Standards for analysis of ventricular late potentials using high-resolution or signal-averaged electrocardiography: a statement by a task force committee of the European Society of Cardiology, the American Heart Association, and the American College of Cardiology

Usefulness of post-ventriculotomy signal averaged electrocardiograms in congenital heart disease

Signal-averaged electrocardiography is a sensitive and specific technique for detecting the slow conduction electrophysiologic substrates of reentrant monomorphic ventricular tachycardia. Although well established, the method has not been used for electrophysiologic assessment after right ventriculotomy for the intracardiac repair of congenital heart disease. This 8-year prospective study provided this assessment. Recordings were obtained from 242 post-ventriculotomy patients with congenital heart disease aged 16 to 72 years (139 males, 103 females). Because ventricular volume or pressure overload can prolong the QRS duration, 40 unoperated patients with hemodynamic overload served as controls. Orthogonal X, Y, and Z body surface electrodes were used to detect ventricular late potentials by permitting the examination of portions of the electrocardiogram otherwise obscured by noise and artifacts. Positive signal-averaged electrocardiographic (SAECG) results were based on established criteria derived from 3 time-domain variables calculated by an automated algorithm. Late potentials were detected in 151 of 242 patients (62%) and were significantly higher than controls (p = 0.0001). Radiofrequency ablation of an inducible slow conduction substrate rendered 20 of 23 positive post-ventriculotomy SAECG results negative, and surgical revision of the ventriculotomy scar rendered 19 of 19 positive SAECG results negative. In conclusion, negative SAECG results connote the absence of a reentrant substrate, and therefore, the absence of risk for reentrant monomorphic ventricular tachycardia, whereas positive SAECG results connote the presence of a slow conduction substrate and the potential risk for monomorphic ventricular tachycardia.

Portable-type signal-averaged electrocardiography with dipyridamole to detect patients with coronary artery disease

BACKGROUND

In a retrospective study portable-type signal-averaged electrocardiography (SAECG) with dipyridamole stress was found to identify patients with coronary artery disease (CAD) at their bedside with high sensitivity and specificity, so the utility of this method was prospectively investigated in the present study.

METHODS AND RESULTS

Standard 12-lead QRS wave SAECG was performed before and after dipyridamole stress at the bedside in 71 patients with chest pain (43 males, mean age 63 +/-9 years). The filtered QRS duration (fQRSd) before and after dipyridamole stress was determined by multiphasic oscillation method for each of the standard 12 leads, and the maximal value of changes in fQRSd (MAX DeltafQRSd) among the 12 leads was determined. The positive test was defined as MAX DeltafQRSd >or=5 ms, and negative as MAX DeltafQRSd <5 ms based on the previous study. Selective coronary arteriography was performed next. In the positive group (n=31), 25 patients had significant stenosis of the coronary artery and 6 did not. In the negative group (n=40), 5 patients had significant stenosis and 35 did not. The sensitivity, specificity, positive predictive accuracy and negative predictive accuracy for CAD detection by SAECG was 83%, 85%, 81% and 88%, respectively.

CONCLUSIONS

Dipyridamole-stress portable SAECG is useful for detecting CAD at the patient's bedside with high sensitivity and specificity.

Risk factors of ventricular tachyarrhythmias after coronary artery bypass grafting

BACKGROUND

Ventricular arrhythmias are rare and represent the most serious arrhythmic complication after coronary artery bypass grafting (CABG).

METHODS

The present retrospective study was conducted for identifying patients at risk of ventricular arrhythmias with ventricular signal averaged ECG, standard deviation of all normal RR intervals (SDNN), angiographic and echocardiographic data. We defined ventricular arrhythmias as sustained ventricular fibrillation and ventricular tachycardia. The study population consisted of 209 consecutive patients with sinus rhythm undergoing CABG. The primary endpoint was the occurrence of VA after CABG. The secondary endpoints were hospital length of stay after CABG and the occurrence of VA after hospital discharge.

RESULTS

During the postoperative follow-up ventricular arrhythmias were observed in 11 patients (5%). Patients with ventricular arrhythmias showed a higher incidence of ventricular late potentials (91 vs. 9% of patients, p<0.0001) than patients without ventricular arrhythmias. In addition patients with ventricular arrhythmias had a lower left ventricular ejection fraction (44.2+/-15.2 vs. 60.1+/-13.1%, p<0.0001) and a SDNN (22.4+/-8.8 vs. 34.4+/-16.1 ms, p<0.02). A stepwise logistic regression analysis of all variables identified the combination of ventricular late potentials, ejection fraction < or = 38% and SDNN < or = 28 ms (odds rate 26.00; 95% CI, 3.44-196.67, p<0.002) as an independent predictor of ventricular arrhythmias.

CONCLUSIONS

The results of our study suggest that the probability of ventricular arrhythmias could be predicted after CABG by a combination of low left ventricular ejection fraction and a measurement of ventricular signal averaged ECG and standard deviation of all normal RR intervals. Patients who can be identified as having a high risk of ventricular arrhythmias should be observed carefully after surgery.

Late potentials and ventricular arrhythmias in acromegaly

BACKGROUND

Sudden death and increased prevalence of ventricular arrhythmias have already been described in acromegaly. Although late potentials (LPs) have been proved to be a new technique in detecting patients at risk for ventricular tachyarrhythmias its use in acromegaly is still unknown.

METHODS

We studied 70 acromegalic patients [32 males, 38 females; age 49+/-12 years (mean+/-S.D.)] and 70 control subjects age- and sex-matched [(35 males and 35 females; 46+/-12 years (mean+/-S.D.)]. Besides hormonal tests, we performed the following cardiovascular investigations: ECG, 24-h ECG Holter monitoring, echocardiography, and signal-averaged ECG (SAECG) time-domain analysis.

RESULTS

LPs occurrence was significantly higher in acromegalic patients as compared to the control group (22.9% vs. 2.9%; p=0.001). A greater duration of disease in patients with positive LPs compared to negative ones was pointed out (18 vs. 12 years; p=0.024). In the group of acromegalic patients with positive LPs we observed a significant association with premature ventricular complexes (PVCs) detected by means of 24-h Holter ECG recording (13 out of 15 patients: 86.7%; p=0.024). The positivity or negativity of LPs proved to be significantly associated with Lown scale PVC trends recorded by 24-h Holter ECG (p=0.014). In the group of patients with left ventricular hypertrophy a significant and pathological worsening of SAECG signals (QRS, LAS, RMS) was documented.

CONCLUSIONS

We observed a higher prevalence of LPs in acromegaly which significantly correlated with Lown scale of PVCs.

Standard Electrocardiographic and Signal-Averaged Electrocardiographic Changes in Congestive Heart Failure

A 54-year-old man with congestive heart failure and peripheral edema was monitored during treatment with serial electrocardiograms (ECGs) and two signal-averaged ECGs. Weights and a host of ECG parameters were monitored. ECGs recorded in the 5 years before his index admission were also considered in the quantitative ECG analysis. Amelioration of his peripheral edema was associated with reduction of his weight and increase in the QRS and P-wave amplitudes, and duration in QRS complexes and QT intervals in the ECGs, but unchanged signal-averaged ECGs. This case report provides insight into the mechanism of the change in QRS duration in ECGs during changing edematous states resulting from clinical deterioration or improved compensation in patients with congestive heart failure.

