P-wave Magnitudes Research Articles

Prognostic significance of ratio of P-wave duration to P-wave vector magnitude for mortality in acute anterior myocardial infarction

The impact of P-wave abnormality in acute anterior MI, where the culprit vessel is the left anterior descending artery, remains undetermined. This study aimed to elucidate the impact of P-wave morphology on clinical outcomes in acute anterior MI. Patients undergoing emergent percutaneous coronary intervention for acute anterior MI were enrolled between September 2014 and April 2019 (derivation cohort) and May 2019 through July 2023 (validation cohort). P-wave duration (Pd) and P-wave vector magnitude (Pvm) were measured. The Pvm was calculated as the square root of the sum of the squared P-wave magnitudes in leads II and V6 and one-half of the P-wave amplitude in V2. The patients were categorized into high and low Pd/Pvm groups using a statistically derived cut-off value. The endpoint comprised the composite of heart failure (HF) hospitalization and all-cause death. Consecutive 426 patients were enrolled in this study (derivation cohort, 213 patients; validation cohort, 216 patients). The calculated cut-off value of Pd/Pvm for predicting the clinical endpoint, determined through receiver operating curve analysis, was 793.5ms/mV (area under the curve [AUC]=0.85, sensitivity of 73.8%, and specificity of 94.0%) in the derivation cohort. Kaplan-Meier analyses revealed a significantly higher risk of the endpoint in patients with high Pd/Pvm than those with low Pd/Pvm in derivation and validation cohorts (Log-rank p<0.001 and p<0.001, respectively). Multivariate Cox proportional hazards analysis identified advanced age, elevated Pd/Pvm, and reduced left ventricular ejection fraction as independent and significant factors associated with the endpoint in the validation cohort (p=0.008, p<0.001, and p<0.001, respectively). High Pd/Pvm was significantly associated with the composite of HF hospitalization and all-cause death after acute anterior MI.

Abstract TP217: Potential Utility Of Magnetocardiogram For Patients With Embolic Stroke Of Undetermined Source

Background: The magnetocardiogram (MCG) is a promising medical tool for detecting and visualizing abnormal cardiac electrical activation in cardiovascular disease patients. MCG has higher spatial resolution than the electrocardiogram (ECG) because the magnetic field is not distorted by flow through tissues. Taking advantage of these features, MCG has been applied for studying arrhythmia, such as atrial fibrillation (AF) and long-QT syndrome. Paroxysmal AF is the most common sources of thromboembolism for ESUS. Since factors that reflect left atrial overload (LAO) are independent predictors of paroxysmal AF, evaluation of these factors in ESUS patients is essential to improve their prognosis. We aimed to investigate the potential utility of MCG in ESUS patients for evaluation of the factors that reflect LAO. Methods: ESUS patients who underwent MCG (MC-6400 MCG system with 64 magnetic sensors) in our hospital were enrolled between September 2018 and July 2021. The peak P-wave magnitude of the right atrium segment and the left atrium segment on the MCG (MCG-RA, MCG-LA) were measured. Subsequently, the ratio of peak magnitude of the LA segment to that of the RA segment (MCG-LA/RA) was used to evaluate LAO. Other factors that reflect LAO, such as PAC frequency on Holter monitoring, LAD in transthoracic echocardiography (TTE), serum level of brain natriuretic peptide, left ventricular ejection fraction (LVEF) in TTE, and P-wave terminal force in lead V1 (PTFV1) on ECG were also evaluated. Results: Fifty-two ESUS patients with a mean age of 67.9±14.3 years (females, 42%) were included. The mean MCV-RA and MCG-LA were 7.70±12.82 and 4.50±7.74 pico-Tesla, respectively. The mean MCG-LA/RA was 0.66±0.31. The MCG-LA/RA was significantly correlated with the PAC frequency (r=0.293, p=0.039), although either MCG-RA or MCG-LA was not correlated. Also, the MCG-LA/RA ratio was significantly correlated with LAD (r=0.301, p=0.03) but not with brain natriuretic peptide (r= 0.25, p= 0.09), LVEF (r= -0.06, p= 0.654), or PTFV1 (r= 0.02, p=0.91). Conclusion: This is the first study that evaluated the relationship of the MCG-LA/RA ratio with factors that reflect LAO in ESUS patients. These results suggest that the MCG-LA/RA ratio is a novel biomarker for LAO in ESUS patients.

