generally recognized, perhaps as an indicator of atrial enlargement from ventricular dysfunction, and warrant further study. In a related study, P-wave morphology changed over time in patients from the MADIT II study who later developed AF, but remained unchanged in those who did not [15]. SUMMARY AND RECOMMENDATIONS Late potentials are primarily used to reflect the presence of substrates for ventricular tachycardia (VT) rather than a dynamic, time-varying predisposition to reentry. Although late potentials reflect slow conduction related to arrhythmogenic substrates, episodes of https://www.uptodate.com/contents/signal-averaged-electrocardiogram-overview-of-technical-aspects-and-clinical-applications/print 11/23 7/6/23, 10:42 AM Signal-averaged electrocardiogram: Overview of technical aspects and clinical applications - UpToDate VT initiation in such patients are uncommon in the absence of additional triggers such as ventricular premature beats, electrolyte abnormalities, increased circulating catecholamines, or ischemia. (See 'Definitions and epidemiology' above.) The signal-averaged electrocardiogram (SAECG) is useful for detecting subtle abnormalities in the surface ECG that are not visible to the naked eye. One example of such an abnormality is the "ventricular late potential," a low-amplitude signal near the end of the QRS complex that can be used to stratify risk for ventricular tachyarrhythmias in patients with cardiomyopathies of various etiologies. (See "Reentry and the development of cardiac arrhythmias".) The SAECG can be acquired by one of three methods (temporal signal averaging, spatial signal averaging, or spectral analysis), all with inherent benefits and limitations (see 'Techniques' above): Temporal signal averaging, the most common method for obtaining the SAECG, averages a number of QRS complexes over time. Spatial signal averaging analyzes electrical potentials simultaneously recorded from multiple pairs of closely spaced electrodes. Spectral analysis considers the QRS complex (or P wave) to be composed of multiple simple waveforms, typically sinusoids. Spectral analysis thus decomposes the QRS complex (or P wave) into these constituent signals for analysis. The following time analyses, derived from temporal signal averaging, are the most frequently used criteria to define an abnormal SAECG (see 'Definition' above): Filtered QRS duration >114 milliseconds Terminal (last 40 milliseconds) QRS root mean square voltage <20 microvolts Low-amplitude (<40 microvolts) late potentials with duration >38 milliseconds SAECG abnormalities are associated with an increased risk of ventricular arrhythmias and cardiac and sudden death mortality in various clinical settings including post-myocardial infarction, ischemic cardiomyopathy, nonischemic cardiomyopathy, hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, and the Brugada syndrome. (See 'Clinical settings' above.) Ventricular late potentials on the intracardiac electrogram may represent critical sustaining mechanisms for VT and may be targeted for catheter ablation with successful arrhythmia elimination. (See 'Late potentials and catheter ablation for ventricular tachycardia' above.) https://www.uptodate.com/contents/signal-averaged-electrocardiogram-overview-of-technical-aspects-and-clinical-applications/print 12/23 7/6/23, 10:42 AM Signal-averaged electrocardiogram: Overview of technical aspects and clinical applications - UpToDate The P-wave SAECG may indicate slow conduction in the atrium and in early work has been used to predict the propensity for atrial fibrillation. Use of UpToDate is subject to the Terms of Use. REFERENCES 1. Liao YC, Lin YJ, Chung FP, et al. Risk stratification of arrhythmogenic right ventricular cardiomyopathy based on signal averaged electrocardiograms. Int J Cardiol 2014; 174:628. 2. Ja s P, Maury P, Khairy P, et al. Elimination of local abnormal ventricular activities: a new end point for substrate modification in patients with scar-related ventricular tachycardia. Circulation 2012; 125:2184. 3. Al-Khatib SM, Stevenson WG, Ackerman MJ, et al. 2017 AHA/ACC/HRS Guideline for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol 2018; 72:e91. 4. Goldberger JJ, Cain ME, Hohnloser SH, et al. American Heart Association/American College of Cardiology Foundation/Heart Rhythm Society scientific statement on noninvasive risk stratification techniques for identifying patients at risk for sudden cardiac death: a scientific statement from the American Heart Association Council on Clinical Cardiology Committee on Electrocardiography and Arrhythmias and Council on Epidemiology and Prevention. Circulation 2008; 118:1497. 5. European Heart Rhythm Association, Heart Rhythm Society, Zipes DP, et al. ACC/AHA/ESC 2006 guidelines for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death: a report of the American College of Cardiology/American Heart Association Task Force and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Develop Guidelines for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death). J Am Coll Cardiol 2006; 48:e247. 6. Kamath GS, Zareba W, Delaney J, et al. Value of the signal-averaged electrocardiogram in arrhythmogenic right ventricular cardiomyopathy/dysplasia. Heart Rhythm 2011; 8:256. 