Fast in vivo detection of myocardial norepinephrine levels in the beating porcine heart.

The sympathetic nervous system modulates cardiac function by controlling key parameters such as chronotropy and inotropy. Sympathetic control of ventricular function occurs through extrinsic innervation arising from the stellate ganglia and thoracic sympathetic chain. In the healthy heart, sympathetic release of norepinephrine (NE) results in positive modulation of chronotropy, inotropy, and dromotropy, significantly increasing cardiac output. However, in the setting of myocardial infarction or injury, sympathetic activation persists, contributing to heart failure and increasing the risk of arrhythmias, including sudden cardiac death. Methodologies for detection of norepinephrine in cardiac tissue are limited. Present techniques rely on microdialysis for analysis by high-performance liquid chromatography coupled to electrochemical detection (HPLC-ED), radioimmunoassay, or other immunoassays, such as enzyme-linked immunosorbent assay (ELISA). Although significant information about the release and action of norepinephrine has been obtained with these methodologies, they are limited in temporal resolution, require large sample volumes, and provide results with a significant delay after sample collection (hours to weeks). In this study, we report a novel approach for measurement of interstitial cardiac norepinephrine, using minimally invasive, electrode-based, fast-scanning cyclic voltammetry (FSCV) applied in a beating porcine heart. The first multispatial and high temporal resolution, multichannel measurements of NE release in vivo are provided. Our data demonstrate rapid changes in interstitial NE profiles with regional differences in response to coronary ischemia, sympathetic nerve stimulation, and alterations in preload/afterload.NEW & NOTEWORTHY Pharmacological, electrical, or surgical regulation of sympathetic neuronal control can be used to modulate cardiac function and treat arrhythmias. However, present methods for monitoring sympathetic release of norepinephrine in the heart are limited in spatial and temporal resolution. Here, we provide for the first time a methodology and demonstration of practice and rapid measures of individualized regional autonomic neurotransmitter levels in a beating heart. We show dynamic, spatially resolved release profiles under normal and pathological conditions.

The use of remote microphone systems in unilateral hearing loss: a preliminary study among Brazilian children and teenagers.

Due to the large number of individuals with Unilateral Hearing Loss (UHL) and the recommendation to use hearing assistive devices, studies are required to define possibilities of intervention for this population. OBJECTIVE: To evaluate the performance of the Remote Microphone System (RMS) in children with UHL. METHODOLOGY: Prospective clinical study with a convenience sample. Eleven children (mean age of 9.2 years) with severe and profound sensorineural UHL, hearing aid users and enrolled in regular schools participated in the study. They were evaluated using the Hearing in Noise Test (HINT), the Classroom Participation Questionnaire (CPQ), and the Sustained Auditory Attention Ability Test (SAAAT) with RMS. RESULTS: HINT results were analyzed using variance to three criteria of repeated measures, which revealed differences between intervention, position, and time factors and significant interaction between these three factors. The comparative analysis of the results from CPQ showed significant differences in the statistical t-test (p=<0.001) for all subscales. The analysis of variance at two repeated measures criteria used in the study of SAAAT revealed a difference between intervention and time, and both interacted significantly. CONCLUSION: The RMS associated with a hearing aid was effective for individuals with UHL.

Improving an open-source commercial system to reliably perform activity-dependent stimulation.

OBJECTIVE: Activity-dependent stimulation (ADS) is designed to strengthen the connections between neuronal circuits and therefore may be a promising tool for promoting neurophysiological reorganization following a brain injury. To successfully perform this technique, two criteria must be met: (1) spikes in the extracellular electrical field potential must be detected accurately at one site of interest, and (2) stimulation pulses generated at fixed (<1 ms jitter), low-latency (<10 ms) intervals relative to each detected spike must be delivered reliably to a second site of interest. Here, we aimed to improve noise rejection in a low-cost commercial system to reliably perform ADS in awake, behaving rats, while maintaining latency requirements. APPROACH: We implemented a spike detection state machine on a field-programmable gate array (FPGA). Because the accuracy of spike detection can be heavily reduced in awake and behaving animals due to biological artifacts such as movement and chewing, the state machine tracks candidate spike waveforms, checking them against multiple programmable thresholds and rejecting any spikes that fail to meet a programmed threshold criterion. MAIN RESULTS: A series of offline analyses showed that our implementation was able to appropriately trigger stimulation during epochs of biological artifacts with an overall accuracy between 72% and 97%, fixed computational latency of 167 µs, and an algorithmic latency of 300 µs to 800 µs. SIGNIFICANCE: Our improvements have been made open-source and are freely available to all scientists working on closed-loop neuroprosthetic devices. Importantly, the improvements are easily incorporated into existing workflows that utilize the Intan Stimulation and Recording Controller.

