Association of early repolarization and sudden cardiac death during an acute coronary event

Transient and rapid QRS-widening associated with a J-wave pattern predicts impending ventricular fibrillation in experimental myocardial infarction

BACKGROUND

Certain types of the early repolarization phenomenon, previously considered to be benign, have been reported to be associated with ventricular fibrillation (VF), both in population-based studies and in the myocardial infarction (MI) settings.

OBJECTIVE

To analyze whether QRS widening and appearance of a J-wave pattern in experimental MI settings is predictive of VF.

METHODS

MI was induced in 32 pigs by 40-minute inflation of an angioplasty balloon in the left descending artery, and electrocardiogram was continuously recorded. Multilead QRS boundaries were computed, and QRS duration was calculated on a beat-to-beat basis during the occlusion period for each pig. An association between QRS widening and subsequent VF was studied using receiver operating characteristic curve analysis. Electrocardiograms at maximum QRS duration were reviewed for the presence of a J-wave pattern.

RESULTS

Sixteen animals had VF episodes during the occlusion period. Two peaks of QRS widening were found in all animals: the first peak immediately on left descending artery occlusion and the second peak 19.1 ± 4.0 minutes later. The magnitude of changes in the QRS width over time had significant interindividual differences. A QRS widening of ≥28 ms during a 3-minute time window was observed in 14 animals and predicted impending VF (selectivity 80%, specificity 73%, positive predictive value 57%, and negative predictive value 89%; P = .008). In 10 of 14 (71%) pigs, a J-wave pattern appeared at maximal QRS duration. The appearance of a J-wave pattern predicted VF with selectivity 80%, specificity 68%, positive predictive value 53%, and negative predictive value 88% (P = .02).

CONCLUSION

Transient QRS widening, commonly associated with a J-wave pattern, appears to predict impending VF in acute ischemia settings and motivates further clinical studies for monitoring immediate risk of VF in MI.

False tendons may be associated with the genesis of J-waves: prospective study in young healthy male

BACKGROUND

Recent studies showed that J-waves are associated with vulnerability to ventricular fibrillation. Recently we reported the association between false tendons (FTs) and J-waves in a retrospective study.

METHODS AND RESULTS

We prospectively studied 50 young healthy men (mean age 24.6±2.7 years). FTs were detected echocardiographically and classified based on their points of attachment as type 1 (longitudinal type), type 2 (diagonal type), and type 3 (transverse type). J-waves were defined as terminal QRS notching or slurring with ≥0.1 mV. The filtered QRS duration (fQRSd), RMS40, and LAS40 were measured on signal-averaged ECGs. FTs were detected in 37 of the 50 subjects (74%). The incidence of J-waves was significantly higher in subjects with type 1 or type 2 FTs than those with no- or type 3 FTs (61% vs. 26%, p<0.05). The leads with J-waves were closely associated with the location of the FT. While no late potential was recorded in any study subjects, fQRSd and LAS40 were significantly longer in subjects with type 1 or type 2 FTs (p<0.05). Univariate and multivariate logistic regression analysis revealed that only the existence of FTs (type 1 or 2) was an independent predictor of the presence of J-waves.

CONCLUSIONS

Our results suggest that FTs were related to the genesis of J-waves with conduction delay.

Early repolarization pattern: its ECG characteristics, arrhythmogeneity and heritability

Early repolarization (ER) has been accepted as a benign ECG variant for decades. Two seminal studies challenged this notion and have demonstrated that ER pattern is associated with an increased risk of arrhythmic and cardiac mortality in patients with idiopathic ventricular fibrillation (IVF) and in the general population. Recent clinical studies demonstrate its varying impact as an arrhythmogenic substrate on different diseases. For example, in ER syndrome, a primary electrical disease, ER appears as a major arrhythmogenic substrate for development of VF whereas in patients with coronary artery disease, an ER pattern may exist as a silent substrate, increasing the risk of VF during episodes of cardiac ischaemia. Due to the high prevalence of an ER pattern in the general population and a low VF event rate, it remains challenging to differentiate a malignant ER pattern from a benign form. Recent research suggests that a J-wave amplitude of more than 0.1 mV combined with a descending/horizontal ST segment may constitute a malignant ER pattern. Further studies are however necessary to evaluate its prognostic value for cardiac and arrhythmic death in the general population as well as in cases with a malignant ER pattern. While genetic testing has revealed putative causal DNA variants in sporadic cases, the lack of co-segregation with the disease in affected families suggests that ER syndrome is not monogenic but is likely a complex disorder influenced by multiple genetic as well as environmental factors.

