Search

Background: Autonomic regulation analysis is useful in risk stratification of ventricular tachycardia and sudden cardiac death in chronic heart failure (CHF). Heart rate variability (HRV) reflects the condition of autonomic regulation. For analyzing the autonomic control the whole cardiovascular system has to be considered. Therefore, the aim of our study was to assess the influence of peripheral arterial disease (PAD) on the autonomic regulation. Methods: In 53 men (age: 67 ± 11 years) from the cardiovascular unit we compared standard HRV parameters in 27 with (ankle brachial index, ABI 0.9) PAD as well as with 12 healthy subjects as reference. High-resolution electrocardiograms were recorded over 30 minutes under resting conditions. Pulse wave velocity as well as ABI was estimated using the vascular screening system VASERA. Results: In cardiac patients with PAD, we found both significant differences in linear and nonlinear HRV parameters. Higher increase of low-than high-frequency components indicated higher elevated sympathetic than vagal activation. Altered autonomic control can be interpreted as a compensatory mechanism for diminished vascular arteriolar vasodilator capacity in PAD. To maintain the arterial blood pressure, an elevated setpoint of sympathovagal balance is required. Conclusions: Our data indicate PAD alters the HRV in cardiaovascular patients. PAD should be considered in the assessment of cardiac autonomic regulation especially in risk stratification.

Background: Early and late restenosis in up to 30% remains a major problem for long-term success after percutaneous coronary intervention (PCI). Compared to bare metal stents, the use of drug-eluting stents reduces restenosis below 10%, but implant coasts have to be considered. In restenosis noninvasive testing lacks diagnostic power. We applied a new approach to identify patients with a high risk for restenosis after PCI by combining heart rate (HR) and blood pressure variability (BPV) analyses. Methods: In 52 patients with clinical suspicion of restenosis and history of PCI, we investigated patterns of cardiovagal autonomic regulation prior to cardiac catheterization. The patients were separated in (i) patients with restenosis (CAD+R) and (ii) patients without restenosis (CAD−R), where restenosis is defined as a stenosis greater than 75% of luminal diameter in at least one main vessel. The following parameters/methods were evaluated: Canadian Cardiovascular Society grade (CCS-grade), vessel disease score (CAD-level), left ventricular ejection fraction (LVEF), heart rate variability (HRV), BPV, baroreflex sensitivity (BRS), as well as HR turbulence and blood pressure (BP) potentiation caused by premature ventricular complexes. Results: Whereas age, LVEF, CAD-level, CCS-grade, and mean BP did not differ between CAD+R and CAD−R, significant differences were found in (i) BPV: diastolic LF/P, systolic, and diastolic UVLF, (ii) in BRS: slope of tachycardic sequences, and (iii) in extrasystolic parameters: heart rate turbulence onset (HRTO) and potentiation of systolic BP (SBPP). Standard HRV parameters did not show significant differences between the groups. Using the two parameters diastolic LF/P (threshold >0.2) and HRTO (threshold >0) restenosis were predicted in 83.4%. Conclusions: These results demonstrate that indicators of sympathetic activation or vagal depression identify restenosis in patients after PCI, thus opening a perspective for a new noninvasive monitoring.

Vortex currents may be of importance in the early diagnosis of myocardial infarction caused by an occlusion of a coronary artery. We investigated the influence of a passive vortex current distribution, modelled by different conductivities in a hollow cylinder, on the localization error and on the signal strength in both the magnetocardiogram and the electrocardiogram. The hollow cylinder was mounted in a realistically shaped physical torso phantom. A platinum dipole was inserted into the cylinder. The compartment boundaries were modelled with two special ionic exchange membranes. The conductivity ratio of the cylinder compartment to the torso compartment was varied from 0.25 to 100. We compared the simultaneously measured magnetic and electric signal strengths as a function of this conductivity ratio. We found that an increasing conductivity ratio causes only a slight increase (about 19%) of the magnetic signal strength but a strong decrease (about 81%) of the electric signal strength. Using a homogeneous torso model, the dipole localization errors were, depending on the conductivity ratio, up to 16 mm. In conclusion, passive vortex currents might partially explain the differences between magnetocardiographic and electrocardiographic recordings observed both experimentally and clinically.

A method of postprocessing and visualizing three-dimensional vector fields, such as current density reconstruction results, is presented. This method is based on equivalent ellipsoids fitted to the vector fields. The technique has been tested with simulated data and current density reconstructions based on bioelectromagnetic data obtained from a physical thorax phantom. Three different approaches based on: (1) longest distance; (2) dominant direction; and (3) principal component analysis, for fitting the equivalent ellipsoids are proposed. Multiple foci in vector fields are extracted by multiple ellipsoids which are fitted iteratively. The method enables statistical postprocessing for the sake of comparisons of different source reconstructions algorithms or comparisons of groups of patients or volunteers.

A new method for visualizing and postprocessing three-dimensional time varying vector fields is presented. This method is based on equivalent ellipsoids fitted to these fields. The new technique has been tested on vector fields representing current density reconstruction results based on biomagnetic data from a cardiac patient and a neurological patient. Multiple foci in the vector fields are extracted by multiple ellipsoids which are fitted in an iterative manner. The new method enables visualization of even very complex vector fields, as well as statistical postprocessing.

