Computer discrimination of atrial fibrillation and regular atrial rhythms from intra-atrial electrograms

Long-term biatrial recordings in post-operative atrial fibrillation

Although atrial fibrillation (AF) is a common complication of cardiac surgery, its pathophysiology remains unclear. The study of post-operative AF demands for the recording of cardiac electrical activity in correspondence of AF onset and progression. Long-term recordings in post-surgery patients could provide this information, but, to date, have been limited to surface signals, which precludes a characterization of the arrhythmic triggers and substrate. In this study we demonstrate the feasibility of a continuous long-term recording of atrial electrical activities from the right and left atria in post-surgery patients. Local atrial epicardial electrograms are acquired by positioning temporary pacing wires in the right and left atria at the end of the intervention, while three day recordings are obtained by a digital holter recorder, adapted to epicardial signal features. The capability of the system to map local atrial activity and the possibility to obtain quantitative information on atrial rate and synchronization from the processed epicardial signals are proven in representative examples. The quantitative description of local atrial properties opens new perspective in the investigation of post-surgery AF.

Manifestation of left atrial events and interatrial frequency gradients in the surface electrocardiogram during atrial fibrillation: contributions from posterior leads

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.

Abrupt changes in fibrillatory wave characteristics at the termination of paroxysmal atrial fibrillation in humans

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.

Short-term dynamics in fibrillatory wave characteristics at the onset of paroxysmal atrial fibrillation in humans

INTRODUCTION

The purpose of this study was to investigate the magnitude and time course of fibrillatory wave dynamics during spontaneous onset of paroxysmal atrial fibrillation (AF).

METHODS

We studied fibrillatory waves in Holter recordings of paroxysmal AF with regard to the fibrillation-free interval (FFI) preceding each episode.

RESULTS

For 38 episodes of paroxysmal AF in 20 patients, dominant frequency (DF) ranged from 4.4 to 6.8 Hz (5.5 +/- 0.5 Hz). Long-FFI episodes showed a gradual increase in DF over the first 4 minutes (P < .0001). Short-FFI episodes showed an increase only from the first to the second minute (P < .003). For all 7 patients exhibiting both long-FFI and short-FFI episodes, short-FFI episodes had a higher initial DF (P < .002).

CONCLUSION

The dynamics during onset and their relation to the FFI are consistent with the influence of short-term electrophysiological changes and their reversal. These findings have implications for the timing of antifibrillatory interventions.

Atrial Fibrillatory Wave Characteristics on Surface Electrogram:

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.

Experimental and clinical AF mechanisms: bridging the divide

There is general agreement that AF is most likely a reentrant rhythm disturbance. However, the precise pathophysiological bases for its initiation and maintenance have not been fully resolved. In the original description of the multiple wavelet hypothesis of atrial fibrillation, as put forward by Moe et al. and later substantiated by Allessie et al., the wavelets were thought to move randomly throughout the atria. However, more recent studies that have applied high resolution mapping of wave propagation and rigorous analyses in the time and frequency domains to long episodes of AF, have provided evidence that atrial fibrillation is not random, but is accompanied by a high degree of spatiotemporal periodicity. This has led to the hypothesis that maintenance of AF may depend on the uninterrupted periodic activity of a small number of discrete reentrant sites, established by the interaction of propagating waves with anatomical heterogeneities in the atria. It has been proposed also that the rapidly successive wave fronts emanating from these sources propagate through both atria and interact with anatomical and/or functional obstacles, leading to fragmentation and wavelet formation. In support of this idea, observations made during radiofrequency ablation of AF in humans suggest that, in some patients, a single, repetitive focal source of activity propagate impulses from an individual pulmonary vein to the remainder of the atrium as fibrillatory waves. These studies underscore the need for identification of continuing AF sources at localized sites, and of transient AF "triggers", which may involve normal or abnormal pacemaker mechanisms or even reentrant activity, and of the manner in which electrical activity initiated by such triggers interacts with the normally propagating electrical waves to initiate fibrillatory activity in the atria.

Role of fibrillation cycle length in spontaneous and drug-induced termination of human atrial fibrillation

The aim of this study was to investigate the mechanism of spontaneous termination of atrial fibrillation (AF) by comparing it with drug-induced termination on the basis of changes in fibrillation cycle length (FCL). Fast Fourier transform analysis was carried out on the electrocardiogram (ECG) records of 27 patients with paroxysmal AF without organic heart disease. In 8 patients with drug-induced termination of AF, spectral analysis of the data from surface ECG lead V1 was performed before and after class I antiarrhythmic drug infusion for 10 min. In 19 patients with spontaneous termination of AF, the analysis used the Holter ECG recordings at 10 min before the spontaneous termination and at the termination. FCL was calculated from the peak frequency of each epoch and the mean FCL and the coefficient of variation (CV) of FCL were determined from the data of 20 epochs. In the 8 episodes of drug-induced AF termination, the mean FCL increased significantly with class I drugs (from 151+/-17 to 203+/-21 ms, p<0.001), whereas in the 19 episodes of spontaneous termination, the mean FCL and CV of FCL at termination did not differ from those at 10 min before the termination. Of the 19 episodes, 10 episodes terminating in the morning showed a significant increase in the FCL of the last epoch of the termination period (from 158 +/-22 to 172+/-17 ms, p<0.05). In the 9 episodes terminating in either the afternoon or the evening, the FCL of the last epoch did not change significantly. Although drug-induced termination of paroxysmal AF may depend on a gradual increase in FCL, the pattern of spontaneous termination may depend on the time of day. Spontaneous termination in the morning may be caused by an abrupt increase in FCL related to vagolytic autonomic balance.

