Evaluation of the normal values for signal-averaged electrocardiogram

Incremental value of the signal-averaged ECG for diagnosing arrhythmogenic cardiomyopathy

BACKGROUND

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is currently diagnosed using a combination of clinical features, imaging, electrocardiography, and genetic investigations. An abnormal signal-averaged electrocardiogram (SAECG) is defined as a minor diagnostic criterion by the 2010 Task Force Criteria, but doubts remain about the value of this investigation.

OBJECTIVE

We evaluated the utility of the SAECG in diagnosing ARVC using the Canadian Arrhythmogenic Right Ventricular Cardiomyopathy Registry, a population representative registry of probands with ARVC and relatives, less influenced by referral bias.

METHODS

Probands with ARVC and family members from the Canadian Arrhythmogenic Right Ventricular Cardiomyopathy Registry underwent phenotype review. SAECG parameters were compared individually and in combination between those with varying degrees of ARVC severity and healthy controls (family members of probands with ARVC and unexplained sudden death, free of evidence of cardiac disease).

RESULTS

A total of 196 patients with ARVC and 205 controls were included (mean age 44 ± 15 years; 186 of 401 men [46%]). SAECG abnormalities were seen in 83 of 205 controls (40%), 33 of 68 patients with ARVC and mild disease (51%), and 31 of 42 with severe disease (74%). The SAECG associated strongly with imaging abnormalities (major: odds ratio 3.0, 95% confidence interval 1.3-6.9; minor: odds ratio 3.5, 95% confidence interval 0.7-16.5) but not with other aspects of phenotype. Patients carrying pathogenic variants but with minimal phenotype had similar SAECGs to healthy controls (filtered QRS duration 111.2 ± 11.2 ms vs 111 ± 7.6 ms, P = .93; duration of low amplitude signals < 40 μV 32.3 ± 8.9 ms vs 34.2 ± 7.2 ms, P = .32; root mean square of the terminal 40 ms of the filtered QRS complex 43.1 ± 25.2 ms vs 38.2 ± 20.2 ms, P = .38).

CONCLUSION

The SAECG appears to be a surrogate marker for structural abnormalities seen on imaging in those with ARVC. Great caution is required in interpreting SAECG findings in those without other corroborating evidence of an ARVC phenotype.

The clinical utility of procainamide-induced late potentials on the signal averaged ECG

BACKGROUND

Late potentials (LPs) identified on the signal averaged electrocardiogram (SAECG) are a marker for an increased risk of arrhythmias in Brugada syndrome (BrS). Procainamide is a sodium channel blocker used to diagnose BrS. The effects of Procainamide on the SAECG in those with BrS and the significance of Procainamide-induced LPs are unknown.

METHODS

Procainamide provocation was performed for suspected BrS with 12-lead and SAECG pre- and post-infusion. Filtered QRS duration (fQRSd), duration of low amplitude signals <40 μV (LAS40) and root-mean-square voltage in the terminal 40 ms (RMS40) were determined.

RESULTS

Data from 150 patients were included in the analysis (mean age 44.5 years, 109 males). Procainamide increased fQRSd (Pre 118.8 ± 10.5 ms, post 121.2 ± 10.2 ms, p < 0.001) and LAS40 (Pre 38.7 ± 9.8 ms, post 40.2 ± 10.5 ms, p = 0.005) and decreased RMS40 (Pre 24.6 ± 12 ms, post 22.8 ± 12 ms, p = 0.002). LPs were present in 68/150 (45%) at baseline. Fifteen patients with negative baseline SAECGs had LPs unmasked by Procainamide, but six patients had LPs at baseline that were no longer present following Procainamide. Comparing those with normal hearts (n = 48) to those with a final diagnosis of BrS (n = 38), Procainamide prolonged fQRSd to a greater extent in those with BrS. Comparing those with Procainamide-induced LPs to those with no LPs at any time did not highlight any aspect of phenotype and did not correlate with a history of ventricular arrhythmias.

CONCLUSIONS

Procainamide influences the SAECG, provoking LPs in a small proportion of patients. However, there is no evidence that Procainamide-induced LPs provide additional diagnostic information or aid risk stratification.