BACKGROUND Neurovegetative and haemodynamic changes impact on the regulation pattern of blood pressure and heart rate in patients with heart failure. We studied these patterns and their interactions in patients with idiopathic dilated cardiomyopathy (IDC) and in healthy subjects (REF). METHODS We continually measured the heart rate and blood pressure (Portapres device) in twenty-five supine IDC patients (age: 51 +/- 13 y; left ventricular end-diastolic diameter 67 +/- 11 mm; ejection fraction 30 +/- 11%) and in twenty-seven REF (age: 50 +/- 11 y) Recording time was 30 minutes. The heart rate (HR) of each beat and the systolic blood pressure (SYS) of the subsequent beat were measured. Code numbers (symbols) were assigned to the beat-to-beat changes in HR and SYS (increase: 1; decrease: 0). The frequencies of the symbols sequences of three successive beats were counted. In this way we obtained a matrix consisting of eight (two to the power of three) HR and SYS combinations: 000, 100, 010, 001, 111, 110, 011 and 101. We then counted the frequencies of the different combinations of the symbol sequences in HR and SYS (2(3) x 2(3) = 64 combinations). The relative frequencies of symbol patterns appearing in HR, SYS and in the combined analysis of HR and SYS, were compared for IDC and REF using the T-test for independent samples. RESULTS Significant differences were seen between IDC and REF. The HR patterns 101 and 010 were more frequent in IDC than in REF patients (11.1 +/- 4.7 vs. 7.7 +/- 2.9%, p = 0.003, and 16.1 +/- 6.3 vs. 11.7 +/- 4.9%, p = 0.008). This finding was even more marked in the analysis of the SYS patterns 101 and 010 (11.0 +/- 7.4 vs. 8.2 +/- 2.9%, p < 0.001, and 11.6 +/- 7.4 vs. 5.4 +/- 2.7%, p < 0.001). Non-alternating patterns were more frequent in REF (e.g. 000HR & 111SYS: 4.6 +/- 3.3 vs. 2.9 +/- 2.4%, p = 0.03). CONCLUSIONS We demonstrated significant interaction of the regulation patterns of blood pressure and heart rate, as also their interactions in IDC. Opposed changes in HR and SYS mediated by the baroreflex, became superimposed by alternans phenomena in IDC. The pattern analysis of changes in HR and SYS detects these disturbances of neurovegetative short-term control.

The heart rate variability (HRV) is related to several mechanisms of the complex autonomic functioning such as respiratory heart rate modulation and phase dependencies between heart beat cycles and breathing cycles. The underlying processes are basically nonlinear. In order to understand and quantitatively assess those physiological interactions an adequate coupling analysis is necessary. We hypothesized that nonlinear measures of HRV and cardiorespiratory interdependencies are superior to the standard HRV measures in classifying patients after acute myocardial infarction. We introduced mutual information measures which provide access to nonlinear interdependencies as counterpart to the classically linear correlation analysis. The nonlinear statistical autodependencies of HRV were quantified by auto mutual information, the respiratory heart rate modulation by cardiorespiratory cross mutual information, respectively. The phase interdependencies between heart beat cycles and breathing cycles were assessed basing on the histograms of the frequency ratios of the instantaneous heart beat and respiratory cycles. Furthermore, the relative duration of phase synchronized intervals was acquired. We investigated 39 patients after acute myocardial infarction versus 24 controls. The discrimination of these groups was improved by cardiorespiratory cross mutual information measures and phase interdependencies measures in comparison to the linear standard HRV measures. This result was statistically confirmed by means of logistic regression models of particular variable subsets and their receiver operating characteristics.

The aim of this study was to detect pathological changes of the complex autonomous regulation of ecg, blood pressure and respiration (synchronously recordings of 30 minutes) in patients with cardiac diseases. We investigated the cardiovascular and cardiorespiratory linear and nonlinear interactions in 10 patients with dilative cardiomyopathy (dcm) and in 10 patients after myocardial infarction (mi). We compared results from the classical linear correlation function analysis with results from the mutual information method (transinformation) for analysis of nonlinear and linear interactions. Both methods yield high significant parameters (p < 0.01). Thus, we found both linear and nonlinear interactions with partly different specificity in patients with dcm and mi compared to healthy subjects (ref).

We extracted and quantified high frequency intra-QRS signals in idiopathic dilated cardiomyopathy (IDC). In IDC the analysis of late potentials in the terminal QRS complex often fails in predicting clinical events because of intraventricular conduction abnormalities and the absence of a circumscribed arrhythmogenic substrate. Therefore, new approaches are required to assess the electrical state of the myocardium. We investigated 21 patients suffering from IDC with (n = 14) and without (n = 7) bundle branch block. High resolution 31 lead magnetocardiograms were filtered with a 67 point 4th order Savitzky-Golay filter. The difference of the measured and filtered signals was calculated (67-200 Hz). The spatio-temporal properties and the areas under the curves of the resulting high frequency intra-QRS signals (IQCs) were studied. We detected IQCs in all patients. The patients had individual patterns regarding the temporal and spatial properties of the IQCs during depolarisation. The IQCs predominantly appeared in the initial portion of the QRS. The ratios of the areas under the curves of the IQCs and the measured signals were linearly correlated to the left ventricular enddiastolic diameter (r = 0.71, significance 0.0012). In IDC the ventricular depolarization is accompanied by individual spatial and temporal patterns of high frequency intra-QRS signals. They can be studied non-invasively from body surface mapping data with the algorithm used in this study. This provides access to the assessment of the electrical status in patients with IDC.