A comparative evaluation of signal quality between a research-grade and a wireless dry-electrode mobile EEG system.

OBJECTIVE: Electroencephalography (EEG) is widely used by clinicians, scientists, engineers and other professionals worldwide, with an increasing number of low-cost, commercially-oriented EEG systems that have become available in recent years. One such system is the Cognionics Quick-20 (Cognionics Inc., San Diego, USA), which uses dry electrodes and offers the convenience of portability thanks to its built-in amplifier and wireless connection. Because of such characteristics, this system has been used in several applications for both clinical and basic research studies. However, an investigation of the quality of the signals that are recorded using this system has not yet been reported. APPROACH: To bridge this gap, here we conducted a systematic comparison of signal quality between the Cognionics Quick-20 system and the Brain Products actiCAP/actiCHamp (Brain Products GmbH, Munich, Germany), a state-of-the-art, wet-electrode, research-oriented EEG system. Resting-state EEG data were recorded from twelve human participants at rest in eyes open and eyes closed conditions. For both systems we evaluated the similarity of mean recorded power spectral density, and detection of alpha suppression associated with eyes open relative to eyes closed. MAIN RESULTS: Power spectral densities were highly correlated across systems, with only minor topographical variability across the scalp. Both systems recorded alpha suppression during eyes open relative to eyes closed conditions. SIGNIFICANCE: These results attest to the robustness and reliability of the dry-electrode Cognionics system relatively to the widely used Brain Products laboratory EEG system, and thus validate its utility for clinical and basic research purposes, at least in studies in which participants do not move.

The use of remote microphone systems in unilateral hearing loss: a preliminary study among Brazilian children and teenagers

Abstract Due to the large number of individuals with Unilateral Hearing Loss (UHL) and the recommendation to use hearing assistive devices, studies are required to define possibilities of intervention for this population. Objective: To evaluate the performance of the Remote Microphone System (RMS) in children with UHL. Methodology: Prospective clinical study with a convenience sample. Eleven children (mean age of 9.2 years) with severe and profound sensorineural UHL, hearing aid users and enrolled in regular schools participated in the study. They were evaluated using the Hearing in Noise Test (HINT), the Classroom Participation Questionnaire (CPQ), and the Sustained Auditory Attention Ability Test (SAAAT) with RMS. Results: HINT results were analyzed using variance to three criteria of repeated measures, which revealed differences between intervention, position, and time factors and significant interaction between these three factors. The comparative analysis of the results from CPQ showed significant differences in the statistical t-test (p=<0.001) for all subscales. The analysis of variance at two repeated measures criteria used in the study of SAAAT revealed a difference between intervention and time, and both interacted significantly. Conclusion: The RMS associated with a hearing aid was effective for individuals with UHL.

Improved single photon time resolution for analog SiPMs with front end readout that reduces influence of electronic noise.

A key step to improve the coincidence time resolution of positron emission tomography detectors that exploit small populations of promptly emitted photons is improving the single photon time resolution (SPTR) of silicon photomultipliers (SiPMs). The influence of electronic noise has previously been identified as the dominant factor affecting SPTR for large area, analog SiPMs. In this work, we measure the achievable SPTR with front end electronic readout that minimizes the influence of electronic noise. With this readout circuit, the SPTR measured for one FBK NUV single avalanche photodiode (SPAD) was also achieved with a [Formula: see text] mm2 FBK NUV SiPM. SPTR for large area devices was also significantly improved. The measured SPTRs for [Formula: see text] mm2 Hamamatsu and SensL SiPMs were [Formula: see text]150 ps FWHM, and SPTR [Formula: see text]100 ps FWHM was measured for [Formula: see text] mm2 and [Formula: see text] mm2 FBK NUV and NUV-HD SiPMs. We also explore additional factors affecting the achievable SPTR for large area, analog SiPMs when the contribution of electronic noise is minimized and pinpoint potential areas of improvement to further reduce the SPTR of large area sensors towards that achievable for a single SPAD.

