Ivo Viscor

Measure of the QT/RR Dynamic Coupling in Patients with the Long QT Syndrome

Background: The patients with the long QT syndrome type‐1 (LQT‐1) have an impaired adaptation of the QT interval to heart rate changes. Yet, the description of the dynamic QT–RR coupling in genotyped LQT‐1 has never been thoroughly investigated.

A multichannel bioimpedance monitor for full-body blood flow monitoring.

Abstract The design, properties, and possible diagnostic contribution of a multichannel bioimpedance monitor (MBM) with three independent current sources are presented in this paper. The simultaneous measurement of bioimpedance at 18 locations (the main part of the body, legs, arms, and neck) provides completely new information, on the basis of which more precise haemodynamic parameters can be obtained. The application of the MBM during various haemodynamic stages, such as resting in a supine position, tilting, exercise stress, and various respiration manoeuvres, is demonstrated. Statistical analysis on a group of 34 healthy volunteers is presented for demonstration of blood flow monitoring by using the proposed method.

Influence of tilt load on pulse wave velocity in the lower limbs

Pulse wave velocity is a marker of the state of health of the arterial system. We have developed a device (hardware unit and software) for concurrent determination of pulse-wave velocity in several parts of body (up to 18). Using this device we measured the change of pulse-wave velocity in the lower limbs when the subject is exposed to a specific load - “Head-up Tilt Test”.

Excitation specificity of repolarization parameters

The excitation specificity of QT dynamic parameters was tested on three groups of subjects: healthy subjects; non-medicated hypertensive subjects with metabolic syndrome; and subjects with essential hypertension. Four different excitations of RR were used: bicycling exercise; tilt with breathing 0.1 and 0.33 Hz; and deep breathing. Linear dynamic feedback model of QT/RR coupling was supposed at the analysis and next repolarization parameters were tested: QTc; gain of QT/RR coupling for slow and fast RR variability; time constant of QT adaptation; and random QT variability. Results: Dynamic repolarization parameters statistically significantly depend on the type of RR excitation. The gain of QT/RR coupling for slow RR variability, the time constant of QT adaptation and QTc are maximal at RR excitation given by the bicycling exercise. The frequency of breathing, i.e. corresponding vagal modulation has no effect on repolarization parameters. The measurements with deep breathing, without any other slow excitation of heart rate, has low signal-to-noise ratio of analyzed data and resulting QT parameters are inaccurate. Conclusion: The use of heart rate excitation and all measurements conditions should be defined for the exact analysis of the repolarization dynamic parameters.

Clock signal requirement for high-frequency, high dynamic range acquisition systems

Analog-to-digital converters (ADC’s) are increasingly replacing mixers in frequency conversion schemes. To achieve superior performances, in terms of bandwidth and dynamic range, a nearly ideal ADC clock is needed, with a spectral purity higher than the reference signal of the classical mixing scheme. These requirements of spectral purity for the ADC clock are discussed by analyzing in detail the nonuniform sampling process and by characterizing an actual acquisition system. The effect of clock phase imperfections on the output is proportional to the input frequency over sampling frequency ratio. Moreover, at the output we may have a multiple folding of the phase jitter spectrum. These effects are illustrated by three sets of measurements performed using our system: transfer of spurious clock components, aliasing of these components, and transfer of clock phase noise.

Ventricular Electrical Delay Measured From Body Surface ECGs Is Associated With Cardiac Resynchronization Therapy Response in Left Bundle Branch Block Patients From the MADIT-CRT Trial (Multicenter Automatic Defibrillator Implantation-Cardiac Resynchronization Therapy)