Noninvasive finger arterial blood pressure and ECG were recorded for 30 min in patients with idiopathic dilated cardiomyopathy (IDC) and healthy control subjects (CON) for the investigation of blood pressure and heart rate regulation following a premature ventricular complex (PVC). The potentiation of blood pressure amplitude of the postextrasystolic beat was fivefold increased in IDC compared with CON (48.7 +/- 32.6% vs. 9.8 +/- 5.4%, p < 0.01). PVC starts a baroreflex response, which last about 10 s in physiological regulation. In contrast, the baroreflex response in IDC is immediately suppressed by the augmented potentiation of the blood pressure amplitude from the first postextrasystolic beat. Thus, the regulation after PVC is determined by the PVC itself and postextrasystic potentiation.

The beat-to-beat variability of the diastolic blood pressure induces small variations in the afterload of the left ventricle. These variations influence myocardial contractility, and thus blood pressure amplitude. We assessed the interdependence of blood pressure and changes in the afterload. We continuously recorded blood pressure (duration 200 s, at rest) in 20 patients with dilated cardiomyopathy (ejection fraction 32 +/- 13%, left ventricular diameter 67 +/- 8 mm) and in 20 healthy volunteers. Interbeat intervals, diastolic pressures, systolic pressure amplitudes and mean slopes of systolic pressure amplitudes were measured. Correlation coefficients (r) were calculated to assess the interdependence of blood pressure amplitudes/mean systolic slopes and the preceding diastolic pressures/interbeat intervals, respectively. In healthy volunteers we found a strong interdependence between blood pressure amplitude and the preceding diastolic pressures (r = 0.62 +/- 0.21 and 0.47 +/- 0.22). Higher diastolic pressures were followed by higher blood pressure amplitudes, and by steeper slopes of the systolic peaks. In patients with dilated cardiomyopathy, such interdependence was significantly lower (r = 0.33 +/- 22 and r = 0.28 +/- 0.35), and in patients with severely reduced left ventricular function (ejection fraction < 32%) was only marginal (r = 0.23 +/- 0.27 and 0.21 +/- 0.44, respectively). The forces of the isovolumetric contraction necessary to initiate the ejection phase of the left ventricle depend on the afterload, i.e. on the diastolic pressure. The responses of amplitude and slope of the systolic blood pressure to small changes in the afterload make it possible to assess left ventricular contractility. The latter is impaired in dilated cardiomyopathy.

Assessment of fluctuations in heart rate (HR) following a premature ventricular complex (PVC) is valuable for identifying patients at high risk of sudden cardiac death. We hypothesised that postextrasystolic potentiation is the main determinant of the regulation patterns of blood pressure (BP) and HR following a PVC. Twelve patients with idiopathic dilated cardiomyopathy (IDC) and 13 control subjects with single PVCs (comparable coupling intervals) were investigated. Non-invasive finger arterial BP and ECGs were analysed. Regulation patterns following a single PVC were quantified using the indices postextrasystolic amplitude potentiation (PEAP) and maximum turbulence slope of five consecutive mean BP values (MBP-TS), and compared with the HR turbulence parameters turbulence slope (HR-TS) and turbulence onset (HR-TO). PEAP was significantly higher in IDC patients compared to controls (48.7 +/- 32.6 vs. 9.8 +/- 5.4 %, P < 0.01), whereas MBP-TS was lower (0.97 +/- 0.60 vs. 2.07 +/- 1.04 mmHg BBI(-1) (BBI, beat-to-beat interval), P < 0.05), as was HR-TS (8.46 +/- 7.90 vs. 30.73 +/- 22.90 ms BBI(-1), P < 0.01). HR-TO was significantly higher in IDC patients (-0.56 +/- 2.19 vs. -5.52 +/- 4.13 %, P < 0.01). In addition, the regulation patterns of BP and HR following a single PVC differed significantly between IDC patients and controls. Specifically, we observed pronounced PEAPs in IDC patients. The baroreflex response initiated by the low pressure amplitude of the PVC was suppressed in IDC patients due to the augmented potentiation of the first postextrasystolic blood pressure. Furthermore, IDC patients displayed impressive postextrasystolic pulsus alternans phenomena, whereas healthy subjects exhibited a typical baroreflex pattern. The pulsus alternans phenomenon seems to be triggered by a PVC.

Arteriovenose Fisteln der Koronararterien sind sehr selten und drainieren meist in den rechten Ventrikel oder rechten Vorhof. Echokardiographie und Koronarangiographie sind etablierte Methoden in der Detektion dieser Anomalien. Es wird uber einen Patienten berichtet, bei dem eine Anomalie mit Dilatation des Ramus circumflexus, Aneurysma und Drainage uber eine arteriovenose Fistel in den rechten Ventrikel vorlag. Mittels Magnetresonanztomographie im Bolustrack-ing-Verfahren konnten Gefasverlauf und Dynamik der Perfusion zusatzlich zur Bildgebung mittels TSE-Sequenz nichtinvasiv dargestellt werden. Durch die Moglichkeit einer mehrfachen Applikation von 2 ml Gd-DTPA eignet sich die Bolustracking-Methode ausgezeichnet zur Bestimmung des individuellen Gefasverlaufes, der Hamodynamik und Drainagerichtung einer Koronaranomalie mit Fistel.

