Martin Oehler

A multichannel portable ECG system with capacitive sensors

Capacitive sensors can be employed for measuring the electrocardiogram of a human heart without electric contact with the skin. This configuration avoids contact problems experienced by conventional electrocardiography. In our studies, we integrated these capacitive electrocardiogram electrodes in a 15-sensor array and combined this array with a tablet personal computer. By placing the system on the patients body, we can measure a 15-channel electrocardiogram even through clothes and without any preparation. The goal of this development is to provide a new diagnostic tool that offers the user a reproducible, easy access to a fast and spatially resolved diagnostic heart view.

Extraction of SSVEP signals of a capacitive EEG helmet for Human Machine Interface

The use of capacitive electrodes for measuring EEG eliminates the preparation procedure known from classical noninvasive EEG measurements. The insulated interface to the brain signals in combination with steady-state visual evoked potentials (SSVEP) enables a zero prep human machine interface triggered by brain signals. This paper presents a 28-channel EEG helmet system based on our capacitive electrodes measuring and analyzing SSVEPs even through scalp hair. Correlation analysis is employed to extract the stimulation frequency of the EEG signal. The system is characterized corresponding to the available detection time with different subjects. As demonstration of the use of capacitive electrodes for SSVEP measurements, preliminary online Brain-Computer Interface (BCI) results of the system are presented. Detection times lie about a factor of 3 higher than in galvanic EEG SSVEP measurements, but are low enough to establish a proper communication channel for Human Machine Interface (HMI).

First clinical evaluation of a novel capacitive ECG system in patients with acute myocardial infarction

ObjectiveThe ECG plays a central role in the rapid diagnosis of acute myocardial infarctions (MI). In haemodynamically instable patients, adhesion of electrodes sometimes is difficult and assessing ECGs through layers of clothes has not been done so far. A novel capacitive measurement of ECG signals is possible without skin contact. Whether this technical innovation can be used in patients with MI is unclear.MethodsWe evaluated a capacitive ECG system (cECG) in patients with anterior and inferior ST elevation MI (STEMI) as compared to patients without ST elevations in anterior and inferior leads. The cECG was assessed using a sensor array consisting of 15 electrodes of which the classical leads I, II, III, aVL, aVF and V1–V3 were calculated from. 66 patients were included in the study. In addition to the conventional ECG (kECG) the novel cECG was registered before reperfusion therapy was started.ResultsIn a first round, 19 patients presented with anterior MI, 23 with inferior MI, and 7 either with left bundle branch block or lateral MI. Regarding anterior MI, a significant correlation (Pxa0<xa00.05) was found between ST elevations in leads I, aVL, V2 and V3 comparing cECG and kECG. In inferior MI, there was only a significant correlation (Pxa0<xa00.05) in lead III between cECG and kECG, but not in II and aVF. Therefore, 17 additional patients were included in the study by placing an additional electrode further away from the sensor array on the chest. ST elevations now correlated in all inferior leads II, III and aVF (Pxa0<xa00.05) as measured in 9 patients with inferior MI. In addition, in 8 patients an inferior MI was correctly ruled out.ConclusionIt is possible to identify STEMIs by cECG. This innovative technique could play an important role in the pre-hospital period as well as in the hospital.

Capacitive ECG system with direct access to standard leads and body surface potential mapping.

Abstract Capacitive electrodes provide the same access to the human electrocardiogram (ECG) as galvanic electrodes, but without the need of direct electrical skin contact and even through layers of clothing. Thus, potential artifacts as a result of poor electrode contact to the skin are avoided and preparation time is significantly reduced. Our system integrates such capacitive electrodes in a 15 sensor array, which is combined with a Tablet PC. This integrated lightweight ECG system (cECG) is easy to place on the chest wall and allows for simultaneous recordings of 14 ECG channels, even if the patient is slightly dressed, e.g., with a t-shirt. In this paper, we present preliminary results on the performance of the cECG regarding the capability of recording body surface potential maps (BSPMs) and obtaining reconstructed standard ECG leads including Einthoven, Goldberger and, with some limitations, Wilson leads. All signals were measured having the subject lie in a supine position and wear a cotton shirt. Signal quality and diagnostic ECG information of the extracted leads are compared with standard ECG measurements. The results show a very close correlation between both types of ECG measurements. It is concluded that the cECG lends itself to rapid screening in clinically unstable patients. Zusammenfassung Kapazitive Elektroden ermöglichen die gleiche Art der Messung des Elektrokardiogramms (EKG), wie sie auch bei herkömmlich genutzten galvanischen Elektroden genutzt wird. Dabei wird jedoch kein direkter Hautkontakt benötigt; stattdessen kann sogar durch Kleidungsschichten gemessen werden. Somit entfallen Kontaktprobleme, wie sie beim konventionellen EKG auftreten können, und gleichzeitig wird die eigentliche Vorbereitungszeit auf ein Minimum reduziert. Im hier vorgestellten System wurden 15 derartige kapazitive Elektroden in einen Sensor-Array integriert und rückseitig mit einem Tablet-PC kombiniert. Durch Aufsetzen des Systems auf die Brust des Patienten können simultan 14 EKG-Kanäle gemessen werden, auch durch Kleidung hindurch und ohne Vorbereitungsaufwand. Dabei wird das EKG direkt auf dem Tablet-PC visuell dargestellt. In dieser Arbeit berichten wir über erste Ergebnisse der Messung von Body-Surface-Potential-Maps (BSPM) und der Extraktion von Standardableitungen nach Einthoven/Goldberger und (mit gewissen Einschränkungen) Wilson aus dem Sensor-Array. Sowohl die Signalqualität als auch die diagnostischen Informationen der gemessenen EKGs werden direkt mit herkömmlichen, galvanisch gemessenen EKGs verglichen. Die Ergebnisse zeigen eine sehr enge Korrelation zwischen beiden Messarten. Insbesondere die schnelle Aufnahme von EKG-Signalen bei klinisch instabilen Patienten wird durch das vorgestellte kapazitive BSPM-System stark erleichtert.

