Results of signal-averaged electrocardiography and electrophysiologic study in patients with nonsustained ventricular tachycardia after healing of acute myocardial infarction

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.

Signal-averaged electrocardiography: Past, present, and future

Signal-averaged electrocardiography records delayed depolarization of myocardial areas with slow conduction that can form the substrate for monomorphic ventricular tachycardia. This technique has been examined mostly in patients with coronary artery disease, but its use has been declined over the years. However, several lines of evidence, derived from hitherto clinical data in patients with healed myocardial infarction, indicate that signal-averaged electrocardiography remains a valuable tool in risk stratification, especially when incorporated into algorithms encompassing invasive and noninvasive indices. Such an approach can aid the more precise identification of candidates for device therapy, in the context of primary prevention of sudden cardiac death. This article reappraises the value of signal-averaged electrocardiography as a predictor of arrhythmic outcome in patients with ischemic heart disease and discusses potential future indications.

SAECG in exercise test for prediction of diabetic coronary artery disease

Signal averaged electrocardiogram (SAECG) is considered an important noninvasive indicator identifying patients at risk for ventricular arrhythmias. The aim of this study was to improve noninvasive prediction of CAD by integrating SAECG with the result of exercise tests in diabetic patients. Diabetic patients with stable angina pectoris underwent exercise testing and SAECG. Then a diagnostic score was derived that combined results of exercise testing and SAECG. A diagnostic score (0 to 2 points) was calculated by assigning 1 point for a positive exercise test result and 1 point for a positive SAECG. One hundred and seventy patients were included in the study. In patients with a score of 0, the likelihood of CAD is 18% whereas the likelihood of CAD is 95% in patients with a score of 2. Triple vessel CAD is present in 54%, 7% and only 1.5% of patients with score 2, 1 and 0 respectively. Therefore, patients with score 2 have a poor prognosis compared with score 1 or 0. A diagnostic score combining exercise testing and SAECG can distinguish patients with CAD from those without CAD with high accuracy in diabetic patients.

Detection of coronary artery stenosis after successful percutaneous coronary intervention by dipyridamole stress portable type signal-averaged electrocardiography: a prospective study

In our previous studies, using portable type signalaveraged electrocardiography (portable SAECG) with dipyridamole stress we reported that patients with coronary artery disease were identified at the bedside with high sensitivity and specificity. In this study we prospectively investigated whether coronary artery stenosis after successful percutaneous coronary intervention (PCI) could be detected. Standard 12-lead QRS wave SAECG was performed before and after dipyridamole stress at the bedside in 61 patients 8.0 +/- 9.4 months after successful PCI for myocardial infarction or angina pectoris (46 males and 15 females, mean age 66 +/- 12 years). The filtered QRS duration (fQRSd) before and after dipyridamole stress was determined by the multiphasic oscillation method at each lead of the standard 12 leads, and the maximal value of changes in fQRSd (MAX DeltafQRSd) among the 12 leads was determined. The positive test was defined as MAX DeltafQRSd > or =5 ms, and negative as MAX DeltafQRSd <5 ms based on our previous studies. Then selective coronary arteriography was performed. In the positive group (n = 24), 21 patients had stenosis (> or =50%) of the coronary artery and 3 did not. In the negative group (n = 37), 8 patients had stenosis and 29 did not. The sensitivity, specificity, positive predictive accuracy, and negative predictive accuracy for the detection of coronary artery stenosis by SAECG were 72%, 91%, 88%, and 78%, respectively. Dipyridamole stress portable SAECG is useful to detect patients with coronary artery stenosis after successful PCI.

Prediction of long-term outcomes by signal-averaged electrocardiography in patients with unsustained ventricular tachycardia, coronary artery disease, and left ventricular dysfunction

BACKGROUND

An abnormal signal-averaged ECG (SAECG) is a noninvasive marker of the substrate of sustained ventricular tachycardia after myocardial infarction. We assessed its prognostic ability in patients with asymptomatic unsustained ventricular tachycardia, coronary artery disease, and left ventricular dysfunction.

METHODS AND RESULTS

A blinded core laboratory analyzed SAECG tracings from 1925 patients in a multicenter trial. Cox proportional hazards modeling was used to examine individual and joint relations between SAECG variables and arrhythmic death or cardiac arrest (primary end point), cardiac death, and total mortality. We also assessed the prognostic utility of SAECG at different levels of ejection fraction (EF). A filtered QRS duration >114 ms (abnormal SAECG) independently predicted the primary end point and cardiac death, independent of clinical variables, cardioverter-defibrillator implantation, and antiarrhythmic drug therapy. With an abnormal SAECG, the 5-year rates of the primary end point (28% versus 17%, P=0.0001), cardiac death (37% versus 25%, P=0.0001), and total mortality (43% versus 35%, P=0.0001) were significantly higher. The combination of EF <30% and abnormal SAECG identified a particularly high-risk subset that constituted 21% of the total population. Thirty-six percent and 44% of patients with this combination succumbed to arrhythmic and cardiac death, respectively.

CONCLUSIONS

SAECG is a powerful predictor of poor outcomes in this population. The noninvasive combination of an abnormal SAECG and reduced EF may have utility in selecting high-risk patients for intervention.

