Brugada Syndrome: Report of the Second Consensus Conference

Since its introduction as a clinical entity in 1992, the Brugada syndrome has progressed from being a rare disease to one that is second only to automobile accidents as a cause of death among young adults in some countries. Electrocardiographically characterized by a distinct ST-segment elevation in the right precordial leads, the syndrome is associated with a high risk for sudden cardiac death in young and otherwise healthy adults, and less frequently in infants and children. Patients with a spontaneously appearing Brugada ECG have a high risk for sudden arrhythmic death secondary to ventricular tachycardia/fibrillation. The ECG manifestations of Brugada syndrome are often dynamic or concealed and may be unmasked or modulated by sodium channel blockers, a febrile state, vagotonic agents, alpha-adrenergic agonists, beta-adrenergic blockers, tricyclic or tetracyclic antidepressants, a combination of glucose and insulin, hypo- and hyperkalemia, hypercalcemia, and alcohol and cocaine toxicity. In recent years, an exponential rise in the number of reported cases and a striking proliferation of articles defining the clinical, genetic, cellular, ionic, and molecular aspects of the disease have occurred. The report of the first consensus conference, published in 2002, focused on diagnostic criteria. The present report, which emanated from the second consensus conference held in September 2003, elaborates further on the diagnostic criteria and examines risk stratification schemes and device and pharmacological approaches to therapy on the basis of the available clinical and basic science data.

Short QT Syndrome and Atrial Fibrillation Caused by Mutation in KCNH2

BACKGROUND

The short QT syndrome is a newly described clinical entity characterized by the presence of a short QT interval associated with cardiac tachyarrhythmias including sudden cardiac death at a young age in otherwise healthy individuals. A genetic basis has been identified linking the disease to mutations in KCNH2 in the familial forms and a mutation in KCNQ1 in a sporadic form of the disease.

METHODS AND RESULTS

We identified a family with short QT syndrome with a high incidence of paroxysmal atrial fibrillation in their members and no known history of sudden cardiac death. QT interval ranged from 225 to 240 ms within normal heart rate ranges in the affected individuals. Programmed electrical stimulation (PES) was performed in all affected members, which revealed a remarkably short atrial and ventricular refractory period, and inducibility of atrial and ventricular fibrillation. Treatment with propafenone has maintained the individuals free of atrial fibrillation to date. Genetic analysis identified a missense mutation (C to G substitution at nucleotide 1764) which resulted in the amino acid change (N588K) in KCNH2. This mutation had been previously described in two other families with a high incidence of sudden cardiac death.

CONCLUSIONS

Our study confirms that N588K is a hotspot for familial form of the short QT syndrome. The disease is clinically heterogeneous, as indicated by the fact that, in the three families with the same mutation, there is a wide range of symptoms, varying from atrial to ventricular fibrillation and sudden death. While the implantation of a defibrillator appears warranted due to the inducibility at PES, the clinical follow-up provides indication that the class Ic agent propafenone could be effective to prevent episodes of paroxysmal atrial fibrillation.

Short QT syndrome: mechanisms, diagnosis and treatment

Short QT syndrome is an inheritable primary electrical disease of the heart that was discovered in 1999. The disorder is characterized by an abnormally short QT interval (<300 ms) and a propensity to atrial fibrillation, sudden cardiac death or both. As in the case of long QT syndrome, more than one relevant genetic mutation has been identified that can lead to a short QT interval on electrocardiography; so far two have been identified. Shortening of the effective refractory period combined with increased dispersion of repolarization is the likely substrate for re-entry and life-threatening tachyarrhythmias. Thus far, 22 people have been classified as having short QT syndrome: 15 from the actual measurement of a short QT interval on electrocardiograms and 7 by history after they died from sudden cardiac death. Several cases, especially among children, have probably been overlooked, since the shortness of the QT interval becomes apparent only at heart rates less than 80 beats/min. The best form of treatment is still unknown, but prevention of atrial fibrillation has been accomplished by propafenone. Implantation of an implantable cardioverter defibrillator is recommended for prevention of sudden cardiac death.