Automatic quantification of the Poincaré plot asymmetry of NN-interval recordings.

We investigated the electrocardiographic substrate underlying the asymmetry of Poincaré plots of NN intervals (NNI) on different time scales and conceived a method for automatic asymmetry quantification (AQUA), which is based on the observation that left-sided comet asymmetry (A(L)) is due to sudden increases (SIC), and right-sided comet asymmetry (A(R)) to sudden decreases (SDC) of cycle lengths, and that both the SIC and SDC episodes were consistently associated with significant changes in P-wave magnitude and/or polarity indicating a shift in dominant pacemaker activity. The performance of AQUA was validated in 15 endurance trained athletes (age: 29 +/- 6 years) exhibiting marked comet asymmetry, and 11 untrained controls (age: 40 +/- 15 years) with symmetrical comet patterns. SICs were reliably identified by AQUA with a sensitivity of 0.950 and a specificity of 0.985, and SDCs with a sensitivity of 0.952 and a specificity of 0.965. In the athletes, the magnitude of SICs exceeded that of SDCs significantly, and the occurrence of SICs and SDCs was closely correlated with periods of increased efferent vagal activity. It is concluded that AQUA is a useful tool for the identification and quantification of specific aspects of nonlinear heart rate dynamics manifesting as Poincaré plot asymmetries.

Evaluation of a novel portable capacitive ECG system in the clinical practice for a fast and simple ECG assessment in patients presenting with chest pain: FIDET (Fast Infarction Diagnosis ECG Trial)

BackgroundElectrocardiogram (ECG) assessment plays a crucial role in patients presenting with chest pain and suspected acute coronary syndrome (ACS). In a pilot study, we previously evaluated a capacitive ECG system (cECG) as a novel ECG technique for a fast and simple ECG assessment in patients with ST-elevation myocardial infarction (STEMI). In a next step, the sensitivity and specificity of this novel ECG technique have to be assessed in patients with ACS.HypothesisThe Fast Infarction Diagnosis ECG Trial (FIDET) is a prospective, bi-center, observer-blinded noninferiority study to evaluate the cECG compared to the conventional ECG (kECG) in the clinical practice for ECG assessment in consecutive patients presenting with suspected ACS.MethodsIn 250 patients who were admitted to the hospital, because of an ACS [including STEMI and non-ST-elevation acute coronary syndrome (NSTE-ACS)], both a kECG and a cECG recording were performed within a time lag of less than 10xa0min.End pointsThe primary end point will be sensitivity and specificity of the cECG compared to the kECG in diagnosing a STEMI with a margin of noninferiority of 7.5xa0%. Secondary end points include sensitivity and specificity of the cECG compared to the kECG in diagnosing an NSTE-ACS, safety of the cECG system (adverse event, serious adverse event and suspected unexpected serious adverse reaction), parameters of the ECG measurement (PQ-interval, QT-interval, ST-amplitude and heart rate) and measurement duration of the two methods.ConclusionFIDET is designed as a noninferiority study to show that a novel cECG system is suitable for the diagnosis of myocardial infarction in the clinical context and might even have benefits, for example by offering a faster and easier ECG assessment.

Novel multichannel capacitive ECG-System for cardiac diagnostics beyond the standard-lead system

Capacitive electrodes provide the same access to the human electrocardiogram (ECG) as galvanic electrodes, however, without the need of direct skin contact and even through thicker layers of cloth. Traditional body surface potential mapping (BSPM) using a multitude of galvanic electrode configurations or magnetocardiography (MCG) may be tedious to perform, particularly in severely ill patients. In contrast, an insulated setup including a multichannel arrangement of capacitive sensors offers direct access to body surface potential maps. We evaluated the capacitive ECG signals (obtained by means of cBSPM) on the basis of ECG data obtained through classical standard electrocardiography including the Einthoven, Goldberger, and Wilson leads. Ten patients with a recent myocardial infarction and sinus rhythmus or arrhythmias were included in the study. Our results with the cBSPM system showed a high correlation with the standard galvanic ECG (gECG) regarding diagnostically relevant scalar ECG data. Moreover, our cBSPM system allowed for a detailed characterization of the cardiac de- and repolarization cycle. In conclusion, our preliminary data suggest that application of cBSPM is feasible, even in very old people, and yields reliable results with regard to infarct and arrhythmia diagnosis. Compared to conventional BSPM systems, the cBSPM system offers the advantage of rapid ECG screening, which may be particularly important in the context of hemodynamically unstable patients.