Role of Antiarrhythmic Therapy in Patients at Risk for Sudden Cardiac Death: An Evidence-Based Review

Sudden cardiac death (SCD) accounts for more than half of all cardiac deaths occurring each year in the United States. Although it has several causes, patients at greatest risk are those with coronary artery disease and impaired left ventricular function, heart failure secondary to ischemia or idiopathic dilated cardiomyopathy, hypertrophic cardiomyopathy, documented sustained ventricular tachycardia or ventricular fibrillation, and survivors of cardiac arrest. The presence of asymptomatic ventricular arrhythmias, positive signal-averaged electrocardiogram (ECG), low heart rate variability index, or inducible ventricular tachycardia or ventricular fibrillation increases the risk. In primary prevention trials in patients with ischemic heart disease, beta-blockers reduced both total mortality and SCD, whereas class I antiarrhythmic drugs, especially class IC, increased mortality. Among class III agents, d,l-sotalol and dofetilide have a neutral effect on mortality, whereas d-sotalol increases mortality. Amiodarone has a neutral effect on total and cardiac mortality but does reduce the risk of arrhythmic death and cardiac arrest. Three primary prevention trials in patients with ischemic heart disease were conducted with implantable cardioverter-defibrillators (ICDs). Patients with low ejection fractions (EFs), asymptomatic ventricular arrhythmias, and inducible ventricular tachycardia or ventricular fibrillation had significant reductions in total, cardiac, and arrhythmic death with ICDs compared with either no drug therapy or conventional antiarrhythmic agents. The ICDs did not reduce mortality in patients with low EFs and a positive signal-averaged ECG undergoing coronary bypass graft. In those with heart failure, beta-blockers reduced total and SCD mortality, but dofetilide and amiodarone had a neutral effect on mortality. In the secondary prevention of SCD, antiarrhythmic drugs alone generally are not thought to improve survival. In three trials in patients with documented sustained ventricular tachycardia or ventricular fibrillation, or survivors of SCD, ICDs reduced cardiac and arrhythmic mortality. Total mortality, however, was significantly reduced in only one of these trials. The role of antiarrhythmic drugs in secondary prevention of SCD is limited to patients in whom ICD is inappropriate or in combination with ICD. Antiarrhythmics can be given selectively with ICDs to decrease episodes of ventricular tachycardia or fibrillation to reduce ICD discharges, to suppress episodes of nonsustained ventricular tachycardia that trigger ICD discharges, to slow the rate of ventricular tachycardia to increase hemodynamic stability, to allow effective antitachycardia pacing, or to suppress supraventricular arrhythmias.

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.

Management of ventricular arrhythmias: a trial-based approach

Sudden cardiac death accounts for approximately 300,000 deaths annually in the U.S., and most of these are secondary to ventricular tachycardia (VT) and fibrillation in patients with coronary artery disease. Most patients with cardiac death die before reaching the hospital, which brought about a tremendous amount of research focused at identifying patients at high risk. Several trials were initiated to test the effectiveness of various therapeutic measures in these high-risk patients. A history of myocardial infarction, depressed left ventricular function and nonsustained VT have all been identified as independent risk factors for future arrhythmic death. Similarly, patients with a history of sustained VT or a history of sudden cardiac death are a high-risk group and should be aggressively evaluated and treated. The purpose of this article is to discuss risk stratification and primary prevention of sustained ventricular arrhythmias. We also review the recent secondary prevention trials and discuss the options available in the management of patients with sustained ventricular arrhythmias.

Value of the signal-averaged P wave analysis in predicting atrial fibrillation after cardiac surgery

Atrial fibrillation (AF) is the most common sustained arrhythmia occurring after cardiac surgery. Beside important implications regarding patient recovery, AF has been shown to substantially lengthen hospital stay--our recent study found a 3-day prolongation after adjusting for all other significant factors. Identification of those at highest risk of AF by clinical or noninvasive characteristics may be a useful strategy for targeted prophylactic therapy. Our data have shown that prolonged atrial conduction as assessed by analysis of the P wave duration from the signal-averaged electrocardiogram (SAECG) imparts a four fold increase in risk for postoperative AF, independently of other measured variables. In addition, abnormal conduction was present on the preoperative P wave ECG (P-SAECG), implying a preexisting substrate that is triggered by surgery. The use of combination abnormal noninvasive variables (eg, abnormal P-SAECG and low left ventricular ejection fraction) can identify groups with a 50% risk of AF, which is nine times as high as when both tests are normal. Thus, the P-SAECG is a useful and accurate predictor of AF after cardiac surgery.

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.

Analysis of abnormal intra-QRS potentials. Improved predictive value for arrhythmic events with the signal-averaged electrocardiogram

BACKGROUND

Using the signal-averaged ECG (SAECG), this study developed a new electrical index for predicting arrhythmic events: abnormal intra-QRS potentials (AIQP).

