The signal-averaged electrocardiogram as a screening test for inducibility of sustained ventricular tachycardia in high risk patients: a prospective study

A novel signal-averaged electrocardiogram and an ambulatory-based signal-averaged electrocardiogram show strong correlations with conventional signal-averaged electrocardiogram in healthy subjects: A validation study

BACKGROUND

A novel signal-averaged electrocardiogram (SAECG) device and a novel ambulatory SAECG device are clinically available, but reference values have not been established. This study aimed to validate the novel SAECG and the novel ambulatory-based SAECG devices by comparison with the conventional SAECG device.

METHODS AND RESULTS

High-resolution SAECGs were recorded consecutively in 83 healthy volunteers using the 3 devices. A novel ambulatory SAECG device was used as real-time recording within 15 min for validation study (15 min ambulatory-based SAECG). We examined the concordance of positive results (at least 2/3 abnormal SAECG parameters) and negative results (0 or 1/3 abnormal parameters), as well as the correlations between SAECG parameters (filtered QRS duration [fQRS]); duration of low-amplitude signals < 40 μV in the terminal filtered QRS complex [LAS₄₀]; root mean square voltage of the terminal 40 ms of the filtered QRS complex [RMS₄₀]). Qualitative analysis showed excellent concordance among the novel SAECG, the 15 min ambulatory-based SAECG, and the conventional SAECG methods (novel SAECG vs. conventional SAECG = 94%; 15 min ambulatory-based SAECG vs. conventional SAECG = 91.6%; p = 0.755), while quantitative analysis indicated strong correlations between the novel SAECG and the conventional SAECG values for fQRS, LAS₄₀, and LnRMS₄₀ (r = 0.838-0.805, p < 0.0001, respectively). Strong correlations were also seen between 15 min ambulatory-based SAECG and conventional SAECG values for fQRS, LAS₄₀, and RMS₄₀ (r = 0.943-0.888, p < 0.0001, respectively). However, Bland-Altman quantitative analysis showed better agreement in fQRS and LnRMS₄₀ measured by the 15 min ambulatory-based SAECG and the conventional SAECG than those by the novel SAECG and the conventional SAECG (fQRS, Lin's rho_c = 0.923 vs. 0757; RMS₄₀, Lin's rho_c = 0.932 vs. 0.818, respectively).

CONCLUSION

In healthy subjects, the parameters of either the novel SAECG or the 15 min ambulatory-based SAECG and those of the conventional SAECG were strongly correlated. Relatively good agreements were observed among 3 SAECGs, especially better between the 15 min ambulatory-based SAECG and the conventional SAECG probably due to similar measurement system of 2 methods.

Rationale and design for the Predictors of Arrhythmic and Cardiovascular Risk in End Stage Renal Disease (PACE) study

BACKGROUND

Sudden cardiac death occurs commonly in the end-stage renal disease population receiving dialysis, with 25% dying of sudden cardiac death over 5 years. Despite this high risk, surprisingly few prospective studies have studied clinical- and dialysis-related risk factors for sudden cardiac death and arrhythmic precursors of sudden cardiac death in end-stage renal disease.

METHODS/DESIGN

We present a brief summary of the risk factors for arrhythmias and sudden cardiac death in persons with end-stage renal disease as the rationale for the Predictors of Arrhythmic and Cardiovascular Risk in End Stage Renal Disease (PACE) study, a prospective cohort study of patients recently initiated on chronic hemodialysis, with the overall goal to understand arrhythmic and sudden cardiac death risk. Participants were screened for eligibility and excluded if they already had a pacemaker or an automatic implantable cardioverter defibrillator. We describe the study aims, design, and data collection of 574 incident hemodialysis participants from the Baltimore region in Maryland, U.S.A.. Participants were recruited from 27 hemodialysis units and underwent detailed clinical, dialysis and cardiovascular evaluation at baseline and follow-up. Cardiovascular phenotyping was conducted on nondialysis days with signal averaged electrocardiogram, echocardiogram, pulse wave velocity, ankle, brachial index, and cardiac computed tomography and angiography conducted at baseline. Participants were followed annually with study visits including electrocardiogram, pulse wave velocity, and ankle brachial index up to 4 years. A biorepository of serum, plasma, DNA, RNA, and nails were collected to study genetic and serologic factors associated with disease.

DISCUSSION

Studies of modifiable risk factors for sudden cardiac death will help set the stage for clinical trials to test therapies to prevent sudden cardiac death in this high-risk population.

Relationship between late ventricular potentials and myocardial 123I-metaiodobenzylguanidine scintigraphy in patients with dilated cardiomyopathy with mild to moderate heart failure: results of a prospective study of sudden death events

PURPOSE

Late ventricular potentials (LPs) are considered to be useful for identifying patients with heart failure at risk of developing ventricular arrhythmias. (123)I-metaiodobenzylguanidine (MIBG) scintigraphy, which is used to evaluate cardiac sympathetic activity, has demonstrated cardiac sympathetic denervation in patients with malignant ventricular tachyarrhythmias. This study was undertaken to clarify the relationship between LPs and (123)I-MIBG scintigraphy findings in patients with dilated cardiomyopathy (DCM).

METHODS

A total of 56 patients with DCM were divided into an LP-positive group (n = 24) and an LP-negative group (n = 32). During the compensated period, the delayed heart/mediastinum count (H/M) ratio, delayed total defect score (TDS), and washout rate (WR) were determined from (123)I-MIBG images and plasma brain natriuretic peptide (BNP) concentrations were measured. Left ventricular end-diastolic volume (LVEDV), left ventricular end-systolic volume (LVESV), and left ventricular ejection fraction (LVEF) were simultaneously determined by echocardiography.

RESULTS

LVEDV, LVESV, LVEF and plasma BNP concentrations were similar in the two groups. However, TDS was significantly higher (35 ± 8 vs. 28 ± 6, p < 0.005), the H/M ratio was significantly lower (1.57 ± 0.23 vs. 1.78 ± 0.20, p < 0.005), and the WR was significantly higher (60 ± 14% vs. 46 ± 12%, p < 0.001) in the LP-positive than in the LP-negative group. The average follow-up time was 4.5 years, and there were nine sudden deaths among the 56 patients (16.1%). In logistic regression analysis, the incidences of sudden death events were similar in those LP-negative with WR <50%, LP-negative with WR ≥ 50% and LP-positive with WR <50% (0%, 10.0% and 14.3%, respectively), but was significantly higher (41.2%) in those LP-positive with WR ≥ 50% (p < 0.01, p < 0.05, and p < 0.05, respectively).

CONCLUSION

The present study demonstrated that the values of cardiac (123)I-MIBG scintigraphic parameters were worse in LP-positive DCM patients than in LP-negative DCM patients. Furthermore, in LP-positive DCM patients with a high WR, the incidence of sudden death events was higher than that in other subgroups of DCM patients.

Signal-averaged electrocardiogram may be a beneficial prognostic procedure in the postoperative follow-up tetralogy of fallot patients to determine the risk of ventricular arrhythmias

Early detection of arrhythmias after congenital heart disease surgery is important because it can help decrease morbidity and mortality. Standard electrocardiograms (ECGs) contain frequencies between 0.05 and 100 Hz, but higher frequencies are also present. Using high-resolution technology, the highest amplitudes of these high-frequency components within the QRS complex can be recorded and analyzed. We studied the relationship between ventricular late potentials, ventricular arrhythmias and right ventricular systolic pressure in 22 patients who underwent tetralogy of Fallot repair (mean follow-up, 40.1 +/- 33.5 months). Holter ECG monitoring and signal-averaged electrocardiograms (SAECGs) were performed. SAECG parameters studied included the duration of the filtered QRS, the duration of terminal QRS below 40 muV, and the root mean square amplitude of the terminal 40 msec. Cardiac catheterization was performed on 19 patients. Eighteen healthy volunteers were studied as a control. Ventricular arrhythmias were found in 13 patients; right ventricular systolic hypertension was found in 1 patient. No significant residual ventricular septal defects were detected. Eight patients had ventricular late potentials. Right ventricular systolic pressure did not differ significantly between patients with or without late potentials. There were significant differences between patients with ventricular arrhythmias and healthy volunteers; filtered QRS duration was significantly longer in patients with ventricular arrhythmias. SAECG may be beneficial in determining ventricular arrhythmia risk in tetralogy of Fallot patients postoperatively.