Subclinical cardiac involvement in patients with facioscapulohumeral muscular dystrophy

Myocardial involvement is a common finding in certain myopathies, while it has not been extensively investigated in facioscapulohumeral muscular dystrophy (FSHD1A). Aim of this study was to assess in FSHD1A patients the electrical and functional properties of the myocardium. Twenty-four patients with FSHD1A (mean age 41.2+/-14.5 years) and 24 matched healthy subjects were studied. Standard- and signal-averaged electrocardiography were recorded to determine QT dispersion and the presence of ventricular late potentials (VLPs). Standard echocardiography with systo-diastolic variations of integrated backscatter signal (CV-IBS) were performed to assess functional properties of the myocardium. Compared with control subjects, patients with FSHD1A had significantly lower CV-IBS and higher QT dispersion. Nine patients had positive VLPs. QT and QTc dispersion were inversely related to CV-IBS at both septum and posterior wall levels. Moreover, septal CV-IBS was inversely related to the Kpnl-BinI4q fragment size. These results suggest a subclinical cardiac involvement in FSHD1A patients, which can represent a substrate for ventricular arrhythmias and heart failure.

Portable type signal-averaged electrocardiography with dipyridamole: a new and convenient method to detect patients with coronary artery disease and ischemia

BACKGROUND

Whether or not patients with coronary artery disease (CAD) could be easily detected at the bedside using dipyridamole stress was investigated using a portable type signal-averaged electrocardiography (portable SAECG).

METHODS AND RESULTS

The standard 12-lead QRS wave SAECG was performed at the bedside before and after dipyridamole stress in 30 patients with angiographically significant stenotic lesions, who had positive myocardial ischemia in the dipyridamole-thallium myocardial perfusion imaging (CAD group), and 33 patients with no significant stenotic lesions, who had negative imaging (control group). The filtered QRS duration (fQRSd) before and after dipyridamole stress was determined by the vector magnitude method and the difference (DeltafQRSd) was obtained. Furthermore, the DeltafQRSd was obtained using the multiphasic oscillation method, as well at the same standard 12-lead, and the maximal value of changes in fQRSd (MAX DeltafQRSd) between the 12 leads was determined. The DeltafQRSd was similar between 2 groups (p = 0.11). The MAX DeltafQRSd associated was significantly greater in the CAD group (p < 0.0001). When a cut-off value of MAX DeltafQRSd > or = 5 ms was used for the detection of CAD, the sensitivity and specificity were 97 and 94%, respectively.

CONCLUSION

The portable dipyridamole-stress SAECG easily detect CAD and myocardial ischemia at the bedside.

Automatic optimum order selection of parametric modelling for the evaluation of abnormal intra-QRS signals in signal-averaged electrocardiograms

Abnormal intra-QRS potentials (AIOPs) in signal-averaged electrocardiograms have been proposed as a risk evaluation index for ventricular arrhythmias. The purpose of the paper was to develop an automatic algorithm for selecting the optimum parametric model order in the analysis of AIOPs to make the modelling approach clinically more feasible. A total of 130 normal Taiwanese subjects and 87 patients with ventricular premature contractions and 23 with sustained ventricular tachycardia were recruited. The unpredictable AIQP signal was estimated from the modelling residual. The cross-correlation coefficient between the original signal and the ORS estimate was employed to evaluate the accuracy of the estimate. A pre-selected threshold cross-correlation coefficient of 0.9999 was used to determine the optimum order. The mean AIQP in lead Y for ventricular tachycardia patients was 3.9 microV, which was significantly smaller than 4.9 microV for ventricular premature contraction patients (p < 0.01) and 6.3 microV for normal subjects (p < 0.001). The linear combination of AIQP in lead Y and the time-domain parameter RMS40 provided the best global performance (the area under the receiver operating characteristic curve was 89.1%). A higher risk of ventricular arrhythmias was associated with lower AIQP in lead Y, and the automatic modelling algorithm improved the clinical feasibility of AIQP analysis.

A theoretical model of the high-frequency arrhythmogenic depolarization signal following myocardial infarction

Theoretical body-surface potentials were computed from single, branching and tortuous strands of Luo-Rudy dynamic model cells, representing different areas of an infarct scar. When action potential (AP) propagation either in longitudinal or transverse direction was slow (3-12 cm/s), the depolarization signals contained high-frequency (100-300 Hz) oscillations. The frequencies were related to macroscopic propagation velocity and strand architecture by simple formulas. Next, we extended a mathematical model of the QRS-complex presented in our earlier work to simulate unstable activation wavefront. It combines signals from different strands with small timing fluctuations relative to a large repetitive QRS-like waveform and can account for dynamic changes of real arrhythmogenic micropotentials. Variance spectrum of wavelet coefficients calculated from the composite QRS-complex contained the high frequencies of the individual abnormal signals. We conclude that slow AP propagation through fibrotic regions after myocardial infarction is a source of high-frequency arrhythmogenic components that increase beat-to-beat variability of the QRS, and wavelet variance parameters can be used for ventricular tachycardia risk assessment.

Increased variability of the coupling interval of premature ventricular beats may help to identify high-risk patients with coronary artery disease

OBJECTIVE

The purpose of this study was to determine the characteristics and predictive value of the variability of coupling interval of ventricular premature beats (VPBs) for cardiac mortality in patients with coronary artery disease (CAD).

BACKGROUND

Frequent VPBs have been linked to an increased risk for cardiac death in patients with coronary artery disease. It is unknown whether analysis of coupling interval of VPBs from ambulatory ECG recordings can be used for risk statification in these patients.

METHODS

In 78 consecutive symptomatic patients with documented CAD who presented with frequent VPBs (>720/24 h), the analysis of VPBs' coupling interval (SDNV) was performed. Left ventricular function, ventricular arrhythmias and simple measures of heart rate variability were assessed. Mean follow-up was 702+/-329 days. Cardiac mortality was the primary end-point of the study.

RESULTS

During follow-up, 14 patients died-11 deaths were cardiac. Left ventricular ejection fraction (LVEF)<40%; no beta-blocker treatment and digoxin use were clinical variables showing a significant association with cardiac mortality. The presence of non-sustained ventricular tachycardia (nsVT), especially if more than five episodes were present; short mean sinus cycle (<750 ms) and SDNV were associated with cardiac deaths. Mean SDNV was 79+/-29 in victims and 63+/-29 in survivors (p<0.05). Univariate Cox regression analysis revealed that the presence of SDNV>80 ms carried a relative risk of 6.7 for cardiac mortality. The adjusted relative risk was 13.3 for nsVT and 4.4 for SDNV>80 ms. Among patients with nsVT, mortality rate was significantly higher with SDNV>80 ms (58%), compared to lower SDNV (14%, p<0.01). Sixty-four percent mortality rate was observed in patients with LVEF<40%, presence of nsVT and SDNV>80 ms, compared to 17% in similar patients with lower SDNV (p<0.05).

CONCLUSION

The analysis of coupling interval of ventricular premature beats form the same 24-h ECG recordings may complement the standard Holter analysis for risk stratification. This seems especially promising in the subgroups of patients at highest risk-those with LV systolic dysfunction, non-sustained VT or both.

