

A survey with 27 questions on screening practices for celiac disease in patients with type 1 diabetes was designed by experts in celiac disease and diabetes. Surveys were sent by email to diabetes educators and dietitians throughout the United States and Canada between December 2010 and May 2011.

Results

There were 514 respondents from 484 endocrine clinics, diabetes clinics, private practices, community nutrition centers, and inpatient centers. Thirty-five percent of work locations screened for celiac disease, with endocrine clinics reporting screening at the highest frequency (80%). Tissue transglutaminase was the most common screening test used. The most frequently recommended treatment of confirmed celiac disease was a gluten-free diet. However, only 71% of respondents recommended biopsy in patients with positive serologies. Most respondents (55.3%) reported that the gluten-free diet resulted in symptom improvement in the majority of patients.

Conclusions

Staff at endocrine clinics were more likely to suggest screening for celiac disease in patients with type 1 diabetes. Both low screening frequency as well as inconsistency in management of positive celiac disease serological tests indicated an increase in education regarding celiac disease in patients with type 1 diabetes is required. In addition uniform guidelines should be developed.

Review of biomedical signal and image processing

This article is a review of the book “Biomedical Signal and Image Processing” by Kayvan Najarian and Robert Splinter, which is published by CRC Press, Taylor & Francis Group. It will evaluate the contents of the book and discuss its suitability as a textbook, while mentioning highlights of the book, and providing comparison with other textbooks.

Quantitative estimates of motility from videocapsule endoscopy are useful to discern celiac patients from controls

BACKGROUND

Prior work has shown that videocapsule endoscopy image features are a useful tool for quantitatively distinguishing the intestinal mucosal surface of untreated celiac patients from that of controls. The use of dynamic estimates of wall motility may further help to improve classification.

METHODS

Videocapsule endoscopy clips (200 frames each, 2 frames/s, 576 × 576 pixels/frame) were acquired at five small intestinal locations in 11 untreated celiac patients (celiacs) and ten controls. Color images were converted to grayscale and analyzed frame-by-frame. Variations in the position and width of the center of the small intestinal lumen were quantitatively estimated. The darkest grayscale pixels were used as an estimate of the lumen center. Over 200 frames, the standard deviation of the lumen center xy position and the mean and standard deviation in lumen center width were used as dynamic estimates of wall motility. These parameters were plotted in three-dimensional space, and the best discriminant function was used to classify celiacs versus controls at each of the following five locations: (1) duodenal bulb, (2) distal duodenum, (3) jejunum, (4) ileum, and (5) distal ileum.

RESULTS

The overall sensitivity for the classification of celiacs versus controls at all five locations was 98.2 %, while the specificity was 96.0 %. From location 1 to 5, there was a tendency for the lumen center width to diminish in terms of frame-to-frame variability by 7.6 % in celiacs (r (2) = 0.4) and 9.7 % in controls (r (2) = 0.7).

CONCLUSIONS

In addition to examining the mucosal surface, videocapsule endoscopy can assess small bowel intestinal motility and aid in distinguishing celiac patients from controls.

Quantitative estimates of motility from videocapsule endoscopy are useful to discern celiac patients from controls

BACKGROUND

Prior work has shown that videocapsule endoscopy image features are a useful tool for quantitatively distinguishing the intestinal mucosal surface of untreated celiac patients from that of controls. The use of dynamic estimates of wall motility may further help to improve classification.

METHODS

Videocapsule endoscopy clips (200 frames each, 2 frames/s, 576 × 576 pixels/frame) were acquired at five small intestinal locations in 11 untreated celiac patients (celiacs) and ten controls. Color images were converted to grayscale and analyzed frame-by-frame. Variations in the position and width of the center of the small intestinal lumen were quantitatively estimated. The darkest grayscale pixels were used as an estimate of the lumen center. Over 200 frames, the standard deviation of the lumen center xy position and the mean and standard deviation in lumen center width were used as dynamic estimates of wall motility. These parameters were plotted in three-dimensional space, and the best discriminant function was used to classify celiacs versus controls at each of the following five locations: (1) duodenal bulb, (2) distal duodenum, (3) jejunum, (4) ileum, and (5) distal ileum.

RESULTS

The overall sensitivity for the classification of celiacs versus controls at all five locations was 98.2 %, while the specificity was 96.0 %. From location 1 to 5, there was a tendency for the lumen center width to diminish in terms of frame-to-frame variability by 7.6 % in celiacs (r (2) = 0.4) and 9.7 % in controls (r (2) = 0.7).

CONCLUSIONS

In addition to examining the mucosal surface, videocapsule endoscopy can assess small bowel intestinal motility and aid in distinguishing celiac patients from controls.

Transformation of videocapsule images to detect small bowel mucosal differences in celiac versus control patients

BACKGROUND

Videocapsule endoscopy can be useful to detect small intestinal pathology in celiac disease patients. However, presence of extraneous features including air bubbles and opaque fluids can complicate the analysis. A technique for quantitative analysis of videocapsule images is presented that is robust to presence of extraneous features.

METHOD

Videocapsule clips were acquired from five small intestinal locations in 12 celiacs with villous atrophy and 11 control patients. Clips were 200 frames in length, their resolution was 576 × 576 pixels and 256 grayscale levels, with 2/s frame rate. The dominant period (DP), defined as the tallest peak in the ensemble average power spectrum, was computed over each clip without removal of extraneous features. Ensemble average basis images were constructed, and measurements were made of their frame-to-frame variation in brightness and texture.

RESULTS

From pooled basis images, celiac images had greater texture than controls and exhibited more brightness variation (p<0.05 in mean and p<0.01 in standard deviation). In celiacs, correlation existed between greater textural alterations versus longer DP (r²=0.47), and between greater brightness variation and longer DP (r²=0.33). There was no significant correlation between quantitative features and DP in controls (r²<0.25).

CONCLUSIONS

Using this new method, celiac videoclips were quantitatively distinguishable from control videoclips without manual or computer-assisted detection, masking, and removal of extraneous image features. Furthermore, in celiac but not control basis images, larger textural and brightness alterations were correlated to longer DP. Greater textural and brightness alterations, and thus longer periodicities, are likely related to presence of villous atrophy.

Video capsule endoscopy in celiac disease

Video capsule endoscopy (VCE) provides a safe, non-invasive way to visualize the small intestine and is helpful in celiac disease patients in select situations. VCE can be performed in patients who are unable or unwilling to undergo conventional endoscopy, those with positive celiac serology with normal duodenal biopsies, and also in those who develop alarm symptoms. VCE has limitations including subjective interpretation. Techniques are being developed to standardize assessment of VCE images in patients with known or suspected celiac disease. Pilot studies using computer-based quantification methods have shown promise in examining the 3-dimensional mucosal structure and motility.

