Comparison of frequency and time domain analysis of the signal-averaged electrocardiogram in patients with ventricular tachycardia and coronary artery disease: methodologic validation and clinical relevance.

Frequency 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. Twenty-one of the 30 patients with ventricular tachycardia had late potentials in the time domain and abnormal Fourier transform of the ST segment (defined as increased spectral area of 60 to 120 Hz and spectral peaks greater than 10 dB). Among the remaining nine patients with ventricular tachycardia all had no late potentials in the time domain and one manifested abnormal frequency spectra. In contrast, of the 15 patients without ventricular tachycardia after infarction, 2 had late potentials in the time domain and only 1 demonstrated abnormal frequency spectra; none of the healthy subjects manifested either phenomenon. Patients with bundle branch block were correctly classified by Fourier analysis, but were frequently missed by time domain analysis. Normalization of the spectra and area ratio proved potential pitfalls, and the choice of an appropriate ST segment was crucial: if the segment was long with respect to the duration of the late potentials and if it extended too far into the QRS complex, fast Fourier transform yielded random results.(ABSTRACT TRUNCATED AT 250 WORDS)

Frequency analysis of the electrocardiogram with maximum entropy method for identification of patients with sustained ventricular tachycardia.

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. Orthogonal electrocardiograms were recorded from the body surface of patients with and without VT, and healthy persons after low noise, high-gain amplification. Multiple 40 ms segments (time intervals 2 ms, AR-parameters tapered) were analyzed (spectrotemporal mapping): low-frequency components were eliminated by building difference spectra with optimal high order and fixed low order. The MEM-spectra revealed high frequency components (40-200 Hz) in the terminal phase of the QRS-complex and in the ST-section in 26/38 patients with VT, but only in 2/20 without VT and in 1/20 healthy persons (p less than 0.05). Unlike FFT, MEM allowed localization of late potentials by the analysis of short data segments. Thus, MEM offers promise for noninvasive identification of patients with sustained VT after myocardial infarction and detailed analysis of late potentials.

Spectral mapping of the electrocardiogram with Fourier transform for identification of patients with sustained ventricular tachycardia and coronary artery disease.

In 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. A total of 18 patients had bundle branch block. In 24 out of 32 patients with VT, three-dimensional spectral plots were characterized by spectral peaks greater than 10 dB in the range of 40-200 Hz in segments only at the end of QRS and the early ST wave, but not far outside the QRS. In only 2 out of 19 patients without VT and in 1 out of 17 healthy subjects could such peaks be observed. Noise caused spectral peaks throughout all segments. Sixteen out of 18 patients with bundle branch block were correctly classified with spectral mapping. With the Simson method, patients with bundle branch block had to be excluded, abnormal results were found in 10 out of 19 patients with VT, but also in 5 out of 15 patients without VT and in 3 out of 16 healthy subjects. Thus, spectral mapping of the electrocardiogram offers promise for better identification of patients prone to sustained VT in the presence of coronary artery disease.

Single-beat analysis of ventricular late potentials in the surface electrocardiogram using the spectrotemporal pattern recognition algorithm in patients with coronary artery disease.

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. Based on the spectrotemporal pattern recognition algorithm two-dimensional correlation function, the typical spectral pattern of late potentials can be identified in spectrotemporal maps of single beats, even in the presence of noise. RESULTS: Surface electrocardiograms of 385 patients after myocardial infarction (85 with documented sustained ventricular tachycardia (group 1), 100 with fast, polymorphic ventricular tachycardia (> 270 cycles.min-1) or primary ventricular fibrillation (group 2), 200 without ventricular arrhythmias (group 3) and 45 healthy volunteers (group 4), were analysed. The spectrotemporal pattern recognition algorithm detected late potentials in single beats in 89% of group 1 patients, in 79% of group 2, in 22% of group 3 and in 4% of normals. The spectrotemporal pattern recognition algorithm measured late potential frequency and extension of late potentials into the ST segment, which was significantly different between groups 1 and 2. Beat-to-beat variations in late potentials, with respect to frequency and extension into the ST segment, were markedly higher in patients with a history of primary ventricular fibrillation. CONCLUSION: Single-beat analysis using the spectrotemporal pattern recognition algorithm may improve risk stratification of patients after myocardial infarction, and provides information on patients prone to ventricular fibrillation.

Circadian variability of late potential analysis in Holter electrocardiograms.

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. Late potential analysis was performed using the Simson method in the time domain in each segment and compared to a conventional short-term registration. Late potential analysis in conventional short-term recordings during arbitrarily chosen daytimes revealed late potentials in 80% of patients in group I, 38% of patients in group II, and in 16% of patients without ventricular arrhythmias. In at least one 60-minute segment late potentials were found in group I in 92%, in group II in 88% (P < 0.05 vs conventional analysis), and in group III in 19%. Interestingly, in patients with a history of ventricular fibrillation late potentials appeared significantly more often during morning hours (6-12 AM: 82% vs 26% at 12 AM-6 PM, 30% at 6 PM-12 PM, and 42% at 12 PM-6 AM, P < 0.05), especially during phases with heart rate accelerations. Late potential analysis for risk stratification in conventional short-term recordings is feasible for patients prone to ventricular tachycardia, but patients prone to ventricular fibrillation would be more effectively stratified using 24-hour registrations with detection of circadian variations of late potential appearance.