Cholinergic atrial fibrillation in a computer model of a two-dimensional sheet of canine atrial cells with realistic ionic properties

Classical concepts of atrial fibrillation (AF) have been rooted in Moe's multiple-wavelet hypothesis and simple cellular-automaton computer model. Recent experimental work has raised questions about the multiple-wavelet mechanism, suggesting a discrete "driver region" underlying AF. We reexplored the theoretical basis for AF with a 2-dimensional computer model of a 5x10-cm sheet of atrial cells with realistic ionic and coupling properties. Vagal actions were formulated based on patch-clamp studies of acetylcholine (ACh) effects. In control, a single extrastimulus resulted in a highly meandering unstable spiral wave. Simulated electrograms showed fibrillatory activity, with a dominant frequency (DF, 6.5 Hz) that correlated with the mean rate. Uniform ACh reduced core meander of the spiral wave by approximately 70% (as measured by the standard deviation of spiral-wave tip position) and accelerated the DF to 17.0 Hz. Simulated vagally induced refractoriness heterogeneity caused wavefront breakup as accelerated reentrant activity in regions of short refractoriness impinged on regions unable to respond in a 1:1 fashion because of longer refractoriness. In 7 simulations spanning the range of conditions giving sustained AF, 5 were maintained by single dominant spiral waves. On average, 3.0+/-1.3 wavelets were present (range, 1 to 7). Most wavelets were short-lived and did not contribute to AF maintenance. In contrast to predictions of the multiple-wavelet hypothesis, but in agreement with recent experimental evidence, our model indicates that AF can result from relatively stable primary spiral-wave generators and is significantly organized. Our results suggest that vagal AF may arise from ACh-induced stabilization of the primary spiral-wave generator and disorganization of the heterogeneous tissue response. The full text of this article is available at http://www.circresaha.org.

New Bayesian discriminator for detection of atrial tachyarrhythmias

BACKGROUND

Accurate, rapid detection of atrial tachyarrhythmias has important implications in the use of implantable devices for treatment of cardiac arrhythmia. Currently available detection algorithms for atrial tachyarrhythmias, which use the single-index method, have limited sensitivity and specificity.

METHODS AND RESULTS

In this study, we evaluated the performance of a new Bayesian discriminator algorithm in the detection of atrial fibrillation (AF), atrial flutter (AFL), and sinus rhythm (SR). Bipolar recording of 364 rhythms (AF=156, AFL=88, SR=120) at the high right atrium were collected from 20 patients who underwent electrophysiological procedures. After initial signal processing, a column vector of 5 features for each rhythm were established, based on the regularity, rate, energy distribution, percent time of quiet interval, and baseline reaching of the rectified autocorrelation coefficient functions. Rhythm identification was obtained by use of Bayes decision rule and assumption of Gaussian distribution. For the new Bayesian discriminator, the overall sensitivity for detection of SR, AF, and AFL was 97%, 97%, and 94%, respectively; and the overall specificity for detection of SR, AF, and AFL was 98%, 98%, and 99%, respectively. The overall accuracy of detection of SR, AF, and AFL was 98%, 97% and 98%, respectively. Furthermore, sensitivity, specificity, and accuracy of this algorithm were not affected by a range of white Gaussian noises with different intensities.

CONCLUSIONS

This new Bayesian discriminator algorithm, based on Bayes decision of multiple features of atrial electrograms, allows rapid on-line and accurate (98%) detection of AF with robust anti-noise performance.

Spectral characteristics of human atrial fibrillation waves of the right atrial free wall with respect to the duration of atrial fibrillation and effect of class I antiarrhythmic drugs

The aim of this study was to use fast Fourier transform analysis to clarify the characteristics of human atrial fibrillation (AF) waves with respect to the duration of AF and the effect of class I antiarrhythmic drugs. Twenty-two patients (10 paroxysmal AF, 12 persistent AF) without organic heart disease were studied by conventional electrophysiological methods. Electrograms were recorded from the right atrial free wall during AF and spectral analysis was performed for 35s (16 consecutive 4096-ms epochs with 50% overlap) and the fibrillation cycle length (FCL) was calculated from the peak frequency. Mean FCL and SD were determined from 16-epoch data, and the temporal variability of FCL was defined as the SD of FCL. Paroxysmal AF had a longer mean FCL than persistent AF (178+/-26ms vs 139+/-16 ms, p<0.001) and AF duration had a significant inverse correlation with mean FCL (r=-0.79, p<0.001). The temporal variability of FCL was significantly greater in paroxysmal AF than in persistent AF (p<0.05) and there was a significant positive correlation between the mean FCL and the temporal variability of FCL (r=0.66, p<0.001). In 8 of 18 patients given a class I antiarrhythmic drug (cibenzoline or procainamide), AF was terminated and in those patients the mean FCLs before administration of class I drugs were significantly greater than in patients without AF termination. With respect to mean FCL before drug administration, conversion occurred in 100% of patients with FCL > or =168 ms and in 17% of those with FCL <168 ms. A longer duration of AF shortens the mean FCL, which is consistent with atrial electrical remodeling. Class I drugs prolong the mean FCL above a critical level and will terminate AF, which can be estimated from the mean FCL before drug administration.