METHODS AND RESULTS

We studied 173 patients followed after myocardial infarction for a mean duration of 14 +/- 7 months. Sixteen arrhythmic events occurred, defined as sudden cardiac death, documented sustained ventricular tachycardia, or non-fatal cardiac arrest. Noninvasive indices of arrhythmia risk were measured, including AIQP, conventional SAECG, Holter, and left ventricular ejection fraction (LVEF). Abnormal intra-QRS potentials were defined as abnormal signals occurring anywhere within the QRS period. They were estimated with a lead-specific, parametric modeling method that removed the smooth, predictable part of the QRS. AIQPs are characterized by the remaining transient, unpredictable component of the QRS and manifest as low-amplitude notches and slurs. A combined XYZ-lead AIQP index exhibited higher specificity (95%) and predictive value (PV) (+PV, 47%; -PV, 94%) than the conventional SAECG in combination with Holter and LVEF (specificity, 89%; +PV, 25%; -PV, 93%).

CONCLUSIONS

AIQP improved specificity and predictive value, compared with conventional tests, for prediction of arrhythmic events. AIQP emerged as the best noninvasive univariate predictor of arrhythmic events after myocardial infarction in this study. A review of several other reports shows that AIQP in the present study outperformed the conventional predictive indices reported in those other data sets.

The signal-averaged electrocardiogram: update on clinical applications

The signal-averaged electrocardiogram (SAECG) facilitates noninvasive recording of low-amplitude cardiac signals such as ventricular late potentials. The SAECG has been used to accurately predict life-threatening ventricular tachyarrhythmias in patients after acute myocardial infarction and with nonischemic dilated cardiomyopathy, and to screen for inducible ventricular tachycardia in patients with unexplained syncope and with nonsustained ventricular tachycardia. This review focuses on currently accepted methodology and clinical and research applications of the SAECG.

Normal values for the childhood signal-averaged ECG

To obtain normative data for the childhood signal-averaged ECG (SAECG), we obtained SAECGs in 155 volunteers, aged 5-15 years, using Frank leads and a Fourier transform filter. Unfiltered QRS duration (QRSDU) and filtered QRS duration (QRSDF) were significantly longer in males, and the root mean square of the terminal 40 ms (RMS40) was significantly higher in females. There were no gender differences in the duration of high frequency low amplitude signals < 40 microV (DHFLA). All SAECG variables were significantly related to body surface area (BSA). Regression models were established for SAECG variables. For males, the predicted mean + 1.96 standard deviations (SD) for QRSDF (97.5th centile) ranged from 114 ms at BSA 0.70 m2 to 123 ms at 1.90 m2. For females, the predicted mean + 1.96 SD for QRSDF ranged from 110 ms at BSA 0.70 m2 to 119 ms at 1.90 m2. For males and females, the predicted mean + 1.96 SD for DHFLA ranged from 34 ms at 0.70 m2 to 38 ms at 1.90 m2. For males, the predicted mean - 1.96 SD (2.5th centile) for RMS40 (based on natural logarithm model) ranged from 30 microV at 0.70 m2 to 15 microV at 1.90 m2. For females, the predicted mean -1.96 SD for RMS40 ranged from 42 microV at 0.70 m2 to 20 microV at 1.90 m2. In children 5-15 years of age, both gender and BSA need to be taken into account when interpreting the SAECG.

Signal-averaged electrocardiography and echocardiography in the evaluation of myocardial involvement in progressive systemic sclerosis

To assess the myocardial involvement in progressive systemic sclerosis we evaluated the presence of late potentials by signal-averaged electrocardiography (signal-averaged ECG) and the left ventricular function by M-mode, two dimensional and Doppler echocardiography. Fifteen outpatients, 7 with diffuse progressive systemic sclerosis and 8 with CREST syndrome variant, without clinical or electrocardiographic evidence of cardiac disease were studied and compared with 18 normal subjects. Late potentials occurred in 5 out of 15 progressive systemic sclerosis patients (33%) with a significant difference versus controls (P < 0.05) and were present only in the patients with diffuse progressive systemic sclerosis (P < or = 0.001 vs. controls). All progressive systemic sclerosis patients showed a normal left ventricular systolic function. Abnormal left ventricular filling was found in 9 progressive systemic sclerosis patients (5 with diffuse progressive systemic sclerosis and 4 with CREST). A more severe impairment of the mean values of diastolic function indexes was found in diffuse progressive systemic sclerosis than in CREST. In all diffuse progressive systemic sclerosis patients at least one method showed altered results, whereas half the CREST patients showed no pathological findings with both techniques. These results confirm a lower myocardial involvement in the CREST syndrome than in diffuse progressive systemic sclerosis and consequently this is probably related to a better prognosis.

The time course and relation of positive signal-averaged electrocardiograms by time-domain and spectral temporal mapping analyses after infarction

We evaluated the time course of development of positive signal-averaged electrocardiograms (SA-ECGs) by time-domain and Spectral Temporal Mapping (STM) analyses after myocardial infarction in 88 patients without bundle branch block. The incidence of positive SA-ECGs by time-domain analysis peaked at 4 to 8 weeks postinfarction whereas the peak incidence by STM analysis varied from 4 days to 4 to 10 months postinfarction. Positive time-domain SA-ECGs demonstrated a significantly reduced factor of normality (NF) compared with negative time-domain SA-ECGs by X, Z, or vector STM analyses, but marked overlap was present for the standard deviations of positive and negative SA-ECGs in all STM leads. Chi square analysis demonstrated a significant correlation only between X-lead STM analysis and time-domain analysis; however, the two methods were markedly discordant. Although there is a statistically significant relation between time-domain and STM analyses of SA-ECGs, the two analyses are not clinically interchangeable.