Top-resolution frequency analysis of electrocardiogram with adaptive frequency determination. Identification of late potentials in patients with coronary artery disease.

Frequency 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. Results were compared with those from Fourier transform and the Simson method. We studied 38 patients after myocardial infarction (MI) with sustained ventricular tachycardia (VT), 21 patients after MI without VT, and 18 healthy subjects. Frequency peaks could be clearly differentiated until a minimal interval of 6 Hz; with fast Fourier transform (Blackman Harris window) in a much longer segment (80 msec), the spectral peaks merged into one another at an interval of about 30 Hz. AFD revealed high-frequency components as narrow peaks in the range of 40-160 Hz in 28 of 38 patients (74%) after MI with VT. Because of the short segment size, exact localization of late potentials was possible; in most of the patients, the peaks occurred in segments inside the QRS complex and ended 20 +/- 10 msec after termination of the QRS complex. In patients after MI without VT, only four of 21 patients (19%) had spectral peaks in segments after the end of the QRS complex; however, 13 of 21 patients demonstrated microvolt potentials in segments within the QRS complex. These potentials did not extend beyond the end of normal ventricular activation. Only two of 18 healthy subjects showed abnormal AFD results. Patients with bundle branch block did not need to be excluded. AFD allowed good differentiation between late potentials and noise by a characteristic pattern of the spectral peaks. For the Simson method, patients with bundle branch block had to be excluded, and overall sensitivity was 42%. In five cases, the cause of failure of the Simson method could be identified as incorrect determination of the QRS limits due to noise. Thus, AFD is a promising method for detailed analysis of late potentials; it combines the advantages of frequency analysis (good differentiation between signal and noise and high-pass filters not necessary) and time domain analysis (localization of late potentials).

[Late potentials as risk parameters after heart infarct]. / Spätpotentiale als Risikoparameter nach Herzinfarkt.

Sustained 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. Special methods have been developed to detect these potentials, which on the surface of the body are very small (1-10 microV). These potentials can be found in 70-80% of post-infarction patients with sustained ventricular tachycardias or fibrillation, but are rarely seen in MI patients with no arrhythmia. Late potential analysis represents a promising method of assessing the arrhythmogenic risk of post-infarction patients.

Evaluation of advanced silica packings for the separation of biopolymers by high-performance liquid chromatography. VI. Design, chromatographic performance and application of non-porous silica-based anion exchangers.

The 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.

Evaluation of advanced silica packings for the separation of biopolymers by high-performance liquid chromatography. III. Retention and selectivity of proteins and peptides in gradient elution on non-porous monodisperse 1.5-microns reversed-phase silicas.

Following 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.g., 35 X 8 mm I.D.) packed with these non-porous reversed-phase materials, mixtures of small peptides and mixtures of proteins can be very efficiently resolved. When the chain length of the bonded ligand was varied, the retention of a test set of proteins in gradient elution followed the ligand sequence C18 greater than C8 approximately C4 approximately phenyl greater than C2 under constant elution conditions, and the selectivity remained unchanged. Comparison of the S values of these proteins, as determined from evaluation of the log k' vs. phi dependences with non-porous silicas and with a LiChrospher Si 1000 C8 with identical accessible ligand surface areas per unit column volume, indicated lower values for the non-porous materials (k' = capacity factor; phi = molar fraction of organic solvent; S = slope of the plot of log k' vs. phi). The origin of this behaviour is discussed.

[Analysis of functional changes in ventricular late potentials for risk assessment of ventricular tachycardias after myocardial infarct]. / Analyse funktioneller Veränderungen ventrikulärer Spätpotentiale zur Risikoabschätzung von Kammertachykardien nach Herzinfarkt.

BACKGROUND: 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. Late potential analysis was performed at rest, during atrial pacing at a rate of 100/min and 120/min (n = 60), during and after occlusion of the coronary artery for coronary angioplasty (PTCA) (n = 70), and immediately after maximum exercise using selective signal averaging. RESULTS: At rest in 72% of patients in the VT group, in 32% of the VF group, and in 6% of the phi VT/VF group late potentials could be found. During atrial pacing in 80% of patients in the VT group, in 72% of the VF group, and in 10% of the patients in the phi VT/VF group and during ischaemia because of occluded coronary artery in 86% of patients in and the VT group, 70% of the VF group, and in 20% of the patients of the phi VT/VF group late potentials were present. Immediately after maximum exercise which let both ischaemia and increased heart rate, late potentials were detectable in 92% of patients in the VT group, 80% of the VF group, and in 14% of patients in the phi VT/VF group. Similar results could be achieved by using the Holter-ECG after exact correction of recorder tape speed variations. 62% of patients with only by ischaemia, increased heart rate or exercise provokable late potentials and all patients with preexistent not by PTCA extinguished late potentials developed recurrent ventricular tachycardias during the one year follow-up period. Patients without late potentials (n = 50) and patients with preexistent by PTCA extinguished late potentials (n = 11) had no recurrent ventricular tachycardias. Cycle length of recurrent and clinical tachycardia in patients with preexistent not by PTCA extinguished late potentials (n = 18) were significantly longer than in patients with only provokable late potentials (n = 21). CONCLUSIONS: Analysis of functional changes of ventricular late potentials with exercise or in Holter ECG recordings promises considerable improvement of postinfarction risk stratification especially in patients prone to ventricular fibrillation.