Flecainide and propafenone induced ST-segment elevation in patients with atrial fibrillation: clue to specificity of Brugada-type electrocardiographic changes

Efficacy and safety of dextrose-insulin in unmasking non-diagnostic Brugada ECG patterns

BACKGROUND

Typical diagnostic, coved-type 1, Brugada ECG patterns fluctuate spontaneously over time with a high proportion of non-diagnostic ECG patterns. Insulin modulates ion transport mechanisms and causes hyperpolarization of the resting potential. We report our experience with unmasking J-ST changes in response to a dextrose-insulin test.

METHODS

Nine patients, mean age 40.5±19.4years (range: 15-65years), presented initially with a non-diagnostic ECG pattern, which was suggestive of Brugada syndrome (group I). They were compared with 10 patients with normal ECG patterns (group II). Participants received an infusion of 50g of 50% dextrose, followed by 10IU of intravenous regular insulin. Positive changes were defined by conversion to a diagnostic ECG pattern.

RESULTS

The dextrose-insulin test was positive in six of seven (85.7%) patients (kappa 0.79, p=0.02) that was confirmed with a pharmacologic test (kappa 1, p=0.003). One had an inconclusive test, and two with a negative test had an early repolarization ECG pattern. All subjects in group II had a negative test (p<0.01). The maximum changes of the J-ST segment were observed 41.3±31.4minutes (range 3-90minutes) after dextrose-insulin infusion. One patient had monomorphic ventricular bigeminy without spontaneous or induced ventricular fibrillation.

CONCLUSION

Changes in J-ST segment in the Brugada syndrome are influenced by glucose-insulin, and this report reproduces and supports the efficacy and safety of this metabolic test in the differential diagnosis of patients with non-diagnostic ECG patterns.

Prevalence, clinical characteristics and management of atrial fibrillation in patients with Brugada syndrome

Atrial fibrillation (AF) can be the first manifestation of latent Brugada syndrome (BS). The aim of our study was to assess the prevalence of AF as the first clinical diagnosis in patients with BS and their demographic and clinical characteristics and diagnosis management in a large cohort of patients. The patient group consisted of 611 patients with BS. The data from those with a diagnosis of AF previous to the identification of BS were analyzed (n = 35). Eleven cases were unmasked after the initiation of a class I antiarrhythmic drug and one during the establishment of general anesthesia. In the remaining population, BS was diagnosed using an ajmaline test performed mainly because of younger age in patients with lone AF (n = 13), previous syncope or sudden cardiac death (n = 3), or a clinical history of sudden cardiac death in the family (n = 5). The mean patient age was 49 ± 15 years, 21 were male patients, 14 had a family history of sudden death, 15 had had previous syncope, and 4 had survived cardiac arrest. Concomitant electrical disorder was found in 13 patients. Remarkably, 21 patients had normal findings on the baseline electrocardiogram. In conclusion, AF could be one of the first clinical manifestations of latent BS in a considerable number of patients. This identification is crucial because the treatment of these patients is subject to relevant changes. The ajmaline test plays an essential role, mainly in young patients with a family history of sudden death, despite having normal findings on a baseline electrocardiogram.

Is this a philosophic issue? Do patients with drug-induced Brugada type ECG have poor prognosis? (Pro)

Brugada syndrome (BS) has an intermittent or concealed type, which can be unmasked by the sodium (Na(+))-channel-blocker challenge test. The appropriate risk stratification of patients with a drug-induced Brugada-type electrocardiographic (ECG), especially those without a history of syncope or aborted sudden cardiac death, remains unclear. The prognosis of patients with BS depends on the clinical type, cardiac arrest, syncope or if asymptomatic. The ratio of the asymptomatic group varies from 56.9% to 63.6% and, furthermore, their annual cardiac event rate is relatively lower at 0.24-3.6% compared with the cardiac arrest group. Patients with a drug-induced Brugada-type ECG have a poor prognosis if they had a history of ventricular fibrillation (VF) or aborted sudden cardiac death, because their risk becomes similar to that of patients with spontaneous Brugada-type ECG. They have the disturbance of the Na(+)-channel and the electrophysiologic substrate of VF, proven by the high inducibility of VF by stimulation test even in patients without spontaneous VF. Spontaneous VF will never occur if there is no VF substrate. Implantable cardioverter-defibrillators will certainly protect them, so patients with a drug-induced Brugada-type ECG, even without a history of VF or aborted sudden cardiac death, should be considered to have a poor prognosis.

