Chris van Groeningen
Publications
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1.08Impact points
Improving sensing and detection performance in subcutaneous monitors.
Journal of electrocardiology. 09/2009;
Implantable loop recorders (ILRs) are used for continuous assessment of patients at risk for syncope and arrhythmia. Device accuracy depends on appropriate sensing of the patient's electrocardiogram (ECG) signal. However, current methods for sensing cardiac electrical activity rely on simple thr... [more] Implantable loop recorders (ILRs) are used for continuous assessment of patients at risk for syncope and arrhythmia. Device accuracy depends on appropriate sensing of the patient's electrocardiogram (ECG) signal. However, current methods for sensing cardiac electrical activity rely on simple threshold detectors that are computationally efficient but nonspecific. We test the hypothesis that better ILR implant positions will increase detection accuracy. Ten healthy subjects were studied as they assumed 12 different postures. Body surface potential map (BSM) recordings were used to estimate bipolar R-wave amplitudes for 64 potential implant sites at 360 orientations per site. Optimal sites were identified as the combination of position and orientation that consistently gave the largest signal and the lowest variability during posture changes. Results showed that posture impacts the R-wave amplitude in both BSM and derived bipolar ECGs in healthy subjects. Specific postures are associated with significant drops in R-wave signal amplitude that could cause loss of signal detection in ILRs, especially in positions likely to displace the diaphragm. R-wave changes occurred abruptly as posture was changed. Optimal implant locations cluster near the center of the chest, aligned with the cardiac axis, consistent with the steeper isoelectric gradients known to be associated with these positions.
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1.58Impact points
Morphology-enhanced atrial event classification improves sensing in pacemakers.
Pacing and clinical electrophysiology : PACE. 12/2007; 30(12):1455-63.
BACKGROUND: In atrial-based pacing, appropriate therapy and reliable diagnostics depend on detection and discrimination of atrial signals. Accurate classification of atrial events is mainly confounded by oversensing of ventricular far-field R-wave signals (FFRW), but attempts to reject FFRWs by mani... [more] BACKGROUND: In atrial-based pacing, appropriate therapy and reliable diagnostics depend on detection and discrimination of atrial signals. Accurate classification of atrial events is mainly confounded by oversensing of ventricular far-field R-wave signals (FFRW), but attempts to reject FFRWs by manipulating atrial sensitivity and/or postventricular atrial blanking period (PVAB) may result in undersensing (especially of atrial fibrillation, AF) or in 2:1 atrial flutter detection. The objective of this study is therefore to evaluate if such methods can be improved by morphology-enhanced atrial event classification (MORPH). METHODS: Twenty-four-hour ambulatory atrial electrograms were recorded from continuous telemetry of digital pacemakers. Half of the recording was used for collecting two individual morphology parameters that discriminated P-waves from FFRWs in every patient (learning phase). The other half was used to test the MORPH algorithm against traditional methods (classification phase). RESULTS: In 44/48 patients, data were suitable for analysis. Average P and FFRW amplitudes were 1.96 mV versus 0.61 mV (P < 0.001). The interval between ventricular events and FFRW oversensing (VA interval) averaged at 14 ms during sensing and at 118 ms during pacing in the ventricle. Compared to nominal ("Factory") settings, the MORPH algorithm improved the sensitivity for P-wave recognition from 97.2% to 99.2%, the specificity from 91.9% to 99.96%, and the accuracy from 95.3% to 99.4% (P < 0.01 for all). CONCLUSIONS: By improving atrial signal discrimination, morphology analysis of atrial electrograms allows for high atrial sensitivity settings, and potentially improves the reliability of atrial arrhythmia diagnostics in heart rhythm devices.
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1.58Impact points
Form analysis using digital signal processing reliably discriminates far-field R waves from P waves.
Pacing and clinical electrophysiology : PACE. 01/2005; 27(12):1615-24.
The correct detection of atrial arrhythmias by pacemakers is often limited by the presence of far-field R waves (FFRWs) in the atrial electrogram. Digital signal processing (DSP) of intracardiac signals is assumed to provide improved discrimination between P waves and FFRWs when compared to current ... [more] The correct detection of atrial arrhythmias by pacemakers is often limited by the presence of far-field R waves (FFRWs) in the atrial electrogram. Digital signal processing (DSP) of intracardiac signals is assumed to provide improved discrimination between P waves and FFRWs when compared to current methods. For this purpose, 100 bipolar and unipolar intracardiac atrial recordings from 31 patients were collected during pacemaker replacement and used for the off-line application of a novel DSP algorithm. Digital processing of the atrial intracardiac electrogram (IEGM) signals (8 bit, 800 samples/s) included filtering and calculation of the maximum amplitude and slope of the detected events. The form parameter was calculated, being the sum of the most negative value of the amplitude and that of the slope of the detected event. The algorithm collects form parameter data of P waves and FFRWs and composes histograms of these data. A sufficiently large gap between the FFRW and P wave histograms allows discrimination of these two signals based on form parameters. Three independent observers reviewed the reliability of classification with this algorithm. Sensitivity and specificity of FFRW detection were 99.63% and 100%, respectively, and no P waves were falsely classified. It can be concluded that this novel DSP algorithm shows excellent discrimination of FFRWs under off-line conditions and justify the implementation of this algorithm in future pacemakers for real-time discrimination between P waves and FFRWs. This method prevents false mode switching and allows correct and immediate intervention pacing for atrial tachyarrhythmias.