Background: The site of atrioventricular pre-excitation can roughly be estimated with the help of schemes basing on a few number of electrocardiogram (ECG) leads. Computer algorithms have been developed which utilize the body surface mapping of the pre-excitation signal for the localization purpose. We tested several new algorithms. Method: A patient suffering from Wolff–Parkinson–White syndrome was investigated prior the catheter ablation. The body surface mapping was performed with a 62-lead magnetocardiograph. The site of pre-excitation was calculated by using different methods: the dipole method with fixed and moving dipoles, the dipole scan on the endocardium, and different current density methods (L1 norm method, L2 norm method, low resolution electromagnetic tomography (LORETA) method, and maximum entropy method). Three-dimensional (3D) magnetic resonance imagings (MRIs) of the heart were used to visualize the results. The source positions were compared to the site of catheter ablation. Results: The accessory pathway was successfully ablated left laterally. This site was correctly identified by the conventional dipole method. By scanning the entire endocardial surface of the heart with the dipole method we found a circumscribed source area. This area too, was located at the lateral segment of the atrio-ventricular grove. The current density methods performed differently. Whereas the L1 norm identified the site of pre-excitation, the L2 norm, the LORETA method and the maximum entropy method resulted in extended source areas and therefore were not suited for the localization purpose. Conclusion: The dipole scan and the L1 norm current density method seem to be useful additions in the computational localization of pre-excitation syndromes. In our single case study they confirmed the localization results obtained with the dipole method, and they estimated the size of the suspected source region.

Die Variabilitat von Regulationsgrosen des Herz-Kreislauf-Systems erlaubt Aussagen uber die Prognose kardialer Erkrankungen. Die veranderte Variabilitat einer Regulationsgrose fuhrt zu Storungen in der Synchronisation interagierender Regelkreise. Die Quantifizierung dieser Storungen konnte Ruckschlusse auf die Schwere der zugrunde liegenden funktionellen Beeintrachtigung erlauben. Diese Studie untersucht die Synchronisation der Regelkreise von Herzfrequenz und Atmung (kardiorespiratorische Synchronisation, CRS) nach akutem Myokardinfarkt. Es wurden 43 Patienten nach Myokardinfarkt und 27 Gesunde untersucht. Zur Quantifizierung der CRS wurde die Phasensynchronisation von Atemfrequenz und Herzfrequenz beurteilt. Ebenfalls wurden die Parameter der Herzfrequenzvariabilitat (HRV) untersucht. Patienten nach Myokardinfarkt haben eine signifikant reduzierte HRV und CRS. Zwischen HRV und CRS besteht eine nichtlineare Abhangigkeit. Infarktpatienten mit linksventrikularer Dilatation und eingeschrankter linksventrikularer Pumpfunktion (EF≤45%) unterschieden sich in dieser Studie in der CRS, nicht aber in der HRV von den ubrigen Infarktpatienten und Gesunden. Sie hatten eine ausgepragte kardiorespiratorische Desynchronisation und konnten durch einen Schwellwert identifiziert werden. Die CRS erfasst die Interaktionen von Herzfrequenz- und Atemregulation. Nach Myokardinfarkt kommt es zu einer Reduktion der HRV. Eine Desynchronisation der Regelkreise von Atmung und Herzfrequenz tritt offenbar insbesondere bei ausgedehnteren Myokardinfarkten ein. Dies kann mit der vorgestellten Methode quantifiziert werden.

In magnetocardiography, averaging of QRS complexes is often used to improve the signal-to-noise ratio. However, averaging of QRS complexes ignores the variation in amplitude and shape of the signals caused, for example, by respiration. This may lead to suppression of signal portions within the QRS complexes. Furthermore, for inverse source, reconstructions of dipoles and of current density distributions errors in the spacial arrangement may occur. To overcome these problems we developed a method for separating and selective averaging QRS complexes with different shapes and amplitudes. The method is based on a spline interpolation of the QRS complex averaged by a standard procedure. This spline function then is fitted to each QRS complex in the raw data by means of nonlinear regression (Levenberg-Marquardt method). Five regression parameters are applied: a linear amplitude scaling, two parameters describing the baseline drift, a time scaling parameter, and a time shift parameter. We found that both amplitude and shape of the QRS complex are influenced by respiration. The baseline shows a weaker influence of the respiration. The regression parameters of two neighboring measurement channels correlate linearly. Thus, selective averaging of a larger number of sensors can be performed simultaneously.