Earthquake Magnitude Estimation Using a Total Noise Enhanced Optimization Model.

In this paper, a heterodyne laser interferometer, which is used as a sensor for high-precision displacement measurement, is introduced to measure ground vibration and seismic waves as a seismometer. The seismic wave is measured precisely through the displacement variation obtained by the heterodyne laser interferometer. The earthquake magnitude is estimated using only the P-wave magnitudes for the first 3 s through the total noise enhanced optimization (TNEO) model. We use data from southern California to investigate the relationship between peak acceleration amplitude () and the earthquake magnitude (). For precise prediction of the earthquake magnitude using only the value, the TNEO model derives the relation equation between and the magnitude, considering the noise present in each measured seismic data. The optimal solution is obtained from the TNEO model based objective function. We proved the performance of the proposed method through simulation and experimental results.

Atrial time and voltage dispersion are both needed to predict new-onset atrial fibrillation in ischemic stroke patients

BackgroundAtrial fibrillation (AF) is a known risk factor for ischemic stroke. Electrocardiographic predictors of AF in population studies such as the Framingham Heart Study, as well as in hypertensive patients have demonstrated a predictive value of the P-wave duration for development of AF. QRS vector magnitude has had a predictive value in ventricular arrhythmia development. We aimed to assess the value of the three-dimensional P-wave vector magnitude and its relationship to P-wave duration for prediction of new-onset AF after ischemic stroke.MethodsFirst-ever ischemic stroke patients without AF at inclusion in the Lund Stroke Register were included. Measurements of P wave duration (Pd), QRS duration, corrected QT interval, and PQ interval were performed automatically using the University of Glasgow 12-lead ECG analysis algorithm. The P-wave vector magnitude (Pvm) was calculated automatically as the square root of the sum of the squared P-wave magnitudes in leads V6, II and one half of the P-wave amplitude in V2 ( sqrt{PV{6}^2+{PII}^2+{left({0.5}^{ast }PV2right)}^2} ), based on the P-wave magnitude (Pvm) as defined by the visually transformed Kors’ Quasi-orthogonal method.ResultsThe median age was 73 (IQR 63–80) years at stroke onset (135 males, 92 females). Multivariate predictors of new-onset atrial fibrillation included age > 65 years, hypertension, and Pd/Pvm. A cut-off value of 870 ms/mV gave sensitivity, specificity, positive and negative predictive values of 51, 79, 30 and 87%, respectively. The Pd/Pvm was the only ECG predictor of AF with a significant multivariate hazard ratio of 2.02 (95% CI 1.18 to 3.46, p = 0.010).ConclusionP-wave dispersion as measured by the Pd/Pvm was the only ECG parameter measured which independently predicted subsequent AF identification in a cohort of stroke patients. Further prospective studies in larger cohorts are needed to validate its clinical usefulness.

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 (AL) is due to sudden increases (SIC), and right-sided comet asymmetry (AR) 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.

Revised Distance and Depth Corrections for Use in the Estimation of Short-Period P-Wave Magnitudes

A new short-period seismic magnitude measure based on uniform, automatic processing of digital P -wave data recorded on the standardized International Monitoring System (IMS) global network of stations has been formulated and tested. The test data consisted of over 220,000 single-station P -wave amplitude and period observations from approximately 25,000 events that were reported in the Reviewed Event Bulletin of the prototype International Data Center, which was established to evaluate various concepts proposed for use in the monitoring of nuclear explosions. Large-scale statistical analyses of these data have been used to define improved corrections for the effects of epicentral distance and focal depth, distance weighting factors for use in the estimation of a new, generalized m b measure ( m b ) that incorporates data observed over the expanded epicentral distance range extending from 2° to 180°, as well as preliminary global station corrections for a number of existing and proposed IMS station sites. The station corrections are considered to be preliminary at this time since possible maximum-likelihood effects are not explicitly considered in the present analysis. However, evidence is presented that indicates that such effects are not significantly biasing the derived distance/depth corrections and that the magnitude of their influence on the estimated station corrections is likely to be rather small with respect to the range encompassed by these corrections. Tests of this new, generalized m b magnitude measure have indicated that it can provide consistent and easily reproducible measures of seismic event magnitude, even for events that are not well recorded at traditional teleseismic distances.