Prolongation of the corrected QT interval in adult patients with anti-Ro/SSA-positive connective tissue diseases

OBJECTIVE

Newborns of mothers positive for anti-Ro/SSA autoantibodies may develop a series of electrocardiographic (EKG) disturbances. Prolongation of the corrected QT (QTc) interval was recently reported in a significant proportion of children with maternally acquired anti-Ro/SSA antibodies, with a concomitant disappearance of EKG abnormalities and acquired maternal autoantibodies during the first year, suggesting a direct, reversible electrophysiologic effect of anti-Ro/SSA antibodies on the ventricular repolarization. On this basis, we investigated whether these antibodies may also affect cardiac repolarization in anti-Ro/SSA-positive adult patients with connective tissue diseases.

METHODS

Fifty-seven patients with connective tissue diseases were selected: 31 had anti-Ro/SSA antibodies and 26 did not (controls). In all subjects, we analyzed the QTc interval, heart rate variability, and signal-averaged high-resolution EKG recording.

RESULTS

Anti-Ro/SSA-positive patients showed a significant prolongation of the mean QTc interval compared with the controls (mean +/- SD 445 +/- 21 versus 419 +/- 17 msec; P = 0.000005). Eighteen of the 31 anti-Ro/SSA-positive patients (58%) and none of the 26 anti-Ro/SSA-negative patients had QTc values above the upper limit of normal (440 msec). Both groups had a reduction in heart rate variability, with a prevalence for the sympathetic nervous system and a high incidence of ventricular late potentials; these values were not significantly different between the 2 groups.

CONCLUSION

Adult patients with anti-Ro/SSA-positive connective tissue diseases showed a high prevalence of QTc interval prolongation. This feature, with the concomitant abnormalities in the autonomic tone and ventricular late excitability observed in all patients studied, suggests that anti-Ro/SSA-positive patients may have a particularly high risk of developing life-threatening arrhythmias.

Prediction of sudden cardiac death after myocardial infarction in the beta-blocking era

OBJECTIVES

This study assessed the predictive power of arrhythmia risk markers after an acute myocardial infarction (AMI).

BACKGROUND

Several risk variables have been suggested to predict the occurrence of sudden cardiac death (SCD), but the utility of these variables has not been well established among patients using medical therapy according to contemporary guidelines.

METHODS

A consecutive series of 700 patients with AMI was studied. The end points were total mortality, SCD, and nonsudden cardiac death (non-SCD). Nonsustained ventricular tachycardia (nsVT), ejection fraction (EF), heart rate variability, baroreflex sensitivity, signal-averaged electrocardiogram (SAECG), QT dispersion, and QRS duration were analyzed (n = 675). Beta-blocking therapy was used by 97% of the patients at discharge and by 95% at one and two years after AMI.

RESULTS

During a mean (+/-SD) follow-up of 43 +/- 15 months, 37 non-SCDs (5.5%) and 22 SCDs (3.2%) occurred. All arrhythmia risk variables differed between the survivors and those with non-SCD (e.g., the standard deviation of N-N intervals was 98 +/- 32 vs. 74 +/- 21 ms [p < 0.001] and the QRS duration was 103 +/- 22 vs.89 +/- 16 ms [p < 0.001]). Sudden cardiac death was weakly predicted only by reduced EF (<0.40; p < 0.05), nsVT (p < 0.05), and abnormal SAECG (p < 0.05), but not by autonomic markers or standard ECG variables. The positive predictive accuracy of EF, nsVT, and abnormal SAECG as predictors of SCD was relatively low (8%, 12%, and 13%, respectively).

CONCLUSIONS

The common arrhythmia risk variables, particularly the autonomic and standard ECG markers, have limited predictive power in identifying patients at risk of SCD after AMI in the beta-blocking era.

Late potentials in female triathletes before and after prolonged strenuous exercise

The objectives of this study were to evaluate the prevalence of late potentials (LP) in female triathletes before and after prolonged strenuous exercise (PSE), and to determine whether LP are related to greater left ventricular (LV) dimensions and/or mass. Thirteen female triathletes were examined immediately before (Pre), one hour after (Post), and 24 to 48 hours after PSE (Recovery) using signal-averaged electrocardiography (SAECG). Late potentials were evaluated by two or more standard SAECG anomalies. Left ventricular dimensions and mass were measured Pre using two-dimensional echocardiography. Results revealed that no significant differences existed between Pre, Post, and Recovery in the SAECG parameters. Four athletes displayed LP during Pre. The incidence of LP during did not increase Post. There were no significant relationships between LV dimensions or mass and SAECG parameters. In conclusion, a small portion of female triathletes display LP before and after PSE, which are not worsened by PSE nor related to increased LV dimensions and/or mass.

Prevalence of potential noninvasive arrhythmia risk predictors in healthy, middle-aged persons

BACKGROUND

To date, prevalence and clinical significance of noninvasive arrhythmia risk predictors in apparently healthy, middle-aged persons are largely unknown.

METHODS

A total of 110 apparently healthy persons 20-75 years old were enrolled in this prospective observational monocenter study and followed up for 32 +/- 15 months. Baseline investigations included symptom-limited bicycle ergometry, echocardiography, time-domain analysis, and spectral turbulence analysis of the signal-averaged electrocardiogram (ECG), ventricular arrhythmias, and heart rate variability on 24-hour Holter ECG, baroreflex sensitivity, and t-wave alternans in all persons.

RESULTS

The prevalence of an abnormal signal-averaged ECG was 1% for spectral turbulence analysis and varied between 1% and 37% for time-domain analysis depending upon the definition used for an abnormal time-domain analysis. A reduced heart rate variability defined as a standard deviation of normal-to-normal intervals < or =105 ms, <100 ms and <70 ms was found in 12%, 9%, and 1% of persons. A baroreflex sensitivity <6 ms/mmHg and <3 ms/mmHg was present in 15% and 2% of persons. Microvolt t-wave alternans was found to be positive in 5%, negative in 88%, and indeterminate in 7% of persons, respectively. During the 32 +/- 15 months follow-up, no arrhythmic events and no cardiovascular mortality were observed in this population.

CONCLUSIONS

Abnormal findings of noninvasive arrhythmia risk stratification can be found in 1-37% of healthy, middle-aged persons when previously reported cut-off values are used.

Combination of QT variability and signal-averaged electrocardiography in association with ventricular tachycardia in postinfarction patients

The authors investigate incidence of ventricular tachycardia/ventricular fibrillation (VT/VF) in relationship with combination of noninvasive arrhythmia risk markers as left ventricular ejection fraction (LVEF), late potentials (LP), and QT variability index (QTVI) and compare the utility of their combination in association with sustained ventricular arrhythmias in patients after myocardial infarction (MI). Fifty-four patients with old MI, among them 27 with documented spontaneous sustained VT/VF entered the study. All of them underwent evaluation for arrhythmias and noninvasive risk stratification. Logistic regression analysis demonstrated that the highest association with ventricular tachyarrhythmia had combination of LP and increased QTVI (13.8, P<.0002), followed then by combination of LVEF and LP (12.2, P<.0005), LP alone (P<.001), QTVI (P<.002) and LVEF (P<.003) alone and age (P<.01). After stepwise regression analysis showed that the model including association of LP and QTVI, age and EF is the best one for delineating patients having the risk of ventricular tachyarrhythmia development. In conclusion, patients with combination of positive LP and increased QTVI after MI have high likelihood for development of serious sustained arrhythmia.

Reduction of electromyographic noise in the signal-averaged electrocardiogram by spectral decomposition

This paper proposes a technique to improve the quality of high-resolution electrocardiogram by weighting the coherent average of beats by a function of the energy of the corrupting myoelectric noise, prior to subsequent detection of ventricular late potentials. The results obtained with 20 patients indicate the method requires fewer beats than conventional nonweighted average to achieve the same noise level.