Prevalence, characteristics and clinical implications of regular atrial tachyarrhythmias in patients with atrial fibrillation: insights from a study using a new implantable device

OBJECTIVES

This study prospectively analyzed atrial tachyarrhythmia (AT) organization and antitachycardia pacing (ATP) success in patients with an implanted device for AT therapy.

BACKGROUND

In patients with atrial fibrillation (AF), the incidence of regular, slow ATs amendable by ATP is unknown.

METHODS

Forty patients with previously documented AT (70% with AF) received a new pacemaker with atrial electrogram (AEG) storage and atrial ATP capabilities for standard pacing indications. The AEGs acquired during the first month (study phase 1) were classified into high (type I), intermediate (type II) and low (type III) degrees of organization. Atrial ATP was then activated, and treated AT episodes were retrieved three and six months after implantation (study phase 2).

RESULTS

Of 824 AEGs retrieved before ATP activation (study phase 1), 351 (43%) were classified as type 1, 47% as type II and 10% as type III. Episodes of AT starting as type I (35%) and type II or III (65%) maintained their type over 1 min in 73%. All patients with an exclusive history of AF also showed type I AEGs. In 361 subsequently treated AT episodes (study phase 2), ATP was successful in 62% of type I and 34% of type II episodes, but not in type III (p < 0.0001).

CONCLUSIONS

The majority of patients with a history of AF show not only disorganized but also highly organized AT episodes, which can be successfully terminated by ATP.

Quantitative analysis of termination of vagally induced canine atrial fibrillation by mutual information

Atrial fibrillation (AF) is often described as a disorganized phenomenon, but many features that qualitatively suggest an underlying order have recently been reported. The present study aimed to disclose this underlying order of AF in a quantitative manner, using a new method of mutual information (MI), which is a measure for gauging the general correlation between 2 time series. Frequency analysis and the MI method were used to analyze 5 epicardial potentials on both atria during AF induced by vagal stimulation (Vs) in 15 dogs. Unipolar electrodes were placed on the right atrial appendage (Rap), the high right atrium (HRA), and the left atrial appendage (Lap). The other 2 electrodes were placed equidistantly between HRA and Rap (RA1-RA2). The power spectrum of AF had a discrete peak around 17Hz during Vs. After Vs was stopped, the discrete peak shifted from 17Hz to 7 Hz on all epicardial leads. Taking RA2 as a reference, MI was calculated between RA2 and each of the other electrodes. The MI values (0.066+/-0.005) were greater than 0.047 (the critical value for correlated data) even during Vs. The MI values increased significantly from the highly active process of AF during Vs to the less active one (0.126+/-0.006) before termination of AF. In addition, the MI values increased more at the electrodes close to RA2 (RA1 and Rap) than at those far from it (HRA and Lap). These findings suggest that multiple wavelets, which are not random, progressively organize into a few major waves toward the termination of AF; therefore, AF is not a random phenomenon in this model.

Spatial correlation analysis of atrial activation patterns during sustained atrial fibrillation in conscious goats

In this study we applied both linear and nonlinear spatial correlation measures to characterize epicardial activation patterns of sustained atrial fibrillation in instrumented conscious goats. It was investigated if nonlinearity was involved in the spatial coupling of atrial regions and to what extent fibrillation was organized in the experimental model of sustained atrial fibrillation (AF) in instrumented goats. Data were collected in five goats during experiments to convert AF by continuous infusion of cibenzoline. Spatial organization during AF was quantified with the linear spatial cross correlation function and the nonlinear spatial cross redundancy which was calculated using the Grassberger-Procaccia correlation integral. Two different types of correlation were evaluated to distinguish simultaneous interaction from non-simultaneous interaction, for instance resulting from propagation of fibrillation waves. The nonlinear association length and the linear correlation length were estimated along the principal axes of iso-correlation contours in two-dimensional correlation maps of the nonlinear spatial redundancy and the linear spatial correlation function, respectively. To quantitatively assess the degree of nonlinearity, the association length was also estimated from the linearized spatial redundancy using multivariate surrogate data. The differences between the nonlinear and linearized association lengths indicated that a nonlinear component in the spatial organization of AF predominantly existed in the right atrium. The degree of organization characterized by association length along the short principal axis was higher in the right atrium (15 +/- 7 mm) than in the left atrium (8 +/- 4 mm). The spatial extension of coherent atrial patches was estimated from a surface of association equal to the area spanned by the principal axes of iso-correlation contours from the redundancy, including the effects from non-simultaneous interaction. Interpreting this area as the spatial domain of a fibrillation wavelet, the results suggest that the mapped region was activated on average by two wavelets in the left atrium and by one wavelet in the right atrium. Therefore, the activation pattern of sustained AF in goats was relatively organized, consistent with type II of AF. It is suggested that the surface of association is a measure of the number of independent wavelets present in the atria during sustained AF, and that larger association lengths result from fewer and larger reentrant circuits.

Spatially distributed dominant excitation frequencies reveal hidden organization in atrial fibrillation in the Langendorff-perfused sheep heart

INTRODUCTION

Atrial fibrillation (AF) is characterized by complex wave propagation, yet periodic excitation suggesting a high degree of organization may be revealed during sustained AF. We provide a systematic quantification of the spatial distribution of dominant frequencies (DFs) of local excitation on the epicardium of the right atrial (RA) free wall and left atrial (LA) appendage of the isolated sheep heart during AF. The data reveal, for the first time, hidden organization, independent of the activation sequences or nature of electrograms.