Factors influencing changes in the signal-averaged electrocardiogram within the first year after a first myocardial infarction

One hundred twenty-nine patients were prospectively studied after a first myocardial infarction. A first signal-averaged electrocardiogram (SAECG-1) was performed in the acute phase (within 48 hours after onset of symptoms) and a second one (SAECG-2) in the late phase (6 to 18 months after hospital discharge). We studied the influence of nine parameters on the evolution of the signal-averaged electrocardiogram: age, gender, myocardial infarction location, number of diseased coronary vessels, infarct-related coronary artery patency, use of thrombolytic therapy or percutaneous transluminal coronary angioplasty in the acute phase, left ventricular ejection fraction, and recurrence of ischemic events. No follow-up data were available in 15 patients. Of the remaining 114 patients, an ischemic event occurred in 25 (22%). The signal-averaged electrocardiogram remained unchanged in 97 (85%) (remaining normal in 78 and abnormal in 19). It became abnormal in 13 (11.5%) and became normal in 4 (3.5%). In patients with a normal SAECG-1, two factors were associated with the change to an abnormal SAECG-2: (1) an ischemic event occurred in 11 (85%) of 13 patients whose SAECG-2 was abnormal compared with only 13 (17%) of 78 patients whose SAECG-2 remained normal (p < 0.0001), and (2) 100% of patients with an abnormal SAECG-2 had an inferior myocardial infarction compared with 54% of patients with a normal SAECG-2 (p = 0.004).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Analysis of high frequency QRS potentials observed during acute myocardial infarction

The value of high frequency QRS potentials (HFQRS) during acute myocardial infarction (AMI) was assessed to define infarct size and prognosis. HFQRS were recorded by signal-averaged ECG with 150-250 Hz frequency ranges, using X, Y, Z orthogonal leads. Recordings were obtained in surviving AMI patients (n = 33, 12 inferior, 11 anterior, 10 anterior-inferior) on the first and tenth days, but in non-survived patients (n = 5, 2 inferior, 1 anterior, 2 anterior-inferior) only on the first day. Additionally, the frequency of ventricular tachycardia (VT) was evaluated by 24-h Holter monitoring in all patients at the same days. The control group consisted of 11 healthy people. In surviving AMI patients, RMS voltage of vector magnitude reduced in anterior and anterior-inferior MI but filtered QRS duration was longer in inferior MI than normals (P < 0.05, < 0.05, < 0.01, respectively). In nonsurvived patients, RMS voltages of leads X, Y, Z and vector magnitude were lower than normals (P < 0.01, < 0.05, < 0.01, < 0.01, respectively) and surviving AMI patients (P < 0.01, < 0.05, < 0.05, < 0.05, respectively), the filtered QRS duration was found to be longer than normals and survived patients (P < 0.01, < 0.01). In patients who had VT on Holter monitoring, filtered QRS duration was significantly longer than in patients without VT (P < 0.05). As a result, HFQRS was important for defining infarct size but not malignant ventricular arrhythmias. VT was related to filtered QRS duration. HFQRS may offer significant prognostic information and contribute to early risk stratification of AMI patients.

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.

Prevention of sudden death in patients with coronary artery disease: the Multicenter Unsustained Tachycardia Trial (MUSTT)

This trial will significantly advance our understanding of the prognostic and therapeutic usefulness of electrophysiologic studies in patients with coronary artery disease. Several features of this trial are worth emphasizing. First, the protocol for performing programmed stimulation and serial drug testing is designed to mirror those currently in use by many practicing electrophysiologists. While practice patterns vary, the procedures used in the trial reflect what is considered "usual and standard" practice. Second, because half of the patients with inducible sustained ventricular tachycardia will be given no antiarrhythmic therapy, we will be able to ascertain the true risk of sudden death in this patient population without the influence of these agents. Third, this trial will assess the usefulness of a method of guiding antiarrhythmic therapy (electrophysiologic testing) to reduce mortality in this high-risk population. It will not evaluate the efficacy of a specific type of antiarrhythmic therapy.

The clinical significance of nonsustained ventricular tachycardia

Nonsustained ventricular tachycardia (NSVT) is an arrhythmia not often associated with symptoms; however, its occurrence in patients with structural heart disease is a prognostic indicator of an increased risk of mortality and sudden death. The management of asymptomatic patients with NSVT should first attempt to identify which patients are at highest risk for cardiac arrest, and second, devise a treatment that can reduce the incidence and/or mortality of cardiac arrest in this group. In patients with chronic coronary artery disease (CAD) and NSVT, programmed electrical stimulation identifies both a low and high risk group with respect to occurrence of ventricular arrhythmias. The negative predictive value of programmed electrical stimulation in patients with CAD and NSVT has been well established; however, uncertainty remains as to the optimal therapy for CAD patients with inducible ventricular arrhythmias. A number of reports suggest that patients whose inducible ventricular arrhythmias are rendered noninducible with antiarrhythmic drugs have a much lower risk of sudden death. It is yet to be resolved whether arrhythmias rendered noninducible identify a subgroup at low risk for cardiac arrest, independent of treatment. There is some evidence to suggest that the frequency of NSVT in patients with nonischemic dilated cardiomyopathy identifies a group at higher risk of sudden death. Programmed electrical stimulation adds little in helping to identify which of these patients are most likely to have cardiac arrest. The presence of NSVT in asymptomatic patients with hypertrophic cardiomyopathy may identify a group at higher risk for cardiac arrest.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Critical analysis of the signal-averaged electrocardiogram. Improved identification of late potentials

BACKGROUND

This study performed a critical analysis of signal-averaging methods. The objective was to optimize detection of late potentials.