Ventricular arrhythmias in patients with COPD are associated with QT dispersion

STUDY OBJECTIVE

QT dispersion (QTd) and late potentials derived from signal-averaged ECG (SAECG) have been proposed as noninvasive predictors of cardiac arrhythmias that occur in patients with COPD. In this study, we aimed to investigate QTd and SAECG in patients with COPD.

DESIGN

Cross-sectional study.

SETTING

Teaching chest disease hospital and cardiology center in a university hospital.

PATIENTS

Thirty patients with COPD (28 men and 2 women; mean +/- SD age, 60 +/- 9 years) and 31 age- and sex-matched control subjects (28 men and 3 women; mean age, 57 +/- 7 years) were included.

MEASUREMENTS AND RESULTS

Respiratory function tests, arterial blood gas analyses, echocardiographic examinations, rhythm Holter recordings, and heart rate variability (HRV) analyses were performed in addition to the measurements of QT intervals and SAECG. Patients with COPD had higher rate of ventricular premature beats (VPBs) as compared to control subjects (924 +/- 493 beats vs 35 +/- 23 beats, p = 0.009). Eight patients with COPD (27%) had nonsustained runs of ventricular tachycardia (VT). QTd rates were significantly increased in patients with COPD as compared to control subjects (57.7 +/- 9.9 ms vs 37.5 +/- 8.2 ms, p < 0.001). On comparing patients with COPD with and without runs of VT, patients with VT had longer QTd (67 +/- 10 ms vs 55 +/- 8 ms, p = 0.001). However no difference in any HRV and late potential parameters were found between patients with COPD with and without runs of VT. VPB rates were strongly correlated with QTd in patients with COPD (r = 0.61, p < 0.001). On SAECG analysis, patients with COPD had significantly increased total QRS duration as compared to control subjects. Nine of the 30 patients with COPD (30%) had positive late potentials. However, QTd and VPB rates were also similar between patients with COPD with and without late potentials.

CONCLUSIONS

The development of ventricular arrhythmia in patients with COPD was associated with increased QTd. Increased QTd may be associated with autonomic changes seen in patients with COPD.

Time and frequency analysis of beat-to-beat R-T interval variability in patients with ischaemic left ventricular dysfunction providing evidence for non-neural control of ventricular repolarisation

BACKGROUND

Determinants of temporal lability in ventricular repolarisation are not fully recognised. We aimed to analyse the sources of RT variability by comparing normal subjects and patients after myocardial infarction (MI) with either depressed or preserved left ventricular (LV) function.

METHODS

One hundred and nine patients (27 women, 82 men, aged 51 +/- 9 years) were divided into three groups: 24 patients (pts) with an uncomplicated angiographically proven coronary heart disease (CHD-group), 59 post-MI pts with preserved LV function (LVEF > 40%, PMI-N-group) and 26 post-MI pts with depressed LV function (LVEF < 40%, PMI-L-group). An ECG signal of low-noise 512 heartbeats was recorded using a computer-assisted amplifier (16 bit, 2 kHz). The onset and offset of the R-wave and T-wave were determined automatically. The magnitude of R-R and R-T variability was measured as the standard deviation of all intervals (SD-RR and SD-RT, ms, respectively). Their relationship was quantified by the correlation coefficient r(RT/RR). Power spectral density of RR or RT variability was estimated with the FFT (Welch's averaged periodogram, Hanning window) and frequency relation was quantified using a squared coherence spectrum (SCS). For all spectral and cross-spectral measurements two frequency ranges were considered: high (0.15-0.50 Hz, HF) and low (0.04-0.15 Hz, LF). Spectral power and SCS of RR and RT variability for both ranges (HF(RR), LF(RR), HF(RT), LF(RT), SCS(HF), SCS(LF)), and the ratios LF/HF(RR) and LF/HF(RT) were drawn for comparisons. The central frequency of HF(RR) was considered as the frequency of respiration (f(resp), Hz).

RESULTS

In the PMI-L group the SD-RT was significantly greater compared to the remaining groups and accounted for almost 10% of the SDRR. Also, the coefficient r(RT/RR) was weakest in this group. The spectral indices of RR variability were similar in all groups, while the greatest value of the HFRT was observed in the PMI-L group. The SCS(LF) was insignificant in this group, contrary to the CHD and PMI-N groups. Additionally, there were significant negative relationships between f(resp) and spectral indices of RT variability in PMI-patients with depressed LV function.

CONCLUSION

A greater beat-to-beat variation in RT interval duration along with increased power of its HF component indicates an important role of respiration in ventricular repolarisation control, while reduced time- and frequency RT-RR relationships seem to relate to an impaired process of ventricular duration adaptation.

Clinical assessment of the effect of digital filtering on the detection of ventricular late potentials

Ventricular late potentials are low-amplitude signals originating from damaged myocardium and detected on the body surface by ECG filtering and averaging. Digital filters present in commercial equipment may interfere with the ability of arrhythmia stratification. We compared 40-Hz BiSpec (BI) and classical 40- to 250-Hz band-pass Butterworth bidirectional (BD) filters in terms of impact on time domain variables and diagnostic properties. In a transverse retrospective age-adjusted case-control study, 221 subjects with sinus rhythm without bundle branch block were divided into three groups after signal-averaged ECG acquisition: GI (N = 40), clinically normal controls, GII (N = 158), subjects with coronary heart disease without sustained monomorphic ventricular tachycardia (SMVT), and GIII (N = 23), subjects with heart disease and documented SMVT. Conventional variables analyzed from vector magnitude data after averaging to 0.3 micro V final noise were obtained by application of each filter to the averaged signal, and evaluated in pairs by numerical comparison and by diagnostic agreement assessment, using conventional and optimized thresholds of normality. Significant differences were found between BI and BD variables in all groups, with diagnostic results showing significant disagreement between both filters [kappa value of 0.61 (P<0.05) for GII and 0.31 for GIII (P = NS)]. Sensitivity for SMVT was lower with BI than with BD (65.2 vs 91.3%, respectively, P<0.05). Filters provided significantly different numerical and diagnostic results and the BI filter showed only limited clinical application to risk stratification of ventricular arrhythmia.

[Heart and sports: modifications of electrocardiogram, late potentials and echocardiography. Study of 75 sportsmen and 46 witnesses]

The authors report the results of prospective study, which compared 75 sports subjects and 45 witnesses. All subjects were male, the differentiating parameter being the type of sport practiced. This work analysed surface Electrocardiogramme, thransthoracic echocardiography and high amplification ECG. The statistical study used the student test t compare means and the Chi2 test for the percentages, the signification limit was fixed to 5%. Clinically, our two series didn't show a significant statistical difference, concerning: age, weight, height or arterial pressure. On the electrocardiographical level, the sport's men have a lower cardiac frequency (p = 0.005), a larger PR space (p = 0.05), an important Sokolow parameter (p < 0.005), and repolarisation disorders represented, essentially by negative T waves (p = 0.02) and an upper movement of ST segment in V2-V3 (p < 0.005). Echocardiography showed a dilatation of the right cavities: right auricular (p = 0.0125) and right ventricular (p = 0.025). Move over, it has been showed that the sport's men left ventricular walls were tabor (septal wall, p = 0.0125), (posterior wall, p = 0.025), despite a difference in the values of the left ventricular telediastolic diameter (4 mm average in the two series). The signification limit was not reached and it was also showed that the left auricular was also dilated (p = 0.025). The study of the delayed Potentials, tried to bring an explication to certain sudden deaths of sport's men which are to date unexplained and which could have a rhythmical origin? It is also to be noted that sport's men present more delayed ventricular Potentials. However, the statistical signification was not reached (p = 0.07).

