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Obstructive sleep apnea (OSA) is a common sleep disorder that causes pauses of breathing due to repetitive obstruction of the upper airways of the respiratory system. The effect of this phenomenon can be observed in other physiological signals like the heart rate variability, oxygen saturation, and the respiratory effort signals. In this study, features from these signals were extracted from 50 control and 50 OSA patients from the Sleep Heart Health Study database and implemented for minute and subject classifications. A support vector machine (SVM) classifier was used with linear and second-order polynomial kernels. For the minute classification, the respiratory features had the highest sensitivity while the oxygen saturation gave the highest specificity. The polynomial kernel always had better performance and the highest accuracy of 82.4% (Sen: 69.9%, Spec: 91.4%) was achieved using the combined-feature classifier. For subject classification, the polynomial kernel had a clear improvement in the oxygen saturation accuracy as the highest accuracy of 95% was achieved by both the oxygen saturation (Sen: 100%, Spec: 90.2%) and the combined-feature (Sen: 91.8%, Spec: 98.0%). Further analysis of the SVM with other kernel types might be useful for optimizing the classifier with the appropriate features for an OSA automated detection algorithm.

To evaluate the use of contrast material-enhanced magnetic resonance (MR) imaging with conventional T1-weighted gradient-recalled echo (GRE) and inversion-recovery (IR)-prepared GRE methods to quantitatively measure the size of irreversible electroporation (IRE) ablation zones in the liver in a rat model.All studies were approved by the institutional animal care and use committee and were performed in accordance with institutional guidelines. Seventeen adult male Sprague-Dawley rats were divided into four groups. Rats in groups 1-3 (n = 15 total) underwent IRE performed by using different IRE parameters after gadopentetate dimeglumine administration. Rats in group 4 (n = 2) underwent IRE ablation without prior gadopentetate dimeglumine injection to serve as control animals. MR imaging measurements (with conventional T1-weighted GRE and IR-prepared GRE methods) were performed 2 hours after IRE to predict the IRE ablation zones, which were correlated with pathology-confirmed necrosis areas 24 hours after IRE by using the Spearman correlation coefficient. Bland-Altman plots were also generated to investigate the agreement between MR imaging-measured ablation zones and reference standard histologic measurements of corresponding ablation zones.The necrotic areas measured on the pathology images were well correlated with the hyperintense regions measured on T1-weighted GRE images (r = 0.891, P.001) and normal tissue-nulled IR images (r = 0.874, P.001); pathology measurements were also well correlated with the smaller hyperintense regions measured on those IR images with inversion times specifically selected to null signal from the peripheral penumbra surrounding the ablation zone (r = 0.939, P.001). Bland-Altman plots indicated that these penumbra-nulled IR images provided more accurate predictions of IRE ablation zones, with T1-weighted GRE measurements tending to overestimate ablation zone sizes.Contrast-enhanced MR imaging permits accurate depiction of ablated tissue zones after IRE procedures. IR-prepared contrast-enhanced MR imaging can be used to quantitatively measure IRE ablation zones in the liver.http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.10100645/-/DC1.

To test the hypothesis that magnetic resonance (MR) imaging measurements can be used to immediately detect treated tissue regions after irreversible electroporation (IRE) ablation procedures in rodent liver tissues.All experiments received institutional animal care and use committee approval. In four rats for preliminary studies and 18 rats for formal assessment, MR imaging-compatible electrodes were inserted into the liver and MR imaging-monitored IRE procedures were performed at one of three electrode voltages (1000, 1500, or 2500 V), with T1- and T2-weighted images acquired before and immediately after application of the IRE pulses. MR imaging measurements were compared with both finite element modeling (FEM)-anticipated ablation zones and histologically confirmed ablation zones at necropsy. Intraclass and Spearman correlation coefficients were calculated for statistical comparisons.MR imaging measurements permitted immediate depiction of IRE ablation zones that were hypointense on T1-weighted images and hyperintense on T2-weighted images. MR imaging-based measurements demonstrated excellent consistency with FEM-anticipated ablation zones (r0.90 and P.001 for both T1- and T2-weighted images). MR imaging measurements were also highly correlated with histologically confirmed ablation zone measurements (rho0.90 and P.001 for both T1- and T2-weighted images).MR imaging permits immediate depiction of ablated tissue zones for monitoring of IRE ablation procedures. These measurements could potentially be used during treatment to elicit repeat application of IRE pulses or adjustments to electrode positions to ensure complete treatment of targeted lesions.

Irreversible electroporation (IRE) is an innovative local-regional therapy that involves delivery of intense electrical pulses to tissue to induce nanoscale cell membrane defects for tissue ablation. The purpose of this study was to investigate the feasibility of using IRE as a liver-directed ablation technique for the treatment of hepatocellular carcinoma (HCC). In the N1-S1 rodent model, hepatomas were grown in 30 Sprague-Dawley rats that were divided into treatment and control groups. For treatment groups, IRE electrodes were inserted and eight 100-μs 2,500-V pulses were applied to ablate the targeted tumor tissues. For both groups, magnetic resonance imaging scans were performed at baseline and 15-day follow-up intervals to determine tumor sizes (one-dimensional maximum diameter, Dmax; estimated two-dimensional cross-sectional area, Cmax) as a tactic to assess longitudinal outcomes. Additional groups of treated animals were sacrificed at 1-, 3-, and 7-day intervals posttherapy for pathology assessment of treatment response. Magnetic resonance images showed significant tumor size reductions within 15 days posttherapy (32 ± 31% Dmax and 52 ± 39% Cmax decreases compared with 110 ± 35% Dmax and 286 ± 125% Cmax increases for untreated tumors). Pathology correlation studies documented progression from poorly differentiated viable HCC tissues before treatment to extensive tumor necrosis and full regression in 9 of 10 treated rats 7 to 15 days after treatment. Our findings suggest that IRE can be an effective strategy for targeted ablation of liver tumors, prompting its further evaluation for HCC therapy. Cancer Res; 70(4); 1555–63