Cardiac remodeling in middle-aged endurance athletes: relation between signal-averaged electrocardiogram and LV mass

The relationship between structural and electrical remodeling in the heart, particularly after long-standing endurance training, remains unclear. Signal-averaged electrocardiogram (SAECG) may provide a more sensitive method to evaluate cardiac remodeling than a 12-lead electrocardiogram (ECG). Accurate measures of electrical function (SAECG filtered QRS duration (fQRSd) and late potentials (LP) and left-ventricular (LV) mass (cardiac magnetic resonance, CMR) can allow an assessment of structural remodeling and QRS prolongation. Endurance athletes (45-65 yr old, >10 yr of endurance sport), screened to exclude cardiac disease, had standardized 12-lead ECG, SAECG, resting echocardiogram (ECHO), and CMR performed. SAECG fQRSd was correlated with QRS duration on the 12-lead ECG, and ECHO and CMR-derived LV mass. Participants (n = 82, 67% male, mean age: 54 ± 6 yr, mean V̇o_2max: 50 ± 7 mL/kg/min) had a CMR-derived LV mass of 118 ± 28 g/m² and a fQRSd of 112 ± 8 ms (46% had abnormal fQRSd (>114 ms), and 51% met clinical threshold for abnormal SAECG). fQRSd was positively correlated with the 12-lead ECG QRS duration (r = 0.83), ECHO-derived LV mass (r = 0.60), CMR-derived LV mass (r = 0.58) and LV end-diastolic volume (r = 0.63, P < 0.001 for all). fQRSd had higher correlations with ECHO and CMR-derived LV mass than 12-lead ECG (P < 0.0008 and P < 0.0005, respectively). In conclusion, in a healthy cohort of middle-aged endurance athletes, the SAECG is often abnormal by conventional criteria, and is correlated with structural remodeling, but CMR evaluation does not indicate pathologic structural remodeling. SAECG fQRSd is superior to the 12-lead ECG for the electrocardiographic evaluation of LV mass.NEW & NOTEWORTHY Study findings indicate that a positive correlation exists between electrical (SAECG fQRSd) and structural indices (LV mass) in middle-aged endurance athletes with normal physiological LV adaptation, in the absence of known cardiac pathology. SAECG fQRSd may also provide an alternative, superior method for identifying increased LV mass compared to other 12-lead ECG criteria.

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.

Genotype-phenotype relationship and risk stratification in loss-of-function SCN5A mutation carriers

INTRODUCTION

Loss-of-function (LoF) mutations in the SCN5A gene cause multiple phenotypes including Brugada Syndrome (BrS) and a diffuse cardiac conduction defect. Markers of increased risk for sudden cardiac death (SCD) in LoF SCN5A mutation carriers are ill defined. We hypothesized that late potentials and fragmented QRS would be more prevalent in SCN5A mutation carriers compared to SCN5A-negative BrS patients and evaluated risk markers for SCD in SCN5A mutation carriers.

METHODS

We included all SCN5A loss-of-function mutation carriers and SCN5A-negative BrS patients from our center. A combined arrhythmic endpoint was defined as appropriate ICD shock or SCD.

RESULTS

Late potentials were more prevalent in 79 SCN5A mutation carriers compared to 39 SCN5A-negative BrS patients (66% versus 44%, p = .021), while there was no difference in the prevalence of fragmented QRS. PR interval prolongation was the only parameter that predicted the presence of a SCN5A mutation in BrS (OR 1.08; p < .001). Four SCN5A mutation carriers, of whom three did not have a diagnostic type 1 ECG either spontaneously or after provocation with a sodium channel blocker, reached the combined arrhythmic endpoint during a follow-up of 44 ± 52 months resulting in an annual incidence rate of 1.37%.

CONCLUSION

LP were more frequently observed in SCN5A mutation carriers, while fQRS was not. In SCN5A mutation carriers, the annual incidence rate of SCD was non-negligible, even in the absence of a spontaneous or induced type 1 ECG. Therefore, proper follow-up of SCN5A mutation carriers without Brugada syndrome phenotype is warranted.