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2.26Impact points
Relation between torque history, firing frequency, decruitment levels and force balance in two flexors of the elbow.
Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale. 01/2000; 129(4):592-604.
By means of intramuscular electromyographic recordings, we studied the firing frequencies and recruitment/decruitment thresholds of individual motor units in two elbow flexors, the biarticular biceps brachii muscle and the monoarticular brachioradialis muscle. Subjects had to perform isometric contr... [more] By means of intramuscular electromyographic recordings, we studied the firing frequencies and recruitment/decruitment thresholds of individual motor units in two elbow flexors, the biarticular biceps brachii muscle and the monoarticular brachioradialis muscle. Subjects had to perform isometric contractions with increasing elbow flexion torque until a specific peak torque level was reached. The torque level was kept constant for 6 s during which firing frequencies were measured. Then the torque was decreased to a lower level and, after 3 s, firing frequencies were again measured for 6 s. By repeating this procedure, the torque level was decreased stepwise until the motor unit under study stopped firing. The last level before the unit stopped firing was considered to be the decruitment torque level. We measured the firing frequency at recruitment and decruitment, the torque-frequency relationship and the recruitment and decruitment torque thresholds after various levels of peak torque. In the biceps, both the firing frequencies at a specific torque level and the decruitment torque level itself were independent of the peak torque. In the brachioradialis, however, firing frequencies at a specific torque level decreased and decruitment torque levels increased after subjects generated higher peak torques. Thus, in this muscle firing frequencies as well as decruitment thresholds show hysteresis effects. The result indicates a shift of force from the brachioradialis muscle during recruitment to the biceps muscle during decruitment. This shift is smaller than was concluded from previous studies in which decruitment threshold levels for the brachioradialis muscle were assumed to be independent of force history. Moreover, we found that in both muscles decruitment firing frequencies were lower than recruitment frequencies and they were independent of the peak torque level. In order to analyse the effect of the peak torque level on the distribution of force over the two muscles, we performed a model study in which we simulated the activation-frequency relation of two elbow flexors: a biceps-like and brachioradialis-like muscle, each contributing equally to the elbow torque during recruitment. In addition, we analysed how the different behaviour of the biceps and the brachioradialis during decruitment alters their contribution to the total torque production and how this redistribution is caused. The model study shows that the shift in contribution to the total torque is not constant during the relaxation phase and is not caused by a simple mechanism like a shift of activation from one muscle to another. Furthermore, changes limited to the muscle in which hysteresis is present do not seem to be sufficient to explain the experimental results.
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1.58Impact points
Full ventricular capture indicated by the QT interval function.
Pacing and clinical electrophysiology : PACE. 12/1998; 21(11 Pt 2):2171-7.
The atrioventricular (AV) interval is critical in dual chamber (DDD) pacing in patients with hypertrophic obstructive cardiomyopathy (HOCM) to obtain full ventricular capture (FVC) with maximal reduction of the left ventricular (LV) outflow gradient and optimal LV diastolic filling. We studied the r... [more] The atrioventricular (AV) interval is critical in dual chamber (DDD) pacing in patients with hypertrophic obstructive cardiomyopathy (HOCM) to obtain full ventricular capture (FVC) with maximal reduction of the left ventricular (LV) outflow gradient and optimal LV diastolic filling. We studied the relationship of FVC, fusion, spontaneous AV conduction, and the QT interval. METHODS: 11 patients with various cardiac diseases and stable AV conduction received a QT sensing Diamond, Vitatron, DDD pacemaker. Software was downloaded into the pacemaker. In the DDD pacing mode, with the QT interval measured from the ventricular pacing stimulus to the end of the T wave, the AV interval was shortened from 400 ms, in 20-ms steps, to 90 ms. At 90 ms the stimulation rate was increased by 30 beats/min and the AV interval was increased stepwise. FVC and fusion was examined on the surface ECG. RESULTS: At 400 ms interval, spontaneous AV conduction inhibited the pacemaker. Shortening the AV interval resulted in pacing with a short QT interval. Further reduction of the AV interval resulted in a longer QT interval up to a point where the QT interval became stable. This point, the bending point in the plot of measured QT interval versus shortened AV intervals, coincided with the point of FVC. The relation of the QT-AV interval plot and the point of fusion was comparable when lengthening the AV interval at a 30 beats/min faster stimulation rate. CONCLUSION: The bending point in the QT interval versus AV interval plots showed a good correlation with the FVC and fusion points observed on ECG. The results suggest that automatic discrimination between fusion and full capture using QT interval measurements may be feasible.
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2.26Impact points
Task-dependent differences between mono- and bi-articular heads of the triceps brachii muscle.
Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale. 02/1994; 100(2):345-52.