Does the abnormal signal-averaged electrocardiogram predict future appropriate therapy in patients with implantable cardioverter-defibrillators?

BACKGROUND

Several studies have documented the prognostic significance of the signal-averaged electrocardiogram (SAECG) both after myocardial infarction and nonischemic cardiomyopathy. However, whether the SAECG can identify patients with implantable cardioverter-defibrillator (ICD) who receive appropriate therapy has not been hitherto completely investigated.

METHODS

Between August 2002 and August 2004, 83 consecutive ICD patients who had had SAECGs recorded were enrolled in this study. All patients were followed up in the outpatient ICD clinic, and interrogated electrograms were collected.

RESULTS

Over 9.0 +/- 2.8 months of follow-up, 27 (32%) patients had appropriate ICD therapy for ventricular tachycardia or fibrillation; 15 (55.6%) patients had abnormal; and the remaining 12 (44.4%) had normal SAECGs. Of the 56 patients with no appropriate therapy, 27 (48.2%) and 29 (51.8%) patients had abnormal and normal SAECGs, respectively. There were no statistically significant differences between the 2 groups in SAECG findings (P = .41). A Cox regression analysis showed that the left ventricular ejection fraction was the only predictor of appropriate therapy (P = .02). Subgroup analysis of the patients with coronary artery disease and spontaneous monomorphic ventricular tachycardia indicated that left ventricular ejection fraction (P = .03) and abnormal SAECG (P = .02) were predictors of appropriate therapy.

CONCLUSIONS

Our data demonstrate that except for the subgroup of patients with coronary artery disease presenting with monomorphic ventricular tachycardia, the SAECG did not predict ventricular tachyarrhythmia recurrence and, hence, appropriate ICD therapy. Thus, SAECG findings should generally not be a factor in decision for ICD implantation.

Filtered QRS Duration on Signal-Averaged Electrocardiography Predicts Inducibility of Ventricular Tachycardia in Arrhythmogenic Right Ventricle Dysplasia

Treatment of arrhythmogenic right ventricular dysplasia (ARVD) is mostly based on the prevention of sudden cardiac death that results from arrhythmias. A clinical history suggestive of ARVD requires careful evaluation including electrophysiological study. The potential ability to identify those patients who will have inducible VT with electrophysiological study will enable better risk stratification and selection of vulnerable patients for electrophysiologically guided therapy. The purpose of the study was to evaluate the predictive ability of signal-averaged electrocardiography (SAECG) to predict inducibility of VT in patients with ARVD. The patient population consisted of 31 ARVD patients diagnosed with McKenna's criteria who underwent electrophysiological study. Electrophysiological study was considered positive if sustained monomorphic VT was induced. The sensitivity, specificity, and predictive accuracy of various SAECG criteria for inducibility of sustained monomorphic VT were also calculated. Twenty-one patients had inducible VT. The filtered QRS duration (fQRS), duration of signal <40 uV (LAS40), and root mean square voltage in the last 40 ms of QRS duration (RMS40) in ARVD patients induced versus noninduced were 122 +/- 21 and 103 +/- 8 ms (P=0.007), 45 +/- 20 and 28 +/- 14 ms (P=0.02), 19 +/- 19 and 32 +/- 22 uV (0.03), respectively. The ejection fractions were comparable in both groups. fQRS duration > or =110 ms had sensitivity of 91%, specificity of 90%, and a total predictive accuracy of 90% in predicting inducibility of VT in these patients. Filtered QRS duration on SAECG is predictive of electrophysiological study outcome in ARVD. Further studies will be needed to determine if SAECG results can predict the development of ventricular arrhythmias during follow-up.

A prospective study to determine the significance of ventricular late potentials in children with mitral valvar prolapse

We aimed prospectively to determine the incidence of ventricular arrhythmias and ventricular late potentials in children with mitral valvar prolapse, and to assess whether signal-averaged electrocardiography could identify which such children were at high risk of developing ventricular tachycardia. In all, we examined 151 children with mitral valvar prolapse, at an age of 12.2 +/- 3.1 years, and 164 healthy subjects aged 12.3 +/- 3.7 years. All children underwent 24-hour ambulatory Holter monitoring and echocardiography. The children with mitral valvar prolapse were followed prospectively for a mean of 64 months. There was a significantly higher prevalence of ventricular arrhythmias in those with prolapse than in the controls (p < 0.0001). Runs of ventricular tachycardia were observed in 3 children with mitral valvar prolapse compared with one from the control group. Late potentials were more frequently observed in the children with mitral valvar prolapse than in those who were healthy (p < 0.0001), and also in those with prolapse suffering ventricular arrhythmias compared with those without ventricular arrhythmias (p < 0.02). During follow-up, 24 children with prolapsing mitral valves developed non-sustained ventricular tachycardia, giving a frequency of 3.1/100 subject-years. The sensitivity of late potentials was low, at 52%, for the identification of children with mitral valvar prolapse who developed ventricular tachycardia, although the specificity was high at 90%. This gave a positive predictive value of 50%, and a negative predictive value of 91%. We conclude that prolapse of the mitral valve predisposes to the development of ventricular arrhythmias and late potentials in children. An abnormal signal-averaged electrocardiogram is a specific, but not very sensitive, predictor for the development of ventricular tachycardia in such children.

Late potentials: are they related to cardiovascular complications in children with type 1 diabetes?

INTRODUCTION

The aim of our study was to assess the influence of cardiovascular complications on the occurrence of late ventricular potentials (LP) in children with diabetes mellitus type 1.

MATERIALS AND METHODS

72 children (36 boys and 36 girls), with average course of diabetes type 1 of 6.5+/-2.8 years, were included into the study. Standard physical examination, blood pressure measurements, signal-averaged electrocardiogram (SAECG), autonomic test, 24-h Holter monitoring, and Doppler echo investigations were performed. The control group consisted of 55 sex- and age-matched healthy children. We utilised nonlinear logistic regression analysis to assess the effect of disease duration, albuminuria, insulin demand, cardiac autonomic neuropathy (CAN), heart rate variability (HRV) indices, diabetes complication score, metabolic control, systolic and diastolic blood pressure, left ventricular parameters, and ventricular arrhythmias on LP occurrence.

RESULTS

LP was discovered in 12 patients with diabetes and in 1 from the control group (P<.014). Diabetic children with LPs had thicker left ventricular posterior wall (LVPW) and longer diabetes duration time than children without LP (P<.045 and.031, respectively). Nonlinear regression model shows that duration of diabetes, CAN, and LVPW were the strongest independent parameters of LP occurrence (P<.001,.01 and.005, respectively).

CONCLUSIONS

Diabetes type 1 is associated not only with increased occurrence of abnormal SAECG but also with LP presence. The disease duration, posterior wall thickness, and CAN are independent predictors of LP appearance in diabetes type 1 children. The presence of cardiovascular complication has no influence on LP occurrence in diabetic children.

Diagnostic evaluation and management of patients with syncope

This article focuses on the evaluation of patients with syncope, a symptom not a disease. Syncope is a transient loss of consciousness associated with loss of postural tone with spontaneous recovery. The authors discuss the utility of an indications for different diagnostic tests, the indications for hospital admission, and the management of patients with certain known causes of syncope, including vasovagal and arrhythmic.

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.