Cell models of arrhythmogenic cardiomyopathy: advances and opportunities

Arrhythmogenic cardiomyopathy is a rare genetic disease that is mostly inherited as an autosomal dominant trait. It is associated predominantly with mutations in desmosomal genes and is characterized by the replacement of the ventricular myocardium with fibrous fatty deposits, arrhythmias and a high risk of sudden death. In vitro studies have contributed to our understanding of the pathogenic mechanisms underlying this disease, including its genetic determinants, as well as its cellular, signaling and molecular defects. Here, we review what is currently known about the pathogenesis of arrhythmogenic cardiomyopathy and focus on the in vitro models that have advanced our understanding of the disease. Finally, we assess the potential of established and innovative cell platforms for elucidating unknown aspects of this disease, and for screening new potential therapeutic agents. This appraisal of in vitro models of arrhythmogenic cardiomyopathy highlights the discoveries made about this disease and the uses of these models for future basic and therapeutic research.

Summary:In vitro models of ACM provide insights into the molecular mechanisms of this disease. This reappraisal offers a comprehensive vision of past discoveries and constitutes a tool for future research.

2015 update on the diagnosis and management of arrhythmogenic right ventricular cardiomyopathy

PURPOSE OF REVIEW

This review will discuss the recent advances in the diagnosis and management of arrhythmogenic right ventricular cardiomyopathy (ARVC).

RECENT FINDINGS

Since the first detailed clinical description of the disease in 1982, we have learned much about the genetics, pathophysiology, diagnosis, and management of ARVC. We now appreciate that pathogenic mutations in desmosomal genes are the most common genetic finding. Although the right ventricle is mostly affected, left ventricular involvement is being increasingly recognized. Electrical instability precipitating sudden cardiac death often presents before structural abnormalities, and therefore early accurate diagnosis is of utmost importance. The broad spectrum of phenotypic variation, age-related penetrance, and lack of a definitive diagnostic test make the clinical diagnosis challenging. The diagnosis is made by fulfilling the 2010 Task Force criteria. Today, genetic testing and cardiac MRI play an important role in the diagnosis. Implantable cardioverter defibrillator implantation is the only lifesaving therapy available today for a subset of patients. In patients with recurrent ventricular arrhythmias, epicardial catheter ablation has demonstrated improved outcomes compared with endocardial ablation. Exercise restriction may delay the progression of disease.

SUMMARY

ARVC is predominantly associated with mutations in desmosomal genes with incomplete penetrance and variable expressivity. Ventricular electrical instability is the hallmark of ARVC, often occurring before structural abnormalities. Goals in the evaluation and management of ARVC are early diagnosis, risk stratification for sudden cardiac death, minimizing ventricular arrhythmias, and delaying the progression of disease.

Clinical Presentation and Outcomes by Sex in Arrhythmogenic Right Ventricular Cardiomyopathy: Findings from the North American ARVC Registry

BACKGROUND

Sex differences in clinical presentation and outcomes of hereditary arrhythmias are commonly reported. We aimed to compare clinical presentation and outcomes in men and women with arrhythmogenic right ventricular cardiomyopathy (ARVC) enrolled in the North American ARVC Registry.

METHODS

A total of 125 ARVC probands (55 females, mean age 38 ± 12; 70 males, mean age 41 ± 15) diagnosed, as either "affected" or "borderline" were included. Baseline clinical characteristics and time-dependent outcomes including syncope, ventricular tachycardia (VT), fast VT (>240 bpm), ventricular fibrillation (VF), and death were compared between males and females.

RESULTS

The percentage of ARVC subjects diagnosed as "affected" (84% vs. 89%; P = 0.424) or "borderline" (16% vs. 11%; P = 0.424) was similar between females and males. Among the baseline characteristics, inverted T-waves in V2 trended to be more common in women (P = 0.09), whereas abnormal signal-averaged ECGs (SAECGs; P < 0.001) and inducible VT/VF (P = 0.026) were more frequent in men. During a mean follow-up of 37 ± 20 months, the probability of ICD-recorded VT/VF or death was not significantly different between men and women (P = 0.456). However, there was a trend toward lower risk of fast VT/VF or death in women compared to men (hazard ratio 0.41, 95% CI 0.151-1.113, P = 0.066). Abnormal SAECG and evidence of intramyocardial fat by cardiac MRI was associated with adverse outcomes in men (P = 0.006 and 0.02 respectively).

