Usefulness of signal-averaged electrocardiogram in idiopathic dilated cardiomyopathy for identifying patients with ventricular arrhythmias

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.

Value of microvolt T-wave alternans for predicting patients who would benefit from implantable cardioverter-defibrillator therapy

Despite considerable progress in the management of coronary artery disease and dilated cardiomyopathy, a substantial proportion of patients remains at the risk of life-threatening arrhythmic events. The Multicenter Automatic Defibrillator Implantation II and Sudden Cardiac Death Heart Failure studies have conclusively demonstrated that prophylactic implantable cardioverter-defibrillator (ICD) therapy reduces mortality among subjects with ischemic and nonischemic cardiomyopathy but at the expense of potentially unnecessary ICD implantation in a large percentage of patients. Microvolt T-wave alternans (MTWA), with a negative predictive value greater than 90%, holds promise for selecting the patients who would likely and patients not likely to benefit from ICD implantation. Accurate identification of high-risk patients by noninvasive MTWA may allow for improved widespread screening for sudden death prevention in the general population.

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.

Microvolt T-wave alternans: a review of techniques, interpretation, utility, clinical studies, and future perspectives

Microvolt T-wave alternans (TWA) testing involves measuring variation in the morphology of the T-wave on an every other beat basis. The magnitude of the variation observed is typically on the order of a few microvolts. Thus in order to detect microvolt TWA, specialized recording and signal processing methods must be employed for reliable measurement. Additionally, microvolt TWA is not generally present at rest even in patients at risk of ventricular tachyarrhythmias and therefore exercise stress, pharmacologic stress, or atrial pacing must be utilized in order to elevate the heart rate. A positive MTWA test is one in which sustained TWA is present with an onset heart rate < or = 110 bpm. With current instrumentation, microvolt TWA represents an inexpensive, convenient non-invasive testing modality. Microvolt TWA has been evaluated prospectively in a variety of patient populations as a means of predicting occurrence of ventricular tachyarrhythmic events and its association with the genesis of ventricular arrhythmias has been demonstrated. Future role of microvolt TWA testing in noninvasive risk stratification is awaiting results of ongoing clinical trials. In this article, we tried to review the techniques, interpretation, indications, clinical studies, and future perspectives of microvolt TWA.

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.

Prognostic significance of heart rate variability in dilated cardiomyopathy

BACKGROUND

Identifying high-risk individuals among patients with nonischemic dilated cardiomyopathy (DCM) is a major and unsolved task of clinical cardiology. We aimed to determine prognostic significance of heart rate variability (HRV) for predicting cardiac events in DCM patients with markedly depressed left ventricular function.

METHODS

In 69 DCM patients in sinus rhythm, with normal coronary angiography and mean ejection fraction 32 (11%) cardiac events defined as cardiac death or heart transplantation during a mean 20-month follow-up were related to baseline time-domain HRV parameters calculated from 24-h digital Holter monitoring.

RESULTS

There were 18 (26%) cardiac events (10 deaths and 8 heart transplantations). In multivariate Cox analysis, standard deviation of normal-to-normal intervals (SDNN) (hazard ratio: 1.35; 95% confidence interval 1.11-1.63; P=0.002) and ejection fraction (hazard ratio: 4.21; confidence interval 1.64-10.78; P=0.003) were significant and independent predictors of cardiac events. One-year event-free survival was significantly lower in patients with SDNN<80 ms compared to those with SDNN>or=80 ms (35% vs. 89%, respectively; P<0.00005). Low SDNN was identifying high-risk patients among those with both depressed and relatively preserved left ventricular function.

CONCLUSIONS

Broadly available time-domain HRV analysis adds independent prognostic information improving risk stratification of DCM patients and therefore it should be incorporated in routine clinical evaluation to determine patients' priority for heart transplantation.

Prevalence and incidence of arrhythmias and sudden death in heart failure

Patients with heart failure are prone to a variety of arrhythmias, symptomatic and asymptomatic, that are prognostically significant and have an important bearing on the management of these patients. However there are some inherent problems in assessing the frequency of these arrhythmias within a large patient population, due to a lack of uniformity in defining heart failure and the transient nature of these rhythms. Patients with heart failure commonly die suddenly. The causes of these deaths are difficult to ascertain accurately and are often presumed arrhythmic. With the advent of effective interventions to prevent sudden death, accurately defining the causal relationship between the arrhythmias and sudden death has assumed great importance to appropriately target therapy. Several attempts have been made to predict such deaths on the basis of non-invasive and invasive diagnostic investigations with variable success. In this article we review the incidence and prevalence of atrial and ventricular arrhythmias and sudden deaths in epidemiological studies, surveys and randomised control trials of patients with heart failure. We discuss the prognostic significance of these arrhythmias, the inherent problems in their diagnosis and whether their presence predicts the risk of sudden deaths and the mode of such deaths in the heart failure population. The role of various investigations in risk stratification of sudden death has also been discussed.