Presence of early repolarization on admission electrocardiography is associated with long-term mortality and MACE in patients with STEMI undergoing primary percutaneous intervention

BACKGROUND

Early repolarization (ER) is associated with increased risk of sudden cardiac death and ventricular fibrillation (VF) in patients with/without structural heart disease. In this trial we examined the short- and long-term prognostic value of ER on admission electrocardiogram (ECG) in patients with ST-elevation myocardial infarction (STEMI) treated with primary percutaneous coronary intervention (PCI).

METHOD

Consecutive 521 patients with acute STEMI who underwent primary PCI were enrolled prospectively. Twelve-lead ECGs obtained during the initial diagnosis were scanned and stored digitally. The leads showing the typical ST segment elevation due to the acute infarction were excluded and the remaining ECG leads were included in the analysis for the presence of ER.

RESULTS

The study group included 61 STEMI patients (55 male; mean age 57.6±12.6 years) with ER and 460 STEMI patients (378 male; mean age 57.1±12.5) without ER on ECG. In the ER group, 14 patients (22.9%) had notching, 10 patients (16.4%) had slurring, and 37 patients (60.7%) had only J-point elevation. When analyzing regional leads, ER was observed mostly in inferior leads (n=40, 65.6%). During the hospitalization period, ventricular tachycardia or VF occurred more frequently in the ER group (19.6% vs. 10.9%; p=0.04) and 6 patients (6.9%) from the ER group and 14 patients (3%) from the control group died (p=0.01). During a follow-up period of 21.1±10.2 months, mortality was significantly higher in the ER group (12.7% vs. 4.2%; p=0.01). When total mortality rates were considered, highest mortality was observed in patients with notching pattern (5/14 subjects; 35.7%) when compared to patients with slurring (3/10 subjects; 30%), patients with only J-point elevation patterns (5/37subjects; 13.5%) and the control group (33/460 subjects; 7.1%). Presence of notching and slurring pattern on admission ECG was found as independent predictors of long-term mortality; whereas presence of only J-point elevation was not.

CONCLUSION

Presence of ER pattern in admission ECG in patients with STEMI is associated with both in-hospital and long-term mortality.

ABCC9 is a novel Brugada and early repolarization syndrome susceptibility gene

BACKGROUND

Genetic defects in KCNJ8, encoding the Kir6.1 subunit of the ATP-sensitive K(+) channel (I(K-ATP)), have previously been associated with early repolarization (ERS) and Brugada (BrS) syndromes. Here we test the hypothesis that genetic variants in ABCC9, encoding the ATP-binding cassette transporter of IK-ATP (SUR2A), are also associated with both BrS and ERS.

METHODS AND RESULTS

Direct sequencing of all ERS/BrS susceptibility genes was performed on 150 probands and family members. Whole-cell and inside-out patch-clamp methods were used to characterize mutant channels expressed in TSA201-cells. Eight ABCC9 mutations were uncovered in 11 male BrS probands. Four probands, diagnosed with ERS, carried a highly-conserved mutation, V734I-ABCC9. Functional expression of the V734I variant yielded a Mg-ATP IC₅₀ that was 5-fold that of wild-type (WT). An 18-y/o male with global ERS inherited an SCN5A-E1784K mutation from his mother, who displayed long QT intervals, and S1402C-ABCC9 mutation from his father, who displayed an ER pattern. ABCC9-S1402C likewise caused a gain of function of IK-ATP with a shift of ATP IC₅₀ from 8.5 ± 2 mM to 13.4 ± 5 μM (p<0.05). The SCN5A mutation reduced peak INa to 39% of WT (p<0.01), shifted steady-state inactivation by -18.0 mV (p<0.01) and increased late I(Na) from 0.14% to 2.01% of peak I(Na) (p<0.01).

CONCLUSION

Our study is the first to identify ABCC9 as a susceptibility gene for ERS and BrS. Our findings also suggest that a gain-of-function in I(K-ATP) when coupled with a loss-of-function in SCN5A may underlie type 3 ERS, which is associated with a severe arrhythmic phenotype.