The prevalence of late potentials after myocardial infarction depends on the site of the infarction. This may be caused by the different activation onsets of the anterior and inferior myocardial segments. Therefore, in anterior infarcts the high frequency signals may be concealed within the QRS whereas in the inferior infarcts they last beyond the end of the QRS. We compared the timing and the spatial patterns of high frequency intra-QRS signals (IQSs) in the different infarction sites. We investigated 14 patients with anterior infarcts, 17 patients with inferior infarcts, and 10 healthy subjects. 31-lead magnetocardiograms were recorded in left precordial position and averaged. The QRS signals were smoothed with a Savitzky-Golay filter. The smoothed QRS signals were subtracted from the measured ones. The difference of the signals (frequency band of about 60-200 Hz) representing the high frequency components was quantified. The percentage of the high frequency signals was calculated for the entire QRS, for the first and for the second half, respectively. We found that in patients with anterior infarcts the high frequency components predominantly appeared in the first half of the QRS whereas in inferior infarcts these components predominantly appeared in the second half of the QRS. The different infarction sites were associated with different spatial patterns of the high frequency signals on the body surface. In healthy subjects there was not such a preferential association of time intervals and high frequency signals. Late potentials are the special case of high frequency signals appearing in the terminal QRS. It is the general property of the myocardium to generate high frequency signals associated with the depolarization of infarcted tissue. The timing of such signals and the spatial distribution patterns on the body surface may help to identify the location of the sources.

The electric heart activity can be localised from body surface mapping data with computer algorithms. At higher heart rates the T and P waves merge. Thus, the offset can not be subtracted in the TP segment. We investigated 28 healthy volunteers with signal averaged 31-lead magnetocardiography. The offset of the baseline was determined in the TP-segment and in the PR-segment, respectively. The electrical heart activity was localised in the initial 30 ms of the QRS complex (Q), at the QRS maximum (R), and at the T wave maximum (T). The volume currents were considered by using a boundary element model with the compartments lungs and torso. The 3D positions of the dipoles, the dipole orientations, and the dipole strengths were calculated using the data preprocessed with two different offset correction intervals. The offsets of the TP and PR segments significantly differed one from another. The average deviations of the dipole localisation were within a few centimetres (Q: 20±31 mm, R: 6±13 mm, T:14±30 mm). However, in a small number of subjects (Q: n = 5, R: n = 2, T: n = 5) we observed a deviation of more than 30 mm. These deviations were not linearly correlated to the differences in the baseline offsets. High resolution recordings continuously detect heart activity in the PR segment. The correction of the baseline in the PR segment instead of the TP segment may introduce artefacts in the source localisation and therefore should be avoided.

In der Risikostratifizierung fur einen plotzlichen Herztod bzw. das Auftreten eines arrhythmogenen Ereignisses nach akutem Myokardinfarkt (AMI) wurden bisher eine hohe Spezifitat und ein hoher negativ pradiktiver Wert durch Kombination mehrerer Methoden erreicht. Sensitivitat und positive Pradiktion sind jedoch weiterhin nicht ausreichend. Wie der Elektro- liegen der Magnetokardiographie (MKG) dieselben physiologischen Prozesse zugrunde, wobei die Signale der jeweiligen Methode jedoch unterschiedliche Informationen beinhalten. Methodik: Wir untersuchten bei 50 Patienten nach AMI und 32 Probanden die von der Erregungsausbreitung erzeugten Magnetfelder und die daraus analog zu der Spatpotential(LP)analyse ermittelten Spatfelder (LF). Wir definierten anhand der 95%-Konfidenzintervalle Normbereiche fur herzgesunde Probanden (QRS (Dauer des gesamten QRS-Komplexes) = 0,6 (Mas fur die Flache des terminalen QRS-Komplexes), LAS (Dauer des terminalen QRS-Komplexes) < 25 ms). Ergebnisse: Wir verglichen mittels der erstellten Normwerte die Befunde der LF- mit denen der LP-Messung hinsichtlich pathologisch-nicht patholotisch und fanden bei 76% der Patienten eine Ubereinstimmung. Bei 4 Patienten waren im ST-Segment im Gegensatz zum EKG im MKG niedrigamplitudige Signale nachweisbar, wahrend bei 6 Patienten, deren Befund “Spatpotential positiv” nur auf RMS und LAS beruht, im MKG keine Spatfelder gefunden werden konnten. Bei der Normwerterstellung zeigte sich, das der magnetische QRS-Komplex kurzer als der elektrische ist. Diskussion: Insgesamt liefert die LF-Berechnung ahnliche Ergebnisse wie die LP-Berechnung. Vermutlich existieren magnetisch detektierbare intrakardiale Erregungskreislaufe, die im oberflachlich abgeleiteten EKG keine Potentialdifferenz erzeugen. Welche der beiden Methoden letztendlich die hohere Sensitivitat bzw. Spezifitat zeigt, bleibt in weiteren Studien mit Hoch-Risikogruppen zu untersuchen.

The influence of lung inhomogeneities on focal source localizations in electrocardiography (ECG) and magnetocardiography (MCG) is investigated. A realistically shaped physical thorax phantom with cylindrical lung inhomogeneities is used for electric and magnetic measurements. The lungs are modelled with a special ionic exchange membrane which allows different conductivity compartments without influencing the free ionic current flow. The dipolar current sources are composed of platinum wire and located at different depths and directions between the lung inhomogeneities. We localized the current dipoles with different boundary element method (BEM) models, based on electrical data and simultaneous electrical and magnetic data. Our results indicate the possibility of superadditive information gain by combining electrical and magnetic data for source reconstructions. We found a significant influence of the inhomogeneities on both the calculated source location and the calculated source strength. Mislocalizations of up to 16 mm and wrong dipole strengths of up to 52% were obtained when the lung inhomogeneities were not taken into account for source localization. Dipoles parallel to the lungs showed a larger localization error in depth than dipoles perpendicular to the lungs. We conclude that the incorporation of lung inhomogeneities will improve source localization accuracy in ECG and MCG.