Background: Although cardiac resynchronization therapy (CRT) is beneficial in heart failure patients with left bundle branch block, 30% of these patients do not respond to the therapy. Identifying these patients before implantation of the device is one of the current challenges in clinical cardiology. Methods: We verified the diagnostic contribution and an optimized computerized approach to measuring ventricular electrical activation delay (VED) from body surface 12-lead ECGs. We applied the method to ECGs acquired before implantation (baseline) in the MADIT-CRT trial (Multicenter Automatic Defibrillator Implantation-Cardiac Resynchronization Therapy). VED values were dichotomized using its quartiles, and we tested the association of VED values with the MADIT-CRT primary end point of heart failure or death. Multivariate Cox proportional models were used to estimate the risk of study end points. In addition, the association between VED values and hemodynamic changes after CRT-D implantation was examined using 1-year follow-up echocardiograms. Results: Our results showed that left bundle branch block patients with baseline VED <31.2 ms had a 35% risk of MADIT-CRT end points, whereas patients with VED ≥31.2 ms had a 14% risk (P<0.001). The hazard ratio for predicting primary end points in patients with low VED was 2.34 (95% confidence interval, 1.53–3.57; P<0.001). Higher VED values were also associated with beneficial hemodynamic changes. These strong VED associations were not found in the right bundle branch block and intraventricular conduction delay cohorts of the MADIT-CRT trial. Conclusions: Left bundle branch block patients with a high baseline VED value benefited most from CRT, whereas left bundle branch block patients with low VED did not show CRT benefits.

Two-channel high dynamic range bioimpedance monitor for cardiography

In the paper we introduce conception of a two-channel bioimpedance monitor. We describe the basic hardware blocks and analyze their limitations from the point of view of the dynamic range. The conception based on the direct digital synthesizer and the digital down converter en- ables high-quality bioimpedance signal and the analysis of the impedance phase.

Intracerebral EEG Artifact Identification Using Convolutional Neural Networks

Manual and semi-automatic identification of artifacts and unwanted physiological signals in large intracerebral electroencephalographic (iEEG) recordings is time consuming and inaccurate. To date, unsupervised methods to accurately detect iEEG artifacts are not available. This study introduces a novel machine-learning approach for detection of artifacts in iEEG signals in clinically controlled conditions using convolutional neural networks (CNN) and benchmarks the method’s performance against expert annotations. The method was trained and tested on data obtained from St Anne’s University Hospital (Brno, Czech Republic) and validated on data from Mayo Clinic (Rochester, Minnesota, U.S.A). We show that the proposed technique can be used as a generalized model for iEEG artifact detection. Moreover, a transfer learning process might be used for retraining of the generalized version to form a data-specific model. The generalized model can be efficiently retrained for use with different EEG acquisition systems and noise environments. The generalized and specialized model F1 scores on the testing dataset were 0.81 and 0.96, respectively. The CNN model provides faster, more objective, and more reproducible iEEG artifact detection compared to manual approaches.

Fully automatic detection of strict left bundle branch block

Strict (true) left bundle branch block (tLBBB) ECG morphology is a new diagnostic marker in cardiology that was proposed to predict cardiac resynchronization therapy (CRT) responders. In this paper we present an algorithm for the automatic detection of tLBBB. This algorithm includes mid-QRS notching and slurring detection, QRS duration measurement and tLBBB morphology detection. All required morphologies are detected in the time domain using thresholding of simple features of signal. In order to test our algorithms, three experts labelled 78 ECG records (12 leads, fs = 5 kHz, 15 min); 51 records were labeled as tLBBB. The proposed algorithms were tested showing overall sensitivity and specificity 98 and 86%, respectively, in cases where all three experts reached full consensus (82% of the dataset). Our method showed lower sensitivity and higher specificity 96% and 88%, respectively, for the dataset including cases where experts mutually disagreed, consensus has been reached through expert discussion in these records.

Can we hear ventricle dyssynchrony? Yes, we can.

This study introduces a method for detection of ventricular depolarization activity and the transfer of this activity into an audible stereo audio signal. Heart potentials are measured by an ultra-high-frequency high-dynamic-range electrocardiograph (UHF-ECG) with a 25-kHz sampling rate. Averaged and prolonged UHF amplitude envelopes of V1-3 and V4-6 leads at a frequency range of 500-1000 Hz are used as a modulating function for two carrier audio frequencies. The right speaker makes it possible to listen to the depolarization of the septum and right ventricle (V1-3) and the left speaker the left ventricle lateral wall (V4-6). In the healthy heart, both speakers can be heard simultaneously. A delayed L or R speaker represents the dyssynchronous electrical activation of the ventricles. Examples of the normal heart, right bundle branch block and left bundle branch block can be heard at www.medisig.com/uhfecg.