Time-domain and spectral turbulence analyses of the signal-averaged electrocardiogram have different predictive values for sustained ventricular tachycardia in patients with myocardial infarction

We performed signal-averaged ECG and programmed stimulation in 15 patients after myocardial infarction with ventricular tachycardia and 49 patients after myocardial infarction without ventricular tachycardia to compare the spectral turbulence analysis and time-domain analysis of signal-averaged ECG for prediction of clinical and induced ventricular tachycardia. Sustained monomorphic ventricular tachycardia was inducible in all 15 patients with clinical sustained monomorphic ventricular tachycardia (group 1) and in 9 patients without clinical sustained monomorphic ventricular tachycardia (group 2). Sustained monomorphic ventricular tachycardia was not inducible in 40 patients without clinical sustained monomorphic ventricular tachycardia (group 3). While there was no difference in time-domain variables between groups 1 and 2, there were significant differences between groups 2 and 3. Values obtained by spectral turbulence analysis differed significantly between groups 1 and 2, but not between groups 2 and 3. Time-domain analysis showed abnormal values in 87% of group 1 patients, 78% of group 2, and 35% of group 3. Spectral turbulence analysis showed abnormal values in 93% of group 1, 11% of group 2, and 30% of group 3. In conclusion, frequency-domain spectral turbulence analysis of signal-averaged ECG is more useful than the time-domain analysis in predicting the spontaneous occurrence of sustained monomorphic ventricular tachycardia in patients after myocardial infarction.

High-resolution electrocardiography

High-resolution electrocardiography, often referred to as signal averaged electrocardiography (SAECG), has clinical utility in human medicine for detecting ventricular late potentials (LP) as predictors of future arrhythmic events, specifically reentrant type of ventricular tachycardia (VT). Time-domain analysis of the SAECG is conceptually similar to standard ECG analysis, but the primary objective is to detect LP, the marker for reentrant pathways within the myocardium. Frequency-domain analysis is investigational but provides the same information as time-domain analysis and both methods of analysis have limitations. The presence of LP has been associated with the ability to induce VT, unexplained syncope, and sudden arrhythmic death. Some cardiomyopathic dogs with VT have SAECG that appear to contain LP, and sudden death has occurred in these dogs.

Mismatch between myocardial accumulation of 123I-MIBG and 99mTc-MIBI and late ventricular potentials in patients after myocardial infarction: association with the development of ventricular arrhythmias

BACKGROUND

Late ventricular potentials are widely used to predict life-threatening arrhythmias, although the predictive value is low. To improve prediction, we correlated the incidence of ventricular arrhythmias with mismatches in myocardial 99mTc-methoxyisobutylisonitrile (MIBI)/(123)I-metaiodobenzylguanidine (MIBG) accumulation and late ventricular potentials (LP).

METHODS AND RESULTS

Fifty patients with old myocardial infarctions were divided into an LP-positive group (n = 19) and an LP-negative group (n = 31). On bull's-eye single photon emission computed tomographic MIBI and MIBG images, the heart was divided into 9 segments to evaluate the accumulation of the 2 nuclides. There was no difference in total defect score (TDS) for MIBI between the LP-positive and LP-negative groups. However, TDS for MIBG and differences TDS between MIBI and MIBG (ATDS) were significantly greater in the LP-positive group.

CONCLUSIONS

The incidence of severe ventricular arrhythmias was greater among patients with an increased ATDS in the LP-positive group. Thus the combination of these two methods may improve the prediction of ventricular arrhythmias after myocardial infarction.

Signal-averaged electrocardiograms in normal Doberman pinschers

Signal-averaged electrocardiograms (SAECGs) were performed on nonsedated normal dogs in left-lateral recumbency. Following signal averaging, both time-domain and 3-dimensional frequency-domain analyses were performed. For time-domain analysis, the high-frequency QRS (HFQRS) duration, duration of the terminal QRS complex less than 40 microV (LAS40), and root mean square (RMS) voltages (microV) of the terminal 40 milliseconds (RMS40) and 30 milliseconds of the QRS complex were calculated. For frequency-domain analysis, correlation ratios were calculated for 30-, 40-, 50-, and 60-millisecond segment lengths begun 10, 15, or 20 milliseconds before the end of the QRS complex. Spectro-temporal mapping was also performed. All of the parameters of the SAECGs analyzed in the time domain were associated with each other. LAS40 and RMS voltages regressed significantly (P < .0000) on the HFQRS duration. Ninety-five percent of the HFQRSs were 55-75 milliseconds, 95% of the LAS40s were 9-26 milliseconds, and 95% of the RMS40 voltages were 177-444 microV. None of the SAECGs contained evidence of ventricular late potentials. Spectro-temporal maps were similar in each dog when the same segment lengths and starting points were compared. No evidence of ventricular late potentials was observed. Correlation ratios were lower when windowed segments included 15 or 20 milliseconds (versus 10 milliseconds) of the terminal QRS complex. When only 10 milliseconds of the terminal QRS complex were included in windowed segments, the mean correlation ratios for 30- and 40-millisecond segment lengths were > 0.8 and > 0.61 in 67% of all analyses, respectively.

Precordial QT dispersion and inducible ventricular tachycardia

We compared the performance of precordial QT dispersion, late potentials on the signal-averaged electrocardiogram (ECG), and reduced left ventricular ejection fraction for identification of inducible ventricular tachycardia (VT) in 162 patients undergoing electrophysiologic study (EPS). QT(apex) dispersion in 56 patients with inducible VT (72 +/- 55 msec) was greater than that in 106 patients without inducible VT (55 +/- 36 msec, p < 0.01); dispersion was greater in both groups than in 144 normal subjects (33 +/- 19 msec). A QT(apex) dispersion partition of more than 68 msec, the upper ninety-fifth percentile in normal subjects, identified inducible VT with a specificity of 75% and a sensitivity of 45%. Although the performances of late potentials (specificity 82%, sensitivity 59%) and reduced ejection fraction (specificity 86%, sensitivity 54%) were each stronger than QT dispersion alone for identification of inducible VT, abnormal QT(apex) dispersion remained a significant additional predictor of inducible VT in a logistic regression model that included the three variables (specificity 78%, sensitivity 75%).

The top ten fallacies of nonsustained ventricular tachycardia

Nonsustained ventricular tachycardia (NSVT) continues to remain a subject of controversy. This is true despite a wealth of epidemiologic and basic/clinical laboratory findings that have accumulated during the past 2 decades. However, these data not only generate the impetus to conduct further research, but also provide compelling arguments against continued adherence to time honored precepts about NSVT that evolved since the inception of the "PVC Hypothesis," although never substantiated by rigorous scientific inquiry. This paper discusses the "top ten" fallacies of NSVT and details the data that support abandonment of them.

The effects of class I drugs on the cycle length of sustained ventricular tachycardia and the signal-averaged electrocardiogram

Evaluation of signal-averaged electrocardiograms (SAECGs) has been reported to be useful for predicting the patients with sustained ventricular tachycardia (SVT) combined with organic heart disease and at high risk for sudden cardiac death. However, the relationship between drug efficacy and SAECGs has not been established. We studied the effects of class I drugs on SVT using SAECGs. The study group consisted of 13 patients with SVT who underwent serial electropharmacologic trials. In 7 trials, SVT could not be induced after administration of class I drugs (group 1). In 17 trials, SVT was still inducible (group 2). Filtered QRS in group 2 were significantly prolonged after administration of class I drugs (p < 0.05). The prolongation of the SVT cycle length was correlated with the prolongation of the original QRS (p < 0.05) and with prolongation of the filtered QRS after administration of class I drugs (p < 0.01). The evaluation of the effects of class I drugs on SAECGs may be useful in predicting the inducibility of SVT and SVT cycle length.