Onset heart rate of microvolt-level T-wave alternans provides clinical and prognostic value in nonischemic dilated cardiomyopathy

OBJECTIVES

This study was designed to determine the prognostic value of onset heart rate (OHR) in T-wave alternans (TWA) in patients with nonischemic dilated cardiomyopathy (DCM).

BACKGROUND

One of the current major issues in DCM is to prevent sudden cardiac death (SCD). However, the value of the OHR of TWA as a prognostic indicator in DCM remains to be elucidated.

METHODS

We prospectively investigated 104 patients with DCM undergoing TWA testing. The end point of this study was defined as SCD, documented sustained ventricular tachycardia/ventricular fibrillation. Relations between clinical parameters and subsequent outcome were evaluated.

RESULTS

Forty-six patients presenting with TWA were assigned to one of the following two subgroups according to OHR for TWA of < or = 100 beats/min: group A (n = 24) with OHR < or = 100 beats/min and group B (n = 22) with 100 < OHR < or = 110 beats/min. T-wave alternans was negative in 37 patients (group C) and indeterminate in 21 patients. The follow-up result comprised 83 patients with determined TWA. During a follow-up duration of 21 +/- 14 months, there was a total of 12 arrhythmic events, nine of which included three SCDs in group A, two in group B and one in group C. The forward stepwise multivariate Cox hazard analysis revealed that TWA with an OHR < or = 100 beats/min and left ventricular ejection fraction were independent predictors of these arrhythmic events (p = 0.0001 and p = 0.0152, respectively).

CONCLUSIONS

The OHR of TWA is of additional prognostic value in DCM.

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

The usefulness of an abnormal signal-averaged ECG (SAECG) for the risk stratification of patients with dilated cardiomyopathy was studied prospectively in 76 patients. Multiple analysis showed that an abnormal SAECG predicted cardiac mortality (p = 0.0046), sudden cardiac death, and the need for resuscitation (p = 0.003); however, it did not predict death from heart failure and heart transplantation.

Relation between microvolt level T wave alternans and other potential noninvasive predictors of arrhythmic risk in the Marburg Cardiomyopathy Study

The relation between microvolt level T wave alternans (TWA) and other noninvasive arrhythmia risk predictors was analyzed in 221 consecutive patients with idiopathic dilated cardiomyopathy (IDC) and sinus rhythm enrolled in the Marburg Cardiomyopathy Study between March 1996 and May 2000. TWA analysis was also performed in 110 healthy controls of similar age and sex. TWA during symptom-limited exercise was positive, negative and indeterminate in, respectively, 108 (49%), 65 (29%) and 48 (22%) patients with IDC versus, respectively, 5 (5%), 98 (89%) and 7 (6%) healthy controls (P < 0.05). Patients with IDC and positive TWA had a lower left ventricular (LV) ejection fraction (29 +/- 9% vs 34 +/- 10%, P < 0.05) and greater LV end-diastolic diameter (69 +/- 8 mm versus 64 +/- 6 mm, P < 0.05) than patients with negative TWA. Other variables, including age, gender, New York Heart Association functional class, presence of bundle branch block, arrhythmias on 24-hour ambulatory electrocardiogram, heart rate variability and baroreflex sensitivity, were not significantly different between patients with positive vs negative TWA. The prognostic significance of TWA in IDC with regard to arrhythmic events and total mortality will be determined by multivariate Cox analysis at the end of a 5-year follow-up in this ongoing study.

Long-term prognostic value of time domain analysis of signal-averaged electrocardiography in idiopathic dilated cardiomyopathy