The noninvasive measurement of magnetic heart activity based on high- T C DC SQUIDs, could be a tool for investigating cardiac electrophysiological properties, if such a system is able to work in unshielded environments. For the realization of such a system we use thin film planar SQUID gradiometers with bicrystal or step-edge Josephson junctions. Even for a small baseline of approximately 4 mm (limited by substrate dimensions), the field gradent resolution is in the range required for clinical analysis. We use a portable system which consists of a glass fiber cryostat with a measuring unit where we can place up to four sensors, different read-out electronics, and signal filtering methods. Firstly, measurements inside a magnetically shielded room were used to show the capability of our magnetocardiography (MCG) system in medical applcations. The system works in an unshielded environment also, without additional field compensation. We demonstrate a measurement of a magnetocardiogram in a real clinical environment, and discuss the possibilties as well as the limitations of this system in magnetocardiography.

Objective: In this paper we present an attempt at noninvasive imaging of distributed myocardial electrical activity in patients suffering from myocardial infarction and in healthy subjects. Although advances have been made, noninvasive three-dimensional imaging of cardiac electrophysiological activity is still in its infancy and extending our knowledge of cardiac electrophysiological properties may be a valuable guide in the treatment of patients with coronary artery disease. Methods: Magnetic field mapping data formed the input for an inverse solution that is based on a multiple dipole model. The lead field normalized minimum norm least square criterion was applied to predefined myocardial source geometry. Current density distributions were calculated for the left ventricle during ventricular depolarization. Images from two patients with previous myocardial infarction were compared to images from two healthy subjects. Results: Low regional and global current density was found in the infarction patients. Regions of low current density corresponded to infarcted segments. The images of the healthy subjects displayed less marked areas of low current density. Conclusion: The proposed multiple dipole model may be able to distinguish viable from scarred myocardium. A prospective clinical study should be undertaken to investigate the spatial resolution and the diagnostic performance of this method.

There is a lack of standard methods for the analysis of magnetocardiograms (MCGs). MCG signals have a shape similar to the ECG (P wave, QRS complex, T wave). High-quality multichannel recordings can indicate even slight disturbances of de- and repolarisation. The purpose of our study was to apply a new approach in the analysis of signal-averaged DC-MCGs. DC-MCGs (31-channel) were recorded in 182 subjects: 110 patients after myocardial infarction and 72 controls. Spatiotemporal correlation analysis of the QRS complex and T wave patterns throughout the entire heart cycle was used to analyse homogeneity of de- and repolarisation. These plots were compared to standard ECG analyses (electrical axis, Q wave, ST deviation, T polarity and shape). Spatiotemporal correlation analyses seem to be applicable in assessing the course of electrical repolarisation with respect to homogeneity. MCG provided all diagnostic information contained in common ECG recordings at high significance levels. The ECG patterns were included in 5/8 of our parameters for electrical axis, 6/8 for Q-wave, 7/8 for ST deviation and 5/8 for T-polarity based on two time series of correlation coefficients. We conclude that our spatiotemporal correlation approach provides a new tool for standardised analysis of cardiac mapping data such as MCG.

Amiodarone is widely used in ventricular tachyarrhythmias and atrial fibrillation, known to prolong QT-intervals. Concurrent administration of drugs prolonging QT- time can induce life-threatening ventricular tachyarrhythmia.QT-interval changes following use of Iohexol contrast-medium for coronarangiography were observed comparing 21 patients taking long-term amiodarone therapy with 21 controls not taking amiodarone or QT-prolonging drugs retrospectively.Concurrent use of Iohexol and amiodarone was associated with significant prolongation of QTc-interval (433, 95%CI: 419-448 ms vs. 480, 95%CI: 422-483 ms, P0.001) the day after coronarangiograpgy. 6/21 patients showed severe prolonged QTc-interval of500 ms.Caution is advised until more is known about pro-arrhythmic effects of Iohexol.

Introduction The purpose of our study was to prove the existence of the U wave using magnetocardiograms (MCGs). Methods The 31-channel MCGs of 25 healthy volunteers were recorded. The onset of the U wave was defined by newly developed spatial correlation analysis; and the end, by different approaches. Results A U wave could be proved in all volunteers. In 10 volunteers (heart rate, 57 ± 19 beats/min) in whom the U wave was found to be separated from the following P wave, the U wave's end could be determined as a threshold value (U wave duration, 310 ± 24 milliseconds). In 15 volunteers (heart rate, 70 ± 38 beats/min), the end of the U waves was concealed by a continuous transition of the U waves into the following P waves. Conclusions The U wave seems to be a regular phenomenon and has a distinct spatiotemporal assembly.