Electrocardiography subtraction method of detecting low-amplitude, high-frequency components (L-HFCs) within the QRS complex of patients with ventricular tachycardia

A new method of extracting the low-amplitude and high-frequency components (L-HFCs) was developed and this study investigated its usefulness in 86 subjects: 28 normal subjects (group 1) and 58 patients with a previous myocardial infarction (MI). The patients were classified into 3 groups: group 2 with 38 patients without ventricular tachycardia (VT), group 3 with 13 patients with non-sustained VT, and group 4 with 7 patients with sustained VT. The new electrocardiography (ECG) subtraction method, using a mathematical filtering procedure, was used instead of conventional complex filtering. The continuous L-HFCs within the QRS complex were analyzed using a Z-lead recording. The duration of the continuous L-HFCs was significantly longer in group 4 than in groups 1 (p<0.0001), 2 (p<0.0001) or 3 (p<0.05) with all 3 filters. The ECG subtraction method is a powerful and useful new technique for identifying patients at risk for either sustained or non-sustained VT after MI, and overcomes several of the problems with the conventional signal-averaging method.

Screening and therapy for patients with nonsustained ventricular tachycardia

Patients with coronary artery disease, nonsustained ventricular tachycardia (VT), and left ventricular dysfunction have an increased risk for sudden cardiac death. Two randomized prospective trials, the Multicenter Unsustained Tachycardia Trial (MUSTT) and the Multicenter Automatic Defibrillator Implantation Trial (MADIT), employed electrophysiologic testing for risk stratification in these types of patients. Individuals with inducible sustained VT were randomized to receive implantable cardioverter defibrillators (ICDs) or "conventional" therapy in MADIT, or were given no specific antiarrhythmic treatment vs electrophysiologically guided therapy in MUSTT. Both trials showed that overall mortality was reduced by approximately 50% with ICD therapy. In MUSTT, patients received no survival benefit with electrophysiologically guided drug treatment. MUSTT also demonstrated that untreated patients with inducible sustained VT had a worse prognosis than patients in whom sustained VT could not be initiated at electrophysiologic study. Even so, the data suggest that electrophysiologic testing alone may not be sensitive enough to identify broader groups of patients at risk for sudden death. In conclusion, patients with nonsustained VT who have coronary artery disease and a left ventricular ejection fraction <0.40 should undergo electrophysiologic testing, and if sustained VT is induced, ICD therapy should be prescribed.

Matching cardiac rhythm management technology to patient needs: pacing/ablation/implantable cardioverter defibrillators

Data from 2 decades of clinical electrophysiologic studies have allowed great progress in the evaluation and treatment of patients with sustained ventricular arrhythmias and the appropriate identification of those patients at high risk for subsequent sudden death. The goals of treatment of the patient with ventricular arrhythmias are to suppress symptoms and prevent a fatal event. The steps in providing such therapy include (1) defining the cardiac anatomy; (2) assessing arrhythmia risk through noninvasive or invasive testing; and (3) prescribing treatment based on these results. Patients may be separated into high- and low-risk groups to help identify appropriate treatment. Although low-risk groups may benefit from reassurance or medications such as beta-blockers or verapamil, high-risk groups have been more difficult to treat. Recent randomized trials of implantable cardioverter defibrillators (ICDs) for ventricular arrhythmias suggest that they may provide better protection for high-risk patients than do antiarrhythmic medications.

Sampling rate and the estimation of ensemble variability for repetitive signals

The measurement of ensemble variability in time-aligned event signals is studied in relation to sampling rate requirements. The theoretical analysis is based on statistical modelling of time misalignment in which the time resolution is limited by the length of the sampling interval. For different signal-to-noise ratios (SNRs), the sampling rate is derived which limits the misalignment effect to less than 10% of the noise effect. Each signal is assumed to be corrupted by additive noise. Using a normal QRS complex with a high SNR (approximately equal to 30 dB), a sampling rate of approximately 3 kHz is needed for accurate ensemble variability measurements. This result is surprising since it implies that the Nyquist rate is far too low for accurate variability measurements. The theoretical results are supplemented with results obtained from an ECG database of 94 subjects for which the ensemble variability is computed at different sampling rates using signal interpolation. The ensemble variability is substantially reduced (40%) when increasing the rate from 1 to 3 kHz, thus corroborating the results suggested by the theoretical analysis.

Normal limits of high-resolution signal-averaged ECG parameters of Japanese adult men and women

High-resolution signal-averaged electrocardiography (Hi-Res ECG) has been found useful in measuring ventricular late potentials for identifying patients prone to life-threatening ventricular arrhythmias. Several studies have reported cut-off values (normal limits) of Hi-Res ECG parameters, including sex-specific limits, for adult population. However, there are no such studies reporting such limits in the Japanese population. Hi-Res ECGs were recorded from 482 normal healthy patients (204 men; 278 women) with no cardiac disease and normal electrocardiogram. Three Hi-Res ECG parameters filtered QRS duration (FQRSD), low amplitude signal duration under 40 microV of terminal QRS (LASD), and root mean square voltage in the terminal 40 milliseconds (RMSV) were analyzed. FQRSD was longer in men than in women (P < .0001). RMSV was larger in men than in women (P < .0001). There was no significant difference in LASD between men and women. The upper limit (90th percentile) of FQRSD was 116 milliseconds for women. The upper limit of LASD was 42 milliseconds for both men and women. The lower limit (10th percentile) of the RMSV was 14 microV for both men and women. There was no significant difference in the distributions of the Hi-Res ECG parameters between our study and an earlier study on mostly whites from the United States and Europe. The upper limits (90th percentile) of FQRSD and LASD in the Japanese normal patients were nearly the same as for whites. But, the lower limit (10th percentile) of RMSV in our Japanese normals was significantly smaller than that for whites. Therefore, it may be necessary to use race-specific normal limits for late potential analysis. Criteria for abnormal late potentials (defined as abnormal values in at least 2 of the 3 Hi-Res ECG parameters) were met in 18 of 482 (3.7%) normal healthy patients. Further studies are needed to evaluate the role of these criteria in identifying cardiac patients with life-threatening arrhythmias in the Japanese population.

Effects of half ironman competition on the development of late potentials

OBJECTIVES

The primary purpose was to evaluate the prevalence of late potentials (LPs) in triathletes before and after a half ironman triathlon. The secondary purpose was to examine whether LPs are the electrocardiographic expression of a greater myocardial mass.

METHODS

Nine asymptomatic male triathletes (mean age +/- SD, 32 +/- 5 yr) were examined using signal-averaged ECG (SAECG) 48-72 h before (PRE), immediately after (POST), and 24-48 h after the completion (RECOVERY) of a half ironman triathlon. Late potentials were considered to be present if two of the following SAECG anomalies were observed: 1) a prolonged filtered QRS (/QRS) complex (> or = 114 ms), 2) a lengthened low amplitude signal (LAS) duration (>38 ms), and/or 3) a low root mean square (RMS) voltage of the last 40 ms of the fQRS (<20 microV). Left ventricular dimensions were determined at PRE using M-mode echocardiography.