METHODS AND RESULTS

In 13 Langendorff-perfused sheep hearts, AF was induced in presence of 0.1 to 0.6 microM acetylcholine. Video movies (potentiometric dye di-4-ANEPPS) of the RA and LA (>30,000 and >20,000 pixels, respectively) were obtained at 120 frames/sec and a biatrial electrogram was recorded. Spectral analyses were performed on movies with DF maps constructed. During AF, the activity formed stable discrete domains with uniform DFs within each domain. Acceleration of AF increased the number of domains (R = 0.81, P < 0.0001) and the DF variance (R = 0.63, P < 0.001), indicating a decrease in organization. Also, the LA was faster and more homogeneous, with smaller number of DF domains, compared to the RA (P < 0.00001).

CONCLUSION

In this model, AF is characterized by multiple domains with distinct DFs on the atrial epicardium. The decrease in domain area with increased rate suggests that AF results from high-frequency impulses that undergo spectral transformations. The LA is generally faster and more organized than the RA, suggesting that the sources for the impulses are localized to the LA.

Automated classification of human atrial fibrillation from intraatrial electrograms

The assessment of the degree of organization and the classification of atrial fibrillation (AF) according to the types defined by Wells usually resorts to the visual inspection of bipolar intraatrial electrograms. The focus of this study was to test seven parameters aimed to quantify the degree of organization of the electrograms, and then to design a final classification scheme based on a multidimensional, minimum-distance analysis. The following parameters were tested: mean atrial period (AP) and its coefficient of variation (CV); number of points lying at the baseline (NO) and the Shannon entropy (EN) of the amplitude probability density function (APDF); depolarization width (F-WIDTH); and correlation waveform analysis (CWA) and electrogram bandwidth (BW). The signal database consisted in a set of 160 AF strips of Type I, II, and III AF, scored by an expert cardiologist (60 Type I, 40 Type II, 60 Type III) and further divided in a training set (60) and a test set (100). Strips were 6 seconds long and were recorded with 5-mm interspace bipolar catheters from electrically induced (n = 13) and chronic (n = 10) patients. A classification algorithm based on a minimum-distance (Mahalanobis distance) discriminant analysis was tested. Using a single parameter, the best discriminations were provided by NO, F-WIDTH, and CV. F-WIDTH was found strongly inversely correlated to NO (r = -0.90). Of all the two-parameter combinations, CV-NO provided the best classification: 92 of 100 segments were correctly classified with sensitivity > 90% and specificity > 92%. A further improvement was obtained by including BW as a third parameter (93/100 correctly classified). The use of more than three parameters not only failed to improve, but even degraded the classification.

Assessment of intersignal variability for discrimination of atrial fibrillation from atrial flutter

The analysis of endocardial signals obtained from an electrode located in the right atrium enabled by new dual chamber implantable cardioverter defibrillators may be helpful to provide additional therapies such as overdrive pacing or low energy atrial cardioversion for the treatment of concomitant atrial flutter (AFL) or atrial fibrillation (AF). Algorithms for discrimination of atrial tachyarrhythmias based on rate counting are of limited efficacy. The aim of this study was to assess the intersignal variability by using fast discrete wavelet transforms (FDWT) as a new method of discrimination of AF from AFL. Patients with spontaneous episodes of AF/AFL or patients who developed AF/AFL during an electrophysiological study were studied. The endocardial signals were recorded from the high right atrium using a transvenous 5 Fr bipolar electrode catheter (interelectrode spacing: 1 cm). The signals were digitized (2 kHz, 12-bit resolution) after amplification and filtering (40-500 Hz). Within data segments of 10-second duration, 25 consecutive signals were selected and normalized and FDWT was applied. Standard deviations of the wavelet coefficients (SD) from coarse scales (scale 4-8) were calculated. A total of 94 data segments (AF: 52, AFL: 42) from 28 patients were analyzed. SD at each considered scale was higher for AF than for AFL (P < 0.001). SD at scale 8 discriminated between AF from AFL with 100% sensitivity and specificity. We conclude that assessment of intersignal variability of bipolar endocardial recordings using FDWT is an effective method for the discrimination of AF from AFL. The implementation of this tool in a discrimination algorithm of an implantable device may help provide the appropriate differential therapy for atrial tachyarrhythmias.

Spatiotemporal periodicity during atrial fibrillation in the isolated sheep heart

BACKGROUND

The activation patterns that underlie the irregular electrical activity during atrial fibrillation (AF) have traditionally been described as disorganized or random. Recent studies, based predominantly on statistical methods, have provided evidence that AF is spatially organized. The objective of this study was to demonstrate the presence of spatial and temporal periodicity during AF.