20 mJ, 1 ps Yb:YAG Thin-disk Regenerative Amplifier.

This is a report on a 100 W, 20 mJ, 1 ps Yb:YAG thin-disk regenerative amplifier. A homemade Yb:YAG thin-disk, Kerr-lens mode-locked oscillator with turn-key performance and microjoule-level pulse energy is used to seed the regenerative chirped-pulse amplifier. The amplifier is placed in airtight housing. It operates at room temperature and exhibits stable operation at a 5 kHz repetition rate, with a pulse-to-pulse stability less than 1%. By employing a 1.5 mm-thick beta barium borate crystal, the frequency of the laser output is doubled to 515 nm, with an average power of 70 W, which corresponds to an optical-to-optical efficiency of 70%. This superior performance makes the system an attractive pump source for optical parametric chirped-pulse amplifiers in the near-infrared and mid-infrared spectral range. Combining the turn-key performance and the superior stability of the regenerative amplifier, the system facilitates the generation of a broadband, CEP-stable seed. Providing the seed and pump of the optical parametric chirped-pulse amplification (OPCPA) from one laser source eliminates the demand of active temporal synchronization between these pulses. This work presents a detailed guide to set up and operate a Yb:YAG thin-disk regenerative amplifier, based on chirped-pulse amplification (CPA), as a pump source for an optical parametric chirped-pulse amplifier.

3D position determination in monolithic crystals coupled to SiPMs for PET.

The interest in using continuous monolithic crystals in positron emission tomography (PET) has grown in the last years. Coupled to silicon photomultipliers (SiPMs), the detector can combine high sensitivity and high resolution, the two main factors to be maximized in a positron emission tomograph. In this work, the position determination capability of a detector comprised of a [Formula: see text] mm(3) LYSO crystal coupled to an [Formula: see text]-pixel array of SiPMs is evaluated. The 3D interaction position of γ-rays is estimated using an analytical model of the light distribution including reflections on the facets of the crystal. Monte Carlo simulations have been performed to evaluate different crystal reflectors and geometries. The method has been characterized and applied to different cases. Intrinsic resolution obtained with the position estimation method used in this work, applied to experimental data, achieves sub-millimetre resolution values. Average resolution over the detector surface for 5 mm thick crystal is ∼0.9 mm FWHM and ∼1.2 mm FWHM for 10 mm thick crystal. Depth of interaction resolution is close to 2 mm FWHM in both cases, while the FWTM is ∼5.3 mm for 5 mm thick crystal and ∼9.6 mm for 10 mm thick crystal.

Monopolar electromyographic signals recorded by a current amplifier in air and under water without insulation.

It was recently proposed that one could use signal current instead of voltage to collect surface electromyography (EMG). With EMG-current, the electrodes remain at the ground potential, thereby eliminating lateral currents. The purpose of this study was to determine whether EMG-currents can be recorded in Tap and Salt water, as well as in air, without electrically shielding the electrodes. It was hypothesized that signals would display consistent information between experimental conditions regarding muscle responses to changes in contraction effort. EMG-currents were recorded from the flexor digitorum muscles as participant's squeezed a pre-inflated blood pressure cuff bladder in each experimental condition at standardized efforts. EMG-current measurements performed underwater showed no loss of signal amplitude when compared to measurements made in air, although some differences in amplitude and spectral components were observed between conditions. However, signal amplitudes and frequencies displayed consistent behavior across contraction effort levels, irrespective of the experimental condition. This new method demonstrates that information regarding muscle activity is comparable between wet and dry conditions when using EMG-current. Considering the difficulties imposed by the need to waterproof traditional bipolar EMG electrodes when underwater, this new methodology is tremendously promising for assessments of muscular function in aquatic environments.

Frequency-comb-referenced mid-infrared source for high-precision spectroscopy.

We report on a tunable continuous-wave mid-infrared optical parametric oscillator (OPO), which is locked to a fully stabilized near-infrared optical frequency comb using a frequency doubling scheme. The OPO is used for 40 GHz mode-hop-free, frequency-comb-locked scans in the wavelength region between 2.7 and 3.4 µm. We demonstrate the applicability of the method to high-precision cavity-ring-down spectroscopy of nitrous oxide (N2O) and water (H2O) at 2.85 µm and of methane (CH4) at 3.2 µm.