METHODS AND RESULTS

We studied two patient populations: a low-arrhythmia-risk group with no evidence of heart disease and a group with clinically documented ventricular tachycardia (VT). Filtered QRS duration (QRSD) and terminal QRS amplitude (RMS40) were measured from the vector magnitude. A QRS duration based on the latest detectable ventricular activity in any of the three individual XYZ leads was also measured. Because of improved signal-to-noise ratio, both individual lead analysis and extended (600-versus 200-beat) averaging yielded significant changes in signal-averaged ECG parameters. Both approaches gave an increased sensitivity for VT identification. Sensitivity, specificity, and accuracy were evaluated as functions of critical values of QRSD and RMS40. RMS measurements in the terminal QRS, ranging from 20 to 100 msec and including RMS40, did not contribute to maximizing sensitivity and were highly correlated with QRSD. Our results from the low-arrhythmia-risk group suggest that age and sex should be considered in the definition of late potentials.

CONCLUSIONS

We propose a VT risk stratification scheme using signal-averaged ECG parameters obtained from both individual lead and vector magnitude analysis. This allows definition of four categories of VT risk derived statistically from the study data. This definition is based on combined measures of sensitivity, specificity, and negative and positive predictive value.

Late potentials in a porcine model of anterior wall myocardial infarction and their relation to inducible ventricular tachycardia

In this study, normal values for signal averaged electrocardiographic parameters were assessed in healthy pigs (n = 100) and the development of late potentials after myocardial infarction (n = 41) in relation to inducible ventricular tachycardia was investigated. Normal values are: filtered QRS duration (QRS) < or = 78 msec; root mean square voltage of the averaged QRS complex (V(tot)) > or = 51 microV, and duration of terminal activity below 30 microV (D30) < or = 37 msec. The distribution of the root mean square voltage in the last 30 msec (V30) was biphasic. Two weeks after myocardial infarction, QRS was prolonged from 55 +/- 10 to 66 +/- 19 msec (P < 0.002). D30 was prolonged from 19 +/- 6 msec to 28 +/- 13 (P < 0.002). V30 was decreased from 107 +/- 135 microV to 45 +/- 77 (P < 0.02). The total voltage (V(tot)) was decreased from 195 +/- 78 to 123 +/- 61 microV (P < 0.002). In four pigs (19%) late potentials developed. Sustained ventricular tachycardia was inducible in 11 pigs (52%), ventricular fibrillation in two pigs (10%) and eight pigs (38%) were noninducible. Three of 11 inducible pigs and one of the noninducible pigs had a late potential. The incidence of late potentials and their relation to inducible sustained ventricular tachycardia is comparable to the situation in man. Therefore, this pig model is an attractive alternative to the commonly used dog models.

Frequency of late potentials on signal-averaged electrocardiograms during thallium stress testing in coronary artery disease

Late potentials detected by signal-averaged electrocardiography (SAECG) are an important noninvasive indicator identifying patients with previous myocardial infarction at risk for developing ventricular tachycardia. The role of myocardial ischemia in the development of late potentials is undefined. This study attempts to determine if late potentials on SAECG can be produced during scintigraphically proven ischemia. A signal-averaged electrocardiogram was obtained before and immediately after single-photon emission computed tomography thallium exercise testing in 51 patients. Reversible ischemia was documented in 25 cases with no significant changes in the parameters of SAECG; patients with previous myocardial infarction (n = 10) also had no significant changes from baseline. Multivariate analysis with respect to reversible ischemia and previous myocardial infarction was unrevealing. Patients with late potentials at baseline (n = 10) who developed reversible ischemia (n = 5) had a shorter QRS duration than those with late potentials at baseline and no reversible ischemia. The data indicate that exercise-induced scintigraphically proven ischemia does not alter SAECG even in the presence of previous myocardial infarction. Patients with late potentials at baseline may actually have a shortened QRS duration during reversible ischemia as opposed to the expected lengthening of the QRS.