The aim of this study was to evaluate the long-term prognostic value of signal-averaged electrocardiography (SAECG) in idiopathic dilated cardiomyopathy (IDC). Time domain analysis of SAECG was assessed in 131 patients with angiographically confirmed IDC (age 52+/-12 years; 108 men; left ventricular ejection fraction 33+/-12%) using specific criteria in 44 patients with bundle branch block. Late potentials (LP) on SAECG were present in 27% of the patients. Patients with LP had a similar left ventricular ejection fraction and a similar left ventricular end-diastolic diameter than patients with a normal SAECG. With a follow-up of 54+/-41 months, 24 patients suffered cardiac death and 19 had major arrhythmic events (sudden death, resuscitated ventricular fibrillation, or sustained ventricular tachycardia). Patients with LP had an increased risk of all-cause cardiac death (RR 3.3, 95% confidence interval 1.5 to 7.5, p = 0.004) and of arrhythmic events (RR 7.2, 95% confidence interval 2.6 to 19.4, p = 0.0001). Using multivariate analysis, only LP on SAECG (p = 0.001), reduced SD of all normal-to-normal intervals (SDNN) (p = 0.002), increased pulmonary capillary wedge pressure (p = 0.005), and history of sustained ventricular tachyarrhythmia (p = 0.02) predicted cardiac death. A history of previous sustained ventricular tachyarrhythmia (p = 0.0001), reduced SDNN (p = 0.003), and LP on SAECG (p = 0.006) were the only independent predictors of major arrhythmic events. Results were not altered when considering separately patients with or without bundle branch block, or after exclusion of patients with a history of sustained ventricular tachyarrhythmia. This study is one of the first to suggest that LP on SAECG is an independent predictor of all-cause cardiac death and is of high interest for arrhythmia risk stratification in IDC.

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.

Spectrotemporal mapping of high-resolution ECGs in experimental myocardial infarction: comparison with time-domain analysis and epicardial electrograms

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

Determinant of microvolt-level T-wave alternans in patients with dilated cardiomyopathy

OBJECTIVES

The aim of this study was to clarify the clinical significance and the determinant of microvolt-level T-wave alternans (TWA) in patients with dilated cardiomyopathy (DCM).

BACKGROUND

The prevention of sudden death in patients with DCM remains the therapeutic target. T-wave alternans has been proposed as a powerful tool for identification of patients at high risk for ventricular arrhythmias and sudden death in coronary artery disease.

METHODS

In 58 DCM patients, TWA was measured during bicycle exercise testing using a CH 2000 system (Cambridge Heart, Bedford, Massachusetts). The New York Heart Association class, signal-averaged electrocardiogram, QT dispersion, left ventricular end-diastolic diameter (LVDd) and percent fractional shortening detected by echocardiogram and the grade of the ventricular arrhythmia were obtained in all patients.

RESULTS

T-wave alternans was positive in 23 patients (TWA+ group), negative in 25 (TWA- group) and indeterminate in 10. Univariate analysis showed that the percentage of patients with ventricular tachycardia (VT) and the LVDd in the TWA+ group was significantly higher than those in the TWA- group (61% vs. 8%, p < 0.001 and 65 +/- 11 mm vs. 58 +/- 8 mm, p < 0.05, respectively). The sensitivity, specificity and predictive accuracy of TWA for VT were 88%, 72% and 77%, respectively. Multivariate analysis showed that the presence of VT was a major independent determinant of TWA in patients with DCM (p = 0.003).

CONCLUSIONS

T-wave alternans was closely related to VT in patients with DCM. T-wave alternans is a useful noninvasive test for identifying high risk patients with DCM who have VT.

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.

Detection of abnormal high-frequency components in the QRS complex by the wavelet transform in patients with idiopathic dilated cardiomyopathy

In order to investigate whether increased fine, fractionated signals within the QRS complex can detect arrhythmogenic substrates and how these fine signals link with ventricular mechanical dysfunction, wavelet analysis was performed on averaged QRS complexes obtained from the left precordial lead in 26 patients with idiopatic dilated cardiomyopathy (IDCM) and in 12 normal subjects. The number of local maxima and the duration of the wavelet transform were significantly greater in patients with IDCM than in normal subjects; the number at 100 Hz was 8.8+/-3.1 vs 6.0+/-1.1 (p<0.01), and the duration at 100Hz was 93+/-15 vs 75+/-7ms (p<0.01). Both of these indices were greater in the patients with than in those without late potentials, repetitive ventricular premature beats or cardiac death. In addition, significant inverse curvilinear relationships were observed between the left ventricular ejection fraction and both the number of local maxima and the duration of the wavelet transform. In conclusion, fine fragmented signals in the QRS complex detected by wavelet analysis would be an important marker for potentially arrhythmogenic substrates and seemed to progress in parallel with left ventricular mechanical dysfunction in IDCM.