Effect of hydrochlorothiazide therapy on cardiac arrhythmias in African-American men with systemic hypertension and moderate to severe left ventricular hypertrophy

The effect of hydrochlorothiazide therapy on ventricular arrhythmias was studied in 45 hypertensive African-American men with moderate to severe left ventricular (LV) hypertrophy. After medication washout, patients were treated with placebo followed by hydrochlorothiazide. Clinical, biochemical, and 48-hour ambulatory electrocardiographic data was collected after each treatment phase. Signal-averaged electrocardiograms were recorded in a subgroup of 24 patients. Average LV posterior wall thickness was 15 +/- 1.1 mm, septum 16 +/- 2 mm, LV mass 420 +/- 90 g, and LV mass index 212 = 51 g/m2. Systolic blood pressure (BP) was 168 +/- 18 mm Hg after the placebo phase and 146 +/- 15 mm Hg after hydrochlorothiazide; diastolic BP was 103 +/- 6 mm Hg and 89 +/- 9 mm Hg, respectively. Serum potassium decreased significantly from 4.2 +/- 0.4 mmol/L to 3.7 +/- 0.6 mmol/L after hydrochlorothiazide therapy. The average hourly incidence of ventricular premature contractions was 22 with placebo and 25 with hydrochlorothiazide. There were 3 and 1 couplets and 0.2 and 0.2 runs of ventricular tachycardia per patient per hour, respectively. Variables of signal-averaged electrocardiography did not differ between the 2 treatments. Thus, in hypertensive African-American men with moderate to severe LV hypertrophy, hydrochlorothiazide does not worsen ventricular arrhythmias or signal-averaged electrocardiographic variables.

Electrocardiographic predictors in the ESVEM trial: unsustained ventricular tachycardia, heart period variability, and the signal-averaged electrocardiogram

Sudden death remains a major problem because the causes are uncontrolled and accurate predictors have not been identified. However, new forms of electrocardiographic (ECG) analyses may provide prognostic information. The Electrophysiologic Study Versus Electrocardiographic Monitoring (ESVEM) trial provides a unique perspective to this issue because baseline and follow-up data were prospectively acquired on a relatively large sample of patients who were homogeneous with respect to sustained ventricular tachyarrhythmias, frequent ectopic activity, and inducible sustained ventricular tachyarrhythmias. Although analysis of the large amount of ECG data collected is in progress, initial studies have provided information about unsustained ventricular tachycardia (VTu), heart period (R-R) variability, and the signal-averaged ECG. VTu has been reported to have prognostic implications in several disorders, but its clinical significance in patients with sustained ventricular tachyarrhythmias is unknown. The significance of VTu recorded in the baseline (antiarrhythmic drug-free) 48-hour ECG recording in ESVEM study patients was examined; no variable representing the presence of VTu, the frequency of VTu events, or the duration of the longest episode of VTu was a significant predictor of arrhythmia recurrence, arrhythmic death, or all-cause mortality, although a trend was present for worse all-cause mortality in patients with VTu. R-R variability provides powerful prognostic information after acute myocardial infarction (AMI) and in patients with chronic ischemic heart disease. In general, R-R variability decreases dramatically at the time of AMI and recovers somewhat during the year after infarction. Although most patients in the ESVEM trial had chronic ischemic heart disease, R-R variability, which has been determined in about three fourths of the patients, was much lower than that reported in patients 1 year after MI. Instead, the mean values were closer to the more depressed values observed shortly after MI. This suggests a greater degree of autonomic dysfunction in patients with sustained ventricular tachyarrhythmias, frequent ventricular ectopic activity, and low ejection fractions, as compared with that for patients with chronic ischemic heart disease in general. Signal-averaged ECGs have also been shown to predict arrhythmic events in patients with ischemic heart disease. In a subset of the ESVEM patients, antiarrhythmic drugs that block sodium channels were found to prolong the filtered, signal-averaged QRS duration, especially the late potential portion. This correlated with prolongation of the cycle length of induced ventricular tachycardia. Sotalol appeared to have a differential effect on the signal-averaged ECG; the signal-averaged QRS shortened slightly in patients in whom induction of VT was suppressed by sotalol, whereas it appeared to lengthen slightly in patients in whom VT remained inducible despite sotalol. This suggests that sotalol may affect conduction in diseased tissue in some patients, and that this may affect suppression of ventricular arrhythmia induction by programmed stimulation.

Immediate and day-to-day reproducibility of the signal-averaged electrocardiogram in patients with coronary artery disease

The purpose of this study was to prospectively evaluate the immediate (5 minutes) and short-term (1 day) reproducibility of the signal-averaged electrocardiogram (SAECG) in patients with coronary artery disease. A total of 59 consecutive patients with coronary artery disease (50 male, 9 female, mean age 59 +/- 13 years) were included. Analysis was performed using a commercially available system with high-pass filters of 25, 40, and 80 Hz without any change in electrode position. The following time-domain parameters were measured: (1) total filtered QRS duration; (2) duration of high-frequency low-amplitude signals (HFLA); and (3) root-mean-square voltage of the terminal 40 ms of the QRS complex (RMS40). Correlation between pairs of measurements was excellent, ranging from 0.91-0.99 for QRS and HFLA duration, and from 0.83-0.98 for RMS40 value. However, the range of differences was wide for all parameters, especially at 25 and 80 Hz, revealing marked individual variations in selected cases. The immediate reproducibility of an initially normal SAECG was 95% at 25 Hz, 100% at 40 Hz, and 81% at 80 Hz; figures for an initially abnormal SAECG were 89%, 91%, and 93%, respectively, and the coefficient of agreement kappa was highest at 40 Hz than at 25 or 80 Hz. Discordant results were most frequently observed in patients with borderline values, or in cases with nonsimilar residual noise levels. In conclusion, the immediate and day-to-day reproducibility of the SAECG is excellent in patients with chronic stable coronary artery disease. However, individual variations are observed in selected cases, leading to modification in interpretation of the result. For this reason, individual reproducibility should be considered before evaluating the effect of any therapeutic intervention on the SAECG, especially in patients with borderline values of the quantitative parameters of the SAECG.

Prevalence, resolution, and determinants of late potentials in patients with unstable angina and left ventricular wall motion abnormalities

Although transient myocardial ischemia such as exercise-induced ischemia has not been reported to be associated with the occurrence of late potentials, the association of late potentials with more profound ischemic damage, which is represented by reversible but prolonged left ventricular wall motion abnormalities, has not been demonstrated. We prospectively evaluated 37 unstable angina patients who had reversible but prolonged wall motion abnormalities after resolution of chest pain and electrocardiogram (ECG) changes. Signal-averaged ECG (SAECG) and echocardiogram were recorded during the acute phase and before hospital discharge. Late potentials were present in 6 (16 percent) patients on the initial SAECG recording and resolved in all 6 patients on the second recording before hospital discharge. Normalization of inferior left ventricular wall motion abnormality and multivessel disease were observed more frequently in patients with late potentials on the initial recording than in patients without (p < 0.05 and p < 0.05, respectively). In conclusion, late potentials were observed in patients who had reversible but prolonged wall motion abnormalities; these late potentials were resolved with improvement of left ventricular wall motion abnormalities. These results suggest that myocardial ischemia with prolonged wall motion abnormalities is a possible mechanism of the occurrence of late potentials.

Is the time domain signal-averaged electrocardiogram helpful in patients with ventricular tachycardia without apparent structural heart disease?

The signal-average electrocardiogram (SAECG) has been a screening method for identifying patients at risk for ventricular tachycardia (VT) in the setting of coronary artery disease (CAD). Its significance in patients with VT unrelated to CAD or left ventricular dysfunction is undetermined. In order to define the value of SAECG in this patient population further, we compared the time domain SAECG at 25, 40, and 80 Hz filters in 35 patients with clinically symptomatic VT in the absence of structural heart disease was compared with 10 normal controls and 10 patients with CAD and inducible VT. SAECG data in patients without structural heart disease were intermediate between normal controls and patients with CAD. No single or combined SAECG criterion helped to differentiate between patients with inducible and noninducible VT. There was no concordance to other arrhythmia testing. It was concluded that signal-averaged electrocardiography may have little screening value in VT unrelated to CAD or left ventricular dysfunction.

Use of signal-averaged electrocardiography for predicting inducible sustained monomorphic ventricular tachycardia in patients with bundle branch block with and without a history of syncope

The aim of this study was to examine the utility of signal-averaged electrocardiography in relation to inducible sustained monomorphic ventricular tachycardia in patients with bundle branch block. One hundred fourteen patients with bundle branch block underwent signal-averaged electrocardiography in the time domain and programmed ventricular stimulation. Sustained monomorphic ventricular tachycardia was induced in 17 patients. The mean values of the three signal-averaged electrocardiographic variables analyzed differed significantly between the inducible and the noninducible group. The filtered QRS duration showed the most prominent difference between the two groups, and a filtered QRS duration > or = 155 msec had a sensitivity of approximately 80%, a specificity of 60%, and a total predictive value of 65%. In the subgroup of patients with syncope, a combination of these criteria with a history of coronary artery disease had a sensitivity of 100% and a specificity of 90%.