Establishment of signal-averaged electrocardiographic criteria with Frank XYZ leads and spectral filter used alone and in combination with ejection fraction to predict inducible ventricular tachycardia in coronary artery disease

Signal-averaged electrocardiographic criteria are reported for corrected Frank XYZ leads and a spectral filter. The new criteria were used alone and in combination with ejection fraction to predict inducibility of ventricular tachycardia (VT) at electrophysiologic testing. Signal-averaged electrocardiographic criteria were developed in 87 control subjects and validated in 182 patients (aged 63 +/- 10 years) with coronary artery disease and QRS duration less than 118 ms. Patients underwent electrophysiologic testing in which up to 3 extra-stimuli were used during 2 paced drives from 2 right ventricular sites. A positive finding was monomorphic VT lasting 30 seconds or needing intervention. An ejection fraction less than 40% was considered abnormal. Signal-averaged electrocardiographic variables that best characterized control subjects and separated patients with and without inducible VT were filtered QRS duration less than 120 ms, low-amplitude signal duration less than 38 ms and root-mean-square voltage greater than 20 muv. With these criteria, signal-averaged electrocardiographic and ejection fraction sensitivities were 87 and 45%, respectively, and specificities were 65 and 77%, respectively. Combining signal-averaged electrocardiography with ejection fraction improved the predictive accuracy. In conclusion, diagnostic criteria for signal-averaged electrocardiography with use of Frank XYZ leads and a spectral filter produced results similar to those reported for use of bipolar XYZ leads and a Butterworth filter. Signal-averaged electrocardiography was a better predictor of VT than was ejection fraction.

Optimal late potential criteria for reducing false positive signal-averaged electrocardiograms

The purposes of this study were to determine for signal-averaged electrocardiograms in normal subjects: (1) the incidence of false positives for various filter frequencies and late potential criteria and (2) reproducibility over time. In 46 normal volunteers, the QRS vector magnitude was bidirectionally high-pass filtered at 25, 40, and 100 Hz. As high-pass filter frequency increased, QRS duration decreased from 98 +/- 9 to 92 +/- 9 msec (p less than 0.0001), terminal QRS root mean square voltage decreased from 60 +/- 41 to 14 +/- 9 microV (p less than 0.0001), and terminal QRS low amplitude signal duration increased from 27 +/- 7 to 41 +/- 14 msec (p less than 0.0001). For individual parameters, the incidence of false positive tests ranged from 2% to 41%, whereas there were no false positive tests for the combination of abnormal QRS duration plus either root mean square voltage or low amplitude signal duration. Measurements were repeated after 6.4 +/- 0.3 months in 26 subjects and were highly reproducible at all filter settings. The potentially high incidence of false positive tests with some criteria has important implications for the use of signal-averaged electrocardiography as a screening test in patient populations with various arrhythmia risks.

The signal-averaged electrocardiogram in predicting coronary artery disease

The ability to noninvasively detect coronary artery disease (CAD) in patients undergoing diagnostic cardiac catheterization was studied using a signal-averaged electrocardiogram. An initial study of 13 patients revealed that a QRS duration greater than or equal to 100 msec, a root mean square voltage in the terminal 40 msec of the QRS less than 50 microV, and a low amplitude signal (LAS) duration greater than 28 msec were suggestive of CAD. These parameters were then used prospectively to examine 40 consecutive patients with chest pain of undetermined etiology referred for cardiac catheterization. Patients with CAD had significantly longer filtered QRS and LAS durations and lower root mean square voltages compared with patients without CAD. The sensitivity, specificity, and positive predictive value of a single parameter ranged from 62% to 76%, 74% to 89%, and 75% to 87%, respectively. Thus the signal-averaged electrocardiogram may be a useful tool in evaluating patients for the presence of CAD.

Survivors of acute myocardial infarction: who is at risk for sudden cardiac death?

Coronary artery disease is the leading cause of death in the United States. Approximately half of the deaths attributable to coronary artery disease are sudden cardiac deaths. A logical approach to prevention of sudden death is to identify those who are at risk and then to initiate effective therapy. Left ventricular dysfunction, frequent ventricular ectopic activity, nonsustained ventricular tachycardia, and late potentials have been identified as markers for increased risk of sudden cardiac death. The sensitivity and specificity of these risk factors vary, and the positive predictive power is less than satisfactory. The value of invasive electrophysiologic testing for risk stratification in the general postinfarction patient population remains unclear. In addition to these diagnostic difficulties, prevention of sudden death also has been limited by imperfect efficacy and potential lethal effects of the currently available antiarrhythmic agents. Automatic implantable defibrillators are effective for aborting sudden death; however, the potential for more general use of automatic defibrillators in asymptomatic but high-risk postinfarction patients has not been evaluated.

Standards for analysis of ventricular late potentials using high-resolution or signal-averaged electrocardiography. A statement by a Task Force Committee of the European Society of Cardiology, the American Heart Association, and the American College of Cardiology

Sufficient data are available to recommend the use of the high-resolution or signal-averaged electrocardiogram in patients recovering from myocardial infarction without bundle branch block to help determine their risk for developing sustained ventricular tachyarrhythmias. However, no data are available about the extent to which pharmacological or nonpharmacological interventions in patients with late potentials have an impact on the incidence of sudden cardiac death. Therefore, controlled, prospective studies are required before this issue can be resolved. As refinements in techniques evolve, it is anticipated that the clinical value of high-resolution or signal-averaged electrocardiography will continue to increase.

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

Sufficient data are available to recommend the use of the high-resolution or signal-averaged electrocardiogram in patients recovering from myocardial infarction without bundle branch block to help determine their risk for developing sustained ventricular tachyarrhythmias. However, no data are available about the extent to which pharmacological or nonpharmacological interventions in patients with late potentials have an impact on the incidence of sudden cardiac death. Therefore, controlled, prospective studies are required before this issue can be resolved. As refinements in techniques evolve, it is anticipated that the clinical value of high-resolution or signal-averaged electrocardiography will continue to increase.