CONCLUSION

In the North American ARVC Registry, we found similar frequency of "affected" and "borderline" subjects between men and women. Sex-related differences were observed in baseline ECG, SAECG, Holter-recorded ventricular arrhythmias, and VT inducibility. Men showed a trend toward greater risk of fast VT than women.

Value of the signal-averaged electrocardiogram in arrhythmogenic right ventricular cardiomyopathy/dysplasia

BACKGROUND

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is an inherited disease that causes structural and functional abnormalities of the right ventricle (RV). The presence of late potentials as assessed by the signal-averaged electrocardiogram (SAECG) is a minor task force criterion.

OBJECTIVE

The purpose of this study was to examine the diagnostic and clinical value of the SAECG in a large population of genotyped ARVC/D probands.

METHODS

We compared the SAECGs of 87 ARVC/D probands (age 37 ± 13 years, 47 males) diagnosed as affected or borderline by task force criteria without using the SAECG criterion with 103 control subjects. The association of SAECG abnormalities was also correlated with clinical presentation, surface ECG, ventricular tachycardia (VT) inducibility at electrophysiologic testing, implantable cardioverter-defibrillator therapy for VT, and RV abnormalities as assessed by cardiac magnetic resonance imaging (cMRI).

RESULTS

Compared with controls, all three components of the SAECG were highly associated with the diagnosis of ARVC/D (P <.001). They include the filtered QRS duration (97.8 ± 8.7 ms vs 119.6 ± 23.8 ms), low-amplitude signal (24.4 ± 9.2 ms vs 46.2 ± 23.7 ms), and root mean square amplitude of the last 40 ms of the QRS (50.4 ± 26.9 μV vs 27.9 ± 36.3 μV). The sensitivity of using SAECG for diagnosis of ARVC/D was increased from 47% using the established 2 of 3 criteria (i.e., late potentials) to 69% by using a modified criterion of any 1 of 3 criteria, while maintaining a high specificity of 95%. Abnormal SAECG as defined by this modified criterion was associated with a dilated RV volume and decreased RV ejection fraction detected by cMRI (P <.05). SAECG abnormalities did not vary with clinical presentation or reliably predict spontaneous or inducible VT and had limited correlation with ECG findings.

CONCLUSION

Using 1 of 3 SAECG criteria contributed to increased sensitivity and specificity for the diagnosis of ARVC/D. This finding is incorporated in the recent modification of the task force criteria.

Diagnosis of arrhythmogenic right ventricular cardiomyopathy/dysplasia: proposed modification of the task force criteria

BACKGROUND

In 1994, an International Task Force proposed criteria for the clinical diagnosis of arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) that facilitated recognition and interpretation of the frequently nonspecific clinical features of ARVC/D. This enabled confirmatory clinical diagnosis in index cases through exclusion of phenocopies and provided a standard on which clinical research and genetic studies could be based. Structural, histological, electrocardiographic, arrhythmic, and familial features of the disease were incorporated into the criteria, subdivided into major and minor categories according to the specificity of their association with ARVC/D. At that time, clinical experience with ARVC/D was dominated by symptomatic index cases and sudden cardiac death victims-the overt or severe end of the disease spectrum. Consequently, the 1994 criteria were highly specific but lacked sensitivity for early and familial disease.

METHODS AND RESULTS

Revision of the diagnostic criteria provides guidance on the role of emerging diagnostic modalities and advances in the genetics of ARVC/D. The criteria have been modified to incorporate new knowledge and technology to improve diagnostic sensitivity, but with the important requisite of maintaining diagnostic specificity. The approach of classifying structural, histological, electrocardiographic, arrhythmic, and genetic features of the disease as major and minor criteria has been maintained. In this modification of the Task Force criteria, quantitative criteria are proposed and abnormalities are defined on the basis of comparison with normal subject data.

CONCLUSIONS

The present modifications of the Task Force Criteria represent a working framework to improve the diagnosis and management of this condition.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00024505.