Background: In most patients, atrial fibrillation (AF) is initiated and maintained by pulmonary vein foci, but the relationship between left atrial (LA) events and the surface electrocardiogram (ECG) is largely unknown. We investigated whether LA events are reflected in the surface ECG and whether additional information can be obtained from recording posterior leads in patients with AF. Methods and Results: In 10 patients undergoing radiofrequency ablation of AF, we identified 103 5-second segments with a significant frequency gradient between right (RA) and left (LA) intraatrial electrograms, or with frequency changes from segment to segment in the same patient. QRS-T cancellation methods were used to isolate atrial activity in the surface ECG and peak frequencies were computed. Peak frequencies of different posterior leads were very similar (6.0 ± 1.3 Hz for V10, 6.0 ± 0.9 Hz for V9, 5.9 ± 1.4 Hz for V8, 6.0 ± 1.3 Hz for V7). We found a strong correlation between V1 and RA and between V9 and LA, 0.89 and 0.88, respectively, while the lowest correlation was found between lead V1 and LA, 0.62, P < 0.0001. Magnitude-squared coherence values were highest between V1 and RA and between V9 and LA. Conclusion: We have demonstrated that, by recording additional surface ECG leads from posterior locations, RA and LA electrical events and interatrial frequency gradients can be monitored noninvasively.

The surface electrocardiogram (ECG) is a convenient, cost effective, and noninvasive tool for the study of atrial fibrillation (AF). It can be used to examine the hypothesized mechanisms of AF as well as to quantify and assess the effect of electrophysiological remodeling and the effectiveness of treatment on different types of AF. Time domain methods can be used to characterize the signal in the surface ECG. The authors described observations that can be obtained directly from the signal, such as the general characteristics of AF in the surface ECG and the ventricular response to AF. A discussion on commonly used methods to characterize atrial activity is also presented. These methods include cancellation techniques, vector analysis, and autocorrelation. Observations show that combining time and frequency domain methods provides a more thorough understanding of the characteristics of the atrial activity in the surface ECG. Whether the study of atrial activity in the surface ECG can be used to distinctively distinguish between different mechanisms of AF is not yet known, but further investigation can improve our understanding of these mechanisms and help with the management of this common arrhythmia

Background: The aim of this study was to examine atrial organization from vectorcardiograms (VCGs) derived from the surface ECG of atrial fibrillatory waves. Methods: We retrieved ECGs recorded during ventricular asystole from 22 patients with AF undergoing ablation of the AV junction. The synthesized VCG of each f-wave cycle of each ECG and its plane of best fit, described by azimuth and elevation angles relative to the frontal plane, were computed. Results: Fifteen of the 22 ECGs had at least 30% of the planes in a single 30-degree region of azimuth angles. Of these 15, 12 had the greatest percentage of planes with azimuth angles within 30 degrees of the sagittal plane; two were near the frontal plane; and one near the right anterior oblique plane. Conclusions: Varying degrees of organization were observed from VCGs of fibrillatory waves with the more organized examples having planes predominately near the sagittal plane.

Introduction: Fibrillatory waves on the surface ECG have been scrutinized to allow inferences about underlying mechanisms and pathophysiology, based on the premise that fibrillatory waves do not vary “randomly” but provide a consistent reflection of the underlying state of the atria in an individual patient. This premise is untested. Methods and Results: Ten standard ECGs were recorded over a 24-hour period in each of 20 clinically stable inpatients with atrial fibrillation. After QRS-T cancellation, the remainder fibrillatory waves were analyzed. Interpatient versus intrapatient differences in fibrillatory wave characteristics were evaluated by analysis of variance (ANOVA). The fibrillatory wave peak-to-peak amplitude of all the patients ranged from 0.06 to 0.35 mV, whereas 1 SD of the amplitude for each patient ranged from 0.004 to 0.053 mV. Short-term peak frequencies of all the patients ranged from 4.6 to 8.0 Hz, whereas 1 SD for each patient varied from 0.2 to 0.5 Hz. For these and all other parameters tested, interpatient differences were significantly greater compared to intrapatient differences (P < 0.0001). Conclusion: Fibrillatory wave characteristics are repeatable from ECG to ECG over 24 hours for clinically stable patients, whereas substantial differences are present between patients. Further study of the relationship of such characteristics to pathophysiology and management decisions is valid and warranted. (J Cardiovasc Electrophysiol, Vol. 15, pp. 911-917, August 2004)

We hypothesized that if the right atrial circuit during isthmus dependent atrial flutter provides the dominant contribution to the surface electrocardiogram (ECG), the three-dimensional vector loop of the flutter waves would primarily be in a plane approximately parallel to the tricuspid ring. Twenty vectorcardiograms of isthmus dependent atrial flutter derived from 12-lead ECGs of 19 patients recorded prior to radiofrequency ablation were analyzed. The plane of each loop, described by azimuth and elevation angles relative to the frontal plane, was estimated with two methods: 1) plane of maximum loop area and 2) plane of best fit. The plane of maximum loop of the loops had mean azimuth of -58 +/- 37 degrees. and elevation of 15 +/- 15 degrees. The plane of best fit of the loops had mean azimuth of -50 +/- 46 degrees and elevation of 15 +/- 14 degrees. Thus, clinical implications include the potential to predict atrial flutter mechanisms prior to intracardiac mapping.