Noninvasive arrhythmia risk stratification in idiopathic dilated cardiomyopathy: design and first results of the Marburg Cardiomyopathy Study

The Marburg Cardiomyopathy Study (MACAS) is a prospective, observational study designed to determine the value of the following potential noninvasive arrhythmia risk predictors in at least 200 patients with idiopathic dilated cardiomyopathy (IDC) over a 5-year follow-up period: NYHA-class, left ventricular ejection fraction (LVEF), left ventricular end-diastolic diameter, left bundle branch block and atrial fibrillation on ECG, QT/JT dispersion on 12-lead ECG, signal-averaged ECG, ventricular arrhythmias and heart rate variability (HRV) on 24-hour Holter ECG, baroreflex sensitivity, and microvolt T wave alternans during exercise. This article describes the findings among the first 159 patients with IDCs enrolled in MACAS until May 1998 (40 women, 119 men; age: 49 +/- 12 years; LVEF: 32 +/- 10%). Twenty-nine patients (18%) had atrial fibrillation and 130 patients (82%) were in sinus rhythm. Patients with sinus rhythm were further stratified according to LVEF < 30% (n = 54) versus LVEF > or = 30% (n = 76). Compared to patients with LVEF > or = 30%, patients with LVEF < 30% more often had left bundle branch block (43% vs 25%, P < 0.05), nonsustained VT (44% vs 22%, P < 0.05), decreased HRV (SDNN: 95 +/- 39 vs 128 +/- 42 ms, P < 0.01), decreased baroreflex sensitivity (5.6 +/- 4 vs 8.3 +/- 6 ms/mmHg, P < 0.01), and T wave alternans (59% vs 37%, P < 0.05). The prognostic significance of these findings will be determined by multivariate Cox analysis at the end of a 5-year follow-up. Primary endpoints in MACAS are overall mortality and arrhythmic events (i.e., sustained VT or VF, or sudden cardiac death).

Mechanisms and management of ventricular dysrhythmias in heart failure

Despite recent pharmacologic and surgical advances in the management of heart failure, the morbidity and mortality rates of this chronic illness remain high. Ventricular dysrhythmias are common in heart failure and may be independently associated with increased mortality rates. Although the risks of sudden cardiac death leading to the patient's death are increased by the presence of complex ventricular dysrhythmias, the management of dysrhythmias is subject to controversy. The purpose of this article is to review the normal electrophysiologic properties of the heart and to examine the likely mechanisms, diagnostic approaches, and proposed treatments for ventricular dysrhythmias in heart failure.

Primary prevention of sudden cardiac death in heart failure: will the solution be shocking?

Sudden cardiac death (SCD) may occur in as many as 40% of all patients who suffer from heart failure. This review describes the scope of the problem, risk factors for SCD, the effect of medications used in heart failure on SCD and the potential effect of the implantable cardioverter-defibrillator in primary prevention.

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.

[Impact of a percutaneous transluminal coronary angioplasty on the prevalence of ventricular late potentials among patients with survived myocardial infarction]

The aim of the study was to evaluate whether a causal antiischemic intervention as percutaneous transluminal coronary angioplasty (PTCA) leads to a reduction of ventricular late potentials in the chronic post myocardial infarction period. In 24 patients, signal-averaged electrocardiograms (SAECG) for two groups were recorded for the analysis of ventricular late potentials (LP) before and after 6.0+/-4.2 months (group A, with PTCA) and 6.2+/-5.2 months, respectively (group B, conservative therapy). All patients presented prior myocardial infarction. LP were defined present if two of the three time domain criteria were met. In the whole study group, LP were positive in 73%. In group A, a PTCA was performed one month after the initial SAECG measurement. In group A, the presence of ventricular late potentials was significantly reduced (64% vs. 18%), whereas in group B only a slight decline of late potentials could be observed (85% vs. 62%). The parameters of the signal averaged ECG varied significantly in group A before and after PTCA (QRS 113.04+/-13.65 vs. 100.55+/-6.97 ms (p<0.05), RMS 24.04+/-24.13 vs. 35.39+/-16.89 muV (p=n.s.), LAS 41.23+/-13.27 vs. 29.68+/-6.47 ms (p<0.05)). The results in group B were not altered significantly.In conclusion, these results show that a PTCA of the infarct-related artery can lead to a reduction in ventricular late potentials in patients with significant coronary artery disease, who are also in the chronic post myocardial infarction period. Whether it is possible to improve the prognosis of these patients has also to be shown in future studies.