RESULTS

There were no significant differences between PRE, POST, and RECOVERY in the fQRS duration, the LAS duration, or the RMS voltage. Two athletes displayed a single SAECG abnormality during PRE and two SAECG anomalies (i.e., LPs) during POST. Late potentials remained in one of the two athletes during RECOVERY. A moderate relationship existed between fQRS and left ventricular mass (r = 0.67, P < 0.05).

CONCLUSIONS

Ultra-endurance training and/or events do not lead to LPs in the majority of triathletes who do not possess ventricular arrhythmias. However, a small subset of triathletes do display SAECG anomalies, which are augmented by an ultra-endurance event and may persist even after recovery from the event. Left ventricular mass does not affect overall SAECG parameters.

Prevalence of late potentials in a sample of 487 healthy, middle-aged men from southwestern France

Late potentials (LPS) have been shown to be predictive of ventricular tachycardia in coronary artery disease subjects, but the prevalence of LP in the general population is not as well-known. The study included 487 men without a history of cardiovascular disease (aged 50-59) living in Southwestern France. Standard-averaged high resolution electrocardiogram was performed using Butterworth filtering at 40-250 Hz. LPS were defined as two or more of the following criteria: QRS > 114 ms, duration of the low amplitude signals in the terminal portion of QRS > 38 ms, root mean square (RMS) voltage of the last 40 ms < 20 microV. The mean QRS duration was 97 +/- 12 ms (mean +/- SD), duration of the low amplitude signals in the terminal portion of QRS was 32 +/- 10 ms, and RMS voltage in the last 40 ms was 39 +/- 27 microV. Eight percent of subjects (95% confidence interval [CI]: 6%-11%) had a QRS duration > 114 ms; 22% (95% CI: 18%-26%) had a duration of low amplitude signals > 38 ms, and 25% (95% CI: 22%-29%) had RMS voltage in the last 40 ms < 20 microV. Finally, the prevalence of LP was 21% (95% CI: 18%-25%). In conclusion, according to commonly used criteria, the prevalence of LP in this healthy population of middle-aged men is 21%, close to the values found in the literature for myocardial infarction patients. Those findings indicate the need for reconsidering the definition of LPS.

Application of noninvasive and invasive tests for risk assessment in patients with ventricular arrhythmias

Sudden cardiac death remains a major public health problem in western society. Because most patients who experience cardiac arrest are not successfully resuscitated, primary prevention of sudden death remains an important challenge. A number of noninvasive risk stratification techniques have been suggested as providing useful information in patients with underlying structural heart defects. Unfortunately, the positive predictive value of most of these techniques has been limited. Left ventricular ejection fraction, the presence of nonsustained ventricular tachycardia on Holter monitoring, and inducible sustained ventricular tachycardia at electrophysiologic testing in patients with coronary artery disease remain the best established prognostic test. However, with the exception of two ICD studies using the combination of these markers, prospective studies have not yet completely validated the use of these and other prognostic markers. Further understanding of the pathophysiology of ventricular fibrillation and other risk stratification techniques will be necessary before a clear algorithm can be developed for application to patients at risk for sudden death.

Late fields of the magnetocardiographic QRS complex as indicators of propensity to sustained ventricular tachycardia after myocardial infarction

INTRODUCTION

Magnetocardiographic (MCG) mapping is a new method to record cardiac signals. This study examined the association of MCG late fields with the propensity to sustained ventricular tachycardia (VT) after myocardial infarction (MI).

METHODS AND RESULTS

One hundred patients with remote MI were studied, 38 with and 62 without history of VT. High-resolution MCG and signal-averaged ECG (SAECG) as a comparative method were recorded. Time-domain parameters describing the abnormal low-amplitude end QRS activity, MCG late fields, and SAECG late potentials were analyzed. Late field parameters differed significantly between the patient groups: filtered QRS duration was 137 +/- 26 msec in the VT group and 110 +/- 18 msec in the control group (P < 0.001), and root mean square amplitude of the last 40 msec was 260 +/- 170 and 510 +/- 360 fT (P < 0.001), respectively. The optimal MCG parameter combination yielded a sensitivity of 92% and a specificity of 61% in classification to the VT group, whereas those for SAECG were 63% and 66%. In a subgroup of 63 patients with marked left ventricular dysfunction and comparable stage of coronary heart disease, only MCG (sensitivity 73%, specificity 67%) but not SAECG could assign a patient to the VT group.

CONCLUSION

Late fields of the MCG QRS complex indicate propensity to life-threatening arrhythmias in post-MI patients. This discriminative ability persists in the presence of severe left ventricular dysfunction where ECG late potentials lose their informative value. MCG late field analysis is a potential new method for noninvasive risk assessment in post-MI patients.

Reproducibility of time-domain and three different frequency-domain techniques for the analysis of the signal-averaged electrocardiogram

Because time-domain (TD) analysis of the signal-averaged ECG (SAECG) has some limitations that limit its use, several frequency-domain analysis techniques were developed in an attempt to improve the diagnostic ability of the SAECG. However, it is not known how reliable these techniques are at detecting late potentials. This prospective study compares the short-term reproducibility of 4 analysis techniques: TD analysis, spectral temporal mapping (STM), spectral turbulence analysis (STA), and acceleration spectrum analysis (ASA), in a large series of normal patients and post-myocardial infarction (MI) patients. Two consecutive SAECGs were recorded in 634 patients that were divided into 3 groups: 117 remote MI patients undergoing programmed electrical stimulation for the inducibility of ventricular tachycardia (Group 1), 407 consecutive acute MI survivors (Group 2), and in 110 healthy volunteers (Group 3). The diagnostic reproducibility of the 4 techniques was evaluated by comparing rates of inconsistent results (1 normal and the other abnormal). The numeric reproducibility for each technique was assessed by comparing the normalized differences of each single SAECG parameter between the 2 recordings. Inconsistent results of diagnostic reproducibility were observed in 4.1%, 6.9%, 9.8%, and 18.0%, with TD, STA, ASA, and STM, respectively. Comparisons of these rates were significantly different (P < .05) except between STA and ASA (P = .07). The numeric reproducibility was highest for TD parameters, lowest for STM factors of normality, and intermediate for STA and ASA indices. TD analysis remains the most reproducible SAECG analysis technique, whereas STM showed the worst reproducibility, which limits its clinical applicability. STA and ASA provide an acceptable intermediate reproducibility, the former being slightly, although not significantly, more reproducible than the latter.

Clinical significance of variability of ventricular late potentials detected before discharge in patients after myocardial infarction

BACKGROUND

Signal-averaged electrocardiography (SAECG) in patients after myocardial infarction (MI) is widely used to identify patients at risk for ventricular tachycardia (VT) and sudden cardiac death (SCD). It is believed that ventricular late potentials when detected after day 5 after MI are relatively stable and carry the most significant relation to subsequent arrhythmic events. This study sought to determine if ventricular late potentials in patients after MI exhibit variability when recordings were made 10 to 12 hours apart on day 7 and to assess the clinical significance of this variability.

