Comparison of Signal-Averaged Electrocardiograms with Different Levels of Noise: Time-Domain, Frequency-Domain, and Spectrotemporal Analysis

In order tn test the effect of noise on the various parameters of the SAECG, 83 patients underwent three consecutive recordings at different noise levels. The high noise (HN) recordings had a noise level of 0.60–0.74 μV. the intermediate noise (IN) had 0.31–0.59 μV, and the low noise (LN) had ≤ 0.30 μV. For the calculation of noise we used the standard deviation of the mean noise of the composite lead high pass filtered at 40 Hz. The recordings were compared using time-domain, frequency-domain, and spectrotemporal analysis. The time-domain parameters of the LN recordings, using 25-Hz, 40-Hz, and 60-Hz high pass cutoffs, were significantly different from those of the HN or IN recordings (P < 0.05). In the frequency-domain analysis, significant differences were found in some of the parameters of the LN compared to the HN. The spectrotemporal analysis of the X and Z leads also showed significant differences among the LN and the other recordings. In the time-domain analysis, both at 40 Hz and 25 Hz, there were more abnormal LN compared to the HN recordings (P < 0.05). In the spectrotemporal analysis, there were significantly more abnormal HN and IN recordings compared to the LN (P < 0.001 and P < 0.01. respectively). Therefore, the level of noise, even within the acceptable range, can significantly affect the SAECG. In the time domain at the lower noise levels the parameters become more abnormal, while the opposite seems to occur in the spectral and the spectrotemporal analysis.     

Influence of Age, Lead Axis, Frequency of Arrhythmic Episodes, and Atrial Dimensions on P Wave Triggered SAECG in Patients with Lone Paroxysmal Atrial Fibrillation

Signal-averaged P wave of 42 patients with lone paroxysmal atrial fibrillation (PAF) and 29 normal subjects (N) were recorded, using three orthogonal leads and analyzed in the time and frequency (entire P wave or a 100-ms segment ranging from 75 ms before to 25 ms after the end of P wave) domains. PAFs were divided into a group of 12 having ≥ 2 attacks a month (HF) and a group of 30 having ≤ 2 attacks a year (LF). Statistically significant differences were absent with regard to ages of PAF and N; ages of HF, LF, and N at the time of signal-averaged ECG; ages of HF and LF at the time of the first arrhythmic episode; and elapsed times from the first episode. Length of P wave and some frequency-domain parameters were found to be significantly correlated with age. PAF showed a significantly longer duration of P wave in the frontal plane using the time-domain analysis. Frequency analysis was found to be useful in evaluating the influence of attack frequency. HF showed significantly higher values of some frequency-domain parameters than LF and N, while the three groups did not differ for time-domain analysis. P wave duration and frequency content of the three orthogonal leads proved to be significantly different in PAF and N. Right and left atrial echocardiographic dimensions proved to be higher (even if within normal limits) in HF than in LF and N. Results suggest that frequency analysis should be performed on the entire P wave.     

Prediction of conversion from paroxysmal to permanent atrial fibrillation

BACKGROUND: Paroxysmal atrial fibrillation (PAF) transits to permanent atrial fibrillation (PEAF). The current study was to determine whether a P wave-triggered P wave signal averaged electrocardiogram (P-SAECG) and chemoreflexsensitivity (CHRS) are useful to predict a conversion to PEAF in patients with PAF. METHODS: The filtered P wave duration (FPD) and the root mean square voltage of the last 20 ms of the P wave (RMS 20) were measured by P-SAECG. The ratio between the difference of RR intervals in the ECG and venous pO2 before and after 5-minutes oxygen inhalation is measured (ms/mmHg) for the determination of CHRS. Results: A total of 180 patients with PAF were enrolled and followed for a mean of 22.5 months. PEAF occurred in 38 patients (21%) and these patients had a significantly larger left atrial size (43.2 +/- 4.9 vs. 41.0 +/- 5.4 mm, P = 0.021), a significantly longer FPD (158.8 +/- 18.2 vs. 136.7 +/- 16.6 ms, P < 0.0001), and a significantly lower CHRS (1.96 +/- 0.99 vs. 2.44 +/- 1.19 ms/mmHg, P = 0.024) than patients with PAF. Patients with PEAF tended to have a lower RMS 20 (2.38 +/- 0.65 vs. 2.75 +/- 1.18 microV, P = 0.067) than patients with PAF. The chi(2) test showed that the combination of FPD > or = 145 ms, RMS 20 < or = 3.0 microV, left atrial size > or = 41 mm, and CHRS < or = 2.0 ms/mmHg had the best predictive power for PEAF. Patients who fulfilled these criteria had a 12-fold increased risk for a conversion from PAF to PEAF. CONCLUSIONS: Our results show that a P-SAECG, an analysis of CHRS, and left atrial enlargement are clinical predictors of a progression from PAF to PEAF.     

