Author + information
- Received February 21, 2011
- Revision received April 5, 2011
- Accepted April 12, 2011
- Published online August 9, 2011.
- Nicolas Derval, MD⁎,
- Christopher S. Simpson, MD#,
- David H. Birnie, MD¶,
- Jeffrey S. Healey, MD‡,
- Vijay Chauhan, MD§,
- Jean Champagne, MD⁎⁎,
- Martin Gardner, MD††,
- Shubhayan Sanatani, MD‡‡,
- Raymond Yee, MD†,
- Allan C. Skanes, MD†,
- Lorne J. Gula, MD†,
- Peter Leong-Sit, MD†,
- Kamran Ahmad, MD∥,
- Michael H. Gollob, MD¶,
- Michel Haïssaguerre, MD⁎,
- George J. Klein, MD† and
- Andrew D. Krahn, MD†,⁎ ()
- ↵⁎Reprint requests and correspondence:
Dr. Andrew Krahn, London Health Sciences Centre, 339 Windermere Road, London, Ontario N6A 5A5, Canada
Objectives We evaluated the prevalence and characteristics of early repolarization in patients in CASPER (Cardiac Arrest Survivors With Preserved Ejection Fraction Registry).
Background Early repolarization has been implicated in a syndrome of polymorphic ventricular tachycardia and fibrillation in patients without organic heart disease.
Methods One hundred patients with apparently unexplained cardiac arrest and preserved ejection fraction underwent extensive clinical and genetic testing to unmask subclinical electrical or structural disease. A blinded independent analysis of the 12-lead electrocardiogram (ECG) was performed. Early repolarization was defined as ≥0.1 mV QRS-ST junction (J-point) elevation with terminal QRS slurring or notching in at least 2 contiguous inferior and/or lateral leads.
Results One hundred cardiac arrest patients were enrolled (40 females, age 43 ± 14 years). Forty-four were diagnosed with an established cause for cardiac arrest. Significant early repolarization was found in 19 patients, including 6 with a primary diagnosis that explained their cardiac arrest (14%), compared with 23% of the 56 patients with idiopathic ventricular fibrillation (IVF) (p = 0.23). J-point elevation in IVF patients had higher amplitude (0.25 ± 0.11 mV vs. 0.13 ± 0.05 mV, p = 0.02) and wider distribution (4.3 ± 1.3 leads vs. 2.8 ± 0.8 leads; p = 0.01) than those with an established cause of cardiac arrest. J-wave amplitude was fluctuant on serial ECGs; at least 1 ECG failed to demonstrate early repolarization in 58% of patients.
Conclusions Early repolarization is present in a significant proportion of causally diagnosed and idiopathic VF. It is often intermittent and more pronounced in IVF patients. (Registry of Unexplained Cardiac Arrest; NCT00292032).
Early repolarization, previously considered a benign electrocardiographic (ECG) phenomenon, has recently been associated with sudden death (1,2). Although the mechanisms underlying early repolarization are unknown, population-based studies have demonstrated an association between early repolarization and sudden death, primarily when the ECG demonstrates ≥0.2 mV of ST-segment elevation (3). It has been demonstrated that a thorough, systematic assessment of the survivors of sudden cardiac death without evidence of infarction or left ventricular dysfunction is able to establish a causative diagnosis in approximately 50% of cases (4). We sought to evaluate the prevalence and characteristics of early repolarization in the CASPER (Cardiac Arrest Survivors with Preserved Ejection Fraction Registry).
Details of the CASPER registry have previously been reported (4). Eligibility criteria included a first unexplained cardiovascular collapse associated with ventricular tachycardia (VT) or fibrillation that required cardioversion or defibrillation, with documented preserved left ventricular function (ejection fraction >50%) and normal coronary arteries on initial evaluation. Patients were excluded if a reversible or secondary cause for cardiac arrest was diagnosed.
This analysis includes the first 100 probands enrolled in the CASPER registry between January 2004 and March 2010 from 9 Canadian electrophysiology centers. All patients provided written informed consent. The protocol was approved by the Health Sciences Research Ethics Board of the University of Western Ontario and at each center.
After completing pre-inclusion tests (monitoring, echocardiogram, and coronary angiogram), patients underwent signal-averaged ECG, exercise testing, cardiac magnetic resonance imaging (MRI), and intravenous adrenaline and procainamide challenge as previously described (4). Targeted genetic testing was performed on the basis of phenotype detection, after clinical testing was complete. Genomic DNA was isolated from blood lymphocytes and screened as previously described (4). Genetic testing with direct sequencing was performed on suspected culprit genes.