METHODS AND RESULTS

SAECG was recorded in 261 patients on the 7th day after MI at 7 to 10 AM (morning) and 6 to 8 PM (evening). Forty of these patients also had recordings 30 to 40 minutes apart to determine the 95% confidence interval of variability of each parameter of SAECG. The data were analyzed with the criteria of the American College of Cardiology policy statement. A prospective analysis for the clinical end points of VT and SCD was carried out for a period of 1 year. We identified 3 groups of patients. Group 1 (54, 20.7%) had consistently positive SAECG by at least 2 abnormal parameters in both morning and evening. Group 2 (37, 14.2%) had positive SAECG at 1 time only, either morning or evening. Group 3 (170, 65.1%) had negative SAECG on both occasions. Diabetes mellitus was an independent predictor of the variability of late potentials (P <.0001). A prospective analysis for the clinical end points of VT and SCD showed that the event rate was significantly higher in group 1 than in group 2 (P <.019).

CONCLUSIONS

To improve the positive predictive value of SAECG in patients after MI, we advise that all positive tests be repeated 10 to 12 hours later, especially in patients with diabetes mellitus. Such testing will identify patients with consistently positive SAECG who appear to be at the highest risk for VT and SCD.

[Spanish Society of Cardiology practice guidelines on ambulatory monitoring of electrocardiogram and blood pressure]

In the present paper, a historical review and a clinical up-date are done on two procedures of great medical interest: Holter electrocardiography and ambulatory blood pressure monitoring. Technical and methodological characteristics of each procedure are carefully exposed, emphasizing each the lack of an international agreement in order to establish regulations that make all the equipment homogeneous and reliable in order to increase both accuracy and reliability in diagnosis. Based on published international scientific documents and the personal experience of the authors, guidelines for clinical applications, indications and limitations of each technique are analyzed in relation to capacities of the Spanish political and social public health system profile. New concepts and dynamics of developments such as; dynamic QT, RR variability or pulse wave velocity are exposed, in the frame of the present time and future for improving efficiency and clinical application.

Effect of hemodialysis on the signal-averaged electrocardiogram

The presence of late potentials (LPs) on signal-averaged electrocardiography (SAECG) is predictive of ventricular tachycardia. The effect of hemodialysis (HD) on SAECG has not been well studied. SAECG was evaluated in 28 patients with chronic renal failure immediately before and after HD. In each SAECG, QRS duration, low-amplitude signal duration (LASd), and root-mean-square voltage of the terminal 40 milliseconds of the QRS (RMS40) were measured. To evaluate the effect of fluid removal on SAECG, the last 12 patients were studied during two different HD sessions, one with and one without fluid removal. Two-dimensional echocardiography was performed before and after HD on these 12 patients. At baseline, four patients met the criteria for LPs on SAECG. Only one patient met the criteria for LPs on SAECG after HD. After HD, the mean LASd decreased (28.3 +/- 12.9 to 24.9 +/- 10.1 milliseconds; P = 0.041) and RMS40 increased (63.0 +/- 56.9 to 79.0 +/- 59.2 microV; P = 0. 006). Among the 12 patients who underwent HD with and without fluid removal, left ventricular end-diastolic dimension decreased with (5. 4 +/- 0.6 to 5.1 +/- 0.6 cm; P = 0.024) but not without fluid removal (5.2 +/- 0.3 to 5.1 +/- 0.4 cm; P = not significant [NS]). RMS40 improved with (43.8 +/- 23.1 to 53.2 +/- 22.6 microV; P = 0. 03) but not without fluid removal (51.0 +/- 26.5 to 51.5 +/- 24.2 microV; P = NS). A significant negative correlation was found between change in body weight and change in RMS40 parameter (r = 0. 456; P = 0.0381). SAECG parameters are abnormal in a significant proportion of patients with chronic renal failure and improve with HD despite electrolyte and other proarrhythmic changes. Decreased left ventricular dimension because of fluid removal during HD is one possible explanation for this improvement.

Significance of late ventricular potentials in myotonic dystrophy

In 39 patients with myotonic dystrophy, we found a high percentage of infrahissian cardiac conduction abnormalities (51%) and late potentials (46%), whereas spontaneous and inducible ventricular arrhythmias were rare. These results suggest that the prolongation of QRSD and the duration of the low-amplitude signal on the signal-averaged electrocardiogram were related to delayed activation of the His and Purkinje tissue rather than true late potentials.

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.

Signal averaged electrocardiography of Japanese

Although studies show that the ventricular tachycardia and sudden cardiac deaths caused by ischemic heart diseases affect Japanese less than Westerners, predictive accuracy of the signal averaged ECG for ventricular tachycardia and sudden cardiac deaths are almost the same as the results for Westerners. The recent prognosis of ischemic heart diseases is showing improvements along with the development of re-perfusion therapy, which is changing the significance of the signal averaged ECG. Therefore a clinical use for signal averaged ECG should be discussed in cases of cardiomyopathy which cause sudden cardiac deaths and other heart diseases. So it is necessary to redetermine normal values of the signal averaged ECG parameters. In this article, the following was reviewed on the basis of our studies regarding the clinical significance of the signal averaged ECG of Japanese and normal signal averaged ECG values. (1) System and gender specific differences on signal averaged ECG of Japanese, (2) His-Purkinje system, pre-P deflection and atrial late potential on signal averaged ECG, (3) Ventricular late potentials of Japanese.

Lack of correlation between ventricular late potentials and left ventricular mass in top-level male athletes

PURPOSE

The aim of this study was to establish: 1) the prevalence of abnormal signal-averaged electrocardiogram (SAECG) in a large population of top-level athletes and 2) the relationship between SAECG parameters and left ventricular mass. One-hundred and fifty-three elite male athletes without apparent heart disease, symptoms, or arrhythmias were studied.

METHODS

Fifty-six athletes (37%) had increased left ventricular mass (> 134 g.m(-2)). All athletes underwent time-domain SAECG on 300-400 heart beats recorded at rest from three bipolar orthogonal tests with a filter setting of 40-250 Hz. Criteria for abnormality were 1) filtered QRS duration > 114 ms, 2) duration of low-amplitude signals > 38 ms, or 3) root mean square voltage of the last 40 ms of the filtered QRS < 20 microV.

RESULTS

The prevalence of abnormal SAECG was 7.2% (abnormality of one parameter), 6.5% (abnormality of two parameters), and 5.8%(abnormality of three parameters). The prevalence of abnormal SAECG was similar in athletes with or without increased left ventricular mass.

CONCLUSIONS

In conclusion, this study showed: 1) the low rate of positive results of SAECG parameters in top-level male athletes, similar to that found in healthy sedentary subjects; and 2) the lack of correlation between left ventricular mass and overall SAECG parameters.

Analysis of the ST-T complex of the electrocardiogram using the Karhunen--Loève transform: adaptive monitoring and alternans detection

The Karhunen-Loève transform (KLT) is applied to study the ventricular repolarisation period as reflected in the ST-T complex of the surface ECG. The KLT coefficients provide a sensitive means of quantitating ST-T shapes. A training set of ST-T complexes is used to derive a set of KLT basis vectors that permits representation of 90% of the signal energy using four KLT coefficients. As a truncated KLT expansion tends to favor representation of the signal over any additive noise, a time series of KLT coefficients obtained from successive ST-T complexes is better suited for representation of both medium-term variations (such as ischemic changes) and short-term variations (such as ST-T alternans) than discrete parameters such as the ST level or other local indices. For analysis of ischemic changes, an adaptive filter is described that can be used to estimate the KLT coefficient, yielding an increase in the signal-to-noise ratio of 10 dB (u = 0.1), with a convergence time of about three beats. A beat spectrum of the unfiltered KLT coefficient series is used for detection of ST-T alterans. These methods are illustrated with examples from the European ST-T Database. About 20% of records revealed quasi-periodic salvos of ischemic ST-T change episodes and another 20% exhibit repetitive, but not clearly periodic patterns of ST-T change episodes. About 5% of ischemic episodes were associated with ST-T alterans.