7. Reddy VY, Reynolds MR, Neuzil P, et al. Prophylactic catheter ablation for the prevention of defibrillator therapy. N Engl J Med 2007; 357:2657. 8. Nogami A, Sugiyasu A, Tada H, et al. Changes in the isolated delayed component as an endpoint of catheter ablation in arrhythmogenic right ventricular cardiomyopathy: https://www.uptodate.com/contents/signal-averaged-electrocardiogram-overview-of-technical-aspects-and-clinical-applications/print 13/23 7/6/23, 10:42 AM Signal-averaged electrocardiogram: Overview of technical aspects and clinical applications - UpToDate predictor for long-term success. J Cardiovasc Electrophysiol 2008; 19:681. 9. Santangeli P, Di Biase L, Horton R, et al. Ablation of atrial fibrillation under therapeutic warfarin reduces periprocedural complications: evidence from a meta-analysis. Circ Arrhythm Electrophysiol 2012; 5:302. 10. Zorzi A, Migliore F, Elmaghawry M, et al. Electrocardiographic predictors of electroanatomic scar size in arrhythmogenic right ventricular cardiomyopathy: implications for arrhythmic risk stratification. J Cardiovasc Electrophysiol 2013; 24:1321. 11. Lackermair K, Kellner S, Kellnar A, et al. Initial single centre experience with the novel Rhythmia high density mapping system in an all comer collective of 400 electrophysiological patients. Int J Cardiol 2018; 272:168. 12. Jamil-Copley S, Vergara P, Carbucicchio C, et al. Application of ripple mapping to visualize slow conduction channels within the infarct-related left ventricular scar. Circ Arrhythm Electrophysiol 2015; 8:76. 13. Lalani GG, Schricker A, Gibson M, et al. Atrial conduction slows immediately before the onset of human atrial fibrillation: a bi-atrial contact mapping study of transitions to atrial fibrillation. J Am Coll Cardiol 2012; 59:595. 14. Holmqvist F, Platonov PG, McNitt S, et al. Abnormal P-wave morphology is a predictor of atrial fibrillation development and cardiac death in MADIT II patients. Ann Noninvasive Electrocardiol 2010; 15:63. 15. Holmqvist F, Platonov PG, Carlson J, et al. Altered interatrial conduction detected in MADIT II patients bound to develop atrial fibrillation. Ann Noninvasive Electrocardiol 2009; 14:268. Topic 984 Version 27.0 https://www.uptodate.com/contents/signal-averaged-electrocardiogram-overview-of-technical-aspects-and-clinical-applications/print 14/23 7/6/23, 10:43 AM Signal-averaged electrocardiogram: Overview of technical aspects and clinical applications - UpToDate GRAPHICS Late potentials on the signal-averaged ECG suggesting possible substrate for reentrant ventricular arrhythmias Signal-averaged electrocardiogram (SAECG) showing a QRS complex after a first and second myocardial infarction (MI) in the same patient. Left panel: After a first MI, no late potentials are present on the SAECG. Right panel: After a second MI, late potentials are seen as low amplitude signals at the end of the QRS complex (arrow). The filtered QRS duration is increased to >120 milliseconds. Graphic 72380 Version 3.0 https://www.uptodate.com/contents/signal-averaged-electrocardiogram-overview-of-technical-aspects-and-clinical-applications/print 15/23 7/6/23, 10:43 AM Signal-averaged electrocardiogram: Overview of technical aspects and clinical applications - UpToDate Computation of the signal averaged ECG Successive QRS complexes meeting a predetermined coefficient of similarity are aligned (within the window indicated by dashed lines) on an ongoing basis. Their rolling arithmetic mean is computed until a predetermined noise threshold is achieved (shown as the typical criterion of the standard deviation of the TP segment <1 microvolts). The QRS complex is then filtered and analyzed for late potentials, defined when the filtered QRS duration is >114 milliseconds, root mean square (RMS) voltage in the terminal 40 milliseconds is <20 microvolts, and low amplitude signal (LAS) duration (the terminal signal duration from 40 mV to isopotential) is >38 milliseconds. Graphic 67428 Version 5.0 https://www.uptodate.com/contents/signal-averaged-electrocardiogram-overview-of-technical-aspects-and-clinical-applications/print 16/23 7/6/23, 10:43 AM Signal-averaged electrocardiogram: Overview of technical aspects and clinical applications - UpToDate Late potentials bridging diastole Shown are surface ECG leads I, II, III, V1, V4, and V6 and electrograms (a to h) recorded from the endocardial surface of the myocardium during ventricular tachycardia. There are presystolic signals in the area of slow myocardial conduction that can be traced through diastole to the preceding QRS complex. During sinus rhythm, late potentials can be recorded from these sites. Graphic 82329 Version 1.0 https://www.uptodate.com/contents/signal-averaged-electrocardiogram-overview-of-technical-aspects-and-clinical-applications/print 17/23 7/6/23, 10:43 AM Signal-averaged electrocardiogram: Overview of technical aspects and clinical applications - UpToDate QRS alignment methods Optimal beat alignment permits the averaging of signals at physiologically corresponding timepoints. Sliding template alignment provides the greatest precision and may be computed by maximizing the dot-product between candidate beats and a template. QRS peak and upstroke fiducial methods are less precise but still used. The P-wave triggered signal averaged ECG requires P- wave alignment, typically