ECG analysis for early repolarization
Serial 12-lead ECGs recorded during hospitalization for cardiac arrest or implantable cardioverter-defibrillator implantation were reviewed. ECGs recorded within 24 h of cardiac resuscitation/defibrillation and while the patient was on intravenous inotropes were excluded. Two cardiologists independently reviewed anonymized ECGs. Early repolarization pattern (ERP) was defined as QRS slurring and/or notching associated with QRS-ST junction (J-point) elevation in at least 2 contiguous leads excluding the anterior precordial leads (V1 to V3) (1,3,5,6). The ECG lead with the most prominent ERP changes was used for analysis. J-wave elevation of ≥0.1 mV above baseline, associated with QRS slurring and/or notching in the inferior leads (II, III, aVF), lateral leads (I, aVL, and V5, V6), or both was classified as significant early repolarization (Type 1) (Fig. 1). When J-wave amplitude was 0.05 to 0.1 mV, it was classified as nonsignificant early repolarization (Type 2) (Fig. 2).
All results are expressed as mean ± SD. Continuous variables were compared using a 2-tailed Student t test, and a chi-square test or Fisher exact test was used for categorical variables. Analyses were performed with SAS version 9.1 (SAS Institute, Cary, North Carolina). Values of p < 0.05 were considered significant.
A specific established diagnosis was reached in 44 of the 100 patients (age 43 ± 14 years, 60 males) after complete investigation (44%,) (Table 1). Among diagnosed patients, long QT syndrome (LQTS) was detected in 13 patients (30%), catecholaminergic polymorphic ventricular tachycardia (CPVT) in 8 (18%), arrhythmogenic right ventricular cardiomyopathy (ARVC) in 7 (16%), coronary spasm in 7 (16%), Brugada syndrome in 5 (11%), myocarditis in 3 (7%), and occult myocardial infarction in 1 (2%) (Fig. 3A). The remaining 56 patients (56%) were labeled as unexplained cardiac arrest due to idiopathic ventricular fibrillation (IVF).
Type I ERP group
A mean of 5 ± 6 12-lead ECGs were analyzed per patient. Nineteen patients (19%) had Type I ERP (14 males [74%], age 42 ± 10 [range 18 to 55] years). ERP was present in the inferior leads in 8 patients (42%), the lateral leads in 2 (10.5%), and both in 7 (37%). In 2 patients (10.5%), ERP was limited to leads V5 and V6. The mean amplitude of the J-wave was 0.21 ± 0.11 mV (range 0.1 to 0.5 mV). Terminal QRS notching and slurring were found in 11 and 8 patients, respectively. J-wave fluctuation was present in all cases, such that at least 1 ECG from the index hospitalization showed no evidence of Type I ERP in 11 of 19 (58%) patients (Fig. 4⇓⇓). Differences in heart rate did not explain intermittent ERP (ECG with ERP vs. ECG without: 76.6 ± 17.0 beats/min vs. 76.0 ± 17.0 beats/min; p = 0.93).
Type I ERP was identified in 13 of 56 patients (23%) patients with IVF, and in 6 of 44 patients with a diagnosed cause of cardiac arrest (14%; p = 0.23). These included 3 patients with LQTS, 2 patients with coronary spasm, and 1 with CPVT (Table 2). Compared to those with a diagnosed cause of cardiac arrest, those with Type I ERP associated with IVF had both a larger maximum J-wave amplitude (0.25 ± 0.11 mV vs. 0.13 ± 0.05 mV, p = 0.02) and a larger number of involved leads (4.3 ± 1.3 leads vs. 2.8 ± 0.8 leads; p = 0.01) (Table 3). The distribution of involved leads and morphology of the ERP (notching and slurring) were not significantly different between the 2 groups, though ERP limited to leads V5 and V6 was only observed in those with a diagnosed cause of cardiac arrest (n = 2).
Type II ERP group
Thirteen (13%) patients had Type II ERP (5 males [38%], age 33 ± 9 [range 13 to 45] years), which was distributed in the inferior leads, inferior and lateral leads, and limited to leads V5 and V6 in 2 patients (15%), 8 patients (62%), and 3 patients (23%), respectively (Fig. 3B). This pattern was identified in 9 of 56 patients with IVF (16%) and in 4 of 44 patients with a diagnosed cause of cardiac arrest (9%; p = 0.2). These included 2 patients with LQTS (positive adrenaline test in both with genetic confirmation of LQT2 in 1 patient) and 1 each with ARVC (MRI and phenotype positive, genotype negative) and coronary spasm.
The CASPER registry is the first prospective study to evaluate the prevalence and characteristics of inferolateral ERP in a cohort with initially unexplained cardiac arrest. We used systematic and rigorous clinical testing to identify subclinical primary electrical disease in survivors. This allowed a strict definition of IVF, and therefore, a potentially more unbiased estimate of symptomatic ERP prevalence than in previous retrospective studies (1,2,7). Significant (Type I) inferolateral ERP was present in 19% of all cardiac arrest survivors in this study, and in 23% of those without a diagnosis after thorough testing. This finding is consistent with prior studies that reported a prevalence of 15% to 41% in those with IVF (1,2,4,7,8).