QRS cancellation methods have been used to analyze atrial activity in the electrocardiogram for such rhythms as atrioventricular dissociated ventricular tachycardia and atrial fibrillation. However, how well the cancellation methods work has never been evaluated by some gold standard. In this study of patients undergoing radiofrequency ablation of the atrioventricular junction, the contribution of imperfect cancellation was evaluated by comparing the “pure” atrial fibrillation (the gold standard) during a brief ventricular asystole to data obtained by a cancellation method during pacing just before and after the asystole. The results were compared by linear regression. The peak frequencies were 4.8–7.3 (6.1 ± 0.8) Hz for the “pure” and 4.8–6.8 (5.9 ± 0.7) Hz for the cancelled electrocardiogram segments (R 2 = 0.89) (similar results for median frequency), and the mean short-time Fourier transform peak frequencies were 4.6–7.1 (5.9 ± 0.8) Hz for the “pure” and 4.7–6.8 (5.9 ± 0.7) Hz for the cancelled segments (R 2 = 0.96). Further comparison was accomplished using synthesized signals. Based on our study, the cancellation method is reliable for studying atrial fibrillatory wave characteristics. As reported previously, the peak frequency and most power for atrial fibrillation in humans are in the 4–9 Hz band.

While the recording of extracellular monophasic action potentials (MAPs) from single epicardial or endocardial sites has been performed for over a century, the authors are unaware of any previous successful attempt to record MAPs simultaneously from a large number of sites in vivo. They report here the design and validation of an array of MAP electrodes which records both depolarization and repolarization simultaneously at up to 16 epicardial sites in a square array on the heart in vivo. The array consists of 16 sintered Ag-AgCl electrodes mounted in a common housing with individual suspensions allowing each electrode to exert a controlled pressure on the epicardial surface. The electrodes are arranged in a square array, with each quadrant of four having an additional recessed sintered Ag-AgCl reference electrode at its center. A saline-soaked sponge establishes ionic contact between the reference electrodes and the tissue. The array was tested on six anesthetized open-chested pigs. Simultaneous diagnostic-quality MAP recordings were obtained from up to 13 out of 16 ventricular sites. Ventricular MAPs had amplitudes of 10-40 mV with uniform morphologies and stable baselines for up to 30 min, MAP duration at 90% repolarization was measured and shown to vary as expected with cycle length during sustained pacing. The relationship between MAP duration and effective refractory period was also confirmed. The ability of the array to detect local differences in repolarization was tested in two ways. Placement of the array straddling the atrioventricular (AV) junction yielded simultaneous atrial or ventricular recordings at corresponding sites during 1:1 and 2:1 AV conduction. Localized ischemia via constriction of a coronary artery branch resulted in shortening of the repolarization phase at the ischemic, but not the nonischemic, sites. In conclusion, these results indicate that the simultaneous multichannel MAP electrode array is a viable method for in vivo epicardial repolarization mapping. The array has the potential to be expanded to increase the number of sites and spatial resolution.

Discusses measuring local activation direction variability using short segment lengths to quickly differentiate fibrillation from regular rhythms. It is concluded that the spatial precision of local activation direction shows promise as a potential discriminator of atrial fibrillation from regular atrial rhythms. For the authors' study set, excellent discrimination of atrial fibrillation from regular rhythms was achieved by spatial precision using segment lengths as short as 20 activations. The authors would expect that this method would be even more accurate using permanently implanted electrodes and could be implemented in real-time using four-electrode elements, and may be applicable in the ventricle as well.

BACKGROUND: The circulating wavelet hypothesis suggests that atrial fibrillation could terminate by either progressive fusion or simultaneous block of all wavelets. METHODS: Intraatrial recordings from the right atrial free wall were made during procainamide induced (n = 8) or spontaneous (n = 7) termination of electrically induced atrial fibrillation in 14 patients. Atrial rate, mean magnitude squared coherence, and direction of activation during sequential electrograms were measured. Rate and coherence were calculated from the earliest point within 5 minutes prior to termination as well as from the 4-second interval just prior to termination. RESULTS: Termination was directly to sinus rhythm (13 episodes) or to atrial flutter (2 episodes). For the eight procainamide induced terminations, rate decreased between the first measurement and the measurement just prior to termination, from 443 +/- 127 beats/min to 322 +/- 119 beats/min. For the seven spontaneous terminations, rate also decreased from 373 +/- 119 beats/min to 323 +/- 88 beats/min; however, a slight increase in atrial rate prior to termination was observed in three episodes. No specific patterns of atrial cycle lengths were seen during the final few seconds of fibrillation. No increase in coherence was observed. In seven episodes, recordings were made using orthogonal bipoles in the x, y, and z directions, allowing direction of activation of wavefronts to be measured. Three episodes showed multiple instances where direction of activation remained similar over several electrograms as we have previously reported for chronic fibrillation. However, no such instances precipitated termination in any of the seven episodes. CONCLUSIONS: Atrial fibrillation usually terminates directly to sinus rhythm and does so abruptly and without forewarning. While we and others have previously reported that the rate of atrial fibrillation decreases with procainamide infusion, a decrease in the rate of atrial fibrillation is not required for the rhythm to terminate and consequently may not be a part of the termination process at all. Coherence does not demonstrate a progressive increase in the organization of atrial fibrillation prior to termination. Lack of stabilization in the direction of activation of wavefronts in the final few seconds also fails to support fusion of wavefronts as the mechanism of termination of atrial fibrillation. Simultaneous block of all wavelets is consistent with, but not proven by, our observations.

Clinical angiography requires hundreds of X-ray images, putting the patients and particularly the medical staff at risk. Dosage reduction involves an inevitable sacrifice in image quality. In this work, the latter problem is addressed by first modeling the signal-dependent, Poisson-distributed noise that arises as a result of this dosage reduction. The commonly utilized noise model for single images is shown to be obtainable from the new model. Stochastic temporal filtering techniques are proposed to enhance clinical fluoroscopy sequences corrupted by quantum mottle. The temporal versions of these filters as developed here are more suitable for filtering image sequences, as correlations along the time axis can be utilized. For these dynamic sequences, the problem of displacement field estimation is treated in conjunction with the filtering stage to ensure that the temporal correlations are taken along the direction of motion to prevent object blur. >

Oscillometry and pulse oximetry rely on signal processing for the detection of cardiogenic events (those arising from the activity of the heart) in a signal which is inherently sensitive to motion and other sources of artifact. In situations where more than one correlated physiological signal is available simultaneously (e.g., when the ECG is being acquired along with the cuff pressure in oscillometry), it is possible to use adaptive or other signal extraction techniques to enhance the desired component of the signal.