Spectral profiles of complex fractionated atrial electrograms are different in longstanding and acute onset atrial fibrillation atrial electrogram spectra

Spectral Profiles of CFAE.

BACKGROUND

Spectral analysis of complex fractionated atrial electrograms (CFAE) may be useful for gaining insight into mechanisms underlying paroxysmal and longstanding atrial fibrillation (AF). The commonly used dominant frequency (DF) measurement has limitations.

METHOD

CFAE recordings were acquired from outside the 4 pulmonary vein ostia and at 2 left atrial free wall sites in 10 paroxysmal and 10 persistent AF patients. Two consecutive 8s-series were analyzed from recordings >16s in duration. Power spectra were computed for each 8s-series in the range 3-12 Hz and normalized. The mean and standard deviation of normalized power spectra (MPS and SPS, respectively) were compared for paroxysmal versus persistent CFAE. Also, the DF and its peak amplitude (ADF) were compared for pulmonary vein sites only. Power spectra were computed using ensemble average and Fourier methods.

RESULTS

No significant changes occurred in any parameter from the first to second recording sequence. For both sequences, MPS and SPS were significantly greater, and DF and ADF were significantly less, in paroxysmals versus persistents. The MPS and ADF measurements from ensemble spectra produced the most significant differences in paroxysmals versus persistents (P < 0.0001). DF differences were less significant, which can be attributed to the relatively high variability of DF in paroxysmals. The MPS was correlated to the duration of uninterrupted persistent AF prior to electrophysiologic study (P = 0.01), and to left atrial volume for all AF (P < 0.05).

CONCLUSIONS

The MPS and ADF measurements introduced in this study are probably superior to DF for discerning power spectral differences in paroxysmal versus longstanding CFAE. (J Cardiovasc Electrophysiol, Vol. 23, pp. 971-979, September 2012).

Improved frequency resolution for characterization of complex fractionated atrial electrograms

BACKGROUND

The dominant frequency of the Fourier power spectrum is useful to analyze complex fractionated atrial electrograms (CFAE), but spectral resolution is limited and uniform from DC to the Nyquist frequency. Herein the spectral resolution of a recently described and relatively new spectral estimation technique is compared to the Fourier radix-2 implementation.

METHODS

In 10 paroxysmal and 10 persistent atrial fibrillation patients, 216 CFAE were acquired from the pulmonary vein ostia and left atrial free wall (977 Hz sampling rate, 8192 sample points, 8.4 s duration). With these parameter values, in the physiologic range of 3-10 Hz, two frequency components can theoretically be resolved at 0.24 Hz using Fourier analysis and at 0.10 Hz on average using the new technique. For testing, two closely-spaced periodic components were synthesized from two different CFAE recordings, and combined with two other CFAE recordings magnified 2×, that served as interference signals. The ability to resolve synthesized frequency components in the range 3-4 Hz, 4-5 Hz, …, 9-10 Hz was determined for 15 trials each (105 total).

RESULTS

With the added interference, frequency resolution averaged 0.29 ± 0.22 Hz for Fourier versus 0.16 ± 0.10 Hz for the new method (p < 0.001). The misalignment error of spectral peaks versus actual values was ±0.023 Hz for Fourier and ±0.009 Hz for the new method (p < 0.001). One or both synthesized peaks were lost in the noise floor 13/105 times using Fourier versus 4/105 times using the new method.

CONCLUSIONS

Within the physiologically relevant frequency range for characterization of CFAE, the new method has approximately twice the spectral resolution of Fourier analysis, there is less error in estimating frequencies, and peaks appear more readily above the noise floor. Theoretically, when interference is not present, to resolve frequency components separated by 0.10 Hz using Fourier analysis would require an 18.2 s sequence duration, versus 8.4 s with the new method.

A new LMS algorithm for analysis of atrial fibrillation signals

BACKGROUND

A biomedical signal can be defined by its extrinsic features (x-axis and y-axis shift and scale) and intrinsic features (shape after normalization of extrinsic features). In this study, an LMS algorithm utilizing the method of differential steepest descent is developed, and is tested by normalization of extrinsic features in complex fractionated atrial electrograms (CFAE).

METHOD

Equations for normalization of x-axis and y-axis shift and scale are first derived. The algorithm is implemented for real-time analysis of CFAE acquired during atrial fibrillation (AF). Data was acquired at a 977 Hz sampling rate from 10 paroxysmal and 10 persistent AF patients undergoing clinical electrophysiologic study and catheter ablation therapy. Over 24 trials, normalization characteristics using the new algorithm with four weights were compared to the Widrow-Hoff LMS algorithm with four tapped delays. The time for convergence, and the mean squared error (MSE) after convergence, were compared. The new LMS algorithm was also applied to lead aVF of the electrocardiogram in one patient with longstanding persistent AF, to enhance the F wave and to monitor extrinsic changes in signal shape. The average waveform over a 25 s interval was used as a prototypical reference signal for matching with the aVF lead.

RESULTS

Based on the derivation equations, the y-shift and y-scale adjustments of the new LMS algorithm were shown to be equivalent to the scalar form of the Widrow-Hoff LMS algorithm. For x-shift and x-scale adjustments, rather than implementing a long tapped delay as in Widrow-Hoff LMS, the new method uses only two weights. After convergence, the MSE for matching paroxysmal CFAE averaged 0.46 ± 0.49 μV(2)/sample for the new LMS algorithm versus 0.72 ± 0.35 μV(2)/sample for Widrow-Hoff LMS. The MSE for matching persistent CFAE averaged 0.55 ± 0.95 μV(2)/sample for the new LMS algorithm versus 0.62 ± 0.55 μV(2)/sample for Widrow-Hoff LMS. There were no significant differences in estimation error for paroxysmal versus persistent data. From all trials, the mean convergence time was approximately 1 second for both algorithms. The new LMS algorithm was useful to enhance the electrocardiogram F wave by subtraction of an adaptively weighted prototypical reference signal from the aVF lead. The extrinsic weighting over 25 s demonstrated that time-varying functions such as patient respiration could be identified and monitored.

CONCLUSIONS

A new LMS algorithm was derived and used for normalization of the extrinsic features in CFAE and for electrocardiogram monitoring. The weighting at convergence provides an estimate of the degree of similarity between two signals in terms of x-axis and y-axis shift and scale. The algorithm is computationally efficient with low estimation error. Based on the results, proposed applications include monitoring of extrinsic and intrinsic features of repetitive patterns in CFAE, enhancement of the electrocardiogram F wave and monitoring of time-varying signal properties, and to quantitatively characterize mechanistic differences in paroxysmal versus persistent AF.