Heart rate variability (HRV) is a marker of autonomous activity in the heart. An important application of HRV measures is the stratification of mortality risk after myocardial infarction. Our hypothesis is that the information entropy of HRV, a non-linear approach, is a suitable measure for this assessment. As a first step, to evaluate the effect of myocardial infarction on the entropy, we compared the entropy to standard HRV parameters. The entropy was estimated by compressing the tachogram with Bzip2. For univariate comparison, statistical tests were used. Multivariate analysis was carried out using automatically generated decision trees. The classification rate and the simplicity of the decision trees were the two evaluation criteria. The findings support our hypothesis. The meanNN-normalized entropy is reduced in patients with myocardial infarction with very high significance. One entropy parameter alone exceeds the discrimination strength of multivariate standards-based trees.

Postextrasystolic potentiation mainly effects short term regulation of blood pressure and heart rate. The objective of our study was to verify how changes in systolic blood pressure (/spl Delta/SBP) from the preextrasystolic to the postextrasystolic beat characterize the pathological behavior in patients with idiopathic dilated cardiomyopathy (IDC). This measure was compared with mean blood pressure turbulence slope (BPTS) and heart rate turbulence onset (HRTO). Therefore, we analyzed the non-invasively recorded finger arterial blood pressure during single premature ventricular complexes (PVC) in IDC (n=10) and healthy subjects (CON; n=7). Although all parameters revealed significant differences (Mann-Whitney test) between IDC and CON (/spl Delta/SBP: 10.7/spl plusmn/9.7 vs -5.1/spl plusmn/1.9 %, p

The inverse solution of the single equivalent current dipole model obviously fails in the explanation of more complex source structures like a distributed myocardial activation wavefront. For this reason we applied depth normalized minimum norm estimation with anatomical constraints in patients with myocardial infarction and known regions of large myocardial damage. Current density was calculated for several hundred myocardial support points using lead field normalized minimum norm least square estimates and overlayed with 3D-MR-images as color coded surfaces. In 55% of 40 patients/normals investigated, MCI had complete correspondence with the other cardiological findings, in 27% we found partly correspondence and 18% MCI failed to provide correct diagnosis. Myocardial current imaging (MCI) is a new and promising method for assessing of myocardial viability.

The frequency domain analysis of cardiac signals is an important tool for arrhythmia rise prediction. The commonly used Butterworth filter leads to artefacts because of oscillating and phase response and is therefore not suitable for the analysis of high frequency components within the QRS complex. We applied discrete Daubechies wavelet transformation in the detection of very high frequency magnetocardiographic signals within the QRS complex. Four study groups (anterior and posterior myocardial infarction, dilated cardiomyopathy, normals) were analyzed. In all patients and normals high frequency components of about 200 Hz were present within the QRS complex. Different pattern occurred between and within the groups. Daubechies wavelet transformation is an appropriate tool for time-frequency domain analysis of magnetocardiographic signals.

Patients with decreased left ventricular function due to either acute myocardial infarction or idiopathic dilatative cardiomyopathy are known to have an increased risk of sudden death due to malignant ventricular arrhythmias. The heart rate variability (HRV) representing the influence of the autonomic nervous system on the heart is one parameter for risk stratification in these conditions, since decreased HRV correlates with increased risk for sudden death. The authors investigate: 1) whether there is a comparable sensitivity in HRV sampling ECG systems with either high (1000 Hz) or low (200 Hz) sampling rate during simultaneously short time measurements (10 minutes) and; 2) if there are differences in HRV parameter after short time measurements (10 minutes) and long time measurements (24 hours) on behalf of its usefulness for risk stratification.

Dilated cardiomyopathy (DCM) is a serious heart disease, characterized by dilatation and impaired contraction of the left or both ventricles. These pathophysiological changes were already studied by various techniques, but no complex investigations have been made concerning the peripheral noninvasive blood pressure. We hypothesize that the influence of DCM on cardiac hemodynamics can be derived by the analysis of the noninvasive finger blood pressure waveform. Therefore, a set of 25 parameters was developed, describing typical time intervals, slopes and areas. We analyzed the blood pressure contour in 20 patients with DCM and 20 healthy subjects as controls. Age and heart rate were matched in both groups. The data, recorded by a Portapres M2 device, were computed on a beat-to-beat basis. The calculated values were averaged over a period of 200 s. Ejection related time in patients with DCM was significantly shorter than in controls. It was also measured that the area under the blood pressure curve was significantly reduced in DCM patients, compared with controls. These effects may be caused by a decreased heart efficiency. This introduced new noninvasive method may lead to a more detailed analysis of pathophysiological changes in DCM patients.