Signal-averaged electrocardiography and ventricular tachycardia as predictors of mortality after acute myocardial infarction in elderly patients

Signal-averaged electrocardiography and 24-hour ambulatory electrocardiographic monitoring were performed in 121 elderly patients > 6 months after acute myocardial infarction. All patients had asymptomatic complex ventricular arrhythmias and a left ventricular ejection fraction > or = 40%. Rates of sudden, cardiac, and total death were compared between groups with and without nonsustained ventricular tachycardia and between normal and abnormal signal-averaged electrocardiographic studies. The prevalence of an abnormal signal-averaged electrocardiographic study was 36%. Thirty-seven percent of the patients had nonsustained ventricular tachycardia, and the remaining patients had complex ventricular arrhythmias other than ventricular tachycardia. There were 27 sudden and 48 total cardiac deaths, and 66 deaths from all causes during a mean follow-up period of 30 months. Kaplan-Meier survival analysis showed a lower rate of sudden and cardiac death in the group without nonsustained ventricular tachycardia. Although there was a trend toward a lower rate of sudden death in patients with a normal signal-averaged electrocardiogram, there was no statistical difference in the rates of sudden, total cardiac, or total death between patients with normal or abnormal studies. The negative predictive value of having neither an abnormal signal-averaged electrocardiogram nor nonsustained ventricular tachycardia was 94% for sudden death. In elderly patients with complex ventricular arrhythmias and ejection fraction > or = 40% at least 6 months after an acute myocardial infarction, presence of nonsustained ventricular tachycardia predicted a higher rate of sudden and cardiac death. Signal-averaged electrocardiography alone was not predictive.

Performance of the signal-averaged electrocardiogram: relation to baseline QRS duration

Analysis of the duration and terminal components of the filtered QRS complex on the signal-averaged electrocardiogram (ECG) has been widely used for the detection of late potentials. Although filtered QRS duration is strongly related to 12-lead QRS duration, the relation of performance of the signal-averaged ECG to baseline QRS duration has not been critically examined. To examine the relation of test performance of the signal-averaged ECG to 12-lead QRS duration and to test the hypothesis that the difference between filtered and baseline 12-lead QRS duration would reflect more accurately the presence of late potentials than would analysis of the filtered QRS alone, we evaluated signal-averaged and 12-lead ECGs in 144 normal subjects and in 132 patients who were examined by electrophysiologic study and of whom 45 had inducible sustained monomorphic ventricular tachycardia. The signal-averaged ECG was considered positive by standard late potential criteria when the filtered vector QRS duration was > 114 msec and either the root-mean-square voltage of the terminal 40 msec of the filtered QRS was < 20 microV or the low-amplitude signal of the terminal filtered QRS was > 38 msec. A new signal-averaged ECG criterion for the presence of late potentials was developed in the 144 normal subjects on the basis of the difference between the longest filtered QRS duration in any of the orthogonal leads and QRS duration on the baseline 12-lead ECG ("the QRS difference"), which was adjusted by regression analysis for the decreasing QRS difference found with increasing baseline QRS duration.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of sympathetic stimulation induced by mental stress on signal-averaged electrocardiogram

We evaluated the influence of sympathetic stimulation, induced by mental stress test, on signal-averaged ECG in 30 healthy subjects and in 30 patients with previous myocardial infarction. Both patient and control groups underwent three consecutive signal-averaged ECG: under basal conditions, during a continuous mental stress test, and 5 min after the mental stress test. The signal-averaged ECG parameters, analyzed by mean of a bandpass filter of 25-250 and 40-250 Hz, were: the filtered QRS duration, the duration of the low-amplitude high frequency signals in the terminal portions of the QRS complex below 40 microV (HFLA), and the root mean square voltage in the last 40 ms of the filtered QRS (RMS). The mathematical stress test was considered effective when the heart rate increased by at least 15 beats/min, remaining stable for the total duration of the signal-averaged ECG acquisition. A significant reduction of the filtered QRS duration and HFLA with a simultaneous increase of RMS were found in control group, while no significant changes occurred in patient group. These results indicate that the sympathetic nervous system may affect the results of signal-averaged ECG, probably by influences on intraventricular conduction, in healthy subjects. On the contrary, myocardial alterations in ischemic heart disease induce modification of signal-averaged ECG not influenced by autonomic nervous system activity.

Time- and frequency-domain analyses of the signal-averaged ECG in patients with arrhythmogenic right ventricular dysplasia

BACKGROUND

Arrhythmogenic right ventricular dysplasia (ARVD) is characterized by recurrent ventricular tachycardia of right ventricular origin and a cardiomyopathy with hypokinetic areas involving the free wall of the right ventricle. Subjects have a risk of sudden cardiac death, particularly during sports and strenuous exercise. Routine clinical examinations may be normal, but fragmented or delayed electrograms are usually recorded in the right ventricle of these patients. However, the frequency with which late potentials are detected by conventional time-domain analysis of the signal-averaged ECG (SAECG) is not high. This study evaluated the usefulness of the frequency-domain analysis of the SAECG in addition to the conventional time-domain analysis for a screening test to detect patients with ARVD.

METHODS AND RESULTS

SAECG was recorded by using a bipolar X, Y, and Z lead system in 28 patients with ARVD (mean age, 38 +/- 13 years) and 35 age-matched normal subjects (mean age, 35 +/- 11 years). The conventional time-domain analysis of the SAECG was performed at two different high-pass filter settings, 25 and 40 Hz, and the low-pass cutoff frequency was fixed at 250 Hz. The fast-Fourier transform analysis of SAECG was performed using a Blackman-Harris window. Area ratio 1 (area of 20 to 50 Hz)/(area of 0 to 20 Hz) and area ratio 2 (area of 40 to 100 Hz)/(area of 0 to 40 Hz) were calculated. In the conventional time-domain analysis, 20 (71%) and 18 (64%) patients had positive criteria at filter settings of 25 and 40 Hz, respectively. In the frequency-domain analysis, 18 (64%) and 20 (71%) patients had abnormal values in area ratios 1 and 2, respectively. Combining the time- and frequency-domain analyses, all patients were judged positive, with a sensitivity of 100% and a specificity of 94%.

CONCLUSIONS

Each result of the time- and frequency-domain analyses revealed that both methods had equivalent value. Combining the two domain analyses improved the sensitivity without reducing the specificity. These findings suggest that combining the time- and frequency-domain analyses of the SAECG may be useful as a screening test to detect patients with ARVD.

Relation between heart rate variability and spontaneous and induced ventricular arrhythmias in patients with coronary artery disease

OBJECTIVES

The aim of this study was to determine the relation between autonomic control of heart rate and the spontaneous occurrence and inducibility of ventricular arrhythmias in patients with coronary artery disease.

BACKGROUND

Low heart rate variability increases the risk of arrhythmic events. It is not known whether impaired autonomic heart rate control reflects alterations in functional factors that contribute to the initiation of spontaneous arrhythmias or whether it is the consequence of an anatomic substrate for reentrant tachyarrhythmias.

METHODS

Fifty-four patients with coronary artery disease with a history of sustained ventricular tachycardia (n = 25) or cardiac arrest (n = 29) were studied by 24-h ambulatory electrocardiographic recording and by programmed electrical stimulation. Heart rate variability was compared among the patients with and without spontaneous ventricular arrhythmias and with and without inducibility of sustained ventricular tachyarrhythmias.