Living with coeliac disease: survey results from the U.S.A

BACKGROUND

The only treatment for coeliac disease is lifelong adherence to a rigorous gluten-free diet. The present study aimed to evaluate the influence of coeliac disease on the social aspects of daily life of individuals in the U.S.A.

METHODS

The present study used a self-administered survey including the standard Quality of Life questionnaire (12-item short-form) with validated disease-specific questions. sas statistical software 2010 (SAS Institute, Cary, NC, U.S.A.) was used to calculate the mean (SD).

RESULTS

Individuals with coeliac disease overall had a low positive health perception. Validated diet and disease-specific questions revealed a significant negative impact on quality of life in social settings. Specifically, the areas of travel, dining out and family life are most affected. The negative impact of diet significantly decreased over time, although it did not resolve for the domains of dining out of the home and travel. Those diagnosed in childhood and maintained on the diet had less of an impact on the quality of life as an adult.

CONCLUSIONS

Individuals with coeliac disease in the U.S.A. have a diminished quality of life, especially in the social aspects of life.

Identification of recurring patterns in fractionated atrial electrograms using new transform coefficients

Background

Identification of recurrent patterns in complex fractionated atrial electrograms (CFAE) has been used to differentiate paroxysmal from persistent atrial fibrillation (AF). Detection of the atrial CFAE patterns might therefore be assistive in guiding radiofrequency catheter ablation to drivers of the arrhythmia. In this study a technique for robust detection and classification of recurrent CFAE patterns is described.

Method

CFAE were obtained from the four pulmonary vein ostia, and from the anterior and posterior left atrium, in 10 patients with paroxysmal AF and 10 patients with longstanding persistent AF (216 recordings in total). Sequences 8.4 s in length were analyzed (8,192 sample points, 977 Hz sampling). Among the 216 sequences, two recurrent patterns A and B were substituted for 4 and 5 of the sequences, respectively. To this data, random interference, and random interference + noise were separately added. Basis vectors were constructed using a new transform that is derived from ensemble averaging. Patterns A and B were then detected and classified using a threshold level of Euclidean distance between spectral signatures as constructed with transform coefficients.

Results

In the presence of interference, sensitivity to detect and distinguish two patterns A and B was 96.2%, while specificity to exclude nonpatterns was 98.0%. In the presence of interference + noise, sensitivity was 89.1% while specificity was 97.0%.

Conclusions

Transform coefficients computed from ensemble averages can be used to succinctly quantify synchronized patterns present in AF data. The technique is useful to automatically detect recurrent patterns in CFAE that are embedded in interference without user bias. This quantitation can be implemented in real-time to map the AF substrate prior to and during catheter ablation.

Electrophysiological abnormalities precede overt structural changes in arrhythmogenic right ventricular cardiomyopathy due to mutations in desmoplakin-A combined murine and human study

AIMS

Anecdotal observations suggest that sub-clinical electrophysiological manifestations of arrhythmogenic right ventricular cardiomyopathy (ARVC) develop before detectable structural changes ensue on cardiac imaging. To test this hypothesis, we investigated a murine model with conditional cardiac genetic deletion of one desmoplakin allele (DSP ±) and compared the findings to patients with non-diagnostic features of ARVC who carried mutations in desmoplakin.

METHODS AND RESULTS

Murine: the DSP (±) mice underwent electrophysiological, echocardiographic, and immunohistochemical studies. They had normal echocardiograms but delayed conduction and inducible ventricular tachycardia associated with mislocalization and reduced intercalated disc expression of Cx43. Sodium current density and myocardial histology were normal at 2 months of age. Human: ten patients with heterozygous mutations in DSP without overt structural heart disease (DSP+) and 12 controls with supraventricular tachycardia were studied by high-density electrophysiological mapping of the right ventricle. Using a standard S(1)-S(2) protocol, restitution curves of local conduction and repolarization parameters were constructed. Significantly greater mean increases in delay were identified particularly in the outflow tract vs. controls (P< 0.01) coupled with more uniform wavefront progression. The odds of a segment with a maximal activation-repolarization interval restitution slope >1 was 99% higher (95% CI: 13%; 351%, P = 0.017) in DSP+ vs. controls. Immunostaining revealed Cx43 mislocalization and variable Na channel distribution.

CONCLUSION

Desmoplakin disease causes connexin mislocalization in the mouse and man preceding any overt histological abnormalities resulting in significant alterations in conduction-repolarization kinetics prior to morphological changes detectable on conventional cardiac imaging. Haploinsufficiency of desmoplakin is sufficient to cause significant Cx43 mislocalization. Changes in sodium current density and histological abnormalities may contribute to a worsening phenotype or disease but are not necessary to generate an arrhythmogenic substrate. This has important implications for the earlier diagnosis of ARVC and risk stratification.

Robust spectral analysis of videocapsule images acquired from celiac disease patients

Background

Dominant frequency (DF) analysis of videocapsule endoscopy images is a new method to detect small intestinal periodicities that may result from mechanical rhythms such as peristalsis. Longer periodicity is related to greater image texture at areas of villous atrophy in celiac disease. However, extraneous features and spatiotemporal phase shift may mask DF rhythms.

Method

The robustness of Fourier and ensemble averaging spectral analysis to compute DF was tested. Videocapsule images from the distal duodenum of 11 celiac patients (frame rate 2/s and pixel resolution 576 × 576) were analyzed. For patients 1, 2, ... 11, respectively, a total of 10, 11, ..., 20 sequential images were extracted from a randomly selected time epoch. Each image sequence was artificially repeated to 200 frames, simulating periodicities of 0.2, 0.18, ..., 0.1Hz, respectively. Random white noise at four different levels, spatiotemporal phase shift, and frames with air bubbles were added. Power spectra were constructed pixel-wise over 200 frames, and an average spectrum was computed from the 576 × 576 individual spectra. The largest spectral peak in the average spectrum was the estimated DF. Error was defined as the absolute difference between actual DF and estimated DF.

Results

For Fourier analysis, the mean absolute error between estimated and actual DF was 0.032 ± 0.052Hz. Error increased with greater degree of random noise imposed. In contrast, all ensemble average estimates precisely predicted the simulated DF.

Conclusions

The ensemble average DF estimate of videocapsule images with simulated periodicity is robust to noise and spatiotemporal phase shift as compared with Fourier analysis. Accurate estimation of DF eliminates the need to impose complex masking, extraction, and/or corrective preprocessing measures.