METHODS AND RESULTS

We used a combination of high-resolution video imaging, ECG recordings, and spectral analysis to identify sequential wave fronts with temporal periodicity and similar spatial patterns of propagation during 20 episodes of AF in 6 Langendorff-perfused sheep hearts. Spectral analysis of AF demonstrated multiple narrow-band peaks with a single dominant peak in all cases (mean, 9.4+/-2.6 Hz; cycle length, 112+/-26 ms). Evidence of spatiotemporal periodicity was found in 12 of 20 optical recordings of the right atrium (RA) and in all (n=19) recordings of the left atrium (LA). The cycle length of spatiotemporal periodic waves correlated with the dominant frequency of their respective optical pseudo-ECGs (LA: R2=0.99, slope=0.94 [95% CI, 0.88 to 0.99]; RA: R2=0.97, slope=0.92 [95% CI, 0.80 to 1.03]). The dominant frequency of the LA pseudo-ECG alone correlated with the global bipolar atrial EG (R2=0.76, slope=0.75 [95% CI, 0.52 to 0.99]). In specific examples, sources of periodic activity were seen as rotors in the epicardial sheet or as periodic breakthroughs that most likely represented transmural pectinate muscle reentry. However, in the majority of cases, periodic waves were seen to enter the mapping area from the edge of the field of view.

CONCLUSIONS

Reentry in anatomically or functionally determined circuits forms the basis of spatiotemporal periodic activity during AF. The cycle length of sources in the LA determines the dominant peak in the frequency spectra in this experimental model of AF.

Discrimination of sinus rhythm, atrial flutter, and atrial fibrillation using bipolar endocardial signals

INTRODUCTION

Analysis of endocardial signals obtained from an electrode located in the right atrium as realized in newly designed dual chamber, implantable cardioverter defibrillators might be used to provide additional therapeutic options, such as overdrive pacing or low-energy atrial cardioversion for the treatment of concomitant atrial flutter (AFL) or atrial fibrillation (AF). Therefore, we developed a computer algorithm for discrimination of normal sinus rhythm (NSR), AFL, and AF that may lead to adequate differential therapy of atrial tachyarrhythmias in an automated mode.

METHODS AND RESULTS

During an electrophysiologic study, bipolar endocardial signals from the high right atrium were obtained in 28 patients during sustained AFL or AF and after restoration of NSR. A total of 286 data segments of 5-second duration were recorded (NSR: 96, AFL: 86, AF: 104). Mean atrial cycle length (MCL), standard deviation of mean atrial cycle length (SDCL), and index of irregularity (IR), defined as the ratio between MCL and SDCL, were calculated for each data segment. A cutoff of 315 msec for MCL allowed discrimination of NSR from atrial tachyarrhythmias with 100% sensitivity and specificity. For discrimination of AF from AFL by using SDCL, a cutoff value of 11.5 msec led to a sensitivity of 99% and a specificity of 90%. Best discrimination of AF from AFL was found for the criterion IR > or = 7.5%, resulting in a sensitivity of 100% with a specificity of 95% for AF detection.

CONCLUSION

The investigated algorithm provides discrimination of NSR, AFL, and AF with high sensitivity and specificity. Incorporation of this algorithm in an implantable automated antitachycardia device may lead to adequate differential therapy in patients suffering from spontaneous episodes of AF and AFL.

Detection of atrial activity from high-voltage leads of implantable ventricular defibrillators using a cancellation technique

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. We 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 (SR) and AFib segments. We 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 ICD's. 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.

Discrimination of atrial fibrillation from regular atrial rhythms by spatial precision of local activation direction

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 > or = 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.

Feasibility of atrial fibrillation detection and use of a preceding synchronization interval as a criterion for shock delivery in humans with atrial fibrillation

OBJECTIVES

This study assessed the feasibility of detecting atrial fibrillation (AF) and delivery of appropriately timed R wave shocks using an implantable atrial defibrillator.

BACKGROUND

For atrial defibrillation therapy to be feasible in an implantable form, AF must be detected in a specific fashion, and the risk of ventricular proarrhythmia should be minimized.

METHODS

Eleven patients with AF underwent testing with an implantable atrial defibrillator (METRIX 3000 Automatic Atrial Defibrillator, InControl, Inc.). Wideband electrograms (EGMs) were recorded from the right ventricular (RV) bipolar catheter and from the multipolar catheters located in the right atrium (RA) and coronary sinus (CS). Atrial fibrillation detection was performed using two serial algorithms-quiet interval analysis and baseline crossing analysis-that detect atrial activity on the RA-CS channel. Ventricular sensing using a minimal preceding synchronization interval of 500 ms as a criterion for synchronous shock delivery was performed from filtered RV and RV-CS EGMs.

RESULTS

The AF detection algorithms were applied to 53 AF data segments and 18 normal sinus rhythm data segments. Atrial fibrillation was detected appropriately in 49 instances, and the specificity for detecting AF and normal sinus rhythm was 100%. Synchronization criterion efficacy was assessed by delivering shock markers and shocks. Of the 2,025 R waves processed, 557 (27.5%) were marked as suitable for shock delivery. In addition, 69 therapeutic and 11 test shocks were delivered during AF. All shock markers and shocks were delivered synchronously with the R wave, and the synchronization criterion was never violated.

CONCLUSIONS

Atrial fibrillation can be detected in a specific fashion using the RA-CS lead configuration and serial detection algorithms for atrial sensing. The delivery of properly timed shocks is feasible and should minimize the risk of ventricular proarrhythmia.

Mode switch despite undersensing of atrial fibrillation in DDD pacing

Mode switching algorithms are commonly used to protect the ventricles against high rates induced by atrial tachycardia. In the case of atrial fibrillation (AF), the response of these algorithms depends on the quality of atrial sensing. The Chorum 7234 DDDR pacemaker uses a new mode switching algorithm, based on a statistical analysis of the atrial rhythm. It includes two criteria of diagnosis: "high" if more than 28 of 32 cycles are abnormally accelerated; and "low" if more than 36 of 64 cycles are abnormally accelerated.

