Predictors of Atrial Tachyarrhythmias in Subjects with Type 1 ECG Pattern of Brugada Syndrome

Effect of noise on the electrocardiographic parameters

PURPOSE

Noise, defined as any sound that is unpleasant, is one of the most important environmental problems. Prolonged exposure to noise has been shown to be associated with the development of cardiovascular diseases. No study investigated the effect of noise on surface electrocardiography (ECG).

AIMS

The aim of our study is to investigate the effect of noise on surface ECG parameters including P-wave dispersion (PWD), QT intervals, corrected QT interval (QTc), T-wave peak to end (Tp-e) interval, and Tp-e/QT and Tp-e/QTc ratios.

METHODS

A total of 51 people working in the textile factory affected by the noise and 43 volunteers without any disease and who were not exposed to noise were included in this study. The average noise level in the textile factory was 112 dB. A 12-lead ECG was obtained from all individuals. PR interval, PWD, QRS duration, QT interval, QTc interval, Tp-e interval, and Tp-e/QT and Tp-e/QTc ratios were calculated for all individuals.

RESULTS

The noise group had significantly increased PWD [35 (28-40) vs. 28 (22-36) p = 0.029], QT interval ( 373.5 ± 27.3 vs. 359.3 ± 2.74, p = 0.001), QTc interval [(409 ± 21 vs. 403 ± 13 p = 0.045)], Tp-e interval [(90.6 ± 6.0 vs. 83.5 ± 7.3 p < 0.001)], Tp-e/QT [(0.24 ± 0.03 vs. 0.23 ± 0.02, p = 0.015)] and Tp-e/QTc [(0.22 ± 0.02 vs. 0.21 ± 0.02 p < 0.001)] compared to control group. Also, duration of working was positively correlated with PWD (r = 0.468, p = 0.001) and Tp-e/QTc ratio (r = 0.328, p = 0.019). In multiple linear regression linear regression analysis, noise was the independent predictor of both PWD (β = 0.244, p = 0.032) and Tp-e/QTc (β = 0.319, p = 0.003) CONCLUSION: We showed that noise significantly increased PWD, QT and Tp-e interval measurements. Also, noise was the independent predictor for both PWD and Tp-e/QTc.

Atrial fibrillation in Brugada syndrome: Current perspectives

The incidence of atrial fibrillation (AF) in Brugada syndrome (BrS) has been reported at between 9% and 53% by different series, but the true prevalence is unknown. However, AF may be the presenting feature in some patients. The underlying mechanisms for AF may be a combination of multiple factors, genetic or acquired, that may impact upon autonomic function, atrial structure, and conduction velocities or other unknown factors. The presence of AF has been associated with a more malignant course, with a greater incidence of syncope and ventricular arrhythmias, thus acting as marker of more advanced disease. Regarding the management of patients with AF, antiarrhythmic drugs effective in preventing malignant arrhythmias in BrS such as quinidine or invasive treatment with pulmonary vein isolation (PVI) may be useful in AF treatment. In this review, we aim to present the current perspectives regarding the genetics, pathophysiology, management, and prognosis of AF in patients with BrS.

Electrocardiographic evidence of abnormal atrial phenotype in Brugada syndrome

BACKGROUND

Brugada syndrome (BrS) is an inherited ion channelopathy that may predispose affected individuals to atrial cardiomyopathy. We tested the hypothesis that BrS patients have higher degrees of atrial electrophysiological abnormalities compared to controls, and these can be reflected by changes in P-wave parameters determined on the electrocardiogram (ECG).

METHODS

This was a single-center retrospective study comparing BrS patients to age- and gender-matched control subjects. Mean P-wave duration (PWDmean), maximum PWD (PWDmax) and minimum PWD (PWDmin), P-wave dispersion (PWDmax - PWDmin), and P-wave terminal force in V1 (PTFV1) were measured. PWDmax ≥ 120 ms, in the presence and absence of biphasic P-waves in the inferior leads, were termed advanced and partial inter-atrial block (IAB), respectively.