A new transform for the analysis of complex fractionated atrial electrograms

BACKGROUND

Representation of independent biophysical sources using Fourier analysis can be inefficient because the basis is sinusoidal and general. When complex fractionated atrial electrograms (CFAE) are acquired during atrial fibrillation (AF), the electrogram morphology depends on the mix of distinct nonsinusoidal generators. Identification of these generators using efficient methods of representation and comparison would be useful for targeting catheter ablation sites to prevent arrhythmia reinduction.

METHOD

A data-driven basis and transform is described which utilizes the ensemble average of signal segments to identify and distinguish CFAE morphologic components and frequencies. Calculation of the dominant frequency (DF) of actual CFAE, and identification of simulated independent generator frequencies and morphologies embedded in CFAE, is done using a total of 216 recordings from 10 paroxysmal and 10 persistent AF patients. The transform is tested versus Fourier analysis to detect spectral components in the presence of phase noise and interference. Correspondence is shown between ensemble basis vectors of highest power and corresponding synthetic drivers embedded in CFAE.

RESULTS

The ensemble basis is orthogonal, and efficient for representation of CFAE components as compared with Fourier analysis (p ≤ 0.002). When three synthetic drivers with additive phase noise and interference were decomposed, the top three peaks in the ensemble power spectrum corresponded to the driver frequencies more closely as compared with top Fourier power spectrum peaks (p ≤ 0.005). The synthesized drivers with phase noise and interference were extractable from their corresponding ensemble basis with a mean error of less than 10%.

CONCLUSIONS

The new transform is able to efficiently identify CFAE features using DF calculation and by discerning morphologic differences. Unlike the Fourier transform method, it does not distort CFAE signals prior to analysis, and is relatively robust to jitter in periodic events. Thus the ensemble method can provide a useful alternative for quantitative characterization of CFAE during clinical study.

Differences in repeating patterns of complex fractionated left atrial electrograms in longstanding persistent atrial fibrillation as compared with paroxysmal atrial fibrillation

BACKGROUND

Complex fractionated atrial electrograms (CFAE) are morphologically more uniform in persistent longstanding as compared with paroxysmal atrial fibrillation (AF). It was hypothesized that this may result from a greater degree of repetitiveness in CFAE patterns at disparate left atrial (LA) sites in longstanding AF.

METHODS AND RESULTS

CFAEs were obtained from recording sites outside the 4 pulmonary vein (PV) ostia and at a posterior and an anterior LA site during paroxysmal and longstanding persistent AF (10 patients each, 120 sequences total). To quantify repetitiveness in CFAE, the dominant frequency was measured from ensemble spectra using 8.4-second sequences, and repetitiveness was calculated by 2 novel techniques: linear prediction and Fourier reconstruction methods. Lower prediction and reconstruction errors were considered indicative of increasing repetitiveness and decreasing randomness. In patients with paroxysmal AF, CFAE pattern repetitiveness was significantly lower (randomness higher) at antral sites outside PV ostia as compared with LA free wall sites (P < 0.001). In longstanding AF, repetitiveness increased outside the PV ostia, especially outside the left superior PV ostium, and diminished at the LA free wall sites. The result was that in persistent AF, there were no significant site-specific differences in CFAE repetitiveness at the selected LA locations used in this study. Average dominant frequency magnitude was 5.32 ± 0.29 Hz in paroxysmal AF and higher in longstanding AF, at 6.27 ± 0.13 Hz (P < 0.001), with the frequency of local activation approaching a common upper bound for all sites.

CONCLUSIONS

In paroxysmal AF, CFAE repetitiveness is low and randomness high outside the PVs, particularly the left superior PV. As evolution to persistent longstanding AF occurs, CFAE repetitiveness becomes more uniformly distributed at disparate sites, possibly signifying an increasing number of drivers from remote PVs.

Characterization of gap junction remodeling in epicardial border zone of healing canine infarcts and electrophysiological effects of partial reversal by rotigaptide

BACKGROUND

The border zone of healing myocardial infarcts is an arrhythmogenic substrate, partly the result of structural and functional remodeling of the ventricular gap junction protein, Connexin43 (Cx43). Cx43 in arrhythmogenic substrates is a potential target for antiarrhythmic therapy.

METHODS AND RESULTS

We characterized Cx43 remodeling in the epicardial border zone (EBZ) of healing canine infarcts 5 days after coronary occlusion and examined whether the gap junction-specific agent rotigaptide could reverse it. Cx43 remodeling in the EBZ was characterized by a decrease in Cx43 protein, lateralization, and increased Cx43 phosphorylation at serine (S) 368. Rotigaptide partially reversed the loss of Cx43 but did not affect the increase in S368 phosphorylation, nor did it reverse Cx43 lateralization. Rotigaptide did not prevent conduction slowing in the EBZ, nor did it decrease the induction of sustained ventricular tachycardia by programmed stimulation, although it did decrease the EBZ effective refractory period.

CONCLUSIONS

We conclude that partial reversal of Cx43 remodeling in healing infarct border zone may not be sufficient to restore normal conduction or prevent arrhythmias.

The Renin-Angiotensin system mediates the effects of stretch on conduction velocity, connexin43 expression, and redistribution in intact ventricle

Effect of Stretch on Conduction and Cx43.

INTRODUCTION

In disease states such as heart failure, myocardial infarction, and hypertrophy, changes in the expression and location of Connexin43 (Cx43) occur (Cx43 remodeling), and may predispose to arrhythmias. Stretch may be an important stimulus to Cx43 remodeling; however, it has only been investigated in neonatal cell cultures, which have different physiological properties than adult myocytes. We hypothesized that localized stretch in vivo causes Cx43 remodeling, with associated changes in conduction, mediated by the renin-angiotensin system (RAS).

METHODS AND RESULTS

In an open-chest canine model, a device was used to stretch part of the right ventricle (RV) by 22% for 6 hours. Activation mapping using a 312-electrode array was performed before and after stretch. Regional stretch did not change longitudinal conduction velocity (post-stretch vs baseline: 51.5 ± 5.2 vs 55.3 ± 8.1 cm/s, P = 0.24, n = 11), but significantly reduced transverse conduction velocity (28.7 ± 2.5 vs 35.4 ± 5.4 cm/s, P < 0.01). It also reduced total Cx43 expression, by Western blotting, compared with nonstretched RV of the same animal (86.1 ± 32.2 vs 100 ± 19.4%, P < 0.02, n = 11). Cx43 labeling redistributed to the lateral cell borders. Stretch caused a small but significant increase in the proportion of the dephosphorylated form of Cx43 (stretch 9.95 ± 1.4% vs control 8.74 ± 1.2%, P < 0.05). Olmesartan, an angiotensin II blocker, prevented the stretch-induced changes in Cx43 levels, localization, and conduction.