METHODS

From a taped database of electrophysiological studies, episodes of AF lasting more than 2 minutes were selected. A tape recorder replayed the atrial signals into an external Chorum device. Each episode was replayed eight times with a programmed atrial sensitivity increasing from 0.4-2.0 mV. For each criterion of diagnosis and each programmed sensitivity, the percentage of atrial sensing, the time to switching, and the mean ventricular rate were measured. Ten episodes of AF from 10 patients (9 men and 1 woman; ages 62 +/- 16 years) were included: 1.95 +/- 0.97 mV and 196 +/- 64 ms. The sensitivity of the algorithm to diagnose atrial tachycardia reached 100%, for an atrial sensitivity set between 0.4 and 1.0 mV. The mean percentages of atrial sensed events were 74% +/- 18% and 46% +/- 9% for the "high" and "low" criteria, respectively. The mean diagnostic times were 28 +/- 26 seconds and 68 +/- 27 seconds, respectively. Sensing of < 23% of AF events resulted in failure to diagnose the arrhythmias by both algorithms. In the event of diagnostic failure, the mean ventricular pacing rate was 79 +/- 9 ppm.

CONCLUSION

Up to an atrial sensitivity of 1 mV, 100% of AF episodes were diagnosed. The Chorum mode switching algorithms are 100% reliable if > 45% of the AF waves are sensed. In the event of switching failure, the ventricle is protected by an average rate remaining below 80 ppm.

Augmented two-channel arrhythmia detection: an efficient diagnostic method for implantable devices

ICDs are highly effective in preventing sudden cardiac death. However, inappropriate device shocks caused by false-positive diagnoses are estimated to happen in 20% of all patients. The need for implantable electrical devices to detect with precision arrhythmias requiring therapy has spawned a variety of proposals for better means of tachycardia identification. To address this problem, the augmented two-channel arrhythmia detection (A2CAD) algorithm, a real-time scheme utilizing timing and morphology from both the atrial and ventricular channels, is introduced. The algorithm uses rate detection as a first stage and augments this with morphological signal analysis in rhythms that confound the rate only diagnoses. The software executes in real-time (online), and has been tested on 60 passages of two-channel intracardiac signals. The following arrhythmias constituted the test set: 10 AF and/or atrial flutter; 15 SVT; 16 VT; 10 ventricular flutter or VF; 5 sinus tachycardia; and 4 cases of AF concurrent with VF. Results from 60 patient cases indicate 57 (95%) of 60 success rate for A2CAD, validating its potential for implementation in future implantable devices.

Atrial defibrillation: can modifications in current implantable cardioverter-defibrillators achieve this?

Atrial fibrillation (AF), the most common arrhythmia resulting in hospital admission, is a major health problem. The limited efficacy of antiarrhythmic drugs to control this rhythm disorder and their potential proarrhythmic risk led to the development of new techniques to ameliorate the treatment of AF. Transvenous atrial defibrillation using endocardial electrodes has been shown to be effective at low energy levels. An implantable atrial defibrillator could be a potentially valuable treatment option for patients with paroxysmal AF that is medically refractory. Research is currently under way to investigate several critical issues concerning this new therapeutic concept: long-term efficacy, safety, patient's tolerance, and an acceptable cost/benefit ratio. It is well known that AF often complicates the use of the implantable cardioverter-defibrillator (ICD) for ventricular tachyarrhythmias. Therefore, it would seem desirable to implement the capability for atrial defibrillation into current ICD systems. It has been shown that atrial defibrillation, using endocardial lead configurations specifically designed for ventricular defibrillation, is feasible at energies well within the capabilities of current ICD technology. Further research is needed to evaluate if some enhancement of the lead configuration in combination with possible advanced technology could reduce the atrial defibrillation threshold to a well tolerated level as a prerequisite for automated atrial defibrillation, in ICD recipients with concomitant paroxysmal AF.

A frequency domain analysis of spatial organization of epicardial maps

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.

Is there any indication for an intracardiac defibrillator for the treatment of atrial fibrillation?

The experience gained using intracardiac cardioverter defibrillators for the treatment of ventricular arrhythmias has prompted the development of an automatic atrial defibrillator capable of detecting and automatically terminating atrial fibrillation (AF). Experimental studies in sheep have shown that it is possible to terminate AF with energies ranging from < 1 to 7 joules [J], using biphasic shocks. The best electrode configuration using intracardiac catheters and/or a subcutaneous patch was two catheters, one in the right atrium and the other in the coronary sinus. Current studies in man focus on the answers to three questions. First, can the experimental results of atrial defibrillation derived from healthy anesthetized sheep without spontaneous AF be extrapolated to AF in man with areas of fibrosis within the atria and/or underlying heart disease in 80% of cases? Preliminary studies in man suggest that cardioversion of AF of short duration is feasible using a mean energy of 2 J. Second, are these energies well tolerated in an awake nonsedated patient? Energies < 1 J were well tolerated, but pain resulting from higher energies needs further investigation. Third, is low-energy atrial defibrillation safe, i.e., is there a risk of ventricular arrhythmias induced by an atrial shock? Experimental results in sheep have shown that the risk of R wave synchronized shock to induce ventricular arrhythmias was only present when the preceding RR interval was shorter than 300 msec. The risk of proarrhythmia in man is undergoing evaluation and must be sufficiently low (< 0.1) before sanctioning implantation of a stand-alone (without associated ventricular defibrillator) automatic atrial defibrillator. Preliminary data on 1212 shocks showed no proarrhythmia.(ABSTRACT TRUNCATED AT 250 WORDS)