Effect of ECG filter settings on J-waves

BACKGROUND

While J-waves were observed in healthy populations, variations in their reported incidence may be partly explicable by the ECG filter setting.

METHODS

We obtained resting 12-lead ECG recordings in 665 consecutive patients and enrolled 112 (56 men, 56 women, mean age 59.3±16.1years) who manifested J-waves on ECGs acquired with a 150-Hz low-pass filter. We then studied the J-waves on individual ECGs to look for morphological changes when 25-, 35-, 75-, 100-, and 150Hz filters were used.

RESULTS

The notching observed with the 150-Hz filter changed to slurring (42%) or was eliminated (28%) with the 25-Hz filter. Similarly, the slurring seen with the 150-Hz filter was eliminated on 71% of ECGs recorded with the 25-Hz filter. The amplitude of J-waves was significantly lower with 25- and 35-Hz than 75-, 100-, and 150-Hz filters (p<0.0001).

CONCLUSIONS

The ECG filter setting significantly affects the J-wave morphology.

Early repolarization syndrome: electrocardiographic signs and clinical implications

Early repolarization syndrome (ERS) was previously considered as a benign variant, but it has recently emerged as a risk marker for idiopathic ventricular fibrillation (VF) and sudden death. As measured by electrocardiogram (ECG), early repolarization is characterized by an elevation of the J point and/or ST segment from the baseline by at least 0.1 mV in at least two adjoining leads. In particular, early repolarization detected by inferior ECG leads was found to be associated with idiopathic VF and has been termed as ERS. This condition is mainly observed in young men, athletes, and blacks. Also, it has become evident that electrocardiographic territory, degree of J-point elevation, and ST-segment morphology are associated with different levels of risk for subsequent ventricular arrhythmia. However, it is unclear whether J waves are more strongly associated with a depolarization abnormality rather than a repolarization abnormality. Several clinical entities can cause ST-segment elevation. Therefore, clinical and ECG data are essential for differential diagnosis. At present, the data set is insufficient to allow risk stratification in asymptomatic individuals. ERS, idiopathic VF, and Brugada syndrome (known as J-wave syndromes) are three clinical conditions that share many common ECG features; however, their clinical consequences are remarkably different. This review summarizes the current electrocardiographic data concerning ERS with clinical implications.

[Early repolarisation. A dilemma of risk stratification]

Early repolarization, involving infero-lateral ST segment elevation and prominent J waves at the QRS-ST junction has been considered a normal ECG variant for more than 80 years. More recent studies suggest that this phenomenon is not as benign as earlier believed and may represent a risk for subsequent ventricular fibrillation in patients with and without structural heart disease. However, based on current data it seems unjustified to consider these often accidental ECG findings a marker for high risk of sudden cardiac death. The concept of a reduced repolarization reserve developed for the Long QT syndrome can be transformed to early repolarization syndrome. In general a "fibrillation reserve" is relatively high but if triggers such as a genetic background, age, gender, influences of the autonomous nervous system, changes in body temperature, or an acute coronary syndrome act together ventricular fibrillation may occur. A combination of an "early repolarization ECG" with syncope and/or a positive family history of sudden cardiac death may justify defibrillator therapy just on an individual basis. This review intends to summarize actual aspects of early repolarizations syndrome and focuses on the dilemma of risk stratification.

What do we know about the "malignant form" of early repolarization?

There is an urgent need to identify electrocardiographic characteristics that differentiate the "benign early repolarization pattern" from "malignant early repolarization." In a previous paper, we considered the different electrocardiographic elements of the early repolarization pattern and analyzed how they confer important prognostic information. In the present article, we review more recent information regarding the importance of the contour of the ST segment, with special emphasis on the currently termed malignant form and its value for risk stratification in early repolarization.

The prevalence of electrocardiographic early repolarization in an adult cohort with chronic kidney disease and its impact upon all-cause mortality and progression to dialysis

BACKGROUND

Electrocardiographic early repolarization (ER) occurring in <5% of general/atherosclerotic populations, is a marker of sudden cardiac death (SCD). The prevalence of ER in chronic kidney disease (CKD) patients, in whom SCD is common, is unknown. We aimed to determine the prevalence, contributing factors, and relationship of ER to all-cause mortality and progression to dialysis in CKD patients.