CONCLUSION

Myocardial stretch in vivo has opposite effects to that in neonatal myocytes in vitro. Stretch in vivo causes conduction changes associated with Cx43 remodeling that are likely caused by local stretch-induced activation of the RAS.

Quantitative assessment of endoscopic images for degree of villous atrophy in celiac disease

BACKGROUND

The degree of villous atrophy in celiac disease is difficult to assess at endoscopy. We sought to develop a quantitative technique for the evaluation of villous atrophy in endoscopic images.

METHOD

In ten celiac patients as identified by standard endoscopy with biopsy, and ten control patients, standard and videocapsule endoscopic images of the duodenum were digitized. Subimages 7.5 × 7.5 mm(2) in area from random locations within each image were assessed by measuring the length of mucosal fissures per unit area (L), and correlating L with the histologic grade of villous atrophy as determined by modified Marsh criteria.

RESULTS

Mean L values for standard endoscopic images were 37.8, 43.3, 64.1, and 83.5 mm for Marsh grades II, IIIa, IIIb, and IIIc, respectively. Mean L values for videocapsule images were 49.1, 50.0, 64.7, and 72.4 mm for Marsh grades II, IIIa, IIIb, and IIIc, respectively. Significant differences in the means existed between celiac images (Marsh scores II-IIIc) versus controls (p < 0.001) for both endoscopic and videocapsule images. There were no significant differences between measurements obtained from endoscopic versus videocapsule images.

CONCLUSIONS

Quantified image analysis correlates with the histologic grade of villous atrophy, is automated, and lacks observer bias, thus lending itself to standardization.

Quantitative assessment of endoscopic images for degree of villous atrophy in celiac disease

BACKGROUND

The degree of villous atrophy in celiac disease is difficult to assess at endoscopy. We sought to develop a quantitative technique for the evaluation of villous atrophy in endoscopic images.

METHOD

In ten celiac patients as identified by standard endoscopy with biopsy, and ten control patients, standard and videocapsule endoscopic images of the duodenum were digitized. Subimages 7.5 × 7.5 mm(2) in area from random locations within each image were assessed by measuring the length of mucosal fissures per unit area (L), and correlating L with the histologic grade of villous atrophy as determined by modified Marsh criteria.

RESULTS

Mean L values for standard endoscopic images were 37.8, 43.3, 64.1, and 83.5 mm for Marsh grades II, IIIa, IIIb, and IIIc, respectively. Mean L values for videocapsule images were 49.1, 50.0, 64.7, and 72.4 mm for Marsh grades II, IIIa, IIIb, and IIIc, respectively. Significant differences in the means existed between celiac images (Marsh scores II-IIIc) versus controls (p < 0.001) for both endoscopic and videocapsule images. There were no significant differences between measurements obtained from endoscopic versus videocapsule images.

CONCLUSIONS

Quantified image analysis correlates with the histologic grade of villous atrophy, is automated, and lacks observer bias, thus lending itself to standardization.

A novel desmocollin-2 mutation reveals insights into the molecular link between desmosomes and gap junctions

Background

Cellular adhesion mediated by cardiac desmosomes is a prerequisite for proper electric propagation mediated by gap junctions in the myocardium. However, the molecular principles underlying this interdependence are not fully understood.

Objective

The purpose of this study was to determine potential causes of right ventricular conduction abnormalities in a patient with borderline diagnosis of arrhythmogenic right ventricular cardiomyopathy.

Methods

To assess molecular changes, the patient's myocardial tissue was analyzed for altered desmosomal and gap junction (connexin43) protein levels and localization. In vitro functional studies were performed to characterize the consequences of the desmosomal mutations.

Results

Loss of plakoglobin signal was evident at the cell junctions despite expression of the protein at control levels. Although the distribution of connexin43 was not altered, total protein levels were reduced and changes in phosphorylation were observed. The truncation mutant in desmocollin-2a is deficient in binding plakoglobin. Moreover, the ability of desmocollin-2a to directly interact with connexin43 was abolished by the mutation. No pathogenic potential of the desmoglein-2 missense change was identified.

Conclusion

The observed abnormalities in gap junction protein expression and phosphorylation, which precede an overt cardiac phenotype, likely are responsible for slow myocardial conduction in this patient. At the molecular level, altered binding properties of the desmocollin-2a mutant may contribute to the changes in connexin43. In particular, the newly identified interaction between the desmocollin-2a isoform and connexin43 provides novel insights into the molecular link between desmosomes and gap junctions.

Frequency domain and time complex analyses manifest low correlation and temporal variability when calculating activation rates in atrial fibrillation patients

BACKGROUND

Atrial fibrillation (AF) activation rates have been calculated using both frequency domain and time complex analyses. Direct comparisons of these methods are limited. We report: (1) their correlation when measuring AF activation rates, (2) comparisons of recording durations required to minimize variability, and (3) differences in the temporal reproducibility.

METHODS

AF activation rates were calculated using domain frequency (DF) (via fast Fourier transform) and time complex (TC) (via beat-to-beat activation measurements) analyses. We compared: (1) AF frequencies derived from each method; (2) successively longer subinterval durations to their 16-second reference intervals, and (3) the correlation between consecutively collected 8-second segments and segments collected 10 minutes apart.

RESULTS

There was low intraclass correlation coefficient (ICC = 0.234) when comparing AF activation rates derived using DF versus TC analysis. There was no difference in the frequencies between any of the subintervals compared to their 16-second reference intervals, but variability of measurements was higher for intervals <8 seconds (P < 0.01). Correlations between successive segments and segments taken 10 minutes apart were 0.92 and 0.75 using DF analysis (P < 0.001), and 0.72 and 0.49 using TC analysis (P < 0.001).

CONCLUSIONS

There is low correlation between the DF and TC methods of analyzing AF activation rates. While AF rates do not differ between subintervals and 16-second reference electrograms, the variability of measurements is dependent upon the subinterval duration, and increases for durations less than 8 seconds. AF rates were prone to change over a 10-minute time period. These results point out existing clinical limitations of measuring atrial activation rates in AF patients.

Book review of applied medical image processing: A basic course

This article is a review of the book: 'Applied Medical Image Processing: A Basic Course', by Wolfgang Birkfellner, which is published by CRC Press. Basic information that should be helpful in deciding whether to read the book and whether to use it as a course textbook is presented. This includes an introduction, the suitability of the book for use in coursework, its coverage of medical imaging and image processing, discussion and conclusions, and an appendix with a relevant computer program for extracting medical images.