Usefulness of signal-averaged electrocardiography in evaluation of idiopathic-dilated cardiomyopathy in families

Family studies have confirmed that familial dilated cardiomyopathy is common and that a large proportion of relatives have mild left ventricular enlargement and therefore potentially early disease. Previous studies have shown that patients with idiopathic dilated cardiomyopathy have abnormalities of the signal-averaged electrocardiogram (ECG). We assessed the usefulness of analysis of the signal-averaged ECG in the evaluation of familial dilated cardiomyopathy. Signal-averaged electrocardiographic recordings were obtained from 58 patients with idiopathic dilated cardiomyopathy, from 161 of their relatives (35 of whom had left ventricular enlargement), and from 59 healthy subjects. Signal-averaged ECGs were analyzed using both time domain and spectral turbulence analysis techniques. The time domain and spectral turbulence analysis variables were markedly abnormal in patients with idiopathic dilated cardiomyopathy compared with relatives considered normal and healthy controls (p <0.05). Late potentials were more common in patients with idiopathic dilated cardiomyopathy (17%) and in relatives with left ventricular enlargement (20%) than in normal relatives (5%) or healthy controls (5%) (p = 0.003). Spectral turbulence analysis was abnormal in 24% of patients with idiopathic dilated cardiomyopathy, 14% of relatives with left ventricular enlargement, 6% of normal relatives, and 5% of healthy controls (p = 0.0006). The sensitivity, specificity, and positive predictive accuracy for identification of relatives with left ventricular enlargement were 20%, 95%, and 54% for time domain analysis and 14%, 94%, and 42% for spectral turbulence analysis. Similar positive predictive accuracy was achievable with spectral turbulence analysis and with time domain analysis. In conclusion, the signal-averaged ECG is frequently abnormal in patients with idiopathic dilated cardiomyopathy and relatives with left ventricular enlargement.

The signal-averaged electrocardiogram is of limited value in patients with bundle branch block and dilated cardiomyopathy in predicting inducible ventricular tachycardia or death

An abnormal signal-averaged electrocardiogram (SAECG) has predictive value for arrhythmic events in patients with idiopathic dilated cardiomyopathy and a normal conduction. The purpose of this study was to investigate whether the presence of a complete bundle branch block (BBB) affects prognostic information of the SAECG. We prospectively obtained SAECGs in 128 patients with idiopathic dilated cardiomyopathy. Forty-three of them had BBB and 85 had a normal QRS duration. According to their clinical history and results of ventricular programmed stimulation, patients were divided into 4 groups: (1) group IA with BBB and ventricular tachycardia (VT) (n = 18); (2) group IB with BBB but without VT (n = 25); (3) group IIA without BBB but with VT (n = 40); (4) group IIB without BBB and without VT (n = 45). Patients were compared with 129 patients without heart disease and without VT. Fifty-seven of them had BBB (group III) and 72 had normal conduction (group IV). The filtered QRS duration was longer in group IB than in group III (175 +/- 21 vs 149 +/- 16 ms, p <0.001), and in group IIB than in group IV (111 +/- 19 vs 96 +/- 12 ms, p <0.05). QRS duration was similar in groups IA and IB (176 +/- 24 vs 175 +/- 21 ms) but longer in group IIA than in group IIB (131 +/- 24 vs 111 +/- 19 ms, p <0.001). The low-amplitude signal duration (LAS) and the root-mean-square voltage (RMS) of the last 40 ms of the filtered QRS did not differ between groups IB and III and IA and IB. LAS and RMS were, respectively, longer (44 +/- 20 vs 31 +/- 13 ms, p <0.01) and lower (21 +/- 20 vs 43 +/- 33 microV, p <0.001) in groups IIA and IIB. In groups IA and IB the combination of 2 of the 3 available criteria: QRS duration >170 ms, RMS <20 microV, LAS >45 ms lead up to the best overall statistical result, with a sensitivity and specificity of 78% and 56%, respectively. In groups IIA and IIB, using conventional late potential criteria, the sensitivity and specificity of the SAECG for VT detection were 65% and 73%, respectively. The risk of sudden death was not predicted by the SAECG, and total cardiac mortality was only dependent on left ventricular ejection fraction. In conclusion, QRS duration was prolonged in all of the patients with a dilated cardiomyopathy compared with those without heart disease. BBB did not change the sensitivity but decreased the specificity of the SAECG to predict any VT risk in dilated cardiomyopathy. The risk of sudden death and total cardiac mortality could not be predicted by the SAECG.