BACKGROUND Atrial fibrillation is usually thought of as a "random" pattern of circulating wavelets. However, local atrial activation should be influenced by the constant anatomy and receding tail of refractoriness from the previous activation. The general tendency for wave fronts to follow paths of previous excitation has been termed "linking." We examined intra-atrial electrograms recorded during atrial fibrillation for evidence of linking. METHODS AND RESULTS Two minutes of atrial fibrillation were recorded in 15 patients with an orthogonal catheter. We have previously demonstrated that this catheter can be used to detect changes in the direction of local atrial activation. A mean vector was calculated for each electrogram. The similarity of the direction of the vectors from two consecutive electrograms can be quantified on a scale of 1 to -1 by calculating the cosine (cos) of the smallest angle (theta) between them. Two vectors pointing in the same or opposite directions then have cos(theta) = 1 or -1, respectively. For the entire group of patients, mean cos(theta) was significantly greater than 0 (mean, 0.36; p less than 0.001). In nine of 15 patients, there were groups of six or more consecutive beats (total, 44 groups; range, six to 14 beats per group) in which the direction of activation of each beat was within 30 degrees of the previous beat. The likelihood of one group of six or 14 consecutive similar beats occurring by chance in any one patient in 1 minute is less than 0.05 and less than 0.0000001, respectively. There was a significant correlation (r = 0.90) between the amount of linking during the first and second minutes of atrial fibrillation in each patient. CONCLUSIONS Transient similarities in the direction of wavelet propagation in the majority of patients with atrial fibrillation is consistent with the presence of transient linking. To our knowledge, this is the first direct evidence that atrial activation during atrial fibrillation in humans is not entirely random.

T-wave alternans (TWA) manifests on the surface ECG as a pattern of alternating amplitude T-waves, typically in the microvolt range. Consequently, TWA is usually invisible at standard ECG display scales and must be detected using signal processing methods. There is a predictive relationship between TWA and sudden cardiac death, so proper detection and estimation may contribute to clinical decision-making. The objective of the 2008 Physionet/Computers in Cardiology Challenge was to estimate the magnitude of TWA in a dataset of 100 multi-lead ECGs. We used a modified moving average method (MMA) to detect and estimate TWA. We found that the TWA magnitude ranged from to 1.3 to 256.9 muV (43.9 plusmn 49.7 muV). The Kendall rank correlation coefficient obtained for the challenge was 0.451. In conclusion, the MMA method can be used for detection and estimation of TWA, though additional work could further improve the method.

Cardiac MR image data is typically acquired over multiple cardiac cycles, thus necessitating the use of a synchronization algorithm. Comparison of such algorithms is challenging, as the MR environment distorts the signals that might be used to derive the gating signal for synchronization. In this study, we evaluated three cardiac synchronization algorithms by means of two full-reference image quality metrics and two no-reference metrics; we compared the resulting values of these metrics with subjective analysis by expert reviewers. Both full-reference metrics indicated that there was a statistically significant difference between the cardiac synchronization algorithms. However, both no-reference metrics indicated that there was no statistically significant difference between any of the synchronization algorithms, which corresponded with the subjective analysis. In conclusion, no-reference image metrics correlated well with expert analysis of cardiac MR images, while the full-reference metrics were most likely oversimplified which provided misleading results.

Self-gating (SG) is a cardiac MRI technique to synchronize data acquisition to the cardiac cycle based upon MR signal triggers as opposed to conventional ECG triggers. Fourteen healthy subjects underwent cardiac MRI scans in four different orientations: two chamber, three chamber, four chamber, and short axis. SG trigger times were computed using two methods, first difference and template matching, and ECG trigger times were also recorded for comparison. The root-mean-square (RMS) error was used to evaluate performance, defined as the variability relative to the mean difference between SG trigger times and ECG trigger times. The mean RMS error was lower for template matching than first difference approach for all scan orientations; the improvement in RMS error was statistically significant for all orientations except short axis. In conclusion, compared to the first difference approach, template matching improved the accuracy of trigger detection for two, three, and four chamber SG cardiac MRI scans.

Pacemaker outputs are poorly recorded and displayed by the standard ECG. A new high resolution ECG system optimized for recording outputs from electronic pacemakers was evaluated. Three ECGs with different pulse settings were recorded in 42 patients with pacemakers at a sampling rate of 75 kHz using a new ECG acquisition module. Atrial and ventricular pulses were detected and the measured pulse widths and amplitudes were compared to the programmed values. For the atrium, the correlations between programmed and measured width and amplitude were 0.85 and 0.74, while for the ventricle they were 0.99 and 0.8. Leads II and V1 had the highest atrial amplitude, and leads V3, V4 and V5 had the highest ventricular amplitude. The new high resolution ECG pacemaker system dramatically improved the reproduction of pacemaker outputs, allowing accurate measurement of pulse duration for both atrial and ventricular pulses.

The magnetohydrodynamic effect generates voltages related to blood flow, which are superimposed on the electrocardiogram (ECG) used for gating during cardiac magnetic resonance imaging (MRI). A method is presented for extracting the magnetohydrodynamic signal from the ECG. The extracted magnetohydrodynamic blood flow potential may be physiologically meaningful due to its relationship to blood flow. Removal of the magnetohydrodynamic voltages from the ECG can potentially lead to improved gating and diagnostically useful ECGs.