Distinguishing patients with celiac disease by quantitative analysis of videocapsule endoscopy images

BACKGROUND

Although videocapsule endoscopy images are helpful in the evaluation of celiac disease, their interpretation is subjective. Quantitative disease markers could assist in determining the extent of villous atrophy and response to treatment.

METHOD

Capsule endoscopy images were acquired from celiac patients with small bowel pathology (N=11) and from control patients (N=10). Image resolution was 576x576 pixels in dimension, 256 grayscale levels, and had a 2 s(-1) frame rate. Pixel brightness and image texture were measured over 10x10 pixel subimages and then averaged for 56x56 subimages per frame. Measurements were obtained at five locations from proximal to distal small intestine in each patient. At each location, measurements were calculated using 200 consecutive image frames (100s). Mean frame-to-frame pixel brightness, image texture, and periodicity in brightness, an estimate of wall motion or intestinal motility, were computed and used for classification with a nonlinear discriminant function.

RESULTS

From pooled data, celiac images had greater texture than did images from control patients (p<0.001) and exhibited more frame-to-frame brightness variation as well (p=0.032). The dominant period of brightness was longer in celiacs (p=0.001), possibly indicating decreased motility. Using the markers for three-dimensional nonlinear classification of celiacs versus controls, sensitivity was 92.7% and specificity was 93.5%. The relationship between dominant period and small intestinal transit time was approximately linear for both celiacs and controls (r(2)=0.42 and r(2)=0.55, respectively).

CONCLUSIONS

Videocapsule images can be quantified to detect villous atrophy throughout the small intestine, and to distinguish individuals with celiac disease from individuals lacking mucosal atrophy.

Classification of videocapsule endoscopy image patterns: comparative analysis between patients with celiac disease and normal individuals

BACKGROUND

Quantitative disease markers were developed to assess videocapsule images acquired from celiac disease patients with villous atrophy, and from control patients.

METHOD

Capsule endoscopy videoclip images (576 x 576 pixels) were acquired at 2/second frame rate (11 celiacs, 10 controls) at regions: 1. bulb, 2. duodenum, 3. jejunum, 4. ileum and 5. distal ileum. Each of 200 images per videoclip (= 100s) were subdivided into 10 x 10 pixel subimages for which mean grayscale brightness level and its standard deviation (texture) were calculated. Pooled subimage values were grouped into low, intermediate, and high texture bands, and mean brightness, texture, and number of subimages in each band (nine features in all) were used for quantifying regions 1-5, and to determine the three best features for threshold and incremental learning classification. Classifiers were developed using 6 celiac and 5 control patients' data as exemplars, and tested on 5 celiacs and 5 controls.

RESULTS

Pooled from all regions, the threshold classifier had 80% sensitivity and 96% specificity and the incremental classifier had 88% sensitivity and 80% specificity for predicting celiac versus control videoclips in the test set. Trends of increasing texture from regions 1 to 5 occurred in the low and high texture bands in celiacs, and the number of subimages in the low texture band diminished (r(2) > 0.5). No trends occurred in controls.

CONCLUSIONS

Celiac videocapsule images have textural properties that vary linearly along the small intestine. Quantitative markers can assist in screening for celiac disease and localize extent and degree of pathology throughout the small intestine.

Classification of videocapsule endoscopy image patterns: comparative analysis between patients with celiac disease and normal individuals

Background

Quantitative disease markers were developed to assess videocapsule images acquired from celiac disease patients with villous atrophy, and from control patients.

Method

Capsule endoscopy videoclip images (576 × 576 pixels) were acquired at 2/second frame rate (11 celiacs, 10 controls) at regions: 1. bulb, 2. duodenum, 3. jejunum, 4. ileum and 5. distal ileum. Each of 200 images per videoclip (= 100s) were subdivided into 10 × 10 pixel subimages for which mean grayscale brightness level and its standard deviation (texture) were calculated. Pooled subimage values were grouped into low, intermediate, and high texture bands, and mean brightness, texture, and number of subimages in each band (nine features in all) were used for quantifying regions 1-5, and to determine the three best features for threshold and incremental learning classification. Classifiers were developed using 6 celiac and 5 control patients' data as exemplars, and tested on 5 celiacs and 5 controls.

Results

Pooled from all regions, the threshold classifier had 80% sensitivity and 96% specificity and the incremental classifier had 88% sensitivity and 80% specificity for predicting celiac versus control videoclips in the test set. Trends of increasing texture from regions 1 to 5 occurred in the low and high texture bands in celiacs, and the number of subimages in the low texture band diminished (r² > 0.5). No trends occurred in controls.

Conclusions

Celiac videocapsule images have textural properties that vary linearly along the small intestine. Quantitative markers can assist in screening for celiac disease and localize extent and degree of pathology throughout the small intestine.

Different characteristics of complex fractionated atrial electrograms in acute paroxysmal versus long-standing persistent atrial fibrillation

BACKGROUND

Complex fractionated atrial electrograms (CFAEs) may represent a phenomenon associated with sources of atrial fibrillation (AF) and are being used increasingly as targets of catheter ablation. However, current methods have limited efficacy for characterizing CFAEs important to substrate arrhythmogenicity and do not measure electrogram morphology.

OBJECTIVE

The purpose of this study was to develop a methodology for quantifying the degree of morphologic heterogeneity in CFAE deflections, and to determine whether there are differences in this measurement between paroxysmal and persistent AF patients.

METHODS

Two successive bipolar CFAEs of length 8.4 seconds each were acquired during AF from two sites each at the ostia of the four pulmonary veins (PVs) and from the anterior and posterior left atrial free wall in patients with paroxysmal AF (N = 10) and long-standing persistent AF (N = 10). Extrinsic and intrinsic features of electrogram shape were used to characterize fractionation in CFAE sequences. The extrinsic parameters were the amplitude, upslope, downslope, and width of each deflection. The intrinsic parameter was the voltage profile as characterized by the sum of absolute values. These measurements were compared to the mean interval between CFAE deflections, a standard fractionation indicator.

RESULTS

The variability of intrinsic/extrinsic morphologic parameters was higher in paroxysmal than persistent AF at the left superior PV (P < or =.003), the posterior left atrial free wall, anterior left atrial free wall, left inferior PV, and right superior PV (P <.05 for most parameters), and the right inferior PV (not significant). Mean CFAE deflection intervals were longer at all locations in paroxysmal AF but were significant only at the left superior PV and posterior left atrial free wall (P <.05). Quantitative morphologic parameters were not well correlated with dominant frequency (r(2) <0.32); thus, our new measures are robust to changes in activation rate.