Atrial Late Potentials in Patients with Paroxysmal Atrial Fibrillation Detected Using a High Gain, Signal-Averaged Esophageal Lead

High gain, signal-averaged ECGs using conventional surface lead technique and a transesophageal lead technique were performed in 45 idiopathic paroxysmal atrial fibrillation patients and in 33 normal controls. Both techniques showed increased P wave duration in patients compared with the controls (P < 0.001), but higher P wave amplitudes were obtained using the transesophageal technique compared with surface leads (patients: 169.8 ± 81.7 μV vs 15.8 ± 7.3 μV; P < 0.0005; controls: 163.5 ± 22.1 μV vs 18.5 ± 5.2 μV; P < 0.0005). The signal-averaged transesophageal lead, but not the surface recordings, identified the presence of atrial late potentials evidenced by lower root wean square voltages in the terminal portion of the P wave: in last 10 seconds, 4.4 ±1.3 μV versus 8.5 ± 3.0 μV; P < 0.001; in last 20 seconds, 7.0 ± 2.3 μV versus 16.0 ± 7.9 μV; P < 0.001; in last 30 seconds, 12.5 ± 5.3 μV versus 23.8 ± 12.8 μV; P < 0.001, in patients with respect to controls. The criterion P wave duration ≥ 110 msec had 85% sensitivity. 100% specificity, and 100% positive predictive value in identifying the patients; the combined criteria P wave duration ≥ 110 msec and root mean square for the last 10 msec ≤ 6.5 showed 80% sensitivity, 100% specificity, and 100% predictive value. The signal-averaged transesophageal lead produces a higher amplitude signal, which reveals fractionation of atrial activation in atrial fibrillation and allows identification of individuals predisposed to this arrhythmia.     

Value of Time- and Frequency-Domain Analysis of Signal-Averaged Electrocardiography for Arrhythmia Risk Prediction in Idiopathic Dilated Cardiomyopathy

Signal-averaged electrocardiography (SAECG) was performed in 120 consecutive patients with idiopathic dilated cardiomyopathy (IDC), and in 60 healthy controls. Time-domain analysis of SAECGs revealed ventricular late potentials in 27 of 120 patients with IDC (23%) compared to 2 of 60 controls (3%; P < 0.05). Frequency-domain analysis of SAECGs showed ventricular late potentials in 9 of 120 patients with IDC (8%) compared to none of the 60 controls (0%, P < 0.05). During a prospective follow-up of 15 ± 7 months, serious arrhythmic events, defined as sustained ventricular tachyarrhythmias or sudden death, occurred in 17 of 120 patients with IDC (14%). The sensitivity, specificity, and positive and negative predictive values of ventricular late potentials for serious arrhythmic events were 35%, 80%, 22%, and 88% for the time-domain analysis, and 18%, 94%, 33%, and 87% for the frequency-domain analysis of SAECG, respectively. Thus, neither the time- nor the frequency-domain analysis of SAECG appears to be useful for risk stratification in the setting of IDC in view of their low sensitivity and low positive predictive value for serious arrhythmic events during follow-up.     

Signal-Averaged P Wave in Patients with Paroxysmal Atrial Fibrillation

The theoretical and experimental rational of atrial signal-averaged ECG in patients with AF is delay in the intra-atrial and interatrial conduction. Similar to the ventricuiar signal-averaged ECG, the atrial signai-averaged ECG is an averaging of a high number of consecutive P waves that match the template created earlier. P wave triggering is preferred over QRS triggering because of more accurate aligning. However, the small amplitude of the atrial ECG and its gradual increase from the isoelectric line may create difficulties in defining the start point if P wave triggering is used. Studies using P wave triggering and those using QRS triggering demonstrate a prolonged P wave duration in patients with paroxysmal AE. The negative predictive value of this test is relatively high at 60%–80%. The positive predictive value of atrial signal-averaged ECGs in predicting the risk of AF is considerably lower than the negative predictive value. All the data accumulated prospectively on the predictive value of P wave signal-averaging was determined only in patients undergoing coronary bypass surgery or following MI; its value in other patients with paroxysmal AF is still not determined. The clinical role of frequency-domain analysis (alone or added to time-domain analysis) remains undefined. Because of this limited knowledge on the predictive value of P wave signal-averaging, it is still not clinical medicine, and further research is needed before atrial signal-averaged ECG will be part of clinical testing.     