A new technology has been developed which measures the magnetic field of the human heart (magnetocardiogram, MCG) by using high temperature superconducting (HTS) sensors. These sensors can be operated at the temperature of liquid nitrogen without electromagnetic shielding. We tested the reproducibility of HTS-MCG measurements in healthy volunteers. Unshielded HTS-MCG measurements were performed in 18 healthy volunteers in left precordial position in two separate sessions in a clinical environment. The heart cycles of 10 min were averaged, smoothed, the baselines were adjusted, and the data were standardized to the respective areas under the curves (AUC) of the absolute values of the QRST amplitudes. The QRS complexes and the ST-T intervals were used to assess the reproducibility of the two measurements. Ratios (R(QRS), R(STT)) were calculated by dividing the AUC of the first measurement by the ones of the second measurement. The linear correlation coefficients (CORR(QRS), CORR(STT)) of the time intervals of the two measurements were calculated, too. The HTS-MCG signal was completely concealed by the high noise level in the raw data. The averaging and smoothing algorithms unmasked the QRS complex and the ST segment. A high reproducibility was found for the QRS complex (R(QRS)=1.2+/-0.3, CORR(QRS)=0.96+/-0.06). Similarly to the shape of the ECG it was characterized by three bends, the Q, R, and S waves. In the ST-T interval, the reproducibility was considerably lower (R(STT)=0.9+/-0.2, CORR(STT)=0.66+/-0.28). In contrast to the shape of the ECG, a baseline deflection after the T wave which may belong to U wave activity was found in a number of volunteers. HTS-MCG devices can be operated in a clinical environment without shielding. Whereas the reproducibility was found to be high for the depolarization interval, it was considerably lower for the ST segment and for the T wave. Therefore, before clinically applying HTS-MCG systems to the detection of repolarization abnormalities in acute coronary syndromes, further technical development of the systems is necessary to improve the signal-to-noise ratio.

Magnetocardiography was introduced to clinical cardiologists in the early 1970’s. The measurement devices were technically unreliable, signal-to-noise ratio was poor and measurements were time consuming. Most measurements were performed in ambient environment without any shielding. Patient material studied included at first normals and myocardial infarction patients. Electromagnetic activity produced by the His-Purkinje conduction system also drew a lot of attention. Later on, pregnant women (fetal MCG), patients with ventricular hypertrophy, Wolff-Parkinson-White (WPW) Syndrome patients as well as patients with tachycardias were studied. The analysis of MCG signals in those days was rather primitive: mostly descriptive, qualitative, and morphological data was published. In order to be useful in the clinic there were many things to be improved: low signal-to-noise ratio, limited mapping and analysis possibilities, and the measurement systems were mostly located outside hospital.

Artificial dipolar sources were applied inside a physical thorax phantom to experimentally investigate the accuracy obtainable for non-invasive magnetocardiographic equivalent current dipole localisation. For the measurements, the phantom was filled with saline solution of electrical conductivity 0.21 S m-1. A multichannel cardiomagnetometer was employed to record the magnetic fields generated by seven dipolar sources at distances from 25 mm to 145 mm below the surface of the phantom. The inverse problem was solved using an equivalent current dipole in a homogeneous boundary element torso model. The dipole parameters were determined with a non-linear least squares fitting algorithm. The signal-to-noise ratio (SNR) and the goodness of fit of the calculated localisations were used in assessing the quality of the results. The dependence between the SNR and the goodness of fit was derived, and the results were found to correspond to the model. With SNR between 5 and 10, the average localisation error was found to be 9 +/- 8 mm, while for SNR between 30 and 40 and goodness of fit between 99.5% and 100%, the average error reduced to 3.2 +/- 0.3 mm. The SNR values obtained in this study were also compared with typical clinical values of SNR.

Data from simulations of the anterior myocardial infarction (AMI) and inferior myocardial infarction (IMI) are presented. One infarct located in the anterior section of the left ventricle and a second one in the inferior wall of the left ventricle were modeled. A high-resolution finite element model of a heart and torso was used in this study. Differences in the normal and infarcted fields were computed. The authors data suggest that the infarcted region contribution to the total magnetic field can be accounted for by an equivalent current dipole. It might also be possible to detect an infarct from these difference fields constructed for different cases of myocardial infarction. More simulations are needed to determine the relations between infarct sizes and locations and magnetic fields. These relations might then be used to detect various cases of myocardial infarction.

Chronic heart failure (CHF) alters heart rate and blood pressure variability (HRV, BPV). Additional prospective studies are needed to clarify their role in cardiac risk stratification. The aim of this study was to prove the value of BPV analysis for risk stratification in CHF compared to HRV. In 88 patients with CHF high-resolution ECG (22 bit resolution, 1600 Hz sampling frequency) and continuous non-invasive blood pressure (NIBP, 22 bit, 500 Hz) were recorded over 30 minutes. Based on volume clamp method the peripheral arterial blood pressure was measured via finger cuff. From the ECG recordings, time series of beat-to-beat intervals were extracted to analyze HRV and from the NIBP recordings, time series of systolic as well as diastolic blood pressure values were extracted to analyze BPV. To get ‘normal-to-normal’ beat time series (NN), ventricular premature beats and artefacts within the time series were detected and replaced by interpolated normal heartbeats. Standard HRV and systolic as well as diastolic BPV parameters were evaluated for patients with ejection fraction above and below 40% (EF+ and EF-) and for 5-year follow up (cardiac death and worsening of NYHA class). Only one HRV parameter (MEAN NN) but six BPV indices separated EF+ from EF-. In the 5-year follow up systolic BPV but not ejection fraction and HRV predicted worsening of NYHA class with 15% positive and 91.2% negative predictive value. Cardiac death was predicted in 81.8% by using the two best diastolic BPV parameters (dLF/HF and dSDNN). We conclude BPV analysis may be useful in medium range risk stratification in patients with CHF. The analysis of autonomic control should focus more on blood pressure regulation.