Evaluation of an automatic cardiac activation detector for bipolar electrograms

Use of phase-locking value in sensorimotor rhythm-based brain-computer interface: zero-phase coupling and effects of spatial filters

Phase-locking value (PLV) is a potentially useful feature in sensorimotor rhythm-based brain-computer interface (BCI). However, volume conduction may cause spurious zero-phase coupling between two EEG signals and it is not clear whether PLV effects are independent of spectral amplitude. Volume conduction might be reduced by spatial filtering, but it is uncertain what impact this might have on PLV. Therefore, the goal of this study was to explore whether zero-phase PLV is meaningful and how it is affected by spatial filtering. Both amplitude and PLV feature were extracted in the frequency band of 10-15 Hz by classical methods using archival EEG data of 18 subjects trained on a two-target BCI task. The results show that with right ear-referenced data, there is meaningful long-range zero-phase synchronization likely involving the primary motor area and the supplementary motor area that cannot be explained by volume conduction. Another novel finding is that the large Laplacian spatial filter enhances the amplitude feature but eliminates most of the phase information seen in ear-referenced data. A bipolar channel using phase-coupled areas also includes both phase and amplitude information and has a significant practical advantage since fewer channels required.

Printed circuit board electrodes for transmural cardiac mapping

Plunge needle recording techniques have provided valuable insights into transmural activation in cardiac tissue. Construction of plunge needles has been a costly and time intensive endeavor. Plunge needles constructed with standard printed circuit board (PCB) technology and methods are outlined. PCB plunge needles are less expensive in terms of raw materials and time required for construction than hypodermic stock or epoxy plunge needles. Tested PCB plunge needles recorded signals comparable to signals recorded by other plunge needles. PCB plunge needles provide an economical and rapid alternative to previously published techniques for plunge needle design.

Purkinje and ventricular contributions to endocardial activation sequence in perfused rabbit right ventricle

Interactions between peripheral conduction system and myocardial wave fronts control the ventricular endocardial activation sequence. To assess those interactions during sinus and paced ventricular beats, we recorded unipolar electrograms from 528 electrodes spaced 0.5 mm apart and placed over most of the perfused rabbit right ventricular free wall endocardium. Left ventricular contributions to electrograms were eliminated by cryoablating that tissue. Electrograms were systematically processed to identify fast (P) deflections separated by >2 ms from slow (V) deflections to measure P-V latencies. By using this criterion during sinus mapping (n = 5), we found P deflections in 22% of electrograms. They preceded V deflections at 91% of sites. Peripheral conduction system wave fronts preceded myocardial wave fronts by an overall P-V latency magnitude that measured 6.7 +/- 3.9 ms. During endocardial pacing (n = 8) at 500 ms cycle length, P deflections were identified on 15% of electrodes and preceded V deflections at only 38% of sites, and wave fronts were separated by a P-V latency magnitude of 5.6 +/- 2.3 ms. The findings were independent of apical, basal, or septal drive site. Modest changes in P-V latency accompanied cycle length accommodation to 125-ms pacing (6.8 +/- 2.6 ms), although more pronounced separation between wave fronts followed premature stimulation (11.7 +/- 10.4 ms). These results suggested peripheral conduction system and myocardial wave fronts became functionally more dissociated after premature stimulation. Furthermore, our analysis of the first ectopic beats that followed 12 of 24 premature stimuli revealed comparable separation between wave fronts (10.7 +/- 5.5 ms), suggesting the dissociation observed during the premature cycles persisted during the initiating cycles of the resulting arrhythmias.

Automatic detection of conduction block based on time-frequency analysis of unipolar electrograms

It is commonly thought that lethal tachyarrhythmias, such as ventricular fibrillation (VF), are perpetuated by functional reentry, which occurs when an activation wave blocks and rotates around tissue that is excitable (i.e., functional block). Electrograms recorded near these regions typically contain two sequential deflections representing activation on either side of the block. By detecting these "double potentials," we hypothesize that functional block can be detected by a single electrode.