Aims We investigated the process of spontaneous termination of atrial fibrillation (AF) to determine its time course from the surface ECG. Methods and results We studied fibrillatory waves in Holter recordings of paroxysmal and sustained AF. Following QRS-T cancellation dominant frequencies (DFs) were computed and the relationship of DF to termination was scrutinized. For 57 episodes of paroxysmal AF (PAF) in 24 patients, DF ranged from 4.4 to 6.5 Hz (5.2 ± 0.4 Hz) compared to 5.8 to 7.4 Hz (6.6 ± 0.6 Hz) for sustained AF recordings. Comparison of the atrial frequency of the ultimate to the penultimate second demonstrated a drop in frequency in 51 of 57 episodes, P < 0.00001. No comparable change was seen at longer time periods. Moments of comparably low frequency without termination were only occasionally seen in patients with PAF but not in patients with sustained AF. Conclusion Low frequency fibrillation was found to be much more likely to terminate. Frequency changes preceding spontaneous termination were abrupt, in contrast to the gradual frequency drop reported with drug-induced termination. The analysis of fibrillatory wave characteristics and their change over time might be used to target specific moments for pacing therapy in patients with AF.

The objective of this study was the evaluation of the accuracy of Dower inverse transform for the derivation of the P wave in orthogonal leads. We tested the accuracy of Dower transform on the P wave and compared it with a P-wave-optimized transform in a database of 123 simultaneous recordings of electrocardiograms and vectorcardiograms. This new transform achieved a lower error when we compared derived vs true measured P waves (mean +/- SD, 12.2 +/- 8.0 VRMS) than Dower transform (14.4 +/- 9.5 Root mean squared voltage) and higher correlation values (Rx, 0.93 +/- 0.12; Ry, 0.90 +/- 0.27; Rz, 0.91 +/- 0.18; vs Dower: Rx, 0.88 +/- 0.15; Ry, 0.91 +/- 0.26; Rz, 0.85 +/- 0.23). We conclude that derivation of orthogonal leads for the P wave can be improved by using an atrial-based transform matrix.

Paroxysmal atrial fibrillation (AF) is self-terminating by definition, but the mechanisms by which this occurs are not wall understood. Holter recordings were used to develop and test algorithms for distinguishing between AF segments that are Non-terminating (N), Terminating within a second (T), and Soon terminating (within a minute, S). From rhe training set, the peak frequency ranges (mean±SD) were 4.8-6.0 (5.3±0.4) Hz for T 4.7- 6.4 (5.2±0.6) Hz for S, 4.8-7.3 (6.5±0.8) Hz for N. In 8 of IO T recordings there was a decrease in peak frequency from the penultimate to the ultimare second and in 8 of 10 T recordings there was a decrease in peak power. The last second had a lower peak frequency for T when compared to S of the same patient in 9 of IO patients. Between Nand T we correctly classified 20 of 20 from the training set and 29 of 30 from the test set. Bemeen S and T we correctly classified 20 of 20 from the training set and 20 of 20 from the test set.

We hypothesized that phase relationships of arrial flutter waves nmong diFerent ECG lends could be used to discriminate atrial flutter mechanisms and that vectorcardiography could be used To identlfy such phase relations hips. Twenry-seven ECGs reflecting counterclockwise (CCW) isthmus-dependent (ID) flutter and eight ECGs reflecting clockwise (CW) ID putter were reviewed. Vector analysis identified the following chronologic sequence in the ECGs of 24 of ihe 27 CCW ID flutter vector loops: iso-electric in all leads, trough in [I9 peak in VI, peak in II, and trough in VI. The CW IDflutter ECGs had the reverse sequence in 11 and V1. The phase relationships of hads JI and VI track the CCW and CW activation sequences of ID flutter, even for ECGs not satisfying the prevalent polarity and morphology criteria.

QRS cancellation methods have been used to analyze atrial activity in the ECG including atrial fibrillation. In this study, the contribution of imperfect cancellation was evaluated by comparing "pure" atrial fibrillation in a brief ventricular asystole after RF ablation of the AV junction, and data obtained by the cancellation method during pacing just before and after. The results were compared by linear regression. The peak frequencies were 4.8-7.3 (5.5/spl plusmn/0.8) Hz for the "pure" and 4.8-6.7 (5.4/spl plusmn/0.7) Hz for the cancelled ECG segments (R/sup 2/=0.89), and the mean STFT peak frequencies were 4.6-6.9 (5.8/spl plusmn/0.7) Hz for the "pure" and 4.8-6.8 (5.8/spl plusmn/0.7) Hz for the cancelled segments (R/sup 2/=0.97). Thus, cancellation is reliable for characterizing atrial fibrillation. The peak frequency and maximum power for atrial fibrillation are in the 4-9 Hz band as reported previously.

The traditional perception of atrial fibrillation (AF) as having random and disorganized electrical activity has begun to fade over recent years. Studies involving intra cardiac mapping have shown evidence of an underlying spatial and temporal organization in the atria during AF. In this study, we used a modified QRS-T cancellation method for multi-lead ECGs and examined vectorcardiograms synthesized from twenty 12-lead ECGs recorded during AF. As a preliminary study we also analyzed ECG recordings taken during an ablation procedure of a typical atrial flutter patient where mechanisms and activation sequences were well known. Of the twenty synthesized vectorcardiograms of AF, five showed a consistent cyclical vector sequence. The other recordings often showed segments of repeated sequences lasting two or three f-wave cycles.

The authors developed an electrode array capable of recording four pairs of opposing epicardial and endocardial monophasic action potentials (MAPs) in the in vivo heart. The array was tested on three anesthetized, open chested pigs. The authors recorded simultaneous, dual surface MAPs from all eight sites in the right and left atria and in both ventricles. Atrial recordings exhibited triangular MAP morphologies, amplitudes ranging from 5 to 10 mV, smooth repolarization phases and stable baselines for up to 90 minutes. Ventricular recordings exhibited MAP waveforms with well defined plateau phases, amplitudes ranging from 15 to 40 mV smooth repolarization and stable baselines. These characteristics were comparable on both the epicardial and endocardial recordings. This multichannel electrode array was capable of recording stable, long-term simultaneous mirror image epicardial and endocardial MAPs that will facilitate the study of atrial and ventricular repolarization.