Fourier transform versus bidirectional digital filters for late potentials recording in the electrocardiogram

Late potentials occur after the QRS complex and can be detected by using signal averaging and filtering techniques. In this study the filtered averaged electrocardiograms (ECGs) obtained using two types of filters were compared: the bidirectional digital recursive filter with a 40 Hz high-pass cut-off frequency, and the Fourier transform non-recursive digital filter with a 60 Hz high-pass cut-off. Strong correlation was found between the numerical values obtained when using these two filtering procedures. In addition, close diagnostic concordance was found between the late potential parameters in patients with normal and abnormal signal averaged ECGs. Visual comparison between the bidirectional and the Fourier plots revealed a close morphological similarity between the vector magnitudes. There was no significant difference in the mean root mean square voltage of the terminal 40 ms and the late potential duration, less than 40 mV, between the bidirectional and the Fourier filters in patients with a normal or an abnormal signal averaged ECG. The QRS duration was found to be significantly longer using Fourier filtering. This can be explained by the contributions of two factors: using the bidirectional procedure with a phase delay from each end of the data window, a shortening of the filtered QRS duration may occur and, alternatively, when using the Fourier filter, minimal stretching of the QRS complex may occur.(ABSTRACT TRUNCATED AT 250 WORDS)

Study of the influence of left bundle branch block on the signal-averaged electrocardiogram: a qualitative and quantitative analysis

To study the influence of left bundle branch block (LBBB) on the signal-averaged electrocardiogram (SAECG), quantitative and qualitative analyses of SAECG parameters were undertaken in 48 patients with electrocardiographic evidence of intrinsic LBBB and in 39 patients with a "normal" surface QRS duration (less than 120 msec) who underwent right ventricular pacing-induced LBBB. We assumed pacing of the right ventricular apex to be a suitable model of this conduction defect. Sustained monomorphic ventricular tachycardia (SMVT) was inducible in 16 of 48 patients with intrinsic LBBB and in 23 of 39 patients with pacing-induced LBBB. Utilizing a filter setting of 25 to 250 Hz, late potentials were defined as a total filtered QRS duration greater than or equal to 120 msec, a root mean square voltage in the terminal 40 msec (RMS 40) of less than or equal to 25 microV, and the duration of signals less than 40 microV (LAS 40) of greater than or equal to 38 msec. Only RMS 40 and LAS 40 criteria were used in patients with LBBB. Prolongation of LAS 40 and fragmentation of signals in the terminal portion of the filtered QRS were characteristic of all patients with LBBB aberration. Of those patients with intrinsic LBBB, the mean total filtered QRS duration, RMS 40, and LAS 40 for inducible and noninducible patients were significantly different (170 +/- 28, 16 +/- 10, 55 +/- 24, and 153 +/- 18 msec, 25 +/- 10 microV, 33 +/- 16.9 msec; p = 0.04, 0.009, and 0.007, respectively). Noninducible patients with a normal QRS duration demonstrated a 60% decrement in the mean RMS 40 value during pacing-induced LBBB. These changes resulted in a 59% false positive incidence of late potentials during pacing-induced LBBB. This correlated with a similarly low mean RMS 40 value in patients with intrinsic LBBB and no inducible SMVT, hence giving rise to a false positive incidence of late potentials of 63%. Since "standard" RMS 40 and LAS 40 criteria resulted in low specificity and positive predictive value, new parameters were selected and analyzed. The combination of RMS 40 less than or equal to 17 microV plus LAS 40 greater than or equal to 55 msec yielded the best overall statistical result, with a sensitivity, specificity, and total predictive accuracy of 69%, 81%, and 77%, respectively.

IN CONCLUSION

(1) A reduction of RMS 40, prolongation of LAS 40, and fragmentation of signals in the terminal portion of the filtered QRS are characteristics of LBBB.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of frequency of late potentials in idiopathic dilated cardiomyopathy and ischemic cardiomyopathy with advanced congestive heart failure and their usefulness in predicting sudden death

Signal-averaged electrocardiograms were obtained in 62 consecutive patients with advanced congestive heart failure (CHF) undergoing evaluation for possible heart transplantation to determine if late potentials: (1) provide unique information compared to assessment of ventricular ectopic activity on ambulatory electrocardiogram, and (2) identify a subgroup of CHF patients with higher sudden death risk. Patients with a history of cardiac arrest or sustained ventricular tachycardia were excluded. CHF was due to old myocardial infarction in 40 patients and idiopathic dilated cardiomyopathy in 22 patients. Late potentials were present in 16 of 40 (40%) patients with old infarction but in only 3 of 22 (14%) patients with nonischemic CHF (p = 0.03). Twenty-four-hour ambulatory electrocardiograms were obtained in 34 patients (55%). Total ventricular ectopic activity and repetitive forms of ectopy were similar in patients with and without late potentials. Nine patients died suddenly, 9 had nonsudden death, 15 underwent heart transplantation and 29 were alive and well after a mean follow-up of 218 +/- 154 days. At 1 year, the actuarial risk of death was 37% and of sudden death was 20%. Sudden death risk was 12% in patients with late potentials versus 21% in those without (p = 0.73). Thus, the incidence of the arrhythmia substrate producing late potentials depends on the CHF etiology. The signal-averaged electrocardiogram and ambulatory electrocardiogram provide independent information for possible risk assessment in CHF. However, late potentials are poor predictors of sudden death risk when CHF is advanced, possibly due to the heterogeneity of causes of sudden death--ventricular tachycardia being only 1 of many possible mechanisms.