Coronary Artery Disease Alters Ventricular Repolarization Dynamics in Type 2 Diabetes

Ventricular repolarization dynamics (VRD) is an important predictor of outcome in diabetes.We examined the potential impact of coronary artery disease (CAD) on VRD in type 2 diabetic patients. We recorded 5-minute high-resolution resting electrocardiograms in 38 diabetic patients undergoing elective coronary angiography, and in 38 age- and gender-matched apparently healthy subjects (controls). Using leads-I and -II, time-domain indices of VRD were calculated. Coronary angiography was regarded as positive if ≥ 50% stenosis was found. Angiography was positive in 21 diabetic patients (55%). Patients with CAD had a significantly higher degree of VRD than controls (SDNN(QT): 15.81 ± 7.22 ms versus 8.94 ± 6.04 ms; P < 0.001, rMSSD(QT): 21.02 ± 7.07 ms versus 11.18 ± 7.45 ms; P < 0.001). Ventricular repolarization dynamics in diabetic patients with negative angiograms did not differ from VRD in controls (SDNN(QT): 8.94 ± 6.04 ms versus 7.44 ± 5.72 ms; P = 0.67, rMSSD(QT): 11.18 ± 7.45 ms versus 10.22 ± 5.35 ms; P = 0.82). CAD increases VRD in patients with type 2 diabetes. Therefore, changes in ventricular repolarization in diabetic patients may be due to silent CAD rather than due to diabetes per se.     

A Critical Appraisal of Quantitative Spectro-Temporal Analysis of the Signal-Averaged ECG: Predicting Arrhythmic Events After Myocardial Infarction

The objective of this study was to determine if spectra-temporal analysis of the signal-averaged ECG (SAECG) predicts spontaneous sustained ventricular tachyarrhythmias and sudden death in patients prospectively followed after myocardial infarction (MI). A SAECG was recorded in 177 patients 9 ± 5 days after MI. Spectro-temporal analysis of the SAECG involved incrementing a Hanning window every 3 ms beginning 20 ms before the end of the QRS complex and extending into the ST segment. Quantitative analysis was performed using a cross-correlation function to create a normality factor. A normality factor < 0.3 was deemed abnormal. The SAECG was abnormal in 41 % of patients using time-domain analysis and 44% of patients using spectra-temporal analysis. There was no correlation between an abnormal SAECG in the time domain and the frequency domain. Patients with inferior wall MI were more likely to have an abnormal spectra-temporal map (odds ratio 2.26, P < 0.05). Time-domain analysis of the SAECG (relative risk (RE) 2.6) was a statistically significant univariate predictor of arrhythmic events. Spectra-temporal analysis of the SAECG was only weakly (RR 1.8) and not significantly (P = 0.15) associated with the spontaneous occurrence of these arrhythmias. When both time-domain analysis and spectra-temporal analysis of the SAECG were abnormal, the relative risk for an arrhythmic event was increased by 3.3-fold. Quantitative spectra-temporal analysis of high frequency signals within the SAECG cannot by itself predict the occurrence of spontaneous ventricular arrhythmias in patients after MI.     

Effects of Hydrophilic and Lipophilic β-Blockers on Heart Rate Variability and Baroreflex Sensitivity in Normal Subjects

To evaluate the effect of a hydrophilic and a lipophilic β- blocker on the autonomic nervous system, 20 normal subjects were studied under baseline conditions and 7 days after being randomly assigned to metoprolol (200 mg/day), nadolol (80 mg/day), and placebo. Under each condition, the time-domain parameters were analyzed by means of 24-hour ECG monitoring and the frequency-domain parameters by means of the autoregressive method using 10-minute ECGs during rest, controlled respiration, and after a head-up tilt test. The alpha index (the gain in the relationship between the RR period and systolic arterial pressure variability) was also calculated. Both nadolol and metoprolol significantly increased all of the time-domain parameters except the standard deviation of the RR intervals; they also modified the frequency-domain parameters. Both blunted the significant reduction in the high frequency (HF) component and alpha index during tilt. In normal subjects, hydrophilic and lipophilic β-blockers similarly modify the time- and frequency-domain parameters that are particularly evident when high sympathetic tone is present (during daytime and tilt). The value of the alpha index was increased by both β-blockers in the HF, but not in the low frequency band; this difference might be due to the fact that the former is a measure of the vagal component of the baroreflex control and the latter a measure of the sympathethic component. The effects of hydrophilic and lipophilic β-blockers on the time- and frequency-domain parameters of heart rate variability are similar.     