Brugada syndrome: report of the second consensus conference: endorsed by the Heart Rhythm Society and the European Heart Rhythm Association

Since its introduction as a clinical entity in 1992, the Brugada syndrome has progressed from being a rare disease to one that is second only to automobile accidents as a cause of death among young adults in some countries. Electrocardiographically characterized by a distinct ST-segment elevation in the right precordial leads, the syndrome is associated with a high risk for sudden cardiac death in young and otherwise healthy adults, and less frequently in infants and children. Patients with a spontaneously appearing Brugada ECG have a high risk for sudden arrhythmic death secondary to ventricular tachycardia/fibrillation. The ECG manifestations of Brugada syndrome are often dynamic or concealed and may be unmasked or modulated by sodium channel blockers, a febrile state, vagotonic agents, alpha-adrenergic agonists, beta-adrenergic blockers, tricyclic or tetracyclic antidepressants, a combination of glucose and insulin, hypo- and hyperkalemia, hypercalcemia, and alcohol and cocaine toxicity. In recent years, an exponential rise in the number of reported cases and a striking proliferation of articles defining the clinical, genetic, cellular, ionic, and molecular aspects of the disease have occurred. The report of the first consensus conference, published in 2002, focused on diagnostic criteria. The present report, which emanated from the second consensus conference held in September 2003, elaborates further on the diagnostic criteria and examines risk stratification schemes and device and pharmacological approaches to therapy on the basis of the available clinical and basic science data.

Drug-induced cardiac toxicity: emphasizing the role of electrocardiography in clinical research and drug development

This review describes the role of electrocardiography in clinical research and drug development, and addresses its utility in defining cardiac toxicity from noncardiac investigational drugs. Principles for designing electrocardiographic monitoring for cardiac safety in clinical trials are also reviewed.

The use of roxifiban (DMP754), a novel oral platelet glycoprotein IIb/IIIa receptor inhibitor, in patients with stable coronary artery disease

INTRODUCTION

Intravenous platelet glycoprotein (GP) IIb/IIIa receptor inhibitors have a significant beneficial impact on the outcomes of patients undergoing high-risk coronary interventions and in the stabilization of patients with unstable angina pectoris refractory to conventional medical treatment. The role of long-term treatment with oral platelet GP IIb/IIIa receptor inhibitors in patients with coronary artery disease is unproven. This study examined the dose-response effect on inhibition of platelet aggregation by roxifiban (DMP754), a novel oral platelet GP IIb/IIIa receptor inhibitor, and its safety and tolerability in patients with a history of chronic stable angina pectoris.

METHODS

Ninety-eight patients were randomized to receive either a placebo or 1 of 8 oral dosages of roxifiban. Twenty-two patients were enrolled in multiple-dose regimens, bringing the total study population to 120. The oral dosages were 0.25, 0.5, 0.75, 1, 1.25, 1.5, 2, or 2.5 mg/day for up to 30 days.

RESULTS

Pharmacodynamic response of roxifiban was clearly dose-dependent. Platelet aggregation inhibition in response to 10 micromol/L slope adenosine diphosphate was sustained throughout the study period (up to 1 month). No serious adverse events, including significant major bleeding events, were associated with roxifiban treatment. Minor bleeding was reported in 5% of participants in the placebo group (1 of 21 cases) versus 26% in the study group (26 of 99 cases). Incidence of minor bleeding associated with roxifiban 2 and 2.5 mg/day was significantly (p < or = 0.05) greater than that with placebo. Adverse events, including gastrointestinal disorders, platelet and clotting disorders, and urinary tract disorders, were observed in 1 of 21 cases (5%) in the placebo group and in 12 of 99 cases (12%) in the study group. Reversible thrombocytopenia without other complications developed in two patients.

CONCLUSIONS

Roxifiban-induced inhibition of platelet aggregation was dose-dependent and sustained throughout the study period: higher drug dosages correlated with higher levels of platelet inhibition and higher incidence of minor bleeding events. No serious adverse events were observed at any dosage. Thus, roxifiban appears to be a potent oral platelet GP IIb/IIIa receptor inhibitor that is clinically well-tolerated and deserves further study as a new treatment strategy in patients with chronic stable angina pectoris.

Brugada syndrome: a decade of progress

The Brugada syndrome has gained wide recognition throughout the world and today is believed to be responsible for 4% to 12% of all sudden deaths and approximately 20% of deaths in patients with structurally normal hearts. The incidence of the disease is on the order of 5 per 10 000 inhabitants and, apart from accidents, is the leading cause of death of men under the age of 50 in regions of the world where the inherited syndrome is endemic. This minireview briefly summarizes the progress made over the past decade in our understanding of the clinical, genetic, cellular, ionic, and molecular aspects of this disease.

False-negative and false-positive ECG diagnoses of Q wave myocardial infarction in the presence of right bundle-branch block

Right bundle-branch block (RBBB) has not traditionally been seen as an obstacle to ECG diagnosis of Q wave myocardial infarction (MI)--in clinical electrocardiography and vectorcardiography--because this conduction disturbance is not believed to cause significant alterations in the spatial orientation of initial excitation wavefronts. In the era of large-scale clinical trials, however, where serial ECG analysis is among the major diagnostic tools in MI classification, both false-positive and false-negative diagnoses of MI in the presence of RBBB have become increasingly evident. Because of the limited detectability of Q wave MI by ECG in the presence of RBBB, the electrocardiographic finding of Q wave MI should not be regarded as an independent diagnostic tool. It is best to utilize independent corroboration to establish the diagnosis of transmural infarction when RBBB is present. Further investigations are warranted to better delineate sensitivity, specificity, and predictive value of Q wave MI in the presence of RBBB.