The impact of sound-field systems on learning and attention in elementary school classrooms.

PURPOSE: The authors evaluated the installation and use of sound-field systems to investigate the impact of these systems on teaching and learning in elementary school classrooms. Methods The evaluation included acoustic surveys of classrooms, questionnaire surveys of students and teachers, and experimental testing of students with and without the use of sound-field systems. In this article, the authors report students' perceptions of classroom environments and objective data evaluating change in performance on cognitive and academic assessments with amplification over a 6-month period. RESULTS: Teachers were positive about the use of sound-field systems in improving children's listening and attention to verbal instructions. Over time, students in amplified classrooms did not differ from those in nonamplified classrooms in their reports of listening conditions, nor did their performance differ in measures of numeracy, reading, or spelling. Use of sound-field systems in the classrooms resulted in significantly larger gains in performance in the number of correct items on the nonverbal measure of speed of processing and the measure of listening comprehension. Analysis controlling for classroom acoustics indicated that students' listening comprehension scores improved significantly in amplified classrooms with poorer acoustics but not in amplified classrooms with better acoustics. CONCLUSIONS: Both teacher ratings and student performance on standardized tests indicated that sound-field systems improved performance on children's understanding of spoken language. However, academic attainments showed no benefits from the use of sound-field systems. Classroom acoustics were a significant factor influencing the efficacy of sound-field systems; children in classes with poorer acoustics benefited in listening comprehension, whereas there was no additional benefit for children in classrooms with better acoustics.

Construction, calibration, and validation of a simple patch-clamp amplifier for physiology education.

A modular patch-clamp amplifier was constructed based on the Strickholm design, which was initially published in 1995. Various parts of the amplifier such as the power supply, input circuit, headstage, feedback circuit, output and nulling circuits were redesigned to use recent software advances and fabricated using the common lithographic printed circuit board fabrication process and commercially available electronic components. The calibration, validation, and regular recording procedures along with the results of an actual recording of inward Ca(2+) currents from PC12 neuronal cells are described in detail. This work describes the construction of a low-cost patch-clamp amplifier and setting up an electrophysiology recording system in a laboratory with regular technical expertise. The constructed amplifier provides an inexpensive yet practical tool for research and teaching purposes while the experience obtained during construction and setting up of the patch-clamp amplifier provides the basic and advanced understanding required for operating an advanced cell potential recording apparatus.

A note on determination of the diffuse-field sensitivity of microphones using the reciprocity technique.

The diffuse-field response of a microphone is usually obtained by adding a random-incidence correction to the pressure response of the microphone. However, the random-incidence correction is determined from a relative measurement, and its accuracy depends not only on the relative response at all angles of incidence but also on the accuracy of the frequency response at normal incidence. By contrast, this paper is concerned with determining the absolute diffuse-field response of a microphone using the reciprocity technique. To examine this possibility, a reciprocity calibration setup is used for measuring the electrical transfer impedance between a pair of microphones placed in a miniature (2 m(3)) reverberation room. The transfer function between the microphones is measured using fast Fourier transform analysis and pseudorandom noise. The calculation of the diffuse-field sensitivity involves (a) separation of the reverberant response from the total response, (b) determination of the reverberation time, and (c) averaging over space and frequency. The resulting diffuse-field correction is compared with an estimate of the random-incidence correction determined in an anechoic room and with a numerical prediction.

Evaluation of the benefit for cochlear implantees of two assistive directional microphone systems in an artificial diffuse noise situation.

OBJECTIVE: People with cochlear implants have severe problems with speech understanding in noisy surroundings. This study evaluates and quantifies the effect of two assistive directional microphone systems compared to the standard headpiece microphone on speech perception in quiet surroundings and in background noise, in a laboratory setting developed to reflect a situation whereby the listener is disturbed by a noise with a mainly diffuse character due to many sources in a reverberant room. DESIGN: Thirteen postlingually deafened patients, implanted in the Leiden University Medical Centre with the Clarion CII device, participated in the study. An experimental set-up with 8 uncorrelated steady-state noise sources was used to test speech perception on monosyllabic words. Each subject was tested with a standard headpiece microphone, and the two assistive directional microphones, TX3 Handymic by Phonak and the Linkit array microphone by Etymotic Research. Testing was done in quiet at a level of 65 dB SPL and with decreasing signal-to-noise ratios (SNR) down to -15 dB. RESULTS: Using the assistive directional microphones, speech recognition in background noise improved substantially and was not affected in quiet. At an SNR of 0 dB, the average CVC scores improved from 45% for the headpiece microphone to 67% and 62% for the TX3 Handymic and the Linkit respectively. Compared to the headpiece, the Speech Reception Threshold (SRT) improved by 8.2 dB SNR and 5.9 dB SNR for the TX3 Handymic and the Linkit respectively. The gain in SRT for TX3 Handymic and Linkit was neither correlated to the SRT score with headpiece nor the duration of CI-use. CONCLUSION: The speech recognition test in background noise showed a clear benefit from the assistive directional microphones for cochlear implantees compared to the standard microphone. In a noisy environment, the significant benefit from these assistive device microphones may allow understanding of speech with greater ease.

