Signal-averaged electrocardiography: a new noninvasive test to identify patients at risk for ventricular arrhythmias

Utility of SAECG in arrhythmogenic right ventricle dysplasia

BACKGROUND

Arrhythmogenic right ventricular dysplasia (ARVD) is characterized by progressive replacement of RV myocardium with fibro-adipose tissue thought to be responsible for the presence of late potentials (LP) detected by SAECG. The general consensus on the role of SAECG in the diagnosis and prognosis of patients with ARVD is lacking. The purpose of this systematic review was to better define the role of SAECG in ARVD.

METHODS

An extensive review of literature was done to specifically describe the prevalence of LP in ARVD and its determinants, explore the various options available to improve the diagnostic ability of SAECG, and provide recommendations for proper utilization of this technique.

RESULTS

LPs are frequent in ARVD (47-100%), and more prevalent in severe disease and in patients with documented spontaneous VT. SAECG is a useful test in following the characteristic evolutivity of the disease. 4-16% of normal family members of patients with ARVD also have abnormal SAECG results. Detection of LP in ARVD can be improved by employing a high-pass filter of 25 Hz and specifically looking for changes in the Z leads.

CONCLUSIONS

SAECG testing should be considered a standard part of the evaluation of patients with known or suspected ARVD. Further research is needed to confirm the value of SAECG testing in predicting arrhythmia risk and assessing the rate of disease progression, as well as to determine if greater prevalence of SAECG abnormalities in family members of patients with ARVD represents early detection of ARVD. The ongoing multidisciplinary study of right ventricular dysplasia will hopefully answer some of these questions.

[Detection of beat-to-beat changes in high frequency components of the QRS complex using a free optimal signal averaging system: relationship with ventricular arrhythmias]

In this study, we evaluated the relationship between beat-to-beat changes in high frequency components of the QRS complex and ventricular arrhythmias by using a newly developed event-related (ER) signal averaging technique. The study involved 82 patients with premature ventricular contractions (PVC), 56 of whom, including 16 with ventricular tachycardia (VT), were enrolled in Analysis I. In Analysis I, averaged sinus beats were classified into three patterns: 1) the sinus beat immediately before PVC (BEF); 2) that immediately after PVC (AFT); and 3) all sinus beats (ALL). Analysis II covered the remaining 26 patients, and involved five modes of event-related signal averaging, using: 1) the second beat preceding PVC (2-B); 2) the beat immediately preceding PVC (1-B); 3) the beat immediately after PVC (1-A); 4) the second beat after PVC (2-A); and 5) the beat isolated (ISO) from PVC. The filtered QRS duration (F-QRS) and the integral voltage of the terminal 40 msec (RMS 40-I) were measured using these averaging patterns. F-QRS in the VT group was longer than that in the non-VT group, but RMS 40-I was shorter. The F-QRS of BEF (1-B) was significantly longer than that of AFT (1-A). The transient difference in the F-QRS was observed in both VT and non-VT groups. This difference was almost eliminated at AFT (1-A) in the non-VT group, but was stable at AFT (1-A) in the VT group. Simultaneousely, RMS 40-I in BEF was significantly shorter than that in AFT. This transient decrease of RMS 40-I was observed in both VT and non-VT groups. Although RMS 40-I after this decrease showed a return almost to the control level at AFT in the non-VT group, it tended to remain even at AFT in the VT group. The sudden prolongation of F-QRS that occurred with the RMS 40-I decrease in BEF was related to the appearance of PVCs. We attributed the fact that these changes in F-QRS and RMS 40-I were observed even at AFT in the VT group to electrophysiologically preferable conditions for reentry.

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.

Signal-averaged electrocardiography in healthy children: relationship with age, sex, and anthropometry

Signal-averaged electrocardiograms (SAECGs) have been found to be influenced by sex and anthropometry in adults. The purpose of this study was to evaluate this relationship in children. Total filtered QRS duration (TQRS), duration of high-frequency, low-amplitude signals in the terminal portion of the QRS complex that were less than 40 microV (HFLA) root-mean-square voltage in the last 40 ms of the filtered QRS (RMS40) were determined by high-resolution electrocardiographic (ECG) recording (MAC 15 ECG System, Marquette Electronics, Milwaukee, WI). These parameters were correlated with age, sex, body weight, height, relative weight, body mass index, and body surface area. As HFLA and RMS40 were not normally distributed, they were logarithmically transformed for regression analysis. The best subset multiple regression procedure was used to evaluate the variables that would optimally influence SAECG measurements and to obtain regression equations for the prediction of each SAECG parameter. Although univariate analysis shows that almost all the body characteristics and age are significantly correlated with SAECGs, multiple regression analysis reveals that TQRS is significantly influenced by height (P < .0001), relative weight (P = .012), and body mass index (P = .041); HFLA is influenced by weight (P = .001), height (P = .004), and body mass index (P = .001); and RMS40 is influenced by height (P < .0001) and relative weight (P = .001). Sex is noted to significantly influence both TQRS and RMS40 (P < .0001, P = .002, respectively), while HFLA is found to be significantly related to age (P = .001). In summary, SAECGs in Chinese children are shown to be influenced by height, weight, and relative weight or body mass index, but not body surface area, while age and sex also significantly contribute to the variation of some SAECG parameters.