Diagnosis of arrhythmogenic right ventricular cardiomyopathy/dysplasia: proposed modification of the Task Force Criteria

BACKGROUND

In 1994, an International Task Force proposed criteria for the clinical diagnosis of arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) that facilitated recognition and interpretation of the frequently nonspecific clinical features of ARVC/D. This enabled confirmatory clinical diagnosis in index cases through exclusion of phenocopies and provided a standard on which clinical research and genetic studies could be based. Structural, histological, electrocardiographic, arrhythmic, and familial features of the disease were incorporated into the criteria, subdivided into major and minor categories according to the specificity of their association with ARVC/D. At that time, clinical experience with ARVC/D was dominated by symptomatic index cases and sudden cardiac death victims-the overt or severe end of the disease spectrum. Consequently, the 1994 criteria were highly specific but lacked sensitivity for early and familial disease.

METHODS AND RESULTS

Revision of the diagnostic criteria provides guidance on the role of emerging diagnostic modalities and advances in the genetics of ARVC/D. The criteria have been modified to incorporate new knowledge and technology to improve diagnostic sensitivity, but with the important requisite of maintaining diagnostic specificity. The approach of classifying structural, histological, electrocardiographic, arrhythmic, and genetic features of the disease as major and minor criteria has been maintained. In this modification of the Task Force criteria, quantitative criteria are proposed and abnormalities are defined on the basis of comparison with normal subject data.

CONCLUSIONS

The present modifications of the Task Force Criteria represent a working framework to improve the diagnosis and management of this condition. Clinical Trial Registration clinicaltrials.gov Identifier: NCT00024505.

The electrocardiogram in right ventricular cardiomyopathy/dysplasia. How can the electrocardiogram assist in understanding the pathologic and functional changes of the heart in this disease?

The electrocardiogram (ECG) provides important information to aid in the diagnosis of arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D). The ECG changes may be explained by the pathophysiology of the disease. The proximity of the right ventricle (RV) to the anterior chest leads (V(1) to V(4)) explains why the characteristic ECG abnormalities are most prominent in those lends. The specific ECG abnormalities reflect the pathophysiology of the disease including T-wave inversion due to scarring of the free wall of the RV, prolonged S-wave duration due to slow depolarization of the terminal part of the QRS because the RV is the last part of the heart to undergo depolatization, and epsilon waves due to slow conduction in the RV. The extent of ECG abnormalities correlate with the degree of structural change in the RV.

Comparison of clinical features of arrhythmogenic right ventricular cardiomyopathy in men versus women

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a heart muscle disease characterized by myocardial necrosis followed by fibrous-fatty replacement. The pathologic process constitutes the basis for ventricular arrhythmias due to re-entrant circuits. Even if this genetic disease is transmitted in the majority of cases with autosomal dominant trait, in all reported series ARVC is prevalent in men. In this study we investigate the impact that gender may have on clinical presentation in a large series of patients with ARVC. A total of 171 consecutive patients (mean 29 +/- 12 years, range 13 to 65) affected by ARVC were examined with family and personal history, 12-lead electrocardiogram (ECG), 24-hour ECG, signal-averaged ECG, and echocardiogram. Moreover, electrophysiological study and ventricular angiography were performed in selected cases. In the 171 subjects, 71% were men and 29% women (p = 0.02). No gender differences were found considering the age at the time of diagnosis and of study enrolment and the prevalence of index cases and family members. The genders differed in prevalence of abnormal ECG (69% vs 52%, p = 0.036) and presence of late potentials (60% vs 40%, p = 0.01). Moreover, men had larger right ventricular dimensions and practiced competitive sports more frequently (26% vs 14%, p <0.001). Nonetheless, gender was not associated with a high incidence of life-threatening ventricular arrhythmias or with a poor outcome. In conclusion, our data show that diagnosis of ARVC is less common in female patients, who present a higher prevalence of mild forms. Nonetheless, the degree of electrical instability does not differ significantly between genders in affected subjects. Even if ARVC remains mainly a male disease, gender does not have a role in patients' outcome. The cause of the under-representation of women is not clear, even if potentially important factors such as sexual hormones and physical activity could play a role.