Magnetocardiographic Intra-QRS Fragmentation Analysis in the Identification of Patients with Sustained Ventricular Tachycardia after Myocardial Infarction

KORHONEN, P., et al. : Magnetocardiographic Intra-QRS Fragmentation Analysis in the Identification of Patients with Sustained Ventricular Tachycardia after Myocardial Infarction. The aim of this study was to investigate if magnetocardiographic (MCG) analysis of cardiac micropotentials within the QRS complex can identity patients prone to ventricular arrhythmias, and to compare it to MCG time-domain, late-field analysis. The study population consisted of 136 patients with remote MI, 53 with and 83 without a history of VT. After averaging and high pass filtering of multichannel MCG signals, time-domain parameters describing the end-QRS activity and fragmentation index M and score S describing the whole QRS complex were computed. Fragmentation and time-domain parameters differed between the VT and control groups: fragmentation index M was  12 ± 3  versus  9 ± 2  (  P < 0.001  ), fragmentation score S was  83 ± 42  versus  56 ± 21  (  P < 0.001  ), and filtered QRS duration was  144 ± 32  versus  114 ± 19 ms  (  P < 0.001  ) in VT and control groups, respectively. A combination of fragmentation parameters yielded 87% sensitivity and 61% specificity in VT identification. Corresponding figures for a time-domain parameter combination were 81% and 72%. Sensitivity of time-domain analysis was 88% and specificity was 75% in a subgroup with anterior MI. In multivariate analysis, fragmentation and time-domain analyses discriminated VT patients from controls independently of the extent of coronary artery disease or left ventricular dysfunction. MCG in postinfarction patients reveals pathology associated with propensity to ventricular arrhythmias inside and not only at the end of the QRS complex. MCG seems most accurate in the anterior infarct location.     

Cardiac interbeat interval increment for the identification of obstructive sleep apnea

The prevalence of obstructive sleep apnea syndrome (OSAS) is high in developed countries but its diagnosis is costly. Based on physiological evidence, the frequency component of heart rate variability (HRV) was evaluated as a simple and inexpensive diagnostic tool in OSAS. The predictive accuracy of frequency-domain HRV variables obtained from 24-hour ECG Holter monitoring (the power spectral density of the interbeat interval increment of very low frequencies, "VLFIpsd," and its percentage over the total power spectral density, "% VLFI"), and of established time-domain HRV variables were analyzed by comparison with respiratory disturbances indexes assessed by complete polysomnography in 124 consecutive patients (98 men aged 53.8 +/- 11.2 years) with clinically suspected OSAS. OSAS was present in 54 (43.5%) patients according to standard criteria. Using receiver operating characteristic curve analysis, two of the three most powerful predictors were frequency-domain variables: % VLFI (W = 0.80, P < 0.0001), and VL-FIpsd (W = 0.79, P < 0.0001). Using a multiple logistic regression analysis, %VLFI was the most strongly associated with diseased status (adjusted OR: 8.4; 95% CI: 3.4-19.5). Using an appropriate threshold, %VLFI demonstrated a diagnostic sensitivity of 87%. A 3-month continuous positive airway pressure treatment significantly improved the same parameter. Frequency-domain analysis of the interbeat interval increment appears as a powerful tool for OSAS diagnosis and follow-up. The simplicity of its analysis and of its use makes of it a well-suited variable for mass screening of OSAS patients.     