An evaluation of serum troponin T and signal-averaged electrocardiography in predicting electrocardiographic abnormalities after blunt chest trauma

OBJECTIVE

Despite multiple inquiries, there are no available tests to definitively detect blunt myocardial injury. The evaluation of patients with chest wall injuries without other indications for intensive care unit (ICU) admission has ranged from a single emergency department electrocardiogram (ECG) to 72 hours of continuous electrocardiographic monitoring. Recently, signal-averaged ECG and serum cardiac troponin T have demonstrated clinical utility in the evaluation of ischemic heart disease. The purpose of this study is to determine the ability of these diagnostic tests to predict the occurrence of significant electrocardiographic rhythm disturbances for patients with chest wall injuries and no other indication for ICU admission.

METHODS

We prospectively evaluated 71 consecutive adult patients admitted to a regional Level I trauma center with chest wall injuries not requiring ICU admission. We obtained admission signal-averaged ECG, serum troponin T level, standard ECG, and creatine phosphokinase (CPK-MB) level. Patients received continuous electrocardiographic monitoring, follow-up 12-lead electrocardiography, and serial monitoring of troponin and CPK-MB. Echocardiography was performed for patients with abnormal CPK-MB levels. Electrocardiographic events were graded as normal, abnormal but clinically insignificant, or clinically significant. Multiple stepwise logistic regression analysis was used to evaluate predictors for the development of clinically significant electrocardiographic events.

RESULTS

On admission, 17 of 71 patients (23.9%) had normal sinus rhythm; 13 (18.3%) had a clinically significant finding. For 50 patients, follow-up ECG was abnormal; for 26, the findings were clinically significant. Of 17 patients with normal initial ECGs, 7 (41%) developed a clinically significant abnormality. Six patients received intervention for ECG findings. Eleven of 71 patients (16%) had positive troponin T; 5 of 71 (7%) had positive CPK-MB; 15 of 71 (21%) had positive signal-averaged ECG; and 4 of 13 had positive echocardiograms. Initial electrocardiographic abnormalities and a troponin T level > 0.20 microg/L were the only variables found to predict clinically significant electrocardiographic events. Sensitivity and specificity of troponin T in predicting clinically significant abnormalities were 27 and 91%, respectively.

CONCLUSIONS

1. The best predictors for the development of significant electrocardiographic changes are an admission ECG abnormality and an elevated serum troponin T level. 2. Both tests have high specificity with low to moderate sensitivity. 3. Patients with normal ECGs may develop clinically significant events. 4. CPK-MB and echocardiograms continue to be poor predictors of significant electrocardiographic events.

QT dispersion as a marker of risk in patients awaiting heart transplantation

OBJECTIVES

The objectives of this study were to determine whether a signal-averaged electrocardiogram (SAECG) or measurement of interlead variability of QT intervals on an electrocardiogram (ECG) obtained at the time of wait-listing could provide prognostic value with respect to cardiac death during the waiting period.

BACKGROUND

Because heart transplantation is a life-saving but limited resource, there remains an urgent need to identify those patients at greatest risk of dying while awaiting heart transplantation as part of the strategy to optimize the allocation of donor organs to those in greatest need. This study was undertaken to prospectively identify clinical, ECG or SAECG variables that might predict mortality during the waiting period.

METHODS

Of 108 consecutive patients referred for heart transplant evaluation, 80 were placed on a waiting list, at which time a standard 12-lead ECG and a SAECG were recorded. In this cohort of 80 patients, QT dispersion was characterized from the 12-lead ECG as either the maximal-minimal QT interval (QTDISP) or as the coefficient of variation of all QT intervals (QTCV).

RESULTS

During the 25-month follow-up period (mean time on waiting list, 201 days), the mortality rate was 27%/year, divided equally between heart failure and sudden deaths. No clinical variable identified at entry predicted mortality. QTDISP and QTCV were strong mortality predictors, with a 4.1-fold increase in mortality in patients with QTDISP > 140 ms compared with those patients with QTDISP < or = 140 ms (95% CI 1.1 to 14.9), whereas a QTCV > or = 9% also predicted a 4.1-fold increased risk of death (95% CI 1.4 to 11.8). Although 88% of all SAECGs were abnormal, no patient with a normal SAECG died suddenly during the waiting period.

CONCLUSIONS

Indexes of QT dispersion provide a means of stratifying a patient's risk of dying while awaiting heart transplantation and may help to establish priority on a heart transplant waiting list.

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.

Failure of signal-averaged electrocardiography with use of time-domain variables to predict inducible ventricular tachycardia in patients with conduction defects

OBJECTIVE

To extend the application of signal-averaged electrocardiography (SAECG) to patients with ventricular conduction defects by analysis of electrocardiographic (ECG) time-domain variables.

