Ventricular fibrillation causes more than 300,000 sudden deaths each year in the USA alone. In approximately 5-12% of these cases, there are no demonstrable cardiac or non-cardiac causes to account for the episode, which is therefore classified as idiopathic ventricular fibrillation (IVF). A distinct group of IVF patients has been found to present with a characteristic electrocardiographic pattern. Because of the small size of most pedigrees and the high incidence of sudden death, however, molecular genetic studies of IVF have not yet been done. Because IVF causes cardiac rhythm disturbance, we investigated whether malfunction of ion channels could cause the disorder by studying mutations in the cardiac sodium channel gene SCN5A. We have now identified a missense mutation, a splice-donor mutation, and a frameshift mutation in the coding region of SCN5A in three IVF families. We show that sodium channels with the missense mutation recover from inactivation more rapidly than normal and that the frameshift mutation causes the sodium channel to be non-functional. Our results indicate that mutations in cardiac ion-channel genes contribute to the risk of developing IVF.

Abstract-Classifications of heart muscle diseases have proved to be exceedingly complex and in many respects contradictory. Indeed, the precise language used to describe these diseases is profoundly important. A new contemporary and rigorous classification of cardiomyopathies (with definitions) is proposed here. This reference document affords an important framework and measure of clarity to this heterogeneous group of diseases. Of particular note, the present classification scheme recognizes the rapid evolution of molecular genetics in cardiology, as well as the introduction of several recently described diseases, and is unique in that it incorporates ion channelopathies as a primary cardiomyopathy.

Background-The Brugada syndrome is characterized by marked ST-segment elevation in the right precordial ECG leads and is associated with a high incidence of sudden and unexpected arrhythmic death. Our study examines the cellular basis for this syndrome. Methods and Results-Using arterially perfused wedges of canine right ventricle (RV), we simultaneously recorded transmembrane action potentials from 2 epicardial and 1 endocardial sites, together