Effect of amplifier gain setting on distal motor latency in normal subjects and CTS patients.

OBJECTIVE: To determine normative cutoffs and sensitivities for median distal latency (MDL), median-thenar to ulnar-thenar latency difference (TTLD), and median-thenar to ulnar-hypothenar latency difference (THLD) at various amplifier gains for carpal tunnel syndrome (CTS) electrodiagnosis. A prior study utilized only an amplifier gain of 0.2 mV/division. METHODS: Abnormal cutoffs for MDL, TTLD and THLD were determined based on 34 control hands at gains of 0.2, 0.5, 1, 2, and 5 mV. Diagnostic sensitivities were determined for 50 patients (80 hands) with clinically and electrodiagnostically defined CTS. RESULTS: At a gain of 0.2 and 0.5 mV/division, abnormal cutoffs for MDL, THLD, and TTLD were: 3.7, 1.2, and 0.8 ms. At gains of 1, 2, and 5 mV the abnormal cutoffs were 4, 1.2, and 1 ms. The sensitivities at gains of 0.2, 0.5, 1, 2, and 5 mV for MDL, THLD, and TTLD were: 65, 66, 53, 57, 61/86, 83, 88, 86, 86/91, 91, 76, 73, 59. CONCLUSIONS: MDL and THLD sensitivities are gain-independent. THLD is substantially more sensitive than MDL at all gains. TTLD sensitivity is maximized with 0.2 and 0.5 mV gains. SIGNIFICANCE: TTLD and THLD increase diagnostic sensitivity with minimal additional effort. TTLD sensitivity is maximized with 0.2 or 0.5 mV gains. The electromyographer's preferred gain may be used.

A new method for dealing with the stimulus artefact in electrically evoked compound action potential measurements.

OBJECTIVE: Residual charge on recording electrodes leads to elevated potentials after the end of the stimulus, which can easily overload the electrically evoked compound action potential (eCAP) recording systems (neural response imaging or neural response telemetry). A new method for dealing with this problem was tested in a series of animal experiments. MATERIAL AND METHODS: We developed an amplifier with a compensation circuit that reduces the effect of the residual charge by electrical subtraction at the input. Using this amplifier we compared different artefact rejection protocols simultaneously in chronically implanted guinea pigs. A new, systematic nomenclature for the various forward masking schemes, based on the number of frames involved, is proposed. RESULTS: Proper adjustment of the compensation circuit reduces the overload time from > 200 micros to < 30 micros, but the compensation signals influence the final output signal considerably. To eliminate this deliberately introduced, reproducible artefact, an additional artefact rejection scheme is necessary. With alternating polarity (AP) and forward masking paradigms we could reliably record the N1 peak. Forward masking responses reveal shorter latencies for cathodic-first biphasic stimuli than for anodic-first pulses. The average of these two closely resembles the response obtained with the AP paradigm. CONCLUSIONS: It is worthwhile implementing the electrical compensation method proposed herein in clinical neural response imaging or neural response telemetry systems, as it represents a more robust way of assessing the eCAP.

Sensitive calibration and measurement procedures based on the amplification principle in motion perception.