Idiopathic short QT interval: a new clinical syndrome?

In this first clinical report of an idiopathic familial persistently short QT interval (QTI), we describe three members of one family (a 17-year-old female, her 21-year-old brother, and their 51-year-old mother) demonstrating this ECG phenomenon, associated in the 17-year-old with several episodes of paroxysmal atrial fibrillation requiring electrical cardioversion. Similar ECG changes seen in an unrelated 37-year-old patient were associated with sudden cardiac death. Our report also describes other manifestations of abnormal shortening of the QTI and considers the possible arrhythmogenic potential of the short QTI.

Exercise-induced ST segment elevation in Q wave leads in postinfarction patients: defining its meaning and utility in today's practice

Most attempts to identify qualitative and quantitative techniques for assessing myocardial viability and the likelihood of improved function after revascularization in patients with healed myocardial infarcts have focused on treatment strategies and prognosis. This review examines the true value of the electrocardiographic phenomenon of exercise-induced ST segment elevation (EISTE) in Q wave leads as a diagnostic tool for the assessment of myocardial viability. The prognostic potential and clinical utility of the EISTE phenomenon are inhibited both by the heart's electrophysiologic response to exercise-induced metabolic and hemodynamic changes, and by the ECG's limited facility in assessing myocardial preservation. The use of EISTE as an independent indicator for surgical intervention is proscribed by these limitations. The EISTE phenomenon could serve as a useful tool in the first line of discrimination in patients with healed Q wave myocardial infarction, and may justify further diagnostic work-up in patients under consideration for a revascularization procedure. In the era of sophisticated nuclear and echo techniques, accurate imaging studies should not be replaced by ECG analysis alone in the search for viable tissue, except when financial costs are of major importance.

Association between new electrocardiographic abnormalities after coronary revascularization and five-year cardiac mortality in BARI randomized and registry patients

There are few data comparing the relative frequency of new electrocardiographic (ECG) abnormalities after coronary artery bypass grafting (CABG) compared with percutaneous transluminal coronary angioplasty (PTCA) and their association with long-term cardiac mortality. The study population consisted of 3,373 patients who were either randomized or eligible to be randomized to CABG or PTCA in the BARI trial. The frequency of new postprocedural ECG abnormalities was significantly greater after a CABG procedure than after PTCA. The incidence of new postprocedural major Q waves, ST-segment elevation, and T-wave abnormalities were significantly more frequent after CABG. After PTCA (n = 1,869), the 5-year cardiac mortality rates associated with the new development of major Q waves, ST-segment elevation, ST-segment depression, T-wave abnormalities, or no abnormality was 18.1%, 8.5%, 8.9%, 6.0%, and 5.4%, respectively. After CABG (n = 1,427), 5-year cardiac mortality rates were 8.0%, 4.2%, 3.8%, 2.8%, and 3.7%, respectively. The adjusted relative risk of 5-year cardiac mortality for new Q-wave abnormalities was 2.6 after CABG (p <0.04) and 4.6 after PTCA (p <0.01). Thus, patients who undergo CABG have more postinitial procedural ECG abnormalities than patients who undergo PTCA. Cardiac mortality is significantly increased by the new development of postprocedural Minnesota code Q-wave abnormalities regardless of whether patients undergo CABG or PTCA.

Early repolarization syndrome: clinical characteristics and possible cellular and ionic mechanisms

Early repolarization syndrome (ERS) has traditionally been regarded as benign. In the electrocardiogram (ECG), it is characterized by a diffuse upward ST-segment concavity ending in a positive T wave in leads V2-V4 (5). Clinical interest in this ECG phenomenon has recently been rekindled because of similarities with the electrocardiographic manifestations of the highly arrhythmogenic Brugada syndrome and the potential for misdiagnosis. This article addresses the clinical characteristics and cellular and ionic basis for ERS. In experimental models, the ECG signature of ERS can be converted to that of the Brugada syndrome, raising the possibility that ERS may not be as benign as generally thought, and that under certain conditions known to predispose to ST-segment elevation, patients with ERS may be at greater risk. Further clinical and experimental data are clearly required to test these hypotheses, and the characteristics of ERS need to be more fully delineated within the framework of what has been learned about the Brugada syndrome in recent years.