RESULTS

Eight patients had a total of 21 episodes of sustained ventricular tachycardia on Holter recordings. Standard deviation of RR intervals and low frequency and very low frequency components of heart rate variability were significantly blunted in patients with sustained ventricular tachycardias compared with those without repetitive ventricular ectopic activity (p < 0.05, p < 0.01 and p < 0.05, respectively). However, no significant alterations were observed in heart rate variability before the onset of 21 episodes of sustained ventricular tachycardia. Heart rate variability did not differ between the patients with or without nonsustained episodes of ventricular tachycardia. In patients with frequent ventricular ectopic activity, low frequency and very low frequency power components were significantly blunted compared with those with infrequent ventricular ectopic activity (p < 0.01 and p < 0.001, respectively). Heart rate variability did not differ significantly between the patients with and without inducible sustained ventricular tachyarrhythmias.

CONCLUSIONS

Impaired very low and low frequency oscillation of heart rate reflects susceptibility to the spontaneous occurrence of ventricular arrhythmias but may not reflect the instantaneous triggers for life-threatening arrhythmias or a specific marker of the arrhythmic substrate for ventricular tachyarrhythmias.

Comparison of signal-averaging electrocardiographic systems using device specific criteria in 104 normal subjects

The advent of several signal-averaged electrocardiogram (SAECG) systems for late potential (LP) assessment warrants comparisons to assess intersystem reproducibility and variability. Simultaneous SAECGs on two systems, Arrhythmia Research Technology (ART) and Marquette (MEI), were performed on 104 normal volunteers (53 males, age 44 +/- 14 years), and analyzed filtered QRS duration (TFQRS), root mean square voltage (RMS40), and low amplitude signal duration (LAS40), filtered at 40-250 Hz. The Gomes criteria (TfQRS > 114 msec, RMS40 < 20 microV and LAS40 > 38 msec) were used as criteria for LP. The data was also analyzed using the recently proposed system specific criteria for MEI (TFQRS > 120 msec, RMS40 < 20 microV and LAS40 > 38 msec). Where appropriate, statistical analysis was performed using simple linear and Spearman's rank correlation, analysis of variance, Finn's R and McNemar's test.

RESULTS

The means +/- SD for ART and MEI were: TFQRS: 97.2 +/- 8.9 vs 108.2 +/- 7.2 msec (R = 0.76), RMS40: 31.8 +/- 17.8 vs 45.3 +/- 19.9 microV (R = 0.53), and LAS40: 32.2 +/- 8.4 vs 30 +/- 7.4 (R = 0.54). When the Gomes criteria were applied, the number of subjects identified by each system as abnormal were: TFQRS = 3 vs 22 (P < 0.001), RMS40 = 20 vs 8 (P = 0.004), LAS40 = 21 vs 9 (P = 0.004), TFQRS/RMS40 = 3 vs 6 (P = 0.38), TFQRS/LAS40 = 3 vs 7 (P = 0.22), RMS40/LAS40 40 = 17 vs 8 (P = 0.02), and all three criteria = 3 vs 6 (P = 0.38) for ART vs MEI, respectively. Percent agreement was 81.7% for TFQRS and 84.6% for RMS40 and LAS40 when single criteria were applied. Agreement improved when combined criteria were utilized (87.5%-95.2% for any two criteria and 95.2% for all three criteria). The intersystem agreement that was not due to chance was 0.63-0.69 for single criteria and 0.75-0.90 for combined criteria. Disagreement was highly significant for the three criteria when used singly and for RMS40 and LAS40 combined. Disagreement was not significant when TFQRS was used in combination with > or = one other criteria. When the MEI criteria were applied, there was a decrease in the number of subjects identified by the MEI system as abnormal, using the TFQRS criteria singly or in combination. Percent agreement for system specific TFQRS measurements was 94.2% for single criteria and 97.1% for combined criteria. The intersystem agreement that was not due to chance improved (88-0.94). Disagreement between system specific criteria for TFQRS was not significant (P > 0.05).

CONCLUSION

Our data indicate that although there is a general correlation between ART and MEI measurements, variability is substantial, leading to significant differences when the criteria for LP are applied, especially for single parameter determinations. Thus, there is a need to establish system specific normal ranges and more accurate criteria for LP parameters.

The effect of successful angioplasty on variables of signal-averaged electrocardiogram and ventricular wall motion in patients with a first myocardial infarction

The correlation among three variables of late potentials (LPs) obtained by signal-averaged electrocardiography (SAECG) and improvement of ventricular wall motion estimated by echocardiography were studied in 66 patients with a first acute myocardial infarction (MI). Patients with bundle-branch block, intraventricular conduction delay, multi-vessel disease, previous MI, repeat percutaneous transluminal coronary angioplasty (PTCA), or evidence of reinfarction during a 6-month follow-up were excluded. A total of 66 patients was divided into two groups, with (Group 1: n = 27, age 56 +/- 11) or without (Group 2: n = 39, age 61 +/- 10) improvement of ventricular wall motion. Three variables of LPs and ventricular wall motion index (WMI) estimated and scored by echocardiography at admission (WMI 1) and at 6 months after MI (WMI 2) were compared in each group. In Group 1 (WMI 1 vs. WMI 2, p < 0.002), 20 of 27 patients underwent successful angioplasty; in Group 2 (WMI 1 vs. WMI 2, p = NS), 7 of 39 patients had successful emergency angioplasty. There were significant differences in three variables of LPs between the time of admission and at 6 months after MI in Group 1 but not in Group 2. Higher incidence of LPs and greater frequency of successful emergency PTCA were found in Group 1 compared with Group 2. These results suggest that because myocardial ischemia is reversed by successful angioplasty, ventricular wall motion is improved and the arrhythmogenic substrate that generates LPs is stabilized electrically. Stunned or hibernating myocardium may be the arrhythmogenic substrate that generates LPs.

Correlation of the endocardial fragmented electrogram with body surface signal-averaged electrocardiographic mapping

We compared signal-averaged electrocardiography (SAE), SAE mapping, and left ventricular catheter mapping in 60 patients with ischemic heart disease. Using the data obtained in patients with no fragmented electrograms (FE) in the left ventricle, the late potential was defined by SAE as a filtered QRS duration > 131 msec or a root mean square voltage < 16 microV for the last 40 msec of the QRS complex. SAE mapping was performed by recording the signal-averaged electrocardiogram at 48 sites on the body surface. With SAE mapping, the filtered QRS duration and the area in the last 20 msec of the QRS complex were significantly different between the patients with and without FEs. The late potential was defined by SAE mapping as a filtered QRS duration > 136 msec or an area < 28 microV.msec for the last 20 msec of the QRS complex. The sensitivity and specificity of detecting FEs were 46% and 88%, respectively, by the SAE filtered QRS criterion, while they were 66% and 88% by the root mean square criterion. In contrast, SAE mapping gave values of 66% and 92% by the filtered QRS criterion, as well as values of 100% and 92% by the area criterion. Thus, SAE mapping provided better detection of the FE and was more closely correlated with the results of catheter mapping, suggesting its potential for clinical application.

Incidence and prediction of induced ventricular tachyarrhythmias in idiopathic dilated cardiomyopathy

The value of time-domain and spectral turbulence analyses of the signal-averaged electrocardiogram (SAECG) for predicting induction of sustained monomorphic ventricular tachycardia (VT) was prospectively investigated in 70 patients with idiopathic dilated cardiomyopathy. Sustained VT was induced in 9 patients (13%). The prevalence of abnormal time-domain and spectral analyses was 16 and 37%, respectively. The total predictive accuracy of time-domain and spectral analyses for VT induction was 86 and 67%, respectively (p < 0.01). The predictive accuracy of time-domain and spectral analysis was similar in patients without an intraventricular conduction defect (94 and 84%, respectively). However, the predictive accuracy of time-domain was higher than that of spectral analysis in patients with an intraventricular conduction defect (65 vs 25%; p < 0.05). The poor concordance between spectral analysis and programmed stimulation results was mainly due to the high number of false-positive recordings in the presence of an intraventricular conduction defect (9 of 20 cases). With the use of stepwise discriminant function analysis, an abnormal time-domain SAECG was the only variable predicting the induction of sustained VT (p < 0.0003). In dilated cardiomyopathy, an abnormal time-domain SAECG and induced sustained VT are rare, both time-domain signal-averaged electrocardiography and spectral analysis have a high predictive accuracy for VT induction in patients without an intraventricular conduction defect, and spectral analysis does not improve VT prediction in those with a conduction defect.