New-onset atrial fibrillation as first clinical manifestation of latent Brugada syndrome: prevalence and clinical significance

AIMS

To evaluate the prevalence, clinical significance, and prognosis of latent Brugada syndrome (BrS) in patients with new-onset atrial fibrillation (AF) unmasked by class 1C antiarrhythmic drugs.

METHODS AND RESULTS

Between January 2000 and June 2008, all consecutive patients with new-onset AF, who after flecainide exhibited typical Brugada ECG pattern, underwent electrophysiologic, pharmacologic, and genetic testing. Among 346 patients [median age 53 years; interquartile range (IQR), 15], 11 (3.2%; median age 51 years; IQR, 19) diagnosed as lone AF exhibited typical Brugada ECG pattern. Genetic testing was negative. Ventricular tachycardia/ventricular fibrillation (VT/VF) was induced by electrophysiologic testing (five patients) or during flecainide infusion (one patient). Six patients with type 1 ECG pattern and inducible VT/VF underwent ICD implantation. During a median follow-up of 31.5 months (range: 10-85) after ICD implantation, three patients developed BrS and one of them experienced VF. Patients without ICD (five patients) remained asymptomatic during a median follow-up of 74 months. Persistent type 1 pattern occurred only in the three patients who developed BrS.

CONCLUSION

This study, for the first time, reveals the prevalence of latent BrS in patients with new-onset lone AF, which may precede VT/VF. Persistence of type 1 and ventricular tachyarrhythmias inducibility represents a marker of electrical instability leading to sudden death.

Mutations in sodium channel β1- and β2-subunits associated with atrial fibrillation

BACKGROUND

We and others have reported mutations in the cardiac predominant sodium channel gene SCN5A in patients with atrial fibrillation (AF). We also have reported that SCN1B is associated with Brugada syndrome and isolated cardiac conduction disease. We tested the hypothesis that mutations in the 4 sodium channel beta-subunit genes SCN1B-SCN4B contribute to AF susceptibility.

METHODS AND RESULTS

Screening for mutations in the 4 beta-subunit genes was performed in 480 patients with AF (118 patients with lone AF and 362 patients with AF and cardiovascular disease) and 548 control subjects (188 ethnically defined anonymized subjects and 360 subjects without AF). The effects of mutant beta-subunits on SCN5A mediated currents were studied using electrophysiological studies. We identified 2 nonsynonymous variants in SCN1B (resulting in R85H, D153N) and 2 in SCN2B (R28Q, R28W) in patients with AF. These occur at residues highly conserved across mammals and were absent in control subjects. In 3 of 4 mutation carriers, the ECGs showed saddleback-type ST-segment elevation in the right precordial leads. Transcripts encoding both SCN1B and SCN2B were detected in human atrium and ventricle. In heterologous expression studies using Chinese hamster ovary cells, the mutant beta1- or beta2-subunits reduced SCN5A-mediated current and altered channel gating compared with coexpression of wild-type subunits.

CONCLUSIONS

Loss of function mutations in sodium channel beta-subunits were identified in patients with AF and were associated with a distinctive ECG phenotype. These findings further support the hypothesis that decreased sodium current enhances AF susceptibility.

Different Effect of the Pure Na+ Channel-Blocker Pilsicainide on the ST-Segment Response in the Right Precordial Leads in Patients With Normal Left Ventricular Function

BACKGROUND

The response of the ST-segment in the right precordial leads to Na+ channel blockers in patients without structural heart disease and a typical Brugada-type ECG has not been fully elucidated.