RESULTS

The proportion of IAB was significantly higher in BrS patients (28/51; 55%) than in control subjects (14/51; 27%; Fisher's Exact test; P < 0.01). Advanced IAB was observed in two BrS patients but none of the control subjects (P = 0.50). Compared to controls, BrS patients showed higher PWDmean (107 [98-113] vs. 97 [90-108] ms; KWANOVA, P < 0.01), PWDmax (123 [110-132] vs. 113 [107-121] ms; P < 0.001) but statistically indistinguishable PWDmin (82 [72-92] vs. 77 [69-85]; P = 0.09), and P-wave dispersion (38 [26-52] vs. 37 [23-45] ms; P = 0.14). PTFV1 was significantly higher in BrS patients than in control subjects (24 [0-40] vs. 0 [0-27] mm.ms; P < 0.05).

CONCLUSION

Atrial conduction abnormalities are frequently observed in BrS. These patients may require monitoring for future development of atrial fibrillation and stroke.

High risk electrocardiographic markers in Brugada syndrome

Several clinical, electrocardiographic (ECG) and electrophysiological markers have been proposed to provide optimal risk stratification in patients with Brugada syndrome (BrS). Of the different markers, only a spontaneous type 1 ECG pattern has clearly shown a sufficiently high predictive value. This review article highlights specific ECG markers based on depolarization and/or repolarization that have been associated with an increased risk of arrhythmic events in patients with BrS.

Prognosis, risk stratification, and management of asymptomatic individuals with Brugada syndrome: A systematic review

Brugada syndrome (BrS) is a primary electrical disease associated with increased risk of sudden cardiac death due to polymorphic ventricular arrhythmias. The prognosis, risk stratification, and management of asymptomatic individuals remain the most controversial issues in BrS. Furthermore, the decision to manage asymptomatic patients with an implantable cardioverter-defibrillator should be made after weighing the potential individual risk of future arrhythmic events against the risk of complications associated with the implant and follow-up of patients living with such devices, and the accompanying impairment of the quality of life. Several clinical, electrocardiographic, and electrophysiological markers have been proposed for risk stratification of subjects with BrS phenotype, but the majority have not yet been tested in a prospective manner in asymptomatic individuals. Recent data suggest that current risk factors are insufficient and cannot accurately predict sudden cardiac death events in this setting. This systematic review aims to discuss contemporary data regarding prognosis, risk stratification, and management of asymptomatic individuals with diagnosis of Brugada electrocardiogram pattern and to delineate the therapeutic approach in such cases.

Brugada Syndrome:Risk Stratification And Management

The Brugada syndrome (BrS) is an arrhythmogenic disease associated with an increased risk of ventricular fibrillation and sudden cardiac death. The risk stratification and management of BrS patients, particularly of asymptomatic ones, still remains challenging. A previous history of aborted sudden cardiac death or arrhythmic syncope in the presence of spontaneous type 1 ECG pattern of BrS phenotype appear to be the most reliable predictors of future arrhythmic events. Several other ECG parameters have been proposed for risk stratification. Among these ECG markers, QRS-fragmentation appears very promising. Although the value of electrophysiological study still remains controversial, it appears to add important information on risk stratification, particularly when incorporated in multiparametric scores in combination with other known risk factors. The present review article provides an update on the pathophysiology, risk stratification and management of patients with BrS.

P-wave dispersion: an update

P-wave dispersion (PWD, Pd or Pdis) is a noninvasive electrocardiographic (ECG) marker for atrial remodeling and predictor for atrial fibrillation (AF). PWD is defined as the difference between the widest and the narrowest P-wave duration recorded from the 12 ECG leads. Increased P-wave duration and PWD reflect prolongation of intraatrial and interatrial conduction time with lack of a well-coordinated conduction system within the atrial muscles, with inhomogeneous, asynchronic, pro-inflammatory and anti-inflammatory effect mediated by interleukin-6 (IL-6) in patients with the CG + GG genotype IL-6 -634C/G polymorphism [1] and discontinuous propagation of sinus impulses mainly between the left and right atria, interstitial/extracellular fibroblast activation and collagen deposition with fibrosis (via TGF-β) in atrial tissue, insufficient blood supply, significant not isotropic myoelectric activity, and thin wall thickness and consequent expansion tendency all well-known electrophysiological characteristics in patients with atrial arrhythmias and especially paroxysmal atrial fibrillation (PAF) [2].