METHODS

A retrospective study of 197 patients with stage 3-5 CKD. Full demographic data were collected including cardiovascular risk factors and history. All patients underwent a 12-lead ECG, analysed for the presence of ER and other ECG findings. ER was defined as elevation of the QRS-ST junction (J point) by at least 0.1 mV from baseline with slurring/notching of the QRS complex. The primary and secondary endpoints were all cause mortality and progression to dialysis respectively at 1 year. To control for the effects of CKD, we evaluated the ECGs of 39 healthy renal transplant donors (RTD).

RESULTS

CKD patients had a mean age of 61.5 (±16.1). Prevalence of ER in pre-dialysis patients with CKD stage 4 and 5 was higher than in RTD (26.4 vs. 7.7%, p = 0.02). ER frequency increased with CKD stage (stage 3: 7.7%, stage 4: 29.7%, and pre-dialysis stage 5: 24.6%), but decreased in dialysis patients (13%). On multivariate analysis only the QRS duration was a significant independent predictor of ER (OR 0.97, 95% CI, 0.94-0.99, p = 0.01). At 1-year follow-up, there were 24 (12%) deaths in the patients with CKD of whom 5 (21%) had ER. ER was not a predictor of all cause mortality (p = 1.00) and had no effects on the rate of progression to dialysis (p = 0.67).

CONCLUSIONS

ER is more common in pre-dialysis CKD patients, compared to healthy RTD but is not associated with increased 1-year mortality or entry onto dialysis programs. Further longitudinal studies are indicated to determine whether this increased prevalence of ER is associated with the rate of SCD seen in this population.

Idiopathic ventricular fibrillation, early repolarization and other J wave-related ventricular fibrillation syndromes: from an electrocardiographic enigma to an electrophysiologic dogma

Current clinical and experimental data demonstrate that the electrocardiographic J wave plays a critical role in the pathogenesis of ventricular fibrillation (VF) in patients with Brugada syndrome (BS) and early repolarization (ER) syndrome (ERS). This has generated renewed interest in the presence of J waves and ERS in the general population, yet the identification of high-risk ECG markers and the risk stratification of subjects with ERS remain to be established. More recently, this concept has been expanded to VF mechanisms in patients with structural heart diseases. Some of the fatal arrhythmias in the setting of acute myocardial ischemia or infarction may share a similar, J wave-related electrophysiologic process. In canine arterially perfused wedge preparations, the occurrence of J wave-related arrhythmias is mediated by phase 2 reentry. The stability of the action potential (AP) dome in the ventricular epicardium is dependent on the prominence of the AP phase 1 notch. The ability to maintain the AP dome depends on a delicate balance between inward and outward ionic currents during depolarization and the early phase of repolarization. Outward shifts of the balance and inability to maintain the AP dome result in marked dispersion of repolarization and vulnerability to VF. This review describes the electrocardiographic and clinical features of the J waves in idiopathic VF and other structural heart diseases.

Association of early repolarization and sudden cardiac death during an acute coronary event

BACKGROUND

Electrocardiographic early repolarization (ER) pattern has been previously associated with arrhythmic mortality and with an increased risk of ventricular fibrillation. We hypothesized that there is an association between ER and sudden cardiac death (SCD) during an acute coronary event.

METHODS AND RESULTS

The present study included 432 consecutive victims of SCD because of acute coronary event and 532 survivors of such an event, in whom 12-lead ECGs recorded before and unrelated to the event could be evaluated. SCDs were verified by medicolegal autopsy to be because of acute coronary event. ER was defined as an elevation of the QRS-ST junction in at least 2 inferior or lateral leads, manifested as QRS notching or slurring. The prevalence of ER pattern ≥0.1 mV was more common in cases (62/432; 14.4%) than controls (42/532; 7.9%) (P=0.001). The victims of SCD were younger, were more commonly men and smokers, had lower body mass index, had elevated heart rate, had prolonged QRS complex, and had lower prevalence of history of prior cardiovascular disease than controls. After adjustments for baseline differences, the odds ratio for J waves without ST-segment elevation in the SCD group was 2.15 (95% CI, 1.20-3.85; P=0.01).

CONCLUSIONS

Higher prevalence of ER in a standard 12-lead ECG in victims of SCD than in survivors of an acute coronary event suggests that the presence of ER increases the vulnerability to fatal arrhythmia during acute myocardial ischemia and provides a plausible mechanistic link between this ECG pattern and higher arrhythmic mortality of middle-aged/elderly subjects.