Spectral seismograms, magnitude spectra and source parameters of a selection of Indian plate earthquakes

Abstract Spectral seismograms of 17 earthquakes in and around the Indian sub-continent as recorded by GRA1 station of the Graefenberg array are presented and their individual and common characteristics discussed. P -wave magnitude spectra for all these earthquakes have been computed. The corner frequency, which corresponds to the frequency at the maximum value of the magnitude spectrum, is found to shift, in general, to a higher value than observed at the recording station. These magnitude spectra are used to estimate model-independent and -dependent source parameters such as seismic moment, apparent stress, stress drop and fault length. For the sake of uniform comparison, one simple omega-square type of source model has been used. No clear classification of events on the basis of source parameters is found possible. However, the model-independent apparent stress appears to have a direct proportionality with the model-dependent stress drop estimates. Also, in conformity with known observations, the highest stress drop is found for the intra-plate Latur earthquake and the lowest, for the Nicobar island arc events.

The effect of the earthquake radiation pattern on mb—A study using aftershocks in the 1976 Gazli sequence

Abstract We use published focal mechanisms to estimate radiation coefficients to four short-period arrays recording teleseismic P from 38 aftershocks in the 1976 Gazli, Uzbekistan, earthquake sequence. We divide the observed P-wave amplitude by its radiation coefficient to estimate the P-wave amplitude that would be observed if it was from the maximum of the double-couple radiation pattern. We use this new P-wave amplitude to calculate a P-wave magnitude, mCb, that is independent of the P-radiation pattern if the focal mechanisms are without error. Analysis of variance shows that the random error in mCb is reduced relative to that in the original P-wave magnitudes mCb and that this reduction is statistically significant at the 11% level. Further, analysis of variance demonstrates that the radiation coefficients calculated from the focal mechanisms contain error but that this error is probably not large enough to mask the detection of the radiation effect in mOb. Published averages of the logarithm of P-radiation coefficients allow an assessment of the differences in network-averaged mb due to the radiation pattern of point earthquake and explosion sources. Network-averaged mb from a vertical strike-slip earthquake can differ from an explosion of similar scalar moment by as much as 1.0 m.u. (magnitude units). However, this difference can be as little as 0.2 m.u. if the earthquake mechanism is 30° dip slip. We argue that, if mb is required to be independent of the earthquake mechanism, the most appropriate network average is mCb − 0.48.

HMS and spectral magnitude approaches to earthquake quantification

The analysis of P-wave magnitudes for 37 shallow earthquakes of the Alpine-Himalayan tectonic belt determined by the Homogeneous Magnitude System (HMS) technique using short- and medium-period standard instruments is carried out. The results are compared with spectral magnitudes obtained with the broadband instrument with digital registration at the Central Seismological Observatory (Grafenberg, FRG). It is shown that for the majority of the earthquakes the HMS magnitudes reveal basic spectral features of seismic radiation from the shallow event foci, though they are insufficient for the analysis of complicated cases. Thus, both the HMS and the spectral magnitude approaches are complementary and highly desirable for seismological practice.

Spectral magnitudes, magnitude spectra and earthquake quantification; the stability issue of the corner period and of the maximum magnitude for a given earthquake

Abstract P-wave magnitude spectra of a foreshock-mainshock-aftershock sequence on 7 and 8 May 1986 in the Aleutian Islands are determined using broad-band seismograms recorded at the GRF-array. The magnitude spectra are compared for different stations of the array. The maximum magnitude is stable with a standard deviation below 1%. The reliability of other source parameters (fault length, seismic moment and stress drop) derived from the magnitude spectrum m(f) depends on the determination of the corner period. Different methods to derive the corner period are compared. Best suited and most stable is the one based on the formula: T c = ∫ 0 ∞ E s (f) df ∫ 0 ∞ E s (f) f df where Es(f) = 102mf−14 is the energy density spectrum of the P-wave, and mf, the spectral P-wave magnitude of the earthquake at the respective period.