Effects of exercise on the signal-averaged electrocardiogram in coronary artery disease

The effects of exercise on the signal-averaged electrocardiogram (SAECG) were investigated in 52 patients with stable coronary artery disease. The SAECG was recorded before and immediately after the exercise test and analyzed at 25 to 250 Hz and 40 to 250 Hz. All patients had SAECG with noise level less than or equal 0.8 microV at 25 Hz and less than or equal to 0.6 microV at 40 Hz and with the difference in noise level between control SAECGs and SAECGs after exercise less than or equal to 0.2 to 0.3 microV. Twenty-eight patients developed ST changes consistent with transient subendocardial ischemia that persisted during the SAECG recording after exercise. There was no significant difference between control SAECGs and SAECGs after exercise in patients with or without a positive exercise test. The absence of significant change on the SAECG was not related to the presence or absence of prior myocardial infarction, site of infarction, development of exercise-induced ventricular arrhythmias or presence of an abnormal recording at baseline. These data suggest that exercise-induced electrophysiologic changes and ventricular arrhythmias may not be related to the anatomic-electrophysiologic substrate that underlies late potentials on the SAECG.

Signal-averaged electrocardiographic late potentials in resuscitated survivors of out-of-hospital ventricular fibrillation

The results of signal-averaged electrocardiography and programmed electrical stimulation were evaluated in 25 patients with recurrent sustained ventricular tachycardia (VT) and 46 patients with a history of out-of-hospital ventricular fibrillation (VF) to characterize the electrophysiologic substrate responsible for these different clinical arrhythmia presentations. Patients with VT had a higher incidence of late potentials (VT 83%, VF 50%, p = 0.005). Significant differences between these groups were also noted in response to programmed electrical stimulation. A sustained ventricular arrhythmia was induced in 24 of 25 (96%) patients with a history of VT but in only 27 of 46 (59%) of VF patients (p = 0.005). In addition, VF was induced in 11 (24%) patients in the VF group but in none of the patients in the VT group (p = 0.005). When the 2 groups were compared on the basis of select clinical characteristics, no significant difference in age, sex, presence of coronary artery disease or ejection fraction was noted. The frequency of prior myocardial infarction was significantly higher in the VT group (VT 20 of 25, 80%; VF 24 of 46, 52%; p = 0.03). Finally, no significant relation between the presence of late potentials and induced arrhythmias was noted in either group. The inability of signal-averaged electrocardiography to predict inducibility in VF patients may represent a significant limitation of this technique in identifying patients at risk for sudden cardiac death.

Lack of correlation between transient myocardial ischemia and late potentials on the signal-averaged electrocardiogram

The relation between transient myocardial ischemia and late potentials was investigated in 100 patients with coronary artery disease who underwent serial recordings of the signal-averaged electrocardiogram before, during and after dipyridamole infusion. During this test, 47 patients (group 1) developed transient myocardial ischemia (with ST elevation in 14 cases and ST depression in 33), whereas 53 patients (group 2) did not. Baseline signal-averaged electrocardiogram was abnormal in 20 patients (20%): a QRS duration greater than 115 ms was seen in 6 patients, a late potential (root mean square voltage of last 40 ms of QRS [RMS40] less than 25 microV) in 9, both abnormalities in 5, with no significant differences between groups 1 and 2 (26 vs 15%, respectively). In both groups, comparison of recordings obtained before, during and after dipyridamole test revealed no significant changes in QRS duration and RMS40. Absence of significant differences was also observed when patients with transient ischemic ST elevation or ST depression were examined separately. During the test, 100% of abnormal basal recordings remained abnormal and 98% of normal recordings remained within normal limits. In only 2 patients (from group 1) RMS40, which showed borderline values at baseline, decreased to abnormal values during dipyridamole test. These data suggest that electrophysiologic abnormalities induced by transient myocardial ischemia may not bear any relation with the substrate for chronic reentrant ventricular tachyarrhythmias, as reflected by late potentials on the signal-averaged electrocardiogram.

Signal-averaged electrocardiography and the significance of late potentials in patients with "idiopathic" ventricular tachycardia: a review

High-frequency, low-amplitude electrical activity during and in continuation with the ventricular electrogram in sinus rhythm is now accepted as an indirect marker for reentrant pathways in ventricular muscle. Because the amplitude of these signals is low, much effort has recently been directed toward finding methods of recording these noninvasively. This essentially involves averaging the electrocardiogram, amplifying it, and filtering out the low frequency and nonrepetitive signals. This review discusses the methods presently available for signal-averaged electrocardiography and their background. The clinical application of signal-averaged electrocardiograms in patients with or suspected to have ventricular tachycardia is summarized. Data regarding the incidence of abnormal signal-averaged electrocardiography in patients with "idiopathic" ventricular tachycardia compared with normal subjects and patients with ventricular tachycardia related to ischemic heart disease are presented.