Signal-averaged electrocardiography in healthy children: influence of age, body size, and gender

Our objective was to determine influence of age, body size, and gender on SAECG signals and to establish normal range for standard SAECG parameters in the pediatric population. Five hundred thirty healthy children and adolescents (290 males, 240 females) aged 6.0-17.3 years were studied with high resolution ECG. Patients were divided into five age groups, and each age group was divided in two subgroups according to gender. Parameters studied were filtered QRS duration, root mean square (RMS) voltage of the last 40 ms and of the last 30 ms of the filtered QRS complex, and duration of the terminal waveform of the filtered QRS < 40 microV of amplitude (LAS). After validation of the distribution of the various variables, means, standard deviations, and 95% confidence intervals were determined for each SAECG parameter at 25- to 250-Hz filtering and at 40- to 250-Hz filtering for the ten subgroups. There was a significant age and body surface area (BSA)-associated increase in filtered QRS duration in boys and girls, and a decrease in RMS voltage of the end of the QRS complex in girls. In addition, girls had a significantly shorter QRS and longer LAS durations than boys. These differences of signal-averaged signals between genders were not related to age or body size differences since analysis of covariance with age at evaluation or BSA as covariates showed the same trend. Three children (0.6%) had a SAECG out of normal range for age for the four parameters studied either at 25- or 40-Hz high pass filter. Due to the large sample studied, our results provide a basis for interpretation of SAECG in children. Normal ranges for the various variables were determined, and it appeared that adjustments for age, body size, and gender are mandatory when studying SAECG in children.

Value of time- and frequency-domain analysis of signal-averaged electrocardiography for arrhythmia risk prediction in idiopathic dilated cardiomyopathy

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

Comparison of time domain and spectral turbulence analysis of the signal-averaged electrocardiogram for the prediction of prognosis in idiopathic dilated cardiomyopathy

BACKGROUND

Despite significant advances in the treatment of heart failure, the prognosis of patients with idiopathic dilated cardiomyopathy remains poor. Although several of prognostic variables have been shown to be useful in risk stratification of patients with idiopathic dilated cardiomyopathy, their predictive accuracy is low and clinical usefulness uncertain.

HYPOTHESIS

This study was undertaken to assess the signal-averaged electrocardiogram (SAECG) in patients with idiopathic dilated cardiomyopathy and to compare the ability of time domain and spectral turbulence analytic techniques to predict clinical outcome.

METHODS

SAECG analysis was performed in 80 patients with idiopathic dilated cardiomyopathy. Nineteen patients had left bundle-branch block and eight were taking low-dose amiodarone for life-threatening arrhythmias. Conventional time domain and spectral turbulence analyses of the SAECG were performed using Del Mar 183 software.

RESULTS

During a follow-up of 27 +/- 19 months, 24 patients developed progressive heart failure, while the others remained clinically stable. Late potentials were detected in 28% of patients and were equally frequent in patients with and without progressive heart failure (38 vs. 23%, p = 0.20). Spectral turbulence analysis was abnormal in 34% of patients, and patients with abnormal results developed progressive heart failure more frequently than those with normal results (50 vs. 17%, p = 0.01). All spectral turbulence analysis parameters were significantly different in patients with progressive heart failure compared with those who remained clinically stable (p < or = 0.01). Furthermore, progressive heart failure-free survival at 2 years was significantly lower in patients with abnormal compared with normal results (63 vs. 87%; p < 0.05), but was similar in patients with and without late potentials (72 vs. 83%; p = 0.30). The relative risk for developing progressive heart failure using spectral turbulence analysis was 3.4 (95% confidence interval 1.2-9.7) and 2.8 (95% confidence interval 1.1-8.7) using time domain analysis. The sensitivity, specificity, and the positive and negative predictive accuracy for identifying patients who developed progressive heart failure were 50, 83, 50, and 83%, respectively, (p = 0.01) for spectral turbulence analysis, and 36, 85, 45 and 80%, respectively, (p = 0.09) for time domain analysis.

CONCLUSION

Abnormalities in the SAECG of patients with idiopathic dilated cardiomyopathy are common and appear to provide a noninvasive marker for development of progressive heart failure.

Time-domain signal-averaged electrocardiogram in nonischemic ventricular tachycardia

The prevalence of late ventricular potentials (LVPs) detected by signal averaged ECG (SAECG) is variable in nonischemic heart diseases. In idiopathic dilated cardiomyopathy, the prevalence increases from about 25% to 70%-90% in cases of spontaneous sustained ventricular tachycardia (VT), is not significantly correlated with hemodynamic and Holter data, and has a good positive predictive value for induced and spontaneous sustained VT. However, its predictive value for cardiac death has not been established. In primary hypertrophic cardiomyopathy, LVPs are rare (about 10%), not correlated to hemodynamic data, enhanced in cases of spontaneous sustained VT (up to 77%), and have a good predictive value of induced VT. LVP-SAECG are frequent in arrhythmogenic right ventricular dysplasia (ARVD) (70%-80%). They can identify patients with VT and an unapparent or limited form of this disease, or ARVD with few ventricular arrhythmias. The prevalence (26%-37%) of LVPs in mitral valve prolapse is clearly higher than in normal individuals or in other valvular diseases and is enhanced in cases of spontaneous and induced VT. Its significance remains speculative. After surgical repair of tetralogy of Fallot, LVPs can identify a group of patients with higher probability of induced and spontaneous risk of VT. The usefulness and significance of LVPs in other nonischemic cardiac diseases have not to date been established. In "true" idiopathic VT, without proved structural cardiac disease, the prevalence of LVPs does not exceed that observed in normal individuals (0%-5%), but in "apparent" idiopathic VT the prevalence of LVPs rises to 20%-40%. In these latter cases more invasive techniques must be used to discover a limited form of myocardiopathy.