The magnitude-squared coherence (MSC) spectrum is introduced as a dimensionless frequency-domain measure of rhythm organization from pairs of intracardiac and/or epicardial leads. The MS spectrum is simply defined as the magnitude of the complex cross-power-spectrum normalized to the product of the two individual auto-power-spectra. In this way, two linearly related signals (in the absence of uncorrelated additive noise) will have MSC values of unity at all signal frequencies present in both signals in any amount. Mean MSC values are shown to discriminate fibrillatory from nonfibrillatory rhythms. Speed/accuracy tradeoffs in estimation of the MSC are considered. >

Stationarity of surface ECG fibrillatory (f) wave characteristics over 24 hours in clinically stable patients was studied. Inter- and intrapatient differences of f wave characteristics (after QRS-T cancellation) in the time and frequency domains were evaluated by ANOVA. Short-term peak frequencies of all the patients ranged from 4.6 to 8.0 Hz, while one SD for each patient ranged from 0.2-0.5 Hz. The f wave amplitude of all the patients ranged from 0.02 to 0.12 mV, while one SD of the amplitude for each patient ranged from 0.001 to 0.01 mV. For these and all other parameters tested inter-patient differences were significantly greater compared to intra-patient differences (p < 0.0001). This demonstration of stationarity provides a foundation for further study of the relationship of f wave characteristics to pathophysiology and management decisions.

Presents a method for determining local 3-dimensional activation directions in human atria. The authors describe the measuring catheter used, the filtering of the raw signals, the detection of electrograms, and finally the calculation of the resultant vector which estimates local activation direction. This technique is then used to demonstrate that transient "linking" of endocardial activation during atrial fibrillation exhibits sudden, not gradual, transitional behavior. >

Presents a method for determining activation time delays in unipolar cardiac mapping data to resolutions considerably smaller than the sample interval. The method involves taking two filtered, differentiated electrograms and computing the Hilbert transform of their cross correlation, which exhibits a negative-to-positive zero crossing at the delay time between the signals. Simultaneous endocardial/epicardial recordings of sinus rhythm were made in the swine right atrium using identical, precisely superpositioned electrode arrays. Data were amplified, lowpass filtered, and digitized at 1000 Hz. A window of data was chosen around each electrogram in an endocardial/epicardial electrogram pair. The windowed electrograms were differentiated and highpass filtered, and the Hilbert transform of the cross correlation between the electrograms was computed. The activation time delay was taken to be the first negative-to-positive zero crossing. Average activation time delays (/spl plusmn/SD) were computed for 4-s sinus rhythm recordings from each endocardial/epicardial electrode pair. For a representative site, the average transmural activation time delay was 0.71/spl plusmn/0.06 ms (n=10 electrograms). Time delays estimated using the Hilbert transform method were compared with time delays estimated using the maximum negative slope criterion. The Hilbert transform results exhibited much smaller standard deviations, indicating that the Hilbert transform method may produce more accurate time delay estimates than the maximum negative slope method.

In this study, the authors examine how the perception of linking during atrial fibrillation (AF) depends on the choice of threshold angle for defining linking. AF recordings were made using an orthogonal catheter, and the direction of each activation was calculated. Threshold angle was varied from 0 to 180 degrees. For each value, pairs of adjacent activations with directions differing by an angle no greater than the threshold were identified; consecutive strings of 5 or more such pairs were defined as one episode of linking. Plots of percentage of electrograms defined as linked vs. threshold angle were made for each recording, and compared with similar plots for sinus rhythm and random vectors. The results indicate that local activation during AF is different from random activation. However, no optimal threshold angle for defining linking could be identified. >

This study tests the hypothesis that atrial fibrillation (AFib) can be discriminated from regular atrial rhythms by the variation in local activation direction. Human endocardial atrial recordings of AFib, sinus rhythm, atrial flutter, and supraventricular tachycardia were collected, and the direction of each activation was calculated using methods previously described. Each recording was divided into segments containing 100 activations, and the spatial precision for each segment was calculated, The spatial precision for all segments of AFib was /spl les/0.85, whereas the spatial precision for regular rhythms was 20.91 in all but 4 of 138 instances, The results indicate that spatial precision of local activation direction is a useful discriminator of AFib.

The ability to monitor body position and physical activity during ambulatory recordings of ECGs can aid in clinical diagnosis in assessing both physiologic changes and motion artifacts. We have developed a device which, through the use of appropriately placed micro-fabricated accelerometers, can simultaneously record body position information along with two channels of ECG. This study validates the functioning of such a device by recording from five healthy subjects and twenty patients who were asked to wear the device for one hour. A predetermined protocol of defined periods of standing, sitting, lying supine, and walking was followed. The recordings show that the assessment of body position and motion are highly reliable (90% accuracy) therefore allowing correlation with ECG signals.

The authors have developed an electrode array capable of recording simultaneous epicardial and endocardial monophasic action potentials (MAPs) on the heart in-vivo. Using this technique, they measured right atrial dual surface MAPs in nine anesthetized open chest pigs during local cooling of the atrial epicardium and intravenous infusions of adenosine. Cooling of the atrial epicardium generated a temperature gradient across the atrial wall and produced MAP duration (MAPd) lengthening on both surfaces. Intravenous infusion of adenosine caused MAPd shortening on both surfaces. Some sites exhibited differences in MAPd across epicardial and endocardial sites that persisted during both interventions. These findings suggest that atrial repolarization has three dimensional characteristics at least in some locations perhaps due to the presence of pectinate musculature on the endocardial surface.

The inability to detect atrial activity limits implantable ventricular cardioverter defibrillators (ICD) in discriminating tachycardias and can result in inappropriate therapy. This study attempted to detect atrial activity on the wide-spaced bipole signals formed by the high-voltage (HV) leads of the ICD during device implantation and to develop an algorithm for the detection of atrial fibrillation (AFib) from these signals. The authors used a method that cancelled ventricular and correlated atrial activity from the HV lead signals and measured frequency and amplitude distribution information to discriminate sinus rhythm (SR) and AFib segments. The authors analyzed 186 data segments from 21 patients (six AFib, 14 SR, one AFib and SR). For individual segments in this data set, the sensitivity of the algorithm was 78%, specificity 92.65%, positive and negative predictive values 79.59 and 91.97%, respectively. These results demonstrate that atrial activity is present in the HV lead signals, and AFib detection can be achieved in many, but not all cases, using information currently available to ICDs. Prior work from surface electrocardiograms suggests that this algorithm can function during ventricular tachycardias. However, specificity of the algorithm is not high enough for clinical use.