Assessment of effects of autonomic stimulation and blockade on the signal-averaged electrocardiogram

BACKGROUND

Signal-averaged ECG is a noninvasive test designed to detect "late potentials." The effects of alterations in autonomic tone on the signal-averaged ECG have not been evaluated systematically.

METHODS AND RESULTS

The effects of autonomic stimulation and blockade on the signal-averaged ECG were evaluated in 14 healthy subjects (8 men and 6 women; age, 28.5 +/- 4.8 years) on 2 separate days. The signal-averaged ECG was recorded at baseline and after physiological and pharmacologic beta-adrenergic stimulation (tilt, exercise, and epinephrine and isoproterenol infusions), sequential and combined beta-adrenergic and parasympathetic blockade, and alpha-adrenergic stimulation before and after parasympathetic blockade. Analysis was performed with a bidirectional filter (40-Hz high-pass). Significant changes in the signal-averaged QRS duration from baseline (105.1 +/- 12.0 milliseconds) were noted with tilt (96.8 +/- 8.8 milliseconds), tilt after double blockade (97.5 +/- 9.0 milliseconds), epinephrine (110.5 +/- 11.8 milliseconds), and isoproterenol (99.6 +/- 12.6 milliseconds). Changes in the root-mean-square voltage of the terminal 40 milliseconds and the low-amplitude (< 40 microV) signal duration paralleled the changes in the QRS duration.

CONCLUSIONS

The signal-averaged ECG does not measure only "fixed" parameters but rather is altered under a variety of physiological and pharmacologic conditions. Upright tilt leads to shortening of the QRS duration before and after autonomic blockade; thus, the decrease in QRS duration with tilt may be related to factors other than changes in autonomic tone. These findings have implications for interpretation of the results of signal-averaged ECG.

Signal-averaged electrocardiography in elderly subjects with and without heart disease

Prevalence of abnormal signal-averaged electrocardiography in normal populations appears to be low, but has not been studied previously in an asymptomatic elderly population. To study the prevalence of abnormal ventricular late potentials in an elderly population, a group of 51 subjects with no evidence of cardiac disease and ranging in age from 62 to 102 years underwent signal-averaged electrocardiography. Results were compared to a group of 179 patients similar in age but with complex ventricular arrhythmias, and to a group of 25 asymptomatic volunteers under the age of 50. The prevalence of an abnormal signal-averaged ECG was 14% in the normal elderly subjects, and 31% in the patients (P = 0.01), and 4% in the young subjects (P = NS). We conclude that the prevalence of abnormal ventricular late potentials in elderly patients without heart disease is similar to levels reported in other populations of normal controls, but elderly patients with cardiac disease have a significantly higher prevalence of abnormal signal-averaged ECG studies than the normals.

Does atrial fibrillation cause false-positive late potentials?

We hypothesized that atrial fibrillation may cause false-positive late potentials due to the recording of baseline atrial activity. We performed signal-averaged ECGs in 26 patients with atrial fibrillation before and after conversion to normal sinus rhythm. Signal-averaged ECGs were recorded for > 200 cycles with a noise level of < or = 0.5 microV. The signals were band-pass filtered at 40-250 Hz. We examined filtered QRS duration (fQRS), duration of low amplitude signal < 40 microV (LAS), and the root mean square (RMS) of the terminal 40 msec of the QRS complex. A late potential was considered present when two of the following three criteria were met: fQRS > or = 114 msec, LAS > or = 38 msec, and RMS < or = 20 microV. The mean +/- standard deviation of the fQRS in atrial fibrillation and sinus rhythm were 113 +/- 28 and 110 +/- 25 msec; of the LAS 38 +/- 17 and 37 +/- 15 msec; of the RMS 27 +/- 22 and 28 +/- 21 microV; of the noise 0.25 +/- 0.08 and 0.22 +/- 0.07 microV (P = NS). Ten signal-averaged ECGs in atrial fibrillation had late potentials. With reversion to sinus rhythm one of these 26 patients gained a late potential; two others lost a late potential (P = NS by McNemar's Chi-square). There was no significant difference in the signal-averaged ECG parameters or noise levels. In conclusion, signal-averaged ECG parameters are not significantly changed by cardioversion of atrial fibrillation to normal sinus rhythm.(ABSTRACT TRUNCATED AT 250 WORDS)

Determinants of induction of ventricular tachycardia in nonsustained ventricular tachycardia after myocardial infarction and the usefulness of the signal-averaged electrocardiogram

Assessment of the implications of clinical and noninvasive variables, including the results of signal-averaged electrocardiography, was performed > or = 3 weeks after myocardial infarction in 57 patients with nonsustained ventricular tachycardia (VT) who underwent programmed ventricular stimulation to guide antiarrhythmic therapy. The clinical and noninvasive parameters assessed included ages, left ventricular ejection fractions, sites of infarction, presence of akinetic or dyskinetic left ventricular segments, history of syncope, history of coronary artery bypass surgery, and presence or absence of late potentials from signal-averaged electrocardiography. Other than the presence of late potentials, no clinical or noninvasive parameters identified such persons with a significantly higher likelihood of inducible VT. When assessed as positive if 1 or more variables were abnormal, 16 of 16 (100%) patients with versus 17 of 41 without inducible VT had late potentials (p < 0.002). With more stringent criteria required (defined as prolongation of the QRS vector complex duration and low root-mean-square voltage of the terminal 40 ms of the vector complex) 8 of 16 patients (50%) with and 4 of 41 (10%) without inducible VT had late potentials recorded (p < 0.002). Thus, the signal-averaged electrocardiogram may enable identification of persons with nonsustained VT after myocardial infarction who are most likely to have VT induced at programmed ventricular stimulation.

Effects of streptokinase during acute myocardial infarction on the signal-averaged electrocardiogram and on the frequency of late arrhythmias

Although a number of studies have shown that the incidence of late potentials is lower after thrombolytic therapy, it is not known whether this is paralleled by fewer arrhythmic events during long-term follow-up. In patients with first acute myocardial infarction, filtered QRS duration was significantly shorter when treated with streptokinase (95 +/- 11 ms, n = 53) than when treated with conventional therapy (99 +/- 12 ms, n = 77, p < 0.05). The low-amplitude signal (D40) was shorter after thrombolysis (28 +/- 11 vs 33 +/- 12 ms, p < 0.02). Terminal root-mean-square voltage did not differ significantly (41 +/- 24 vs 35 +/- 23 microV). Irrespective of treatment, late potentials were predictive in the complete group (n = 171) for arrhythmic events during follow-up (13 +/- 6 months, range 6 to 24) (hazard ratio 7.7, p < 0.02, Cox proportional-hazards survival analysis), but treatment (streptokinase vs conventional) did not significantly affect outcome when added to the model. It is concluded that thrombolysis prevents the development of late potentials. However, this study does not confirm the hypothesis that prevention of late potentials leads to a decrease in arrhythmic events.

Nonsustained ventricular tachycardia: identification and management of high-risk patients

NSVT is common in normal persons and in patients with a variety of heart diseases. When present in patients with coronary artery disease, particularly after a recent myocardial infarction, it is associated with an increased risk of sudden and nonsudden cardiac death. However, its prognostic significance in patients with nonischemic heart disease, with the possible exception of hypertrophic cardiomyopathy, remains controversial. In patients with coronary artery disease, certain diagnostic tools (e.g., determination of left ventricular function. PVS) help to identify low- and high-risk patients who may or may not benefit from antiarrhythmic treatment. There is no consensus at this point as to the best approach for identifying and treating high-risk patients. Ongoing clinical trials should provide important information on the roles of signal-averaged ECGs and PVS in the management of patients with NSVT and coronary artery disease. In the meantime, treatment should be individualized for each patient. beta-Blockers should probably be the first line of therapy to control symptoms. Asymptomatic potentially high-risk patients (i.e., those with LVEF < 40%) should be referred for enrollment in randomized controlled studies.