Spectral P-wave magnitudes, Aki's ω-square model and source parameters of earthquakes

Abstract The earthquake magnitude is a quantity sampling the spectrum of the far-field radiation. With a suit of properly defined magnitudes in a sufficiently broad range of frequencies, the radiated spectrum can be restored and analyzed. A method is proposed for the extraction of stress drop, fault length and seismic moment from magnitudes on a routine basis. Thereby, the theoretical spectrum as predicted by the ω-square model of Aki is utilized. In applying the method to earthquakes which occurred in several parts of Asia over a time-span of 3 years, it is shown that in most cases earthquakes in a given region are characterized by the same stress drop, varying however from region to region. In one region a change of the stress drop with time is found, eventually indicating a change in the state of stress in the particular region during the time interval investigated.

Determination of spectral properties of earthquakes from their magnitudes

Abstract Following the recommendation of the “IASPEI Commission on Magnitudes” from 1967, P-wave magnitudes of distant earthquakes are being computed with the aid of the calibration functions of Gutenberg and Richter (1956). With the development of the instrumental seismology, especially in view of the availability of broad-band recordings, the question arises whether the functions are still adequate. In this investigation new calibration functions for P- and S-waves are presented, which are not only dependent on epicentral distance and focal depth, but also on the period of the spectral component of the wave. The determination of calibration functions is based on the currently most plausible global models for the velocity and anelasticity distribution. Taking into account the effective bandwidth of the instruments employed, eventually leads to the so-called spectral magnitudes. From the spectral magnitudes m ( T ) , the energy density spectrum E ( T ) of the respective wave can readily be computed. The corresponding formula is E ( T ) = 10 2m(T)− 1.4 , with E ( T ) in joules per hertz.

The amplitude spectra of P- and S-waves and the body-wave magnitude of earthquakes

Abstract Synthetic calibration functions for body-wave magnitudes are presented. They have been obtained from computations made under the assumption that the variation of amplitude spectra along the earth's surface is due to radial velocity heterogeneity and radial changes of the dissipation factor Q inside the earth only. The new calibration functions depend on the epicentral distance and the focal depth of the earthquake, as well as on the period of the body-wave under consideration. No single calibration function exists which would produce magnitude figures identical for all Fourier components of a body-wave. Observations on several hundreds of strong earthquakes in recent years show that the P-wave magnitudes vary systematically with the period of the wave. With the application of the synthetic calibration function a general increase of the teleseismically determined P-wave magnitudes with frequency is observed. This fact reconciles acceleration response spectra from narrowband strong-motion analyzers in the near-field of an earthquake and spectral magnitudes determined from far-field observations by sensitive narrow-band seismographs. The strength of high-frequent spectral components generally exceeds the strength of low-frequent components determined in both cases.

Interpretation of short-period P-wave magnitude anomalies at selected LRSM stations

abstract The amplification of P -wave amplitudes by the receiver crust was modeled for 34 LRSM (Long Range Seismic Measurement) stations by using crustal structures derived from geological and geophysical information in the literature. If two subsets of stations in western and eastern North America (WNA and ENA), respectively, are taken a linear trend between the computed crustal amplification and the magnitude residuals of Booth et al. (1974) can be seen within each set, but there is a separation of about 0.3 magnitude units between the two groups. The most likely explanation of the separation is anelastic attenuation in the mantle under the western United States. About 75 per cent of the variance in the magnitude residuals, for the U.S. stations used, can be correlated with anelasticity and crustal amplification as known at present. The residual variance must be due to uncertainties in the above factors and other causes.