Tachycardia detection by antitachycardia devices: present limitations and future strategies

Early experience with three generations of implantable devices has demonstrated the need to further refine the accuracy of automated rhythm analysis. Although initial experience with commercially utilized morphological waveform analysis has been disappointing, other time and frequency domain electrogram features have been developed and show potential promise for future devices. While single chamber algorithms for rate and rate variations have theoretical appeal because of their limited power demands, practical experience has demonstrated that inaccurate arrhythmia diagnosis continues to occur by antitachycardia devices that utilize them. Technological advancement in hardware manufacturing and the design of increasingly more efficient software algorithms for tachycardia detection will continue to yield lower power digital circuitry, to increase device battery power and life, and to permit more and more accurate automated arrhythmia diagnosis and treatment by antitachycardia devices. Two chamber sensing has been available for decades in dual chamber antibradycardia pacemakers. The introduction of this technology into antitachycardia devices is not only inevitable but should dramatically improve the precision of diagnosis in future generation devices.

Left atrial appendage function and thrombus formation in atrial fibrillation-flutter: a transesophageal echocardiographic study

OBJECTIVES

The purpose of this study was to investigate left atrial appendage size, function and thrombus prevalence in patients with atrial "fibrillation-flutter."

BACKGROUND

Thrombus formation and peripheral embolization in atrial fibrillation are related to left atrial appendage dysfunction. Embolization occurs less frequently in atrial flutter. It is not known whether the atrial appendage in fibrillation-flutter, which has an intermediate appearance on the surface electrocardiogram (ECG), has distinct characteristics that could affect thrombus formation.

METHODS

Sixty-one patients with atrial tachyarrhythmias underwent transesophageal echocardiographic examination of the left atrial appendage. Appendage area, peak emptying velocity and the presence of thrombus and spontaneous echo contrast were determined. The results for 14 patients with fibrillation-flutter (based on ECG fibrillatory wave characteristics) were compared with those for 30 patients with atrial fibrillation and 17 patients with atrial flutter.

RESULTS

Both fibrillation-flutter and atrial fibrillation were associated with chaotic appendage flow patterns with similarly low peak emptying velocities (18 +/- 8 and 17 +/- 10 cm/s, mean +/- 1 SD, respectively). Atrial flutter was associated with a regular pattern of appendage contraction and a significantly higher peak emptying velocity (42 +/- 18 cm/s, p < 0.0001). Mean appendage area was similar for fibrillation-flutter and fibrillation (6.3 +/- 2.2 and 6.7 +/- 2.1 cm2, respectively) but was significantly smaller for atrial flutter (5.3 +/- 1.4 cm2, p < 0.05). The prevalence of left atrial appendage thrombus was similar for fibrillation-flutter and atrial fibrillation (40% and 29%, respectively), whereas no patient with atrial flutter had a thrombus (p < 0.05). Similarly, the presence of spontaneous echo contrast was higher for fibrillation-flutter (50%) and atrial fibrillation (40%) than for atrial flutter (6%, p < 0.05).

CONCLUSIONS

Left atrial appendage size and function in atrial fibrillation-flutter are indistinguishable from those of typical atrial fibrillation, and the frequency of thrombus and spontaneous echo contrast is similarly high. This is in contrast to atrial flutter, which is characterized by a smaller, more contractile left atrial appendage and a lower frequency of thrombus and spontaneous echo contrast.

Adaptive filters for analysis of intra-cardiac signals

Implantable cardioverters and defibrillators must discriminate malignant ventricular arrhythmias from other supraventricular tachycardias. Electrogram signals are sensed by a single floating endocardial catheter with multiple sensors. The sensors acquire composite atrial and ventricular complexes from atrial and ventricular chambers. Two adaptive filters are utilised to discriminate atrial signals from ventricular signals. The adaptive impulse correlated filter utilises an impulse sequence correlated with the ventricular depolarisations in order to filter the composite signal. This filter should be useful in the analysis of atrial arrhythmias. The adaptive series feedback filter utilises two back-to-back coupled filters to simultaneously extract ventricular depolarisations from one input channel and atrial depolarisations from another channel. This filter should be useful in the analysis of ventricular arrhythmias. Theoretical analysis of the adaptation capabilities of these filters and criteria for convergence are presented. Experimental electrogram recordings are analysed to demonstrate the performance of the two filters. Computational simplicity of these filters makes them particularly suitable for programmable implantable devices.

Observations from intraatrial recordings on the termination of electrically induced atrial fibrillation in humans

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.