We compare two types of sampled motion stimuli: ordinary periodic displays with modulation amplitude m(o=e) that translate 90 degrees between successive frames and amplifier sandwich displays. In sandwich displays, even-numbered frames are of one type, odd-numbered frames are of the same or different type, and (1) both types have the same period, (2) translate in a consistent direction 90 degrees between frames, and (3) even frames have modulation amplitude m(e), odd frames have modulation amplitude m(o). In both first-order motion (van Santen, J.P.H. & Sperling, G. (1984). Temporal covariance model of human motion perception. Journal of the Optical Society of America A, 1, 451-73) and second-order motion (Werkhoven, P., Sperling, G., & Chubb, C. (1993). Motion perception between dissimilar gratings: a single channel theory. Vision Research, 33, 463-85) the motion strength of amplifier sandwich displays is proportional to the product m(o)m(e) for a wide range of m(e). By setting m(e) to a large value, an amplifier sandwich stimulus with a very small value of m(o) can still produce visible motion. The amplification factor is the ratio of two threshold modulation amplitudes: ordinary circumflexm(o=e) over amplified circumflexm(o), circumflexm(o=e)/circumflexm(o). We find amplification factors of up to about 8x. Light adaptation and contrast gain control in early visual processing distort the representations of visual stimuli so that inputs to subsequent perceptual processes contain undesired distortion products or 'impurities'. Motion amplification is used to measure and thence to reduce these unwanted components in a stimulus to a small fraction of their threshold. Such stimuli are certifiably pure in the sense that the residual impurity is less than a specified value. Six applications are considered: (1) removing (first-order) luminance contamination from moving (second-order) texture gratings; (2) removing luminance contamination from moving chromatic gratings to produce pure isoluminant gratings; (3) removing distortion products in luminance-modulated (first-order) gratings - by iterative application, all significant distortion products can be removed; (4) removing second-order texture contamination from third-order motion displays; (5) removing feature bias from third-order motion displays; (6) and the same general principles are applied to texture-slant discrimination in which x,y spatial coordinates replace the x,t motion coordinates. In all applicable domains, the amplification principle provides a powerful assay method for the precise measurement of very weak stimuli, and thereby a means of producing visual displays of certifiable purity.

Evaluation and design of a small portable EMG amplifier with potential RMS output.

The present study attempted to design and evaluate a small portable electromyogram (EMG) amplifier that can output enhanced EMG and its root mean square (RMS) value. The production and design were of a laboratory scale without any special or high cost circuit construction. The designed amplifier was actually innovated according to the actual working conditions based on physiological anthropology. The present amplifier was compared with commercially available products and proved to be of practical use. The device was installed with a sufficiently small body depicting 8-channel variable gain AC amplifier and variable time-window RMS-to-DC converter. The prototype was battery-driven and well-shielded to minimize external noise interference.

Waveforms of cochlear implant-evoked auditory brain stem responses in anesthetized young children, recorded with a new preamplifier.

An ultra-low-noise preamplifier has been specifically designed for the conditions in lightly anesthetized young children, to record cochlear implant--evoked auditory brain stem responses (impEABRs). The preamplifier linearly filters out the signal from the radio-frequency implant-driver. The preamplifier provides simultaneous accurate records of the stimulus-current artifact and impEABR, both ipsilaterally and contralaterally. It is convenient to label electrically evoked vertex-positive peaks, eg, eII, on probable analogy with acoustically evoked potentials. In order to label all the commonly observed peaks with latency less than 5 milliseconds, it is necessary at times to use labels eIIa, eIIb, eIIIa, eIIIb, eIVa, eIVb, eVa, and eVb. The records also show two distinct nadirs, with latencies about 2.5 milliseconds and about 6 milliseconds. The details of the waveforms are preserved as the stimulus strength descends towards threshold.

Myopotential inhibition of unipolar demand pacemakers: utility of provocative manoeuvres in assessment and management.

Fifty patients with permanent unipolar pacemakers (48 multiprogrammable, 2 non programmable) with protective insulating sheath placed against the muscular side of the pacemaker pocket were studied to determine the occurrence of inhibition of pacing by sensing of the myopotentials. All the patients were subjected to a combination of different provocative manoeuvres at their nominal R wave sensitivity settings. Myopotential inhibition was exhibited in 35 (70%) patients. Only 3 patients however had reported symptoms suggesting loss of pacing. The most useful provocative manoeuvre was shoulder flexion with adduction against resistance (94.3% positivity). Appropriate sensitivity adjustments resulted in amelioration of the problem in 86% of the patients while still retaining R wave sensing. Myopotential interference continues to be a frequently observed problem even in the present generation of unipolar pacemakers. Provocative tests and appropriate reprogramming should be done in all such patients as a routine.