Prognostic value of the signal-averaged electrocardiogram and a prolonged QRS in ischemic and nonischemic cardiomyopathy

Studies of electrocardiographic predictors of mortality in patients with chronic heart failure have reached varying conclusions. Differences in the characteristics of the patients studied may explain the conflicting results regarding both a prolonged QRS and an abnormal signal-averaged electrocardiogram (SAE). We therefore investigated the impact of the etiology of heart failure on the prognostic importance of a prolonged QRS and an abnormal SAE in 200 patients with heart failure. Patients were categorized according to etiology of heart failure and electrocardiographic parameters. The mortality of patients with a prolonged QRS was compared with mortality in those with both abnormal and normal SAEs. This was done for the entire group, and separately for those with ischemic and those with nonischemic cardiomyopathy. The mean follow-up was 18.8 months. Nonischemic patients with a prolonged QRS had significantly worse survival than other patients. However, nonischemic patients with an abnormal SAE did not have a worse prognosis than patients with a normal SAE. One-year survival of patients with a prolonged QRS was 71%, compared with 98% in patients with a normal and 87% in patients with an abnormal SAE (p < 0.05). In contrast, a prolonged QRS was not a predictor of poor prognosis in patients with ischemic cardiomyopathy (81% one year mortality). Patients with ischemic cardiomyopathy and an abnormal SAE tended to have a poorer survival than patients with a normal SAE (73% and 81% one year mortality, respectively). Thus, the etiology of heart failure affects the prognostic importance of both a prolonged QRS and an abnormal SAE.

Prognostic significance of spectral turbulence analysis of the signal-averaged electrocardiogram in patients with idiopathic dilated cardiomyopathy

The aim of this study was to assess whether spectral turbulence analysis (STA) of the signal-averaged electrocardiogram (SAECG) is of prognostic use in patients with idiopathic dilated cardiomyopathy. SAECGs were recorded at presentation in 84 patients with idiopathic dilated cardiomyopathy and STA was performed using 183 Del Mar software. STA was abnormal (> or = 3 of the 4 standard parameters beyond the normal range) in 31 patients (37%). Patients were followed for a mean duration of 24 +/- 18 months (range 1 to 59) during which time 24 (29%) developed progressive heart failure (14 underwent cardiac transplantation), 4 died suddenly or had aborted sudden death, and the others remained clinically stable. Progressive heart failure occurred more often in patients who had an abnormal versus a normal STA result (15 [48%] vs 9 [17%]; p < 0.002). Actuarial survival revealed a 1-year survival of 90% in patients with a normal STA result, and 63% in patients with an abnormal STA result (p < 0.01). The predictive ability of STA to identify patients with progressive heart failure was sensitivity 63%, specificity 77%, positive predictive value 54%, and negative predictive value 83%. Univariate analysis identified peak oxygen consumption as having the largest relative risk for the development of progressive heart failure (9.55, 95% confidence interval [CI] 2.1 to 43.9). Left ventricular end-diastolic dimension (relative risk 4.18, 95% CI 1.5 to 11.4) and STA (relative risk 3.81, 95% CI 1.7 to 8.8) were also significantly associated with the development of progressive heart failure.(ABSTRACT TRUNCATED AT 250 WORDS)

Risk stratification for arrhythmic events in patients with nonischemic dilated cardiomyopathy and nonsustained ventricular tachycardia: role of programmed ventricular stimulation and the signal-averaged electrocardiogram

OBJECTIVES

This study investigated prediction of arrhythmic events by the signal-averaged electrocardiogram (ECG) and programmed stimulation in patients with nonischemic dilated cardiomyopathy.

BACKGROUND

Risk stratification in patients with nonischemic dilated cardiomyopathy remains controversial.

METHODS

Eighty patients with nonischemic dilated cardiomyopathy and spontaneous nonsustained ventricular tachycardia underwent signal-averaged electrocardiography (both time-domain and spectral turbulence analysis) and programmed stimulation. All patients were followed up for a mean of 22 +/- 26 months.