This study tests the hypothesis that atrial fibrillation (AFib) can be discriminated from regular atrial rhythms by a measure of the variation in local activation direction. Human endocardial atrial recordings of AFib, sinus rhythm, atrial flutter, and supraventricular tachycardia were collected using a catheter with orthogonally placed electrodes, and the direction of each activation was calculated using methods previously described by our laboratory. Each recording was divided into segments containing 100 activations, and the spatial precision for each segment was calculated in three dimensions, as well as in each of the three two-dimensional (2-D) planes. The three-dimensional (3-D) spatial precision for 1161 segments of AFib in 11 recordings ranged from 0.09-0.85 (mean=0.45), whereas the spatial precision for 138 segments of regular rhythms in 28 recordings was /spl ges/0.91 in all but four instances. The 2-D spatial precision values overlapped for all rhythms. The results indicate that 3-D spatial precision of local activation direction is a useful discriminator of AFib.

Mapping of organized rhythms like sinus rhythm uses activation times from individual electrograms, and often assumes that the map for a single activation is similar to maps for subsequent activations. However, during fibrillation, activation times and electrograms are not easy to define, and maps change from activation to activation. Volume and complexity of data make analysis of more than a few seconds of fibrillation difficult. Magnitude squared coherence (MSC), a frequency domain measure of the phase consistency between two signals, can be used to help interpret longer data segments without defining activation times or electrograms. Sinus rhythm, flutter, and fibrillation in humans and swine were mapped with an array of unipolar electrodes (2.5 mm apart) at 240 sites on the atrial or ventricular epicardium. Four-second data segments were analyzed. One site near the center of the array was chosen ad hoc as a reference. MSC maps were made by measuring mean MSC from 0-50 Hz between every point in the array relative to the reference. Isocoherence contours were drawn. The effects of bias in the coherence estimate due to misalignment were investigated. Average MSC versus distance from the reference was measured for all rhythms. Results indicate that in a 4-s segment of fibrillation, there can exist some phase consistency between one site and the reference and little or none between a second site and the reference even when both sites are equidistant from the reference. In fibrillation, isocoherence contours are elongated and irregularly shaped, reflecting long-term, but nonuniform, spatial organization. That is, activation during fibrillation cannot be considered as random over a 4-s interval, Bias in the coherence estimate due to misalignment is significant for sinus rhythm and flutter, but can be corrected by manual realignment. Average MSC drops with distance for all rhythms, being most pronounced for fibrillation, MSC maps may provide insights into long-term spatial organization of rhythms that would otherwise be cumbersome and difficult to interpret with standard time domain analysis. >

Clinical x-ray image sequences acquired through fluoroscopy systems may be corrupted by quantum mottle--a Poisson-distributed, signal-dependent noise that arises with a controlled x- ray dosage reduction in an attempt to lower the exposure to the patient and the medical staff. In this paper, an approach to temporally filter this sequence is presented. It relies on a joint estimation of the signal and the displacement field through a maximum likelihood approach. Implementation is done via a modified EM algorithm to facilitate a more tractable solution.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A computerized method to detect atrial fibrillatory activity on the surface electrocardiogram is presented. After ventricular activity was canceled by creating a remainder electrocardiogram, significant differences were found in the percent power of the remainder electrocardiograms for a group of rhythms with atrial fibrillation (mean +/- SD; lead V1, 47.4 +/- 29.7%; lead II, 39.4 +/- 26.8%) and a control group (irregular rhythms or rhythms without readily detectable P waves; lead V1, 17.6 +/- 14.6%; lead II, 19.2 +/- 13.9%) for both leads (p less than 0.0001). A discrimination algorithm that classified a rhythm as atrial fibrillation if the percent power was greater than 32% and if noncoupled P waves were not present had a specificity of 90.0% and a sensitivity of 69.7% for the training set and a specificity of 87.8% and a sensitivity of 68.3% for the test set. In addition, the algorithm correctly detected all 66 of the 66 sinus rhythms tested. The algorithm produced good results that may be incorporated into arrhythmia interpretation systems to improve their specificity.

Implantable devices capable of several modes of therapy will require differentiation of various ventricular tachyarrhythmias. Three methods of arrhythmia analysis, magnitude-squared coherence, ventricular rate, and irregularity of cycle length were performed for 45 episodes of induced ventricular tachyarrhythmia in 15 patients. Differentiation of monomorphic ventricular tachycardia from polymorphic ventricular tachycardia and ventricular fibrillation was possible by mean magnitude-squared coherence, less possible by rate, and not possible by beat-to-beat irregularity. Faster monomorphic ventricular tachycardia overlapped with rates of polymorphic ventricular tachycardia and ventricular fibrillation. Differentiation of polymorphic ventricular tachycardia and ventricular fibrillation was not possible by rate or irregularity. A progressive decrease in mean magnitude-squared coherence from monomorphic ventricular tachycardia to polymorphic ventricular tachycardia to ventricular fibrillation strengthens previous observations that coherence is a measure of rhythm "organization."