Threshold-based system for noise detection in multilead ECG recordings

This paper presents a system for detection of the most common noise types seen on the electrocardiogram (ECG) in order to evaluate whether an episode from 12-lead ECG is reliable for diagnosis. It implements criteria for estimation of the noise corruption level in specific frequency bands, aiming to identify the main sources of ECG quality disruption, such as missing signal or limited dynamics of the QRS components above 4?Hz; presence of high amplitude and steep artifacts seen above 1?Hz; baseline drift estimated at frequencies below 1?Hz; power-line interference in a band ±2?Hz around its central frequency; high-frequency and electromyographic noises above 20?Hz. All noise tests are designed to process the ECG series in the time domain, including 13 adjustable thresholds for amplitude and slope criteria which are evaluated in adjustable time intervals, as well as number of leads. The system allows flexible extension toward application-specific requirements for the noise levels in acceptable quality ECGs. Training of different thresholds' settings to determine different positive noise detection rates is performed with the annotated set of 1000?ECGs from the PhysioNet database created for the Computing in Cardiology Challenge 2011. Two implementations are highlighted on the receiver operating characteristic (area 0.968) to fit to different applications. The implementation with high sensitivity (Se = 98.7%, Sp = 80.9%) appears as a reliable alarm when there are any incidental problems with the ECG acquisition, while the implementation with high specificity (Sp = 97.8%, Se = 81.8%) is less susceptible to transient problems but rather validates noisy ECGs with acceptable quality during a small portion of the recording.     

Impaired cardiovagal and vasomotor responses to baroreceptor stimulation in type II diabetes mellitus

BACKGROUND: In diabetic patients, impairment of the cardiovagal limb of the baroreflex has been well established. However, the role of sympathetic mediated baroreflex vasomotor control of the blood vessels is not well defined. We therefore assessed the vasomotor responses to sinusoidal baroreceptor stimulation in diabetic patients. MATERIALS AND METHODS: We studied 14 type II diabetic patients (age; 57 +/- 7 years) and 18 healthy controls (age; 59 +/- 11 years). Oscillatory neck suction was applied at 0.1 Hz to assess the sympathetic modulation of the heart and blood vessels, and at 0.2 Hz to assess the effect of parasympathetic stimulation on the heart. Breathing was paced at 0.25 Hz. Spectral analysis was used to evaluate the oscillatory responses of RR-interval and blood pressure. RESULTS: The diabetic patients showed a significantly lower RR-interval response (P < 0.05) to the 0.1 Hz neck suction (2.52 +/- 0.50-3.62 +/- 0.54 ln ms2) than the controls (4.23 +/- 0.31-6.74 +/- 0.36 ln ms2). The increase in power of 0.1 Hz systolic blood pressure oscillations during 0.1 Hz suction was also significantly smaller (P < 0.05) in the diabetics (1.17 +/- 0.44-1.69 +/- 0.44 mmHg2) than in the controls (1.60 +/- 0.29 mmHg2-5.87 +/- 1.25 mmHg2). The magnitude of the peak of the 0.2 Hz oscillation in the RR-interval in response to 0.2 Hz neck stimulation was significantly greater (P < 0.05) in the controls (3.42 +/- 0.46 ln ms2) than in the diabetics (1.58 +/- 0.44 ln ms2). CONCLUSION: In addition to cardiovagal dysfunction, baroreflex-mediated sympathetic modulation of the blood vessels is impaired in type II diabetic patients.     

Heart rate variability in diabetes patients

Diabetes mellitus can cause cardiovascular autonomic neuropathy and is associated with increased cardiovascular deaths. We investigated cardiovascular autonomic neuropathy in diabetics and healthy controls by analysis of heart rate variability. Thirty-one diabetics and 30 age- and sex-matched controls were included. In the time domain we measured the mean R - R interval (NN), the standard deviation of the R - R interval index (SDNN), the standard deviation of the 5-min R - R interval mean (SDANN), the root mean square of successive R - R interval differences (RMSSD) and the percentage of beats with a consecutive R - R interval difference > 50 ms (pNN50). In the frequency domain we measured high-frequency power (HF), low-frequency power (LF) and the LF/HF ratio. Diabetes patients had lower values for time-domain and frequency-domain parameters than controls. Most heart rate variability parameters were lower in diabetes patients with chronic complications than in those without chronic complications.     