Sensitivity and specificity of a dual-chamber arrhythmia recognition algorithm for implantable devices

Present ventricular rate-based arrhythmia detection algorithms lack specificity. Using a training set of 109 endocardial electrogram recordings, a sensitive and specific dual-chamber arrhythmia recognition algorithm has been developed. The algorithm uses atrial and ventricular rates, irregularity, degree of beat-to-beat similarity, and measure of electrogram complex distinctiveness to arrive at a diagnostic conclusion. A test set of 121 endocardial electrogram recordings obtained during provocative electrophysiology studies was then used for blinded validation of the algorithm. In normal rhythm, 1:1 tachycardia, atrial tachycardia, atrial flutter, atrial fibrillation, ventricular tachycardia, and ventricular fibrillation, the percentages of sensitivity/specificity were, respectively, 100/99, 100/99, 80/99, 89/98, 91/97, 92/100, and 100/98. Although ventricular rate alone can usually distinguish normal rhythm, ventricular tachycardia, and ventricular fibrillation, it is confounded by atrial arrhythmias and 1:1 tachycardias. When tested on a database, a ventricular rate-only algorithm resulted in sensitivity/specificity of 100/65, 90/78, and 100/99%, respectively, for these three rhythms. Therefore, the dual-chamber algorithm based on both temporal and morphologic measures provides better distinction of normal rhythm and ventricular tachycardia than existing methods, without sacrificing sensitivity.

Statistical discriminant analysis of arrhythmias using intracardial electrograms

The problem of classifying ventricular arrhythmias from intracardial electrograms is considered. Standard statistical discrimination procedures are applied using a simple parametric model for the shape of the pulse near its peak. This approach makes simultaneous use of the model parameters, has well known statistical properties, and involves computations that can be carried out efficiently. Preliminary analyses of real data sets, using both linear and quadratic discrimination functions, yield promising results.

Evidence for transient linking of atrial excitation during atrial fibrillation in humans

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.

Diagnosis of atrial fibrillation from surface electrocardiograms based on computer-detected atrial activity

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.

Effects of increased heart rate and sympathetic tone on intraventricular electrogram morphology

Electrogram pattern recognition by way of morphologic analysis has been proposed as a technique that may improve discrimination of ventricular tachycardia from sinus rhythm by antitachycardia devices. The potential impact that increases in heart rate and sympathetic tone could have on such techniques, however, has not been previously determined. A comparative study was undertaken to quantify possible changes in ventricular electrogram morphology using correlation waveform, area of difference, and amplitude analyses in 6 patients during atrial overdrive pacing at cycle lengths of 600 and 400 ms (group A), in 13 patients during infusions of physiologic doses of epinephrine (group B), and in 20 patients undergoing infusions of isoproterenol (group C). Four patients were in both groups A and B. A bipolar intraventricular template of cardiac depolarization during sinus rhythm at rest was compared with depolarization during subsequent passages of sinus rhythm at rest and subsequently increased heart rate. In 36 of 39 patients, waveform configuration as assessed by correlation waveform analysis remained relatively stable during atrial overdrive pacing, epinephrine infusion, and isoproterenol infusion when compared with sinus rhythm at rest. The correlation value did not fall below 0.950 in any patient. Area of difference values for the same 36 patients changed by an average of 6 and 37% during atrial overdrive pacing at cycle lengths of 600 and 400 ms intervals, respectively, by 3% during epinephrine infusion, and by 17% during isoproterenol infusion. In these same patients, there was an average change in electrogram amplitude of -1% during atrial overdrive pacing at 600 ms, 26% during pacing at 400 ms, -1% during epinephrine infusion, and 12% during isoproterenol infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial electrograms and the characterization of atrial fibrillation

An improved method of calculating magnitude-squared coherence spectra on pairs of short-duration electrogram recordings is discussed. This method is based on adaptive signal processing techniques and yields spectra with higher resolution than those obtained using a straightforward direct method. The high-resolution spectra will make it possible to examine the time-varying relationship between activity at two sites during atrial fibrillation and may be useful for quick rhythm characterization by implanted devices or for constructing coherence maps in research studies. Example high-resolution spectra for sinus rhythm, atrial flutter, and atrial fibrillation are presented.

Differentiation of ventricular tachyarrhythmias

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."

Nonhomogeneous local atrial activity during acute atrial fibrillation: spectral and dynamic analysis

Atrial fibrillation (A Fib) has been categorized into four different types (I-IV) based on the morphology of the epicardial bipolar electrogram. In the present study, we hypothesized that these same types of A Fib also exist at endocardial sites. Simultaneous high, mid, and low right atrial endocardial bipolar electrograms were analyzed during acute A Fib induced by a rapid train of stimuli (20-40 Hz) for 1-3 seconds in anesthetized closed-chest dogs (N = 7, total of 72 episodes). A Fib lasted between 3 seconds and a few minutes (22.3 +/- 22.8 sec). During A Fib, bipolar electrograms (0.5-500 Hz) were both discrete (types I and II) on electrograms recorded at one site and at the same time irregular (type III) on electrograms recorded at another site. The three simultaneously recorded electrograms encompassed all combinations of the four types of A Fib. When A Fib had a discrete electrogram morphology (types I and/or II), the mean rate of the A Fib was 494 +/- 93 beats/min. At a given site, electrogram morphology also changed type over time. Fast Fourier transform (FFT) of the digitized electrograms (8-10 sec, 800 Hz digitization) showed peaks mostly below 15 Hz (range 0-30 Hz), that were either discrete (narrow band) with clear harmonic components, or had continuous (broad band) spectra, that changed in a time and site dependent manner. Phase plane plots (PPP), a plot of voltage versus rate of change of voltage, varied with respect to time and location. However, the morphology of these PPP often inscribed well defined structure suggesting dynamics compatible with deterministic chaos, rather than random dynamics.(ABSTRACT TRUNCATED AT 250 WORDS)