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Background Electronic pacemaker pulses are poorly reproduced in computerized electrocardiogram (ECG) tracings, impairing both automated and human interpretation. In this study, a high-bandwidth system is used to examine ECG and vectorcardiogram characteristics of pacemaker pulses. Methods In 69 subjects with artificial pacemakers, electrocardiograms were recorded at 75 000 samples per second with a high-bandwidth ECG system (GE Healthcare, Milwaukee, WI). Vectorcardiograms, as estimated with the Dower transform, were examined. Results Pulse loops in the vectorcardiogram consisted of distinct discharge and recharge waves, with an angle difference of 174° ± 10° (mean ± SD) in 3 dimensions. Atrial pulses were on average oriented anteriorly, superiorly, and to the left; right ventricular pulses were oriented posteriorly, superiorly, and to the right; and left ventricular pulses were oriented posteriorly, inferiorly, and to the right. Other details of pacemaker pulses could be readily observed. Conclusions The high-bandwidth ECG has the potential to improve interpretation of paced rhythms in computerized ECGs.

Background Recording and displaying outputs from electronic pacemakers with electrocardiogram (ECG) recorders typically used in clinical practice have presented a number of technical limitations. We have recently reported on a new high-bandwidth ECG system and have shown that it is capable of reproducing accurate pulse amplitudes and durations from the body surface. In the present work, we have used our data to calculate a transform function between the programmed pacemaker output voltage and the amplitude on the body surface. Methods We recorded 3 high-bandwidth (75,000 samples per second) ECGs from each of 100 pacemaker patients at 3 different programmed outputs. Each pacemaker pulse was isolated using the criterion standard annotations, and the pulses were transformed from the 8 independent leads to an XYZ vector using the Dower transform. The magnitude of the vector was calculated. Linear regression techniques were used to learn a transfer function over the records of the first 50 patients. These results were tested against the second 50 patients. Results The measured pacemaker pulse vector magnitude has a linear relationship to the programmed pacemaker amplitude on a per-patient basis for most of the patients in the training database. The linear transform models were tested against the testing set with an R2 metric of 0.38 for the atrial pulses and 0.54 for the right ventricular pulses. Conclusion Understanding the relationship between the generated pacemaker pulses and the measurements at the body surface will help drive specifications for pacemaker pulse detection among the various device manufactures.

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.

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.

Although the atrial free wall is a thin structure, atrial depolarization has been shown to have aspects of three-dimensionality. This study asks whether the same is true for atrial repolarization. By using a multi-element dual-surface probe, monophasic action potentials (MAPs) were recorded simultaneously at several opposing sites on the right atrial endocardial and epicardial surfaces in six open-chest pigs. The times of depolarization and repolarization were marked in recordings during sinus, paced rhythms, and during infusions of cold saline to the epicardial surface, which generated a temperature gradient across the atrial wall. Repolarization times were similar on endocardial and epicardial surfaces in some cites, but others showed significant differences during sinus and paced rhythms. Cold saline infusion produced a significant lengthening of MAP duration, and this was more pronouced on the atrial endocardial sites than on the epicardial sites. The observed differences in endocardial and epicardial repolarization times may be due to the presence of atrial pectinate muscles on the endocardial surface. These results suggest that in some regions atrial repolarization is a three-dimensional process. Possible limitations of this study include the fact that the depth of view of MAPs recorded from the atrial wall may extend to the opposing surface.

A two-dimensional anisotropic model of cardiac ventricular muscle was used to study the effects of discontinuities (barriers), such as dead cells or high-resistance areas, on longitudinal plane-wave propagation. Problems in propagation appear when long barriers become thicker and their spacing closer. Short barriers with large widths and small spacing also cause propagation disturbances and significant delays in their vicinity. If the plane wave front propagates through the barriers, the velocity returns to near normal within one-length constant away from the end of the barrier region. For a funnel-like structure, an opening of 13 cells should exist for longitudinal plane wave propagation. For smaller openings, the ratio of openings required for propagation to occur when traveling from a narrow to a wider area of tissue is proportional to the anisotropy ratio, which can cause unidirectional block. Tortuosity, created by spatial distribution of dead cell barriers, can facilitate propagation by changing the effective impedance the wave front sees, and can create multiple local delays, which may result in discrepancies when measuring propagation velocity.

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.

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

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.

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.