METHODS AND RESULTS

A pilsicainide challenge test was performed in 161 patients and according to recently established ECG criteria and an organized computer algorithm, the ST morphology was classified and the maximum increase in the J wave amplitude (maxDeltaJ) from the standard and high right precordial leads V1-3 was examined. Before the test, subjects exhibiting type 1 ECG in the standard leads were excluded. After administering pilsicainide, type 1 ECGs in the standard leads were observed in 31 cases and a maxDeltaJ of >or=200 microV was observed in 29 cases (23 type 1, 2 type 2/3 and 4 normal ECGs). In the additional higher right precordial leads, type 1 ECGs were observed in 55 cases and a maxDeltaJ of >or=200 microV was observed in 45 cases (42 type 1 and 3 type 2/3 ECGs).

CONCLUSIONS

A maxDeltaJ>or=200 microV induced by pilsicainide, including that measured in the high right precordial leads, was associated with a change mainly to a type 1 ECG.

Risk Stratification of Individuals with the Brugada Electrocardiogram: A Meta-Analysis

OBJECTIVES

We performed a meta-analysis of prognostic studies of patients with a Brugada ECG to assess predictors of events.

BACKGROUND

The Brugada syndrome is an increasingly recognized cause of idiopathic ventricular fibrillation; however, there is wide variation in the prognosis of patients with the Brugada ECG.

METHODS AND RESULTS

We retrieved 30 prospective studies of patients with the Brugada ECG, accumulating data on 1,545 patients. Summary estimates of the relative risk (RR) of events (sudden cardiac death [SCD], syncope, or internal defibrillator shock) for a variety of potential predictors were made using a random-effects model. The overall event rate at an average of 32 months follow-up was 10.0% (95% CI 8.5%, 11.5%). The RR of an event was increased (P < 0.001) among patients with a history of syncope or SCD (RR 3.24 [95% CI 2.13, 4.93]), men compared with women (RR 3.47 [95% CI 1.58, 7.63]), and patients with a spontaneous compared with sodium-channel blocker induced Type I Brugada ECG (RR 4.65 [95% CI 2.25, 9.58]). The RR of events was not significantly increased in patients with a family history of SCD (P = 0.97) or a mutation of the SCN5A gene (P = 0.18). The RR of events was also not significantly increased in patients inducible compared with noninducible by electrophysiologic study (EPS) (RR 1.88 [95% CI 0.62, 5.73], P = 0.27); however, there was significant heterogeneity of the studies included.

CONCLUSIONS

Our findings suggest that a history of syncope or SCD, the presence of a spontaneous Type I Brugada ECG, and male gender predict a more malignant natural history. Our findings do not support the use of a family history of SCD, the presence of an SCN5A gene mutation, or EPS to guide the management of patients with a Brugada ECG.

The Role of Genotyping in Diagnosing Cardiac Channelopathies

The role of genotyping for diagnosis of the cardiac ion channelopathies is a work in progress. No formal guidelines or other publications discussing current recommendations for genotyping exist, particularly for clinical/commercial genotyping. Further, the field is changing rapidly, opinions vary and, additionally, circumstances inside the US are different from outside. The following considerations are a current summary based on a review of the literature, discussions with experts in the field, and our own opinions and also include a brief discussion about genotyping for therapeutic decision making. Research-based genotyping is very important for continued understanding of the details of pathophysiology and the complex regulatory processes in these diseases. Clinical/commercial genotyping for diagnosis is important for identifying patients with reduced penetrance of the phenotype since effective therapies to prevent sudden death exist. Clinical genotyping for therapeutic advantage has limited application at present but will become much more important if and when genotype-/mutation-type specific therapies are shown to be effective. The recommendations will progressively change as new research findings and new genotyping technologies appear.