Pacing Clin Electrophysiol
October 1999
Appearance of ventricular tachycardia, ventricular fibrillation, and sudden cardiac death has diurnal variations. We retrospectively studied, using digital Holter electrocardiogram, whether a time course in the appearance of late potentials may be associated with malignant ventricular arrhythmias. The 24-hour recordings in 200 patients after myocardial infarction (50 patients with documented, sustained, monomorphic and reproducibly inducible ventricular tachycardia (< 270/min) (group I), 50 patients resuscitated from ventricular fibrillation (group II), and 100 patients without ventricular arrhythmias (group III) were divided into 24 segments, 60 minutes each.
View Article and Find Full Text PDFBackground: Electrophysiological abnormalities during ischaemia and increased heart rate may influence the detection of ventricular late potentials in the surface electrocardiogram. Whether the analysis of functional changes adds information to the risk stratification of patients prone to ventricular tachycardia is unclear.
Methods: We therefore retrospectively investigated 100 selected patients (25 with documented, sustained ventricular tachycardia (< 230/min) ( = VT group), 25 resuscitated from ventricular fibrillation (VF group) and 50 without ventricular arrhythmias (phi VT/VF group)) in the chronic phase after myocardial infarction.
Aims: Post-infarction risk stratification can be ascertained from beat-to-beat variations in ventricular late potentials. However, gaining such information by conventional late potential analysis using signal averaging is still not possible.
Methods: We therefore developed the spectrotemporal pattern recognition algorithm in order to detect beat-to-beat variations in late potentials.
Pacing Clin Electrophysiol
March 1994
Late potentials in the terminal phase of the QRS-complex during sinus rhythm have been proposed to identify a subgroup of patients with myocardial infarction at risk of ventricular tachycardia (VT). Frequency analysis of the ECG with Fourier transform (FFT) has been applied for detection of these microvolt level signals, but is limited by poor frequency resolution of short data segments and spectral leakage. We therefore developed frequency analysis using the maximum entropy method (MEM) based on an autoregressive (AR) model.
View Article and Find Full Text PDFSustained ventricular tachycardias and sudden death can pose a threat to post-infarction patients. Patients at risk cannot be identified with adequate reliability with Holter monitoring or programmed ventricular stimulation. Late potentials arise as a result of delayed excitation in the marginal region of an infarct and reflect structural myocardial changes that represent the precondition for circus movement.
View Article and Find Full Text PDFFrequency analysis of the electrocardiogram with Fourier transform is a sensitive method of detecting late potentials. However, information about localization of late potentials is lost, frequency resolution is poor, and window functions have to be applied. We therefore analyzed multiple segments (25 msec long) of the surface electrocardiogram ("spectrotemporal mapping") with adaptive frequency determination (AFD), an autoregressive algorithm that is characterized by high-frequency resolution in very short segments without the use of window functions.
View Article and Find Full Text PDFThe linear solvent strength model of Snyder was applied to describe fast protein separations on 2.1-micron non-porous, silica-based strong anion exchangers. It was demonstrated on short columns packed with these anion exchangers that (i) a substantially higher resolution of proteins and nucleotides was obtained at gradient times of less than 5 min than on porous anion exchangers; (ii) the low external surface area of the non-porous anion exchanger is not a critical parameter in analytical separations and (iii) microgram-amounts of enzymes of high purity and full biological activity were isolated.
View Article and Find Full Text PDFIn time domain analysis, detection of late potentials is limited by high pass filtering, noise interference and the necessity to exclude patients with bundle branch block. We therefore used frequency analysis with Fourier transform of multiple segments of the surface electrocardiogram (25 segments, size 80 ms, time shift 3 ms) during sinus rhythm after signal averaging. Thirty-two post-myocardial infarction patients with sustained ventricular tachycardia (VT), 19 post-myocardial infarction patients without VT and 17 healthy subjects were studied.
View Article and Find Full Text PDFFrequency analysis with fast Fourier transform and time domain analysis after signal averaging of the electrocardiogram (ECG) have given contradictory results in patients with sustained ventricular tachycardia after myocardial infarction. Therefore, the same orthogonal ECGs were analyzed in the frequency domain (Blackman-Harris window) and the time domain after signal averaging and high gain, low noise amplification (0 to 300 Hz) in 30 patients with sustained ventricular tachycardia after myocardial infarction, 15 patients without ventricular tachycardia after infarction and 15 healthy subjects. Patients with bundle branch block were not excluded.
View Article and Find Full Text PDFFollowing previous studies of the use of non-porous monodisperse 1.5-microns n-octyl- and n-octadecyl-bonded silicas in gradient elution of proteins, this work was aimed at elucidating further the properties of this novel column material for peptide and protein separations in comparison with wide-pore silicas. First, it is demonstrated that with short columns (e.
View Article and Find Full Text PDF