We studied motor-unit recruitment and decruitment thresholds in the three heads of the human elbow extensor, the triceps brachii muscle (caput mediale and laterale, both mono-articular heads, and caput longum, the bi-articular head) by means of intramuscular electromyographic-recordings. Two experim... [more] We studied motor-unit recruitment and decruitment thresholds in the three heads of the human elbow extensor, the triceps brachii muscle (caput mediale and laterale, both mono-articular heads, and caput longum, the bi-articular head) by means of intramuscular electromyographic-recordings. Two experiments were performed: an 'isometric' and a 'movement' experiment. In the isometric experiment, subjects were asked to increase the elbow extension torque isometrically to a specific level, keep the torque at the level for 10 s, and then decrease the torque again to zero. In the movement experimental subjects moved their forearm from 90 degrees to 110 degrees extension against an increasing flexion torque, kept the latter position for 10 s and then moved their forearm back while the torque decreased. Results for caput longum showed that recruitment thresholds were higher than decruitment thresholds, whereas in caput mediale and laterale no difference in thresholds was found. In caput longum recruitment thresholds were found to be lower in movement conditions than in isometric conditions. The reverse effect was observed in caput mediale, whereas no difference in recruitment thresholds was found in caput laterale. Our results point to a transfer of force from mono-articular muscles in isometric conditions to bi-articular muscles in movement conditions. A similar transfer is found when recruitment and decruitment are compared. This means that the transfer is not only a property of the elbow-flexor muscles, but is a more common trait. A qualitative analysis of firing frequencies at recruitment and at decruitment in both conditions supports our findings.
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3.29Impact points
Quantitative aspects of transduction in an electroreceptor organ studied by means of experimental manipulation of the interspike interval.
Neuroscience. 02/1991; 42(1):283-9.
The interspike interval histogram of spontaneously firing electroreceptor organs of freshwater catfish (Ictalurus nebulosus LeS.) fits well with the probability density function of a gamma distribution. The shape parameter r of this probability density function can be used as a measure for the firin... [more] The interspike interval histogram of spontaneously firing electroreceptor organs of freshwater catfish (Ictalurus nebulosus LeS.) fits well with the probability density function of a gamma distribution. The shape parameter r of this probability density function can be used as a measure for the firing threshold of the spike generator, and the scale parameter lambda provides a measure for the input rate of synaptic quanta. Here, we have studied the physiological meaning of the two parameters of the fitted gamma probability density function by manipulating the mean firing rate. This was done in two ways: "frequency clamp" stimulation and a change in temperature. Frequency clamp stimulation, compensating for adaptation of the response, keeps the afferent firing rate at a fixed value for a limited period. We show that within such a period not only the mean spike rate remains constant, but these spike trains can be regarded as renewal series: the spike generator is functionally uncoupled from the frequency-dependent parts of the transduction path. Concerning the gamma parameters, two types of responses are found: at strong excitation lambda increases, r does not change; with small stimuli r is inversely proportional to the stimulus strength, lambda remains unchanged. This is difficult to explain when stimulus transduction acts via the synaptic input rate only. Stimulation seems to influence the firing threshold of the spike generator directly. At strong inhibition a regular firing pattern suddenly takes over; the major part of the variability suddenly disappears from the spike train. A change in temperature causes a shift in lambda (Q10 approximately 2.3), but not in r. This points to a temperature effect on the input rate only.
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Quantitative aspects of transduction in an electroreceptor organ studied by means of experimental manipulation of the interspike interval
Neuroscience.
The interspike interval histogram of spontaneously firing electroreceptor organs of freshwater catfish (Ictalurus nebulosus LeS.) fits well with the probability density function of a gamma distribution. The shape parameter r of this probability density function can be used as a measure for the firin... [more] The interspike interval histogram of spontaneously firing electroreceptor organs of freshwater catfish (Ictalurus nebulosus LeS.) fits well with the probability density function of a gamma distribution. The shape parameter r of this probability density function can be used as a measure for the firing threshold of the spike generator, and the scale parameter λ provides a measure for the input rate of synaptic quanta.Here, we have studied the physiological meaning of the two parameters of the fitted gamma probability density function by manipulating the mean firing rate. This was done in two ways: “frequency clamp” stimulation and a change in temperature.Frequency clamp stimulation, compensating for adaptation of the response, keeps the afferent firing rate at a fixed value for a limited period. We show that within such a period not only the mean spike rate remains constant, but these spike trains can be regarded as renewal series: the spike generator is functionally uncoupled from the frequency-dependent parts of the transduction path.Concerning the gamma parameters, two types of responses are found: at strong excitation λ increases, r does not change; with small stimuli r is inversely proportional to the stimulus strength, λ remains unchanged. This is difficult to explain when stimulus transduction acts via the synaptic input rate only. Stimulation seems to influence the firing threshold of the spike generator directly.At strong inhibition a regular firing pattern suddenly takes over; the major part of the variability suddenly disappears from the spike train.A change in temperature causes a shift in λ (Q10 ≈ 2.3), but not in r. This points to a temperature effect on the input rate only.
Following (1)
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David Hampton
Stone Bridge Biomedical