Atrial Fibrillation and Brugada Syndrome

Since its first description in 1992, the Brugada syndrome (BrS) has attracted significant attention from the cardiology community because of its association with malignant ventricular arrhythmias and sudden cardiac death. Supraventricular tachyarrhythmias in BrS represent a unique and seemingly higher-risk clinical subgroup of patients with BrS. Atrial fibrillation represents the most common supraventricular arrhythmia in patients with BrS, with average ranges reported in the literature of 20% to 40%. This article summarizes the current literature regarding the patient with BrS with atrial fibrillation and discusses the management of these clinically challenging and potentially higher-risk individuals.

Increased intraatrial conduction abnormality assessed by P-wave signal-averaged electrocardiogram in patients with Brugada syndrome

BACKGROUND

Atrial fibrillation (AF) is observed in patients with Brugada syndrome (BS), especially those showing coved-type electrocardiogram (ECG) pattern. Using P-wave signal-averaged ECG (P-SAE), we investigated whether increased intraatrial conduction abnormality contributed to AF generation in BS patients.

METHODS

Twenty BS patients and 20 age- and gender-matched healthy controls were enrolled. At the P-SAE recording, 12 of the 20 BS patients showed coved-type (C-BS) and eight showed saddleback-type (S-BS). The total duration (Ad) and root mean square voltage for the terminal 20 ms (LP(20) ) of the filtered P wave were measured. P-wave dispersion (P-disp) was defined as the difference between the maximum and minimum, measured from 16 precordial recording sites.

RESULTS

BS patients had a significantly longer Ad (128.2 ± 7.6 vs 116.3 ± 8.2 ms, P < 0.0001), lower LP(20) (2.6 ± 0.9 vs 3.4 ± 0.8 μV, P < 0.01), and greater P-disp (15.5 ± 7.0 vs 7.4 ± 3.2 ms, P < 0.0001) than the controls. C-BS patients had significantly longer Ad (131.0 ± 7.2 vs 124.1 ± 6.8 ms, P < 0.05) and lower LP(20) (2.2 ± 0.6 vs 3.2 ± 1.0 μV, P < 0.05) than S-BS patients. All C-BS patients and only three S-BS patients had atrial late potential (100% vs 38%, P < 0.01).

CONCLUSION

Intraatrial conduction delay and its heterogeneity may exist in BS patients, especially those showing coved-type ECG patterns. These atrial electrical abnormalities could be a substrate for atrial reentrant tachycardia such as AF.

Facilitatory and inhibitory effects of SCN5A mutations on atrial fibrillation in Brugada syndrome

AIMS

Brugada syndrome (BrS) is associated with increased risk for atrial fibrillation (AFib). However, the role of SCN5A mutations in the occurrence of AFib remains unclear. Cardiac sodium current reduction caused by SCN5A mutations may facilitate AFib by slowing intra-atrial conduction and inducing structural changes, but also prevent it by suppressing atrial ectopic activity. Here, we examined the relation between SCN5A mutations, atrial conduction velocity, atrial structural changes, and atrial ectopic activity in BrS.

METHODS AND RESULTS

Data from 214 BrS patients [78 with an SCN5A mutation (patients with an SCN5A mutation, BrSSCN5A+) and 136 without an SCN5A mutation (patients without an SCN5A mutation, BrSSCN5A-)] were collected. Intra-atrial conduction velocity was assessed by measuring P-wave durations at baseline and during sodium channel provocation testing. Atrial structural changes were assessed by measuring atrial dimensions using cardiac magnetic resonance imaging. Atrial ectopic activity was assessed by determining the incidence of atrial ectopic beats using 24 h Holter recordings. Clinical characteristics (including AFib occurrence) did not differ between BrSSCN5A+ and BrSSCN5A-. Baseline P-wave durations were longer in BrSSCN5A+ than in BrSSCN5A-, but lengthened markedly in BrSSCN5A- during provocation testing. Atrial dimensions did not differ. Atrial ectopic beats occurred more often in BrSSCN5A-, and the proportion of patients experiencing one or more atrial ectopic beats was larger in BrSSCN5A- than in BrSSCN5A+.

CONCLUSION

In BrS, the presence of an SCN5A mutation is associated with intra-atrial conduction slowing and suppressed atrial ectopic activity. Intra-atrial conduction slowing may provide a plausible substrate for AFib maintenance, while reduced atrial ectopic activity may constitute inhibition of the trigger for AFib initiation.