Rapid ventricular repolarization in rodents: electrocardiographic manifestations, molecular mechanisms, and clinical insights

This article examines specific electrocardiographic (ECG) and electrophysiological features of ventricular repolarization in rats and mice, and the role of depolarization-activated potassium currents in mediating the unique features of ECG recordings in these rodents. This article describes the currents that underlie ventricular repolarization in these rodents, identifies terminology that appropriately describes the unique features of murine ECG recordings, and correlates these unique findings with selected human ECG ventricular repolarization abnormalities. The absence of a distinct isoelectric interval between the QRS complex and the T wave, accompanied by a relatively short QT interval, are common features of ECG recordings in mice and rats, but not in ECGs in guinea pigs. The murine ECG morphology is apparently attributable to the presence of large outward K+ currents that dominate the early phase of ventricular repolarization. In rats and mice, the predominant current underlying the early phase of repolarization appears to be the rapidly activating and inactivating 4-aminopyridine-sensitive transient outward current (ie, I(to)). Importantly, the density of I(to) in rats and mice is high, whereas this current is not evident in the ventricular myocytes of guinea pigs. The high density of I(to) appears to underlie the prominent J wave or downsloping ST-segment elevation seen in rats and mice, whereas the ST-segment is isoelectric in guinea pigs. The unusual J wave and ST-segment pattern in murine ECGs, however, does bear some resemblance to ECG features observed in humans with Brugada syndrome, and with hypothermia and ischemia. These patterns in rats and mice might, therefore, serve as an experimental model for the idiopathic J wave.

Right bundle branch block as a cause of false-negative ECG classification of inferior myocardial infarction

It is generally accepted in clinical electrocardiography that a right bundle branch block (RBBB) does not interfere with the electrocardiographic (ECG) diagnosis of myocardial infarction (MI). The basic assumption is that the initial excitation wavefronts are relatively unchanged in RBBB. This study compared serial changes in Q wave duration in inferior leads II, III, and aVF in 9 patients who developed RBBB within 3 weeks after myocardial revascularization procedure (RBBB group) and in 41 revascularized patients without RBBB in the same observation period (control group). Q wave durations in the electrocardiograms obtained before the patients' procedures were not significantly different between the study and control groups. However, Q wave durations shortened significantly more in the RBBB group than in the control group. The most pronounced Q wave duration shortening took place in lead aVF, -18.2 ms in the RBBB group versus -3.8 ms in the control group (P = .0001). The shortening was less pronounced, although significant, in leads II and III: II, -7.6 +/- -10.9 ms in the RBBB group vs -2.3 +/- -3.5 ms in the control group (P = .01); III, -11.3 +/- -10.5 ms vs -2.6 +/- -6.5 ms (P = .002); aVF, -18.2 +/- -13.5 ms vs -3.8 +/- -5.3 ms (P < .0001). It is concluded that incident RBBB complicating revascularization procedures may cause significant alterations in spatial orientation of the initial excitation wavefronts. This may be a potential source of false-negative ECG diagnosis of inferior MI, particularly in clinical trials where serial ECG analysis is an important part in MI classification.

The Brugada syndrome: clinical, electrophysiologic and genetic aspects

This review deals with the clinical, basic and genetic aspects of a recently highlighted form of idiopathic ventricular fibrillation known as the Brugada syndrome. Our primary objective in this review is to identify the full scope of the syndrome and attempt to correlate the electrocardiographic manifestations of the Brugada syndrome with cellular and ionic heterogeneity known to exist within the heart under normal and pathophysiologic conditions so as to identify the cellular basis and thus potential diagnostic and therapeutic approaches. The available data suggest that the Brugada syndrome is a primary electrical disease resulting in abnormal electrophysiologic activity in right ventricular epicardium. Recent genetic data linking the Brugada syndrome to an ion channel gene mutation (SCN5A) provides further support for the hypothesis. The electrocardiographic manifestations of the Brugada syndrome show transient normalization in many patients, but can be unmasked using sodium channel blockers such as flecainide, ajmaline or procainamide, thus identifying patients at risk. The available data suggest that loss of the action potential dome in right ventricular epicardium but not endocardium underlies the ST segment elevation seen in the Brugada syndrome and that electrical heterogeneity within right ventricular epicardium leads to the development of closely coupled premature ventricular contractions via a phase 2 reentrant mechanism that then precipitates ventricular tachycardia/ventricular fibrillation (VT/VF). Currently, implantable cardiac defibrillator implantation is the only proven effective therapy in preventing sudden death in patients with the Brugada syndrome and is indicated in symptomatic patients and should be considered in asymptomatic patients in whom VT/VF is inducible at time of electrophysiologic study.