CONCLUSION

A novel method for quantifying CFAEs, independent of activation rate, has been developed. The method demonstrates greater significance in the difference between CFAE morphology in paroxysmal and long-standing AF compared with mean interval between CFAE deflections. The differences identified suggest that CFAE morphology may evolve as AF persists.

High-density substrate mapping in Brugada syndrome: combined role of conduction and repolarization heterogeneities in arrhythmogenesis

BACKGROUND

Two principal mechanisms are thought to be responsible for Brugada syndrome (BS): (1) right ventricular (RV) conduction delay and (2) RV subepicardial action potential shortening. This in vivo high-density mapping study evaluated the conduction and repolarization properties of the RV in BS subjects.

METHODS AND RESULTS

A noncontact mapping array was positioned in the RV of 18 BS patients and 20 controls. Using a standard S(1)-S(2) protocol, restitution curves of local activation time and activation recovery interval were constructed to determine local maximal restitution slopes. Significant regional conduction delays in the anterolateral free wall of the RV outflow tract of BS patients were identified. The mean increase in delay was 3-fold greater in this region than in control (P=0<0.001). Local activation gradient was also maximally reduced in this area: 0.33+/-0.1 (mean+/-SD) mm/ms in BS patients versus 0.51+/-0.15 mm/ms in controls (P<0.0005). The uniformity of wavefront propagation as measured by the square of the correlation coefficient, r(2), was greater in BS patients versus controls (0.94+/-0.04 versus 0.89+/-0.09 [mean+/-SD]; P<0.05). The odds ratio of BS hearts having any RV segment with maximal restitution slope >1 was 3.86 versus controls. Five episodes of provoked ventricular tachycardia arose from wave breaks originating from RV outflow tract slow-conduction zones in 5 BS patients.

CONCLUSIONS

Marked regional endocardial conduction delay and heterogeneities in repolarization exist in BS. Wave break in areas of maximal conduction delay appears to be critical in the initiation and maintenance of ventricular tachycardia. These data indicate that further studies of mapping BS to identify slow-conduction zones should be considered to determine their role in spontaneous ventricular arrhythmias.

The effect of substituting alternative grains in the diet on the nutritional profile of the gluten-free diet

BACKGROUND

The only treatment for coeliac disease is lifelong adherence to a gluten-free diet. Several studies have reported nutritional deficiencies in individuals on a gluten-free diet. The present study aimed to determine whether the nutritional profile of gluten-free diet could be improved through the use of alternative grains.

METHODS

A retrospective review of diet history records by a celiac specialist dietitian were used to establish a 'standard' gluten-free dietary pattern. An 'alternative' gluten-free dietary pattern was developed that substituted naturally gluten-free grains or gluten-free products made from 'alternative' flours (oats, high fibre gluten-free bread and quinoa) in the standard pattern. A paired t-test was performed to identify statistical significance between the 'alternative' and standard gluten-free dietary pattern.

RESULTS

Analysis of standard pattern indicated that 38% of meals and snacks contained no grain or starch choice. Of those meals that contained a grain or starch component, rice was the grain chosen 44% of the time. The inclusion of alternative grains or grain products provided a higher nutrient profile compared to the standard gluten-free dietary pattern (P = 0.002). Several nutrients; protein (20.6 g versus 11 g), iron (18.4 mg versus 1.4 mg), calcium (182 mg versus 0 mg) and fibre (12.7 g versus 5 g) were significantly increased by changing the grain or starch component in the dietary pattern. The B vitamin content (riboflavin, niacin and folate) was improved, although this was not statistically significant (P = 0.125).

DISCUSSION

The inclusion of alternative grain-based products increased the nutrient profile of the gluten-free dietary pattern significantly.

Tonometric arterial pulse sensor with noise cancellation

Arterial tonometry provides for the continuous and noninvasive recording of the arterial pressure waveform. However, tonometers are affected by motion artifact that degrades the signal. An arterial tonometer was constructed using two piezoelectric transducers centered within a solid base. In two subjects, one transducer was positioned over the radial pulse (p) and the other was positioned on the wrist not overlying the pulse (n). The presence of induced motion artifact and any noise was removed after signal digitization by noise cancellation. Besides fixed weighting, two adaptive algorithms were used for cancellation-LMS and differential steepest descent (DSD). Criteria were developed for comparison of the adaptive techniques. The best fixed weighting for noise cancellation was w=0.6. For fixed-weighting, LMS, and DSD, the mean peak-to-peak errors were 1.22+/-0.54, 1.18+/-0.30, and 1.16+/-0.23 V, respectively, and the mean point-to-point errors were 15.86+/-3.15, 11.40+/-1.96, and 10.13+/-1.25 V, respectively. Noise cancellation using a common-mode reference input substantially reduces motion artifact and other noise from the acquired tonometric arterial pulse signal. Adaptive weighting provides better cancellation than fixed weighting, likely because the mechanical gain at the transducer-skin interface is time-varying.

Tissue transglutaminase antibodies in individuals with celiac disease bind to thyroid follicles and extracellular matrix and may contribute to thyroid dysfunction

BACKGROUND

Individuals with active celiac disease (CD+) have an increased incidence of thyroid dysfunction, which improves on a gluten-free diet (CD-). We investigated whether tissue transglutaminase-2 IgA antibodies (anti-TGase II) present in sera of patients with celiac disease react with thyroid tissue and possibly contribute to thyroid disease.

METHODS

Serum from 40 active celiac patients taken before a gluten-free diet (CD+), 46 patients on a gluten-free diet (CD-), 40 normal controls (NC), and 25 with Crohn's disease (CROHN) was used. All sera were screened for antithyroperoxidase antibodies (TPO-AB) and thyroglobulin antibodies (TG-AB), and indirect immunofluorescence (IIF) was performed on primate thyroid tissue sections using TPO-AB- and TG-AB-negative sera.

RESULTS

IIF with thyroid seronegative, anti-TGase II-positive CD+ sera (n = 23) demonstrated staining of thyroid follicular cells and extracellular matrix, in an identical pattern with monoclonal anti-human TGase II antibody. Evidence of TGase II as the antigen in thyroid tissue was supported by elimination of the IIF pattern when sera were depleted of anti-TGase II by pretreatment with human recombinant TGase II. No staining of thyroid tissue was observed when sera from CD+ patients that were negative for TGase II antibodies, or sera from NC subjects were used. Thyroid antibodies were found in 43% of CD+ patients, significantly higher than NC and CROHN patients (p < 0.0001). In addition, a positive correlation was observed between anti-TGase II and TPO-AB titers (p = 0.0001; r = 0.63).