The signal-averaged P wave duration: a rapid and noninvasive marker of risk of atrial fibrillation

OBJECTIVES

This study was undertaken to determine the ability of the signal-averaged electrocardiogram (ECG) to identify evidence of delayed atrial activation in patients with a history of atrial fibrillation.

BACKGROUND

Atrial fibrillation is a reentrant rhythm and depends on atrial conduction delay for its development. The signal-averaging technique is useful for accurately measuring total cardiac activation times, including delayed low amplitude signals, and thus can help identify the substrate for reentrant arrhythmias.

METHODS

Standard 12-lead and signal-averaged ECGs were recorded from 15 patients with a documented history of prior paroxysmal or chronic atrial fibrillation and 15 age- and disease-matched control subjects without a history of atrial fibrillation. Signal averaging was performed using an orthogonal lead system with the QRS complex as a trigger and the P wave as a template for the signal-averaging process. Total P wave duration was measured before and after filtering with a least squares fit filter. The P wave complexes on the three bipolar leads were combined into a vector combination of orthogonal leads. The total P wave duration of the individual unfiltered and filtered leads and the vector combination of filtered leads were calculated and used for analysis.

RESULTS

The P wave duration by standard ECG was not significantly different in patients with a history of atrial fibrillation and control subjects. Signal-averaged P wave durations were measured from orthogonal leads before and after digital filtering. Mean unfiltered P wave duration was significantly longer in patients with a history of atrial fibrillation than in control subjects (132 +/- 22 vs. 114 +/- 14 ms [p < 0.03] in the X lead, 135 +/- 21 vs. 115 +/- 15 ms [p < 0.03] in the Y lead and 133 +/- 23 vs. 114 +/- 14 ms [p < 0.03] in the Z lead). Mean filtered P wave duration was also longer in patients with atrial fibrillation than in control subjects (151 +/- 23 vs. 130 +/- 19 ms [p < 0.01] in the X lead, 157 +/- 22 vs. 136 +/- 17 ms [p < 0.01] in the Y lead and 154 +/- 23 vs. 135 +/- 15 ms [p < 0.01] in the Z lead). After filtering, a vector composite of orthogonal leads was determined. Again, P wave duration in patients with a history of atrial fibrillation exceeded that in the control subjects (162 +/- 15 vs. 140 +/- 12 ms [p < 0.01]). Using the vector composite of filtered orthogonal leads, a P wave duration > or = 155 ms was associated with a sensitivity of 80%, a specificity of 93% and a positive predictive value of 92% for identifying patients with history of atrial fibrillation.

CONCLUSIONS

A prolonged signal-averaged P wave duration may be a simple noninvasive marker of the risk for development of atrial fibrillation.

Current usefulness of the signal-averaged electrocardiogram

Signal-averaged electrocardiography is a relatively simple, noninvasive technique by which valuable information can be gained to help in the management of patients with cardiovascular disease. The presence of late potentials on the SAECG is a good marker for the presence of an arrhythmogenic substrate that is believed to be the source of ventricular tachycardia in patients with coronary artery disease. The value of the detection of late potentials has been studied best after myocardial infarction, when the absence of late potentials makes the occurrence of an arrhythmic event very unlikely. The positive predictive value for an arrhythmic event to occur in the presence of late potentials is low, however, comparable to the predictive value of decreased left ventricular function, complex ventricular ectopy, or abnormal autonomic tone. This appears to have its explanation in the complex pathophysiology behind the occurrence of arrhythmic events. Improved accuracy for the SAECG is achieved when the result of the test is interpreted with consideration of the presence or absence of other predictive markers. A thorough understanding of the signal-averaged electrocardiogram makes optimal clinical use of the information gained from this easily acquired test possible.

Identification of patients with ventricular tachycardia after myocardial infarction by high-resolution magnetocardiography and electrocardiography

The value of time domain analysis of late fields in the high-resolution magnetocardiogram in the identification of myocardial infarction patients with ventricular tachycardia was investigated in 30 subjects: 10 patients with documented sustained ventricular tachycardia and old myocardial infarction, 10 patients with old myocardial infarction without complex ventricular arrhythmias, and 10 normal volunteers. The duration of the QRS complex in the magnetocardiogram was significantly longer in ventricular tachycardia patients compared to myocardial infarction patients (144 (SD, 33) vs 109 (SD, 8) ms; p = 0.004). The root-mean-square field of the last 60 ms of the QRS complex was smaller in ventricular tachycardia patients than in myocardial infarction patients (830 (SD, 650) vs 1,480 (SD, 730) fT, respectively; p = 0.047). Also, the duration of the low-amplitude signal less than 700 fT was longer in ventricular tachycardia patients than in myocardial infarction patients (47 (SD, 28) vs 28 (SD, 8) ms, respectively; p = 0.048). The sensitivity and specificity in identifying ventricular tachycardia patients were both 80%, and the positive and negative predictive values were 78% and 86%, respectively. High-resolution electrocardiography recorded during the same session performed slightly better: sensitivity 90%, specificity 90%, and positive and negative predictive values 90%. The signal-to-noise ratio of electrocardiogram was higher (approximately 2 x) than that of magnetocardiogram. It is concluded that the new magnetocardiographic technique seems helpful in screening patients at risk of ventricular arrhythmias after myocardial infarction. The results encourage further refinement of the technique and application in prospective studies.

Prognostic value of an abnormal signal-averaged electrocardiogram in patients with nonischemic congestive cardiomyopathy

BACKGROUND

An abnormal signal-averaged ECG (SAECG) has predictive value for arrhythmic events in patients with coronary artery disease. The purpose of this study was to investigate whether an abnormal SAECG could provide prognostic information in patients with nonischemic dilated cardiomyopathy.

METHODS AND RESULTS

We prospectively obtained SAECGs in 114 patients with dilated nonischemic cardiomyopathy. Twelve-lead ECGs, left ventricular ejection fractions, hemodynamic measurements, and peak exercise oxygen consumption (VO2) also were measured. An SAECG was defined as abnormal by any one of the three following criteria: filtered QRS duration > 120 msec, root-mean-square voltage in the last 40 msec < 20 microV, or duration < 40 microV > 38 msec at 40 Hz. Sixty-six patients had a normal SAECG, 20 patients had an abnormal SAECG, and 28 patients had bundle branch block (BBB). Mean follow-up was 10 +/- 5 months. Age, ejection fraction, peak VO2, pulmonary capillary wedge pressure, and cardiac index were not statistically different among the three groups. Use of antiarrhythmic drugs was similar among the three groups, although patients with BBB had more implantable defibrillators (p < 0.05). The incidence of previous atrial arrhythmias was similar for the three groups. Patients with abnormal SAECG or BBB had more past episodes of sustained ventricular tachycardia and/or sudden death episodes (n = 9) than patients with normal SAECG (n = 1) (p < 0.01). Prospectively, none of the 66 patients with normal SAECG died suddenly or had sustained ventricular arrhythmias. Two deaths occurred from progressive heart failure, and three patients required urgent transplant. In the 20 patients with an abnormal SAECG, four patients had sustained ventricular tachycardia, five patients died suddenly, two patients died from progressive heart failure, and one patient required urgent transplant. In the patients with BBB, four patients had sustained ventricular tachycardia, and four patients required urgent transplant. One-year event-free survival, i.e., absence of ventricular tachycardia and/or death, was 95% in patients with normal SAECG, 88% in patients with BBB, and only 39% in patients with an abnormal SAECG (p < 0.001). Multivariate analysis demonstrated that SAECG and New York Heart Association classification were independent predictors of survival.

CONCLUSIONS

Patients with an abnormal SAECG had a statistically significant increase in sustained ventricular arrhythmias and/or death than did patients with a normal SAECG or BBB. This study demonstrates that an abnormal SAECG is a marker of past and future arrhythmic events in patients with nonischemic dilated cardiomyopathy. In contrast, patients with a dilated cardiomyopathy with a normal SAECG have an excellent prognosis with adverse outcome only from progressive heart failure.