Frequency Analysis of the P Wave: Comparative Techniques

Frequency domain analysis of the signal-averaged P wave (SAPW) may provide additional information over time domain analysis in patients with paroxysmal atrial fibrillation (PAF), but an optimum method has not yet been defined. We compared two different approaches using SAPW and test signals. We analyzed the frequency spectrum of the entire P wave (method A) or of only its terminal 100 msec (method B) using SAPW from 24 patients with idiopathic PAF and 34 normal controls. Absolute powers in frequency bands above 20, 30, 40, 60, and 80Hz (P20, P30, P40, P60, and P80) and power ratios about these frequencies (PR20, PR30, PR40, PR60, and PR80) were calculated. Patients had greater P30, P60, and P80 using method A (P30: 28.6 [± 2.2] vs 22.8 [± 1.6] μV².s; P = 0.04; P60: 4.7 [± 0.5] vs 3.4 [± 0.3] μV².s; P = 0.03; P80:1.9 [± 0.2] vs 1.3 [± 0.09] μV².s; P = 0.01) but differences were smaller with method B. Moving the P wave endpoint 10 msec into the P wave had no effect on frequency domain parameters using method A but produced important changes using method B. Both methods were also applied to test signals of different durations but equal powers and power ratios. Method A gave predicted values for power and PR40 at all signal durations, but method B produced variable results. Frequency domain analysis of the SAPW shows significant increases in P wave energy in patients with PAF compared to controls. Analysis of the entire P wave is influenced less by signal duration and variations of the P wave endpoint than analysis of the terminal P wave alone and may define patient and control populations more precisely.     

Impact of Filtering Upon Ventricular Tachycardia Identification by Correlation Waveform Analysis

Signal analysis of digitized waveforms has been postulated as a method for improving sensitivity and specificity of ventricular tachycardia (VTJ detection in implantable antitachycardia devices. Such improvement may alleviate the problem of unwarranted delivery of therapy by adding precision to the identification of the pathological VT. Morphological analysis could also allow distinct therapies to be initialized for multiple VTs in the same patient. Correlation waveform analysis (CWA) has been demon-struted to be effective in separating benign rhythms from VT in wideband recordings (1–500 Hz) but the effect of filtering has not been previously examined. Bipolar (1 cm) intraventricular recordings (1–500 Hz) of sinus rhythm (SR) and 25 distinct VTs in 18 patients were analyzed by CWA using a signal-averaged SR template. Passages contained 65.9 ± 19.8 VT depolarizations (range 45–108). Digital filtering was performed on all data passages with varying passbands. Results for passages with a bandwidth of 1–250 Hz were equivalent to wideband results, i.e., ≥92% paired sets of SR and VT were separable at a 95% confidence level. A bandwidth of 1–100 Hz decreased discrimination to 84%. At a bandwidth of 1–80 Hz, 80% of cases were successfully separated, but at 10–80 Hz these results improved to 88%. Bandwidths of 20–80 and 30–80 Hz reduced reliability of CWA performance to 72% and 60%, respectively. Filtering at typical pace-maker/defibrillator passbands produced morphological analysis results equivalent to those yielded at wideband settings. Differences in the range between SR versus VT decreased in filtered recordings but overall detection of VT was not degraded.     

Spectrotemporal Mapping of High-Resolution ECGs in Experimental Myocardial Infarction: Comparison with Time-Domain Analysis and Epicardial Electrograms

The study was undertaken to evaluate the relationship of signal-averaged ECG (SA-ECG) readings in the frequency domain (STM) and epicardial electrograms (EE) recorded before and after acute myocardial infarction (AMI) in pigs and to compare the changes with findings in time-domain analysis (TDA). In 20 pigs the left anterior descending artery (LAD) was ligated. Prior to ligation, a SA-ECG was recorded (method of Simson) and bipolar electrodes were used to register EE in the areas supplied by the LAD and the circumflex artery (CIRC). Five minutes after LAD ligation, all measurements were repeated. Time-domain parameters were QRS duration (QRS D) and the duration of the signal below 30 microV (LAS 30). Beginning at a point of 20 ms before the QRS end, the frequency spectra (0-200 Hz) of 25 segments of 80-ms duration at the QRS end were analyzed. The volumes below the 25 curves were analyzed separately for 0-50 Hz, 51-100 Hz, 101-150 Hz, and 151-200 Hz. After AMI, five pigs died within 7 minutes. In 15 pigs, QRS D as well as LAS 30 lengthened significantly (P<0.05; P<0.001). Spectrotemporal mapping (STM) showed a significant decrease of the frequencies above 50 Hz (51-200 Hz) in the entire group and in the animals with late potentials (P<0.05). EE of the LAD area were significantly prolonged (P<0.01); this did not correlate with the changes in STM parameters. In pigs acute myocardial infarction causes a shift towards lower frequencies in the STM which most likely reflects the slowed depolarisation in the ischemic area.     