CONCLUSIONS

Anti-TGase II antibodies bind to TGase II in thyroid tissue, and titers correlate with TPO antibody titers. These findings suggest that anti-TGase II antibodies could contribute to the development of thyroid disease in celiac disease.

Quantitative assessment of the degree of villous atrophy in patients with coeliac disease

BACKGROUND

Endoscopy and biopsy are used to diagnose coeliac disease. There are, however, observer-dependent interpretations of the degree of villous atrophy in biopsies. A pilot study using quantitative image-processing procedures was performed to quantify the degree of villous atrophy in patients with coeliac disease.

METHOD

The degree of villous atrophy in duodenal biopsy images was quantified by calculating the ratio of villous edge-to-piecewise arc length (E/P ratio), and this value was compared with the blinded assessment of Marsh score for degree of villous atrophy.

RESULTS

Mean E/P ratios for n = 31 biopsy images, 2.76 (SD 0.44) (Marsh IIIa), 1.91 (0.50) (Marsh IIIb) and 1.18 (0.22) (Marsh IIIc), were significantly different (p = 0.006). Based on non-parametric testing, the E/P ratios were inversely correlated with Marsh scores (Spearman coefficient rho = -0.798, Kendall tau = -0.681; p<0.0001).

CONCLUSIONS

Biopsy images quantified by image analysis correlated exceedingly well with the histopathological grade of villous atrophy. Since quantified measurements are real-numbered values and lack observer bias, measurement of villous atrophy based on image analysis lends itself to standardisation of histological grading.

Detection of the diastolic pathway, circuit morphology, and inducibility of human postinfarction ventricular tachycardia from mapping in sinus rhythm

OBJECTIVE

The purpose of this study was to determine whether sinus rhythm activation maps could be used to detect the origin and characteristics of reentrant ventricular tachycardia in postinfarction patients.

METHODS

In each of 11 post-myocardial infarction patients, unipolar electrograms were acquired at 256 virtual endocardial sites using noncontact mapping. Electrograms were marked for activation time and mapped on a three-dimensional grid. Spatial differences in sinus rhythm activation time were correlated to isthmus characteristics and to activation through the diastolic pathway during tachycardia on the basis of the presence of contiguous lines of slow conduction and block.

RESULTS

Twenty tachycardia morphologies were analyzed. Fourteen sustained reentrant circuit morphologies occurred in nine patients, with dual morphologies having a shared isthmus occurring in five of nine patients. Dual morphologies were caused by changes in entrance-exit point location about a common isthmus. One transient circuit morphology of <10 beats occurred in three of nine patients also having sustained reentry. The estimated isthmus determined from sinus rhythm activation overlapped the diastolic pathway determined from tachycardia maps with 83.8% sensitivity and 89.2% specificity. The mean difference in sinus rhythm activation time across the isthmus border was larger in transient compared with sustained morphologies (32.8 +/- 9.5 ms vs. 22.8 +/- 1.8 ms), with smaller isthmus size (4.8 +/- 1.1 cm(2) vs. 10.0 +/- 1.1 cm(2); P < .05), narrower entrance-exit points (7.0 +/- 1.5 mm vs. 9.3 +/- 0.8 mm; P < .05), and greater activation time difference across them (16.3 +/- 3.5 ms vs. 10.1 +/- 1.0 ms; P < .05).

CONCLUSION

In post-myocardial infarction patients, the reentry isthmus can be localized in the endocardial border zone from sinus rhythm activation maps. Nonsustained reentry occurs when isthmus size is small and entrance-exit points are narrow and more electrically discontinuous.

Chronic hepatitis C virus and celiac disease, is there an association?

Celiac disease (CD) has been epidemiologically associated with chronic hepatitis C (HCV), and CD activation after the initiation of interferon (IFN-alpha) in patients with HCV is documented. However, clear association of CD and HCV is lacking. A prospectively maintained database of 878 CD patients showed a prevalence of 0.68% (six patients). Symptoms of diarrhea, weight loss, and depression prompted the diagnosis of CD during or after IFN-alpha therapy in four cases. Also, 294 subjects with liver disease (195 with HCV, 80 normal controls and 19 disease controls) were prospectively screened for CD. The mean age of the subjects was 50.1 years (SD 12.3), 58% males:42% females. A total of 30% received IFN-alpha therapy (16% at the time of testing for CD). Two HCV patients (1%) had positive tTG-IgA but these had negative endomysial antibody (EMA) and normal duodenal biopsies. CD prevalence is not increased in patients with HCV. Routine screening of CD in HCV patients is not warranted, however, the presence of CD should be considered in the setting of clinical deterioration during or after IFN-alpha therapy.

Model of reentrant ventricular tachycardia based on infarct border zone geometry predicts reentrant circuit features as determined by activation mapping

BACKGROUND

Infarct border zone (IBZ) geometry likely affects inducibility and characteristics of postinfarction reentrant ventricular tachycardia, but the connection has not been established.

OBJECTIVE

The purpose of this study was to determine characteristics of postinfarction ventricular tachycardia in the IBZ.

METHODS

A geometric model describing the relationship between IBZ geometry and wavefront propagation in reentrant circuits was developed. Based on the formulation, slow conduction and block were expected to coincide with areas where IBZ thickness (T) is minimal and the local spatial gradient in thickness (DeltaT) is maximal, so that the degree of wavefront curvature rho proportional, variant DeltaT/T is maximal. Regions of fastest conduction velocity were predicted to coincide with areas of minimum DeltaT. In seven arrhythmogenic postinfarction canine heart experiments, tachycardia was induced by programmed stimulation, and activation maps were constructed from multichannel recordings. IBZ thickness was measured in excised hearts from histologic analysis or magnetic resonance imaging. Reentrant circuit properties were predicted from IBZ geometry and compared with ventricular activation maps after tachycardia induction.

RESULTS

Mean IBZ thickness was 231 +/- 140 microm at the reentry isthmus and 1440 +/- 770 microm in the outer pathway (P <0.001). Mean curvature rho was 1.63 +/- 0.45 mm(-1) at functional block line locations, 0.71 +/- 0.18 mm(-1) at isthmus entrance-exit points, and 0.33 +/- 0.13 mm(-1) in the outer reentrant circuit pathway. The mean conduction velocity about the circuit during reentrant tachycardia was 0.32 +/- 0.04 mm/ms at entrance-exit points, 0.42 +/- 0.13 mm/ms for the entire outer pathway, and 0.64 +/- 0.16 mm/ms at outer pathway regions with minimum DeltaT. Model sensitivity and specificity to detect isthmus location was 75.0% and 97.2%.

CONCLUSIONS

Reentrant circuit features as determined by activation mapping can be predicted on the basis of IBZ geometrical relationships.