Previous work has suggested that a comparison of electrograms from two or more sites may best differentiate fibrillatory from nonfibrillatory rhythms. The coherence spectrum is a measure by which two signals may be compared quantitatively in the frequency domain. In the present study, the coherence spectrum was used to quantify the relation between spectral components of electrograms from two sites in either the atrium or ventricle during both fibrillatory and nonfibrillatory rhythms. Bipolar recordings of 35 rhythms from 20 patients were analyzed for coherence in the 1-59 Hz band. The 17 nonfibrillatory rhythms were sinus rhythm (six), paroxysmal supraventricular tachycardia (two), atrial flutter (four), and monomorphic ventricular tachycardia (five). The 18 fibrillatory rhythms were atrial fibrillation (12) and ventricular fibrillation (six). Nonfibrillatory rhythms exhibited moderate-to-high levels of coherence throughout the 1-59 Hz band, with peaks concentrated at the rhythm's fundamental frequency and its harmonics. Fibrillatory rhythms exhibited little coherence throughout the 1-59 Hz band, and harmonics were not evident. The mean magnitude-squared coherence (scale of 0 to 1) for the 1-59 Hz band ranged from 0.22 to 0.86 (mean +/- SD, 0.52 +/- 0.19) for nonfibrillatory rhythms and from 0.042 to 0.12 (0.067 +/- 0.021) for fibrillatory rhythms. Separation of fibrillatory and nonfibrillatory rhythms was possible whether signals were recorded by floating or fixed-electrode configurations. These findings indicate that comparison of two electrograms with magnitude-squared coherence measurements differentiates fibrillatory from nonfibrillatory rhythms. A recognition algorithm based on coherence spectra may provide a major variations in lead configuration.(ABSTRACT TRUNCATED AT 250 WORDS)

The ability of a catheter with an orthogonal electrode configuration to sense differences in the direction of local atrial endocardial activation was tested in 18 consecutive patients with intact retrograde conduction. In all 18, discrimination of anterograde from retrograde conduction at a single atrial site was examined; in 5 of the 18, multiple sites were examined to determine if the discriminatory ability of the catheter was site dependent. The catheter was specially designed with bipoles in the x, y and z directions. A vector was computed for each electrogram during anterograde and retrograde conduction. Electrogram amplitude along the standard bipole was also compared for anterograde and retrograde conduction. Mean electrogram amplitude for the standard bipole was significantly different for anterograde than for retrograde conduction in 17 of 18 patients (mean +/- SD 4 +/- 1.9 vs. 2.7 +/- 1.3 mV; p less than 0.005), with complete separation of amplitude distributions in 4 patients. The electrogram vector during anterograde conduction was significantly different from that during retrograde conduction in all 18 patients (p less than 0.0001), with complete separation of vector distributions in 14. In some patients with multiple site recordings, the choice of site greatly affected separation based on electrogram amplitude or vector, or both. The orthogonal catheter can be used to sense directional differences in local endocardial activation. The catheter shows promise for discriminating anterograde from retrograde conduction and examining the direction of endocardial activation in the heart during an electrophysiologic examination.

Fibrillatory rhythms are poorly characterized by traditional time-domain measures, such as rate. The authors describe two measures not commonly applied in intracardiac signal processing; the median frequency (MF) in the 2 to 9 Hz region of the power spectrum, and the magnitude-squared coherence (MSC) function. These two measures are formally defined. The MF is a robust measure of drug-induced changes in atrial fibrillation, and the MSC is a measure of the degree of organization of atrial and ventricular cardiac rhythms. >

Irregularity of the ventricular rhythm is a hallmark of patients with atrial fibrillation, yet the genesis of the irregularity is not yet fully understood. The role of the atrioventricular (AV) node in determining the irregularity of the ventricular response to atrial fibrillation was investigated by comparing the frequency distributions of the atrial (AA) and the ventricular (RR) intervals.Atrial electrograms and surface electrocardiographic leads were recorded during sustained atrial fibrillation in 12 patients with conduction over the AV node. The scaling factor (mean RR interval/mean AA interval) quantified the ability of the conduction pathway to scale the atrial input to a slower ventricular response and ranged from 2.55 to 5.92 (mean ± SD 3.77 ± 0.92). The coefficient of variation (SD/ mean) measured the relative variability of the AA and RR interval distributions. The atrial and ventricular coefficients of variation were not significantly different (0.20 ± 8.04 versus 0.21 ± 0.03, p > 0.27).Similar recordings were analyzed in six patients with conduction over an accessory AV pathway. The scaling factor ranged from 1.54 to 2.46 (2.02 ± 0.39) and, as was significantly differ (0.24 ± 0.68 versus 0,27 ± 0.10, p > 0.6). For both groups of patients, ventricular variability and the maximal RR intervals were predicted by the product of the scaling factor and either atrial variability or maximal AA intervals, respectively.This study adds direct observation of atrial events to a body of data that suggests that the irregularity of the ventricular response to atrial fibrillation is primarily a consequence of the irregularity inherent in the atrial activity. This relation was observed regardless of the nature of the AV conduction pathway, suggssting that no special properties of the AV node need to he considered to account for the irregularity of the ventricular response to atrial fibrillation.

Changes in body position are known to change the electrical axis of the heart, resulting in changes in the QRS amplitude, ST segment shifts and T-wave inversions. We investigated the effect of body position changes on the frontal-plane P-wave axes of 10 healthy volunteers. The subjects were monitored using three accelerometers recorded with two ECG channels. The 10 subjects followed a protocol of standing, sitting, walking, lying supine and lying on their right and left sides for five minutes each. Median P-wave and QRS vectors in the frontal plane were computed. With standing, sitting, right and left positions, the P-axis had mean shifts of 10/spl plusmn/11 deg, 7/spl plusmn/12 deg, 2/spl plusmn/11 deg and 12/spl plusmn/6 deg, respectively, when compared to the supine position. When compared to QRS shifts, P-wave shifts were larger, with more variability, and were poorly correlated with QRS axis shifts.

In this study, the authors examined the atrial activity content of high voltage (HV) lead signals of implantable cardioverter defibrillators (ICDs) during device implantation. They also attempted to detect atrial fibrillation (AFib) by analyzing these signals. They used a method that canceled ventricular and correlated atrial activity from the HV lead signals and measured frequency and amplitude distribution information to discriminate sinus rhythm and AFib segments. The results suggest that atrial activity is present in HV lead signals, and AFib detection can be achieved in many, but not all cases, using information currently available to ICDs.