Prevalence of ventricular late potentials in patients with obstructive sleep apnea syndrome

BACKGROUND

It is known from various cardiac disorders that the presence of ventricular late potentials (VLP) in the signal-averaged electrocardiogram (ECG) is associated with an increased risk of sudden cardiac death.

HYPOTHESIS

In view of the increased cardiovascular mortality of patients with obstructive sleep apnea syndrome (OSAS), we assessed the prevalence of VLP in these patients.

METHODS

In all, 118 consecutive patients with polysomnographically verified OSAS were prospectively studied; 21 snorers without evidence of a sleep-related breathing disorder served as a control group. Signal-averaged ECG and 24-h Holter ECG were performed in all patients and controls, and left ventricular function was determined by radionuclide ventriculography in the OSAS group. Furthermore, patients and controls were followed for up to 45.5 months for arrhythmic events, syncopes, or sudden cardiac death.

RESULTS

An abnormal signal-averaged ECG was seen in seven patients (5.9%) and in one snorer (4.8%). Patients with and without VLP did not differ with respect to age, body mass index, left ventricular ejection fraction, or ectopic activity in the 24-h Holter ECG, but the former had significantly higher mean (standard deviation) apnea/hypopnea indices [55.4 (25.2)/h vs. 37.4 (22.6)/h; p < 0.05]. Of the 118 patients, 110 could be followed for 26.7 (7.9) months. During this period, two patients had syncopes and one patient had sudden cardiac death. The seven patients with VLP remained free of events during the follow-up period, as did the 21 snorers.

CONCLUSIONS

Patients with OSAS have a low prevalence of VLP in the signal-averaged ECG, not exceeding that in normal subjects. Moreover, abnormal signal-averaged ECGs do not appear to be useful as a prognostic marker.

The utility of quantitative body surface isoarea mapping for predicting ventricular tachyarrhythmias

Noninvasive techniques, such as the signal averaged ECG, have been used to assess risk of ventricular tachyarrhythmias (VT). However, these methods produce false positive and negative results. The purpose of this study was to develop body surface map algorithms which would enhance prediction of susceptibility to VT. Fifty-three patients referred for programmed electrical stimulation were enrolled in this study. All patients underwent signal averaged ECG, body surface map, programmed electrical stimulation. Group I patients had no sustained inducible VT and group II patients had either inducible sustained VT at electrophysiology study or previously documented spontaneous, sustained VT. For body surface map analysis, the difference between extrema on isoarea maps was calculated and defined as the gradient range. An abnormal body surface map was defined as a QRST gradient range < or = 109 mv.ms. The mean QRST gradient range in group II was significantly < that in group I (P < 0.05). By logistic regression analysis, the presence of coronary artery disease, a QRST gradient range < or = 109 mv.ms, an EF < 40% and a signal averaged ECG QRS duration > 114 ms predicted VT. The sensitivity, specificity, positive and negative predictive values for predicting VT susceptibility of an algorithm which combines the signal averaged ECG QRS duration and the QRST gradients were 0.93, 0.76, 0.79, and 0.91, respectively, while those for the signal averaged ECG alone were 0.52, 0.69, 0.63, and 0.59 for VT susceptibility. A combined body surface map-signal averaged ECG algorithm was more sensitive in detecting susceptibility to VT than the signal averaged ECG alone.

Improved diagnostic value of combined time and frequency domain analysis of the signal-averaged electrocardiogram after myocardial infarction

BACKGROUND

Time domain analysis (TD) of the signal-averaged electrocardiogram (SAECG) presents a higher incidence of false positives in inferior myocardial infarction (MI), whereas spectral turbulence analysis (STA) suffers from a higher incidence of false positives in anterior MI. We investigated the hypothesis that a combined TD and STA (TD+STA) analysis of the SAECG could improve its predictive accuracy for major arrhythmic events (MAE) after MI.

METHODS

Signal-averaged electrocardiograms were prospectively recorded 10.1 +/- 2.6 days after acute MI in 602 patients. Time domain analysis and STA were performed using standard parameters and criteria for abnormality. For the combined TD+STA model, stepwise discriminant analysis was utilized to optimize prediction of MAE. Receiver operating characteristic curves were utilized to optimize cutoff values for each SAECG parameter separately, and also for the combined TD+STA model.

RESULTS

During a one-year follow-up period, 38 patients had MAE: 14 sustained ventricular tachycardia, 2 resuscitated ventricular fibrillation and 22 sudden cardiac deaths. The total predictive accuracy of combined TD+STA (89.9%) was significantly higher than TD (75.1%) or STA (77.6%). The negative predictive accuracy of all three analyses was high (98%). The positive predictive accuracy of TD (19.6%) or STA (18.3%) was quite low, and significantly improved to 35.8% by combined TD+STA analysis. The positive predictive accuracy of TD+STA improved to 51.2% in patients with left ventricular ejection fraction <40%.

CONCLUSIONS

Combined TD + STA analysis of the SAECG significantly improves its prognostic ability for MAE in post-MI patients compared with TD or STA analyzed separately.

T wave alternans as a predictor of recurrent ventricular tachyarrhythmias in ICD recipients: prospective comparison with conventional risk markers

INTRODUCTION

The current standard for arrhythmic risk stratification is electrophysiologic (EP) testing, which, due to its invasive nature, is limited to patients already known to be at high risk. A number of noninvasive tests, such as determination of left ventricular ejection fraction (LVEF) or heart rate variability, have been evaluated as additional risk stratifiers. Microvolt T wave alternans (TWA) is a promising new risk marker. Prospective evaluation of noninvasive risk markers in low- or moderate-risk populations requires studies involving very large numbers of patients, and in such studies, documentation of the occurrence of ventricular tachyarrhythmias is difficult. In the present study, we identified a high-risk population, recipients of an implantable cardioverter defibrillator (ICD), and prospectively compared microvolt TWA with invasive EP testing and other risk markers with respect to their ability to predict recurrence of ventricular tachyarrhythmias as documented by ICD electrograms.

METHODS AND RESULTS

Ninety-five patients with a history of ventricular tachyarrhythmias undergoing implantation of an ICD underwent EP testing, assessment of TWA, as well as determination of LVEF, baroreflex sensitivity, signal-averaged ECG, analysis of 24-hour Holter monitoring, and QT dispersion from the 12-lead surface ECG. The endpoint of the study was first appropriate ICD therapy for electrogram-documented ventricular fibrillation or tachycardia during follow-up. Kaplan-Meier survival analysis revealed that TWA (P < 0.006) and LVEF (P < 0.04) were the only significant univariate risk stratifiers. EP testing was not statistically significant (P < 0.2). Multivariate Cox regression analysis revealed that TWA was the only statistically significant independent risk factor.

CONCLUSIONS

Measurement of microvolt TWA compared favorably with both invasive EP testing and other currently used noninvasive risk assessment methods in predicting recurrence of ventricular tachyarrhythmias in ICD recipients. This study suggests that TWA might also be a powerful tool for risk stratification in low- or moderate-risk patients, and needs to be prospectively evaluated in such populations.