with a sliding template approach. Graphic 75403 Version 1.0 https://www.uptodate.com/contents/signal-averaged-electrocardiogram-overview-of-technical-aspects-and-clinical-applications/print 18/23 7/6/23, 10:43 AM Signal-averaged electrocardiogram: Overview of technical aspects and clinical applications - UpToDate Incidence of sustained ventricular arrhythmias or sudden cardiac death in patients after myocardial infarction Percent adverse outcomes Test For normal test For abnormal test results results SAECG and ejection fraction 0-1 31-38 SAECG and Holter monitor 0-1 27-35 Ejection fraction and Holter monitor 7 29 SAECG, ejection fraction, and Holter monitor 0 50 SAECG and programmed stimulation 2 27 SAECG and HRV 7 33 SAECG, HRV, and Holter monitor 4 43 SAECG: signal-averaged electrocardiogram; HRV: heart rate variability. Adapted from Cain, et al. J Am Coll Cardiol 1996; 27:238. Graphic 53211 Version 2.0 https://www.uptodate.com/contents/signal-averaged-electrocardiogram-overview-of-technical-aspects-and-clinical-applications/print 19/23 7/6/23, 10:43 AM Signal-averaged electrocardiogram: Overview of technical aspects and clinical applications - UpToDate Repolarization alternans (RPA) and late potentials (LP) predict arrhythmic events following myocardial infarction In a study of 102 patients with a prior myocardial infarction (MI) followed for 13 months, the combination of repolarization alternans (RPA) and late potentials (LP) on a signal averaged ECG had a specificity and negative predictive value for an arrhythmic event of 91 and 92 percent, respectively. However, the positive predictive value was only 50 percent. The very low event rate in the group "RPA negative and LP positive" may be due to the small number of patients in this subset (n = 5). Data from Ikeda T, Sakata T, Takami M, et al, J Am Coll Cardiol 2000; 35:722. Graphic 51831 Version 3.0 https://www.uptodate.com/contents/signal-averaged-electrocardiogram-overview-of-technical-aspects-and-clinical-applications/print 20/23 7/6/23, 10:43 AM Signal-averaged electrocardiogram: Overview of technical aspects and clinical applications - UpToDate The signal averaged ECG predicts outcome in patients with nonsustained ventricular tachycardia In a trial of 1925 patients with coronary artery disease, asymptomatic nonsustained ventricular tachycardia, and left ventricular dysfunction, the signal averaged ECG (SAECG) predicted outcome, particularly in those with a left ventricular ejection fraction (LVEF) <30 percent. The two- and five-year event rates for patients with filtered QRS duration >114 milliseconds were 17 and 36 percent, respectively, compared with 10 and 23 percent, respectively, with a QRS 114 milliseconds (p = 0.0001). In patients with an LVEF 30 percent, the two- and five-year event rates were 6 and 13 percent, respectively and 11 and 22 percent, respectively, for a QRS or >114 milliseconds (p = 0.01). Data from: Gomes JA, Cain ME, et al. Circulation 2001; 104:436. Graphic 66009 Version 6.0 https://www.uptodate.com/contents/signal-averaged-electrocardiogram-overview-of-technical-aspects-and-clinical-applications/print 21/23 7/6/23, 10:43 AM Signal-averaged electrocardiogram: Overview of technical aspects and clinical applications - UpToDate Signal averaged electrocardiogram predicts atrial fibrillation after coronary artery bypass graft (CABG) surgery The incidence of atrial fibrillation (AF) after coronary artery bypass graft surgery is directly related to the duration of the P wave on a signal averaged ECG. Data from Zaman AG, Archbold RA, Helft G, et al. Circulation 2000; 101:1403. Graphic 60431 Version 4.0 https://www.uptodate.com/contents/signal-averaged-electrocardiogram-overview-of-technical-aspects-and-clinical-applications/print 22/23 7/6/23, 10:43 AM Signal-averaged electrocardiogram: Overview of technical aspects and clinical applications - UpToDate Contributor Disclosures Sanjiv M Narayan, MD, PhD Patent Holder: Stanford University [Atrial fibrillation, machine learning, arrhythmias]; University of California [Atrial fibrillation, machine learning, arrhythmias]. Grant/Research/Clinical Trial Support: NIH [Atrial fibrillation]. Consultant/Advisory Boards: Abbott [Cardiac arrhythmias]; Life Signals Inc [Ambulatory monitoring for general health including COVID-19]; TDK Inc [Magnetocardiography]. All of the relevant financial relationships listed have been mitigated. Michael E Cain, MD No relevant financial relationship(s) with ineligible companies to disclose. Ary L Goldberger, MD Other Financial Interest: Elsevier book royalties [Clinical electrocardiography]. All of the relevant financial relationships listed have been mitigated. Nisha Parikh, MD, MPH No relevant financial relationship(s) with ineligible companies to disclose. Contributor disclosures are reviewed for conflicts of interest by the editorial group. When found, these are addressed by vetting through a multi-level review process, and through requirements for references to be provided to support the content. Appropriately referenced content is required of all authors and must conform to UpToDate standards of evidence. Conflict of interest policy https://www.uptodate.com/contents/signal-averaged-electrocardiogram-overview-of-technical-aspects-and-clinical-applications/print 23/23