METHODS

Unipolar electrograms were recorded from a 24 x 21 mapping array on the intact ventricular epicardium of five pigs during electrically-induced VF. The short time Fourier Transform (STFT) of each electrogram was analyzed to identify double potentials. To evaluate the performance of the STFT algorithm, conduction block was located in activation maps using a minimum conduction velocity criterion (10 cm/s) and then compared to the results of the STFT algorithm.

RESULTS

The STFT algorithm detected conduction block with a sensitivity of 0.74 +/- 0.12 and a specificity of 0.99 +/- 0.00.

CONCLUSION

We have developed an automated algorithm that can detect functional block during VF from a single electrode recording. Possible applications include fast, objective identification of block in mapping data and realtime localization of reentrant substrates using mapping catheters.

Wave mapping: detection of co-existing multiple wavefronts in high-resolution electrical mapping

High-resolution mapping makes it possible to reconstruct and display the conduction pattern of the action potential as it propagates through cardiac or smooth muscles. During slow and regular activity, time mapping of the spread of activation muscles. During slow and regular activity, time mapping of the spread of activation is relatively simple and straightforward. However, when frequencies are high or conduction is slow, such as seen during atrial fibrillation or found in the pregnant uterus, the tracking of individual waves may become more difficult and uncertain. In order to reconstruct the pathway of a single wave, a search and sorting routine was developed which makes it possible to distinguish, track and display individual wavelets. The algorithm is able to detect variations in conduction block, spontaneous shifts in the location of the pacemaker and changes in the direction of conduction. It is less sensitive when two or more wavefronts intermingle in space and time, such as during collision or fusion. Wave mapping is especially useful, in addition to current time mapping, in sorting quickly through the large amount of data produced by high-resolution mapping of electrical activities in cardiac and smooth muscle.

Activation time determination by high-resolution unipolar and bipolar extracellular electrograms in the canine heart

INTRODUCTION

To identify the optimal criteria for activation time (AT) determination of bipolar electrograms from normal hearts, a high-resolution cross electrode array comprising 128 unipolar electrodes of 500-microns spacing was used to record extracellular potentials from the left ventricular epicardium of 12 dog hearts.

METHODS AND RESULTS

Recordings were made during broad wavefront propagation (B wave) and local elliptical wavefront propagation (E wave). Characteristics of 863 bipolar electrograms (1-mm spacing) were constructed from unipolar data standardized for differences in polarity, then classified morphologically. Features for bipolar AT determination were compared to the time of the negative peak of the first temporal derivative of a unipolar electrogram situated mid-way between the bipoles. During B wave, three distinct morphologies were observed: uniphasic (61%), biphasic (23%), and triphasic (16%). Peak voltage of uniphasic and triphasic signals was the best predictor of AT (error: 0.6 +/- 0.6 msec and 0.6 +/- 0.8 msec, respectively). During E wave, parallel orientation of the bipoles with respect to the direction of impulse propagation wavefront resulted in uniphasic signals (> 99%), while for perpendicular orientation of the bipoles, electrogram morphology was variable. For parallel orientation of the bipoles, peak negative voltage was the best predictor of AT for both longitudinal and transverse propagation, while for perpendicular bipole orientation, peak negative voltage was a less reliable predictor for propagation along both fiber axes. Increasing interpolar distance resulted in a degradation in AT accuracy for B wave (from 0.6 +/- 0.6 msec at 1 mm to 1.1 +/- 1.2 msec at 7 mm) and for E wave (from 0.4 +/- 0.3 msec at 1 mm to 3.1 +/- 2.9 msec at 7 mm).

CONCLUSIONS

(1) The accuracy of bipolar electrograms is sensitive to wavefront direction, bipole orientation, and interpolar distance; (2) peak negative voltage of uniphasic and triphasic signals is a reliable predictor of AT, but only for B wave; (3) a maximum interpolar distance of 2 mm and bipole orientation parallel to the direction of the impulse wavefront are minimally required for accurate determination of AT during impulse propagation initiated near the recording electrodes; and (4) for impulses initiated near the recording site in normal tissue, a biphasic or triphasic morphology almost certainly indicates that the bipolar electrode is oriented perpendicular to the wavefront direction, irrespective of fiber orientation.