Almost one-third of patients with a Type I ERP had evidence of another substrate predisposing them to cardiac arrest. These patients had a range of underlying mechanisms, including repolarization abnormalities, coronary spasm, and myocarditis. Notably, strong clinical phenotypes and positive genetic tests for the underlying condition were absent in this subgroup, raising the possibility that early repolarization is part of a multifactorial process leading to cardiac arrest in some patients.
ERP has a prevalence of 5% to 13% in the general population (1,3). Consequently, distinguishing those with propensity to arrhythmia from so-called “benign” ERP is challenging. There are neither established risk-stratifying tools nor an established provocative test for malignant inferolateral ERP, although some ECG features have been reported more frequently with “malignant” ERP.
Key findings in the current study include:
1 J-wave amplitude: We found that J-wave amplitude was substantially higher than 0.1 mV in cardiac arrest survivors, particularly the patients with IVF. Tikkanen et al. (3) reported that subjects with J-point elevation >0.2 mV in the inferior leads had an almost 3-fold higher risk of death from cardiac causes, including arrhythmia, compared with J-point elevation of <0.2 mV. They also reported a low prevalence of J-wave elevation >0.2 mV in the general population (0.3%, or 68 [10.7%] of 630 subjects with ERP).
2 J-wave distribution: Localization of early repolarization has been suggested to have prognostic implications. Type I ERP was present in more leads in the group with IVF. ERP confined to leads V5 and V6 was only seen in those patients who had a primary diagnosis explaining cardiac arrest.
3 J-wave morphology: Two small studies reported that QRS notching in the precordial leads was more prevalent in patients with IVF than controls (2,8). In our study, ERP morphology was similar in those with and without a specific diagnosis.
4 J-wave fluctuation: Spontaneous fluctuation in ERP morphology was a universal finding in our study, and 58% of patients had at least 1 ECG that failed to demonstrate Type I ERP. Spontaneous accentuation of the J-wave amplitude or global appearance of an otherwise regionally observed ERP has been reported prior to ventricular fibrillation storm (1). Although demonstrating association between dynamic J-wave morphology and a malignant form of early repolarization remains challenging, this highlights the importance of serial ECGs in this population. Furthermore, most population-based studies evaluated ERP from a single resting ECG, potentially biasing prevalence estimates.
Type II ERP
In our study, we found a maximal ERP of <0.1 mV (Type II) in 13% of all cardiac arrest patients and 16% of patients with a final diagnosis of IVF. The significance of less-pronounced J-wave elevation in cardiac arrest survivors remains unknown. Redefining the ERP as terminal QRS slurring/notching in association with J-point elevation of ≥0.05 mV would increase the prevalence of early repolarization in IVF to 39% (22 of 56 patients) but would undoubtedly decrease specificity of the observation in asymptomatic cohorts. These results highlight the complexity of the risk stratification of patients with ERP and strengthen the need for better markers and provocative tests to unmask subclinical contributors to risk of cardiac arrest.
Most importantly, a causal relationship between ERP and cardiac arrest remains to be established. Since IVF is uncommon, and inclusion in prospective studies is difficult, the sample size is modest. The current study examined ERP in arrest survivors with and without a recognized “latent” diagnosis. This represents 2 populations for comparison, but is not a priori a control group. This may lead to underestimating the true risk of ERP in patients without obvious heart disease. The diagnosis of IVF is a diagnosis of exclusion. Long-term follow-up, which is ongoing, may provide an insight into confirming the diagnosis. Finally, long-term changes in morphology of ERP were not evaluated.
This study demonstrates a high prevalence of significant inferolateral early repolarization in survivors of initially unexplained cardiac arrest. This pattern occurs in those with and without another specific diagnosis, though it is more pronounced, and involves a larger number of leads in those with IVF. These data support the importance of ERP in patients with IVF.
The authors are indebted to the tireless work of the study coordinators, Bonnie Spindler, Wendy Meyer, Karen MacDonald, Karen Gibbs, Lyne Charbonneau, Isabelle Deneufbourg, Jabeen Khan, Sharlene Hammond, Alecia Jones, and Katherine Allan, and to their patients who gladly participate to advance our understanding of cardiac arrest and inherited arrhythmias.
The study was supported by the Heart and Stroke Foundation of Ontario (T6730), and by an unrestricted research grant from Boston Scientific. Dr. Gollob is a Clinician Scientist of the Heart and Stroke Foundation of Ontario. Dr. Krahn is a Career Investigator of the Heart and Stroke Foundation of Ontario (CI6498). All other authors have reported that they have no relationships to disclose.
- Abbreviations and Acronyms
- arrhythmogenic right ventricular cardiomyopathy
- catecholaminergic polymorphic ventricular tachycardia
- early repolarization pattern
- idiopathic ventricular fibrillation
- long QT syndrome
- magnetic resonance imaging
- Received February 21, 2011.
- Revision received April 5, 2011.
- Accepted April 12, 2011.
- American College of Cardiology Foundation
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- Kogan E.,
- Belhassen B.,
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- Healey J.S.,
- Chauhan V.,
- et al.