On the relation between modified Mercalli intensity and body-wave magnitude

abstractThis paper is concerned with estimating body-wave magnitude, mb, from the intensity distribution of an earthquake. Initially, it is assumed that modified Mercalli (MM) intensity values are directly related to the (A/T)z values of 1-Hz, Lg-wave ground motion. By comparison with the intensity values of a reference earthquake, magnitudes are calculated for 41 western and central United States earthquakes. Magnitudes of these earthquakes also are determined independently, in the conventional manner, using teleseismic P-wave amplitudes. Comparison of the two sets of magnitude values indicates that the assumed relation between 1-Hz, Lg-wave (A/T)z values and MM intensity does not hold exactly over the mb range of 4.0 to 6.2. An empirical equation is derived to adjust the mb values obtained from intensity data so that they agree with the teleseismic P-wave magnitudes.The method then is applied to estimate mb of some historical earthquakes which occurred prior to 1962. These include the set for which Kanamori and Jennings (1978) estimated ML from strong-motion accelerograms. Some noteworthy United States earthquakes also are considered. These include: the 1811 New Madrid earthquake for which mb is estimated to be 7.3; the 1886 Charleston, South Carolina earthquake, for which mb is estimated to be 6.6 to 6.9; the 1897 Giles County, Virginia earthquake, for which mb is estimated to be 5.8; the 1906 San Francisco, California earthquake, for which mb is estimated to be 6.8 to 7.1.The intensity-attenuation method cannot be used for estimating mb of all historical earthquakes because the intensity data are not always adequate. In some cases, however, the total felt area or the area enclosed by the Modified Mercalli IV isoseism can be determined. It was found that empirical equations relating mb to these areas, which were derived for central and northeastern United States earthquakes, also apply for events in the southeast. These empirical methods are used to estimate mb values for a set of historical Virginia earthquakes.

Seismic magnitudes of underground nuclear explosions

abstract Using an Ms computational procedure that minimizes path-propagation effects, and with Ms values found to be empirically independent of test site and detonation medium among consolidated rock explosions, available yield information is employed to illustrate that the seismic scaling of explosions in realistic detonation environments produces teleseismic Rayleigh-wave displacements proportional to the 1.2-power of yield over the range from low yields to greater than three megatons. Ms values independent of network, path, and site can be employed to estimate unknown yields at uncalibrated test sites to within average errors judged to be about 20 per cent. P-wave magnitudes, in the form of a calibrated teleseismic measure of short-period P-wave displacements, show a theoretically supported dependence of displacement on the 1.1-power of yield over the range from 6 kt to 1 mt. Studied explosions separate into two categories: the Nevada Test Site granite explosions, LONG SHOT, the Sahara February 1965 explosion and (by empirical inference) Novaya Zemlya and Eastern Kazakh explosions exhibit P-wave displacements about a factor of 3 greater than explosions of the same yield in tuff, rhyolite, and shale. P-wave magnitudes of explosions are subject to such a diversity of source, propagation, and measurement phenomena that any estimation of unknown yields without a closely controlled site and network calibration can be subject to large errors.

Mechanism of Love-Wave excitation by explosive sources

Love-wave excitation by large underground nuclear explosions at the Nevada Test Site is uniquely different from that by small explosions at shallow depths in its dependence on shot depth and its change with repeated experiments. There appears to be a magnitude threshold (or depth threshold: the two parameters are correlated) for strong excitation of Love waves from shots in a given geologic area, and the magnitude threshold for Yucca Flat has increased with time during the period 1962–1967. These results support the hypothesis that the tectonic stress release is the major cause of Love waves from the NTS explosions. Two working models of the stress release process are tested against observations. One model is the cavity model, in which pre-existing stress vanishes within a spherical zone around the shot point. The other is the trigger model, in which a fault displacement is triggered outside the immediate vicinity of the shot point. We favor the trigger model because of its better consistency with various observations. Under the assumption of the trigger model, we found that the process was characterized by a low stress drop (around 10 bars), the released energy being comparable to or smaller than the total seismic energy estimated from P-wave magnitude.

A method of correctingP-wave magnitudes for the effect of earthquake focal mechanism

abstractThis paper presents a methodology for correcting body-wave magnitudes for the effect of focal mechanism in a routine manner. The method requires a knowledge of the prevailing or dominant mechanism for a geographic region, from which tables are constructed which enable one to make the necessary correction. Included in the paper are tables for Aleutian Island, Kamchatka and mid-Atlantic Ocean earthquakes.From a study of seven earthquakes, it is concluded that the present method gives essentially the same average magnitude with the same standard deviation as a more exact method of correcting for the focal mechanism. The latter method uses the focal-mechanism parameters of the earthquake, which must be determined independently for each earthquake.The existing distribution of seismograph stations is such that transform-fault earthquakes of the mid-Atlantic Ocean will consistently have their P-wave magnitudes underestimated by about 0.2 magnitude units, if no correction is made for the focal mechanism. On the other hand, P-wave magnitudes of earthquakes in Kamchatka and south of the axis of the Aleutian Trench will be overestimated by about 0.2 units.