RESULTS

Sustained monomorphic ventricular tachycardia was induced in 10 patients (13%), who all received amiodarone. The remaining 70 patients were followed up without antiarrhythmic therapy. Of the 80 patients, 15% had abnormal findings on the time-domain signal-averaged ECG, and 39% had abnormal findings on spectral turbulence analysis. Time-domain signal-averaged electrocardiography had a better predictive accuracy for induced ventricular tachycardia than spectral turbulence analysis (88% vs. 66%, p < 0.01). During follow-up, there were 9 arrhythmic events (5 sudden deaths, 4 spontaneous ventricular tachycardia/fibrillation) and 10 nonsudden cardiac deaths. Cox regression analysis showed that no variables predicted arrhythmic events or total cardiac deaths. The 2-year actuarial survival free of arrhythmic events was similar in patients with or without abnormal findings on the signal-averaged ECG or induced ventricular tachycardia.

CONCLUSIONS

In patients with nonischemic dilated cardiomyopathy, 1) there is a strong correlation between abnormal findings on the time-domain signal-averaged ECG and induced ventricular tachycardia, but both findings are uncommon; and 2) normal findings on the signal-averaged ECG, as well as failure to induce ventricular tachycardia, do not imply a benign outcome.

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.

Time-domain and frequency-domain analyses of the signal-averaged ECG in patients with ventricular tachycardia and ischemic versus nonischemic dilated cardiomyopathy

The value of time-domain and frequency-domain (spectral turbulence) analyses of the signal-averaged electrocardiogram was investigated to predict induced sustained monomorphic ventricular tachycardia (VT). Two groups of patients with spontaneous nonsustained VT and left ventricular ejection fraction less than 50% were enrolled: 70 patients with idiopathic dilated cardiomyopathy (group 1) and 70 patients with ischemic heart disease (group 2). Sustained VT was induced in 9 cases (13%) in group 1 and 16 (23%) in group 2. The prevalence of abnormal time-domain and spectral turbulence analysis was 16 and 37%, respectively, in group 1 and 27 and 51%, respectively, in group 2 (NS). In group 1, the predictive accuracy of time-domain and spectral turbulence analysis for induced VT was 86 and 67%, respectively (P < .01). In group 2, the predictive accuracy of the two techniques for induced VT was, respectively, 79 and 66% (NS). In both groups, the predictive accuracy of time-domain analysis was higher than that of spectral turbulence analysis in patients with intraventricular conduction defect (IVCD): 65 versus 25%, respectively, in group 1 (P < .01), and 81 versus 44%, respectively, in group 2 (P < .05). However, the predictive accuracy of time-domain and spectral analyses was similar in patients without IVCD: 94 versus 84%, respectively, in group 1, and 77 versus 74%, respectively, in group 2. Thus, in patients with dilated cardiomyopathy, (1) the etiology does not affect the predictive accuracy of time and frequency domain and frequency-domain analyses have high predictive accuracy in patients without IVCD; and (3) spectral turbulence analysis does not improve VT prediction in patients with IVCD.

Time-domain and frequency-domain analyses of the signal-averaged ECG in patients with sustained ventricular tachyarrhythmia and nonischemic heart diseases

Signal-averaged electrocardiogram (ECG) variables were analyzed in 81 patients with ventricular tachyarrhythmia and nonischemic heart disease using the ART LVP 101 EPX system (Austin, TX): 15 ventricular tachycardia patients with arrhythmogenic right ventricular dysplasia (ARVD), 7 ventricular tachycardia patients with dilated cardiomyopathy, 25 patients with "idiopathic" verapamil-sensitive left ventricular tachycardia, 24 patients with "idiopathic" right ventricular tachycardia, and 10 "idiopathic" ventricular fibrillation (IVF) patients with rbbb pattern and ST-segment elevation in the precordial leads. Data from 52 normal control subjects were also analyzed. The first study was to test the hypothesis of any difference in signal-averaged ECG indices between patients with ARVD and patients with dilated cardiomyopathy. Longer filtered QRS duration and T40 and higher amplitude of the terminal filtered QRS complex outside the end of the standard QRS complex (log V-outside) were noted in patients with ARVD (filtered QRS duration, 172 vs 144 ms, P < .05; T40, 94 vs 62 ms, P < .05; log V-outside, 1.48 vs 0.56, P < .01). Endocardial mapping showed noticeable extension of fractionated electrograms in the right ventricle and longer duration of fractionated intracardiac electrograms in patients with ARVD, which might explain the difference in signal-averaged ECG indices between these two diseases. The second study was to test the hypothesis of and the variables that can suggest the arrhythmogenic substrate in patients with idiopathic ventricular tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)