Predictors of Syncope in Patients with Hypertrophic Cardiomyopathy

Background: Approximately 30% of patients with hypertrophic cardiomyopathy (HCM) suffer syncope and syncope was the only symptom associated with sudden death. However, no systematic studies in large cohorts looking at predictors of syncope are available in the literature. Therefore, we sought to determine predictors of syncope in patients with HCM.
Methods: One hundred and seventy-three consecutive patients with HCM and a mean age of 42 ± 18 years (range 10–78) underwent extensive clinical, electrocardiographic, and echocardiographic testing to identify predictors of syncope.
Results: During the mean follow-up duration of 50 months, syncope occurred in 28% of the HCM patients. Univariate analysis showed male gender, age <40 years, family history of sudden death, PR interval, QRS width, ≥2 bursts of nonsustained ventricular tachycardia (NSVT), ≥3 bursts of nonsustained supraventricular tachycardia (NSSVT), maximum left ventricular wall thickness ≥30 mm, and abnormal blood pressure response, out of 24 demographic, clinical, hemodynamic, electrocardiographic, and echocardiographic features, to be significantly associated with syncope. Of these nine variables, the only independent predictors of syncope at multivariate analysis were age <40 years (odds ratio [OR]: 4.4, 95% confidence interval [CI]: 2.2–16, P = 0.003), ≥2 bursts of NSVT (OR: 9.9, 95% CI: 2.0–46, P = 0.0001), and ≥3 bursts of NSSVT (OR: 2.7, 95% CI: 0.38–8.25, P = 0.001). The concomitant occurrence of all three variables had a sensitivity of 87% and specificity of 73% in identifying the patients with syncopal events.
Conclusions: The results of this study showed that age <40 years, bursts of NSVT, and NSSVT were independently associated with the risk of syncope in patients with HCM. Demographic data and ambulatory ECG findings could help in risk stratification of patients with HCM.     

Time- Versus Frequency-Domain Analysis in Predicting Cycle Length of Inducible Ventricular Tachycardia After Myocardial Infarction

To determine whether time- and frequency-domain analyses differ in their ability to predict sustained ventricular tachycardia (VT) induced by programmed ventricular stimulation, 60 consecutive patients with myocardial infarction and 30 healthy control subjects were evaluated. Programmed ventricular stimulation using three extrastimuli and signal-averaged ECG recordings were performed in patients with myocardial infarction. Of the 60 patients, sustained monomorphic VT (SMVT) with cycle length (CL) ± 250 ms (slow SMVT) was inducible in 9, and SMVT with CL < 250 ms (fast SMVT) was inducible in 9. The durations of the filtered QRS (f-QRS) at each high-pass filter (25, 40, and 80 Hz) and the low amplitude signal (LAS) at 25-Hz high-pass filtering were significantly longer in the slow SMVT group than in the fast SMVT, no VT, or normal control group. The root-mean- square voltages at 25-Hz and 8Q-Hz high-pass filters in the slow SMVT group were significantly lower than in the fast SMVT, no VT, or normal control group. There was no significant difference in time- domain variables among fast SMVT, no VT, and normal control groups. The CL of the induced sustained VT was significantly correlated with the durations of f-QRS and LAS, Concerning frequency-domain variables (area ratio and factor of normality), there was no significant difference between slow and fast SMVT groups. Both the slow and fast SMVT groups had a significantly higher area ratio and a significantly lower factor of normality than the group with no VT or the normal control subjects. In conclusion, there were significant correlations between time-domain variables and CL of SMVT, while there was no correlation when using frequency-domain parameters.     

Long-latency auditory event related potentials in migraine

The pathophysiology of migraine and its associated perceptual symptoms remains controversial. We recorded long-latency auditory event related potentials (AEPs) in 30 unmedicated patients with common migraine, and compared them to 20 controls. 1,000 and 3,000 Hz tones were presented in an 80:20 ratio at 75 dB SL. 200 responses were recorded and replicated from Cz-A1 + A2, with filter band-pass of 1-100 Hz, analysis time of 1,000 ms., and interstimulus interval of 1.1 second. N100, P200, and N200 ERP components did not differ in latency or amplitude between migraine patients and controls. P300 was longer in latency among those with common migraine, and P300 amplitude was significantly reduced (P greater than 0.05). These findings suggest that migraine may have a central mechanism, and that migraineurs may have a difference in task involvement or perception which may influence their clinical course and response to therapy.