MATERIAL AND METHODS

In 123 consecutive patients with a QRS duration of 118 ms or more on a resting ECG and without evidence of an accessory pathway, SAECG was done at the time of electrophysiologic (EP) study. For EP testing, up to three stimuli were delivered during two paced drives from two right ventricular sites. A "positive" EP result was defined as monomorphic ventricular tachycardia that lasted for more than 30 seconds or necessitated intervention. Data were obtained for four time-domain variables. All variables were analyzed for differences between patients with EP-positive and those with EP-negative results.

RESULTS

Unfiltered QRS duration was the only time-domain ECG variable that was statistically different (P = 0.02) between patients with EP-positive and those with EP-negative results (141.3 and 147.8 ms, respectively); this difference persisted when patients with right bundle branch block were excluded from analysis. This finding is the opposite of previously reported observations. When only patients with ischemic heart disease were analyzed, no SAECG variables were significantly different between patients with inducible ventricular tachycardia and those without it.

CONCLUSION

High-resolution ECG time-domain variables cannot be used to predict inducibility of ventricular tachycardia during EP testing in patients with conduction defects.

Arrhythmias and acute myocardial infarction

The most common arrhythmias associated with inferior-wall and anterior-wall myocardial infarction are bradycardia and supraventricular and ventricular tachycardia. Optimal treatment approaches are based on the pathophysiology of the infarct and the presence of contributing medical factors (eg, congestive heart failure, metabolic disorders). Temporary or permanent pacemaker therapy is helpful in some patients. Sudden death due to arrhythmia after myocardial infarction may be predicted and avoided in certain situations.

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.

Late potentials on signal-averaged electrocardiograms and patency of the infarct-related artery in survivors of acute myocardial infarction

This study evaluated the relation between patency of the infarct-related artery and the presence of late potentials on the signal-averaged electrocardiogram (ECG) in 124 consecutive patients (98 men, 26 women; mean age 59 years) with acute myocardial infarction receiving thrombolytic therapy, acute percutaneous transluminal coronary angioplasty or standard care. All patients were studied by coronary angiography, measurement of ejection fraction and signal-averaged ECG. The infarct-related artery was closed in 51 patients and open in 73. Among patients with no prior myocardial infarction undergoing early attempted reperfusion therapy, a patent artery was associated with a decreased incidence of late potentials (20% versus 71%; no significant difference in ejection fraction). In the 48 patients receiving thrombolytic agents within 4 h of symptom onset, the incidence of late potentials was 24% and 83% among patients with an open or closed artery, respectively (p less than 0.04). The most powerful predictors of late potentials were the presence of a closed infarct-related artery, followed by prior infarction and patient age. Among patients receiving thrombolytic agents within 4 h of symptom onset, the only variable that was predictive of the presence of late potentials was a closed infarct-related artery. These data imply that reperfusion of an infarct-related artery has a beneficial effect on the electrophysiologic substrate for serious ventricular arrhythmias that is independent of change in left ventricular ejection fraction as an index of infarct size. These findings might explain, in part, the low late mortality rate in survivors of myocardial infarction with documented reperfusion of the infarct-related artery.

Signal-averaged electrocardiography. Promising tool for predicting sudden cardiac death

Signal-averaged electrocardiography has shown great promise as an adjunct in identifying patients at risk for sudden cardiac death. Clearly, much research remains to be done. Methods and criteria must be standardized so studies can be compared and the most effective ways in which to use this technology can be determined.

Acute myocardial infarction: initial manifestations, management, and prognosis

In patients with suspected acute myocardial infarction (AMI), obtaining a thorough history is important for identifying both the cause of chest pain and any concurrent conditions that may complicate the management. Physical examination--including cardiac auscultation and determining the status of the peripheral vasculature--is important as a guide to immediate management and as a baseline for future comparison. The differential diagnosis of AMI is extensive, and various laboratory tests, such as electrocardiography, cardiac enzymes, radionuclide techniques, echocardiography, and cardiac catheterization, can aid in the diagnosis. The routine management of patients with AMI can include medical therapy with antithrombotic agents, nitrates, beta-adrenergic blockers, or calcium channel blocking agents. The major differences between Q-wave and non-Q-wave infarction are discussed. Some factors that affect early and late prognosis in patients with AMI are age of the patient, residual left ventricular function, residual myocardial ischemia, and substrates for sustained ventricular arrhythmias. Although much of the current enthusiasm in management of AMI is related to revascularization strategies, other important aspects of diagnosis and treatment should not be overlooked.

Clinical application of the signal-averaged electrocardiogram and "late potentials"

The signal-averaged ECG has proven to be a valuable tool for identifying patients at risk of ventricular arrhythmias. This computerized method of analyzing standard ECGs identifies microvolt-level late potentials that represent delayed conduction through diseased myocardium. This diseased myocardium is a potential substrate for reentrant ventricular arrhythmias. In select patient groups, the signal-averaged ECG predicts electrophysiologic testing results. Problems remain and continued development is needed to evaluate patients with conduction system disease, the patient without coronary artery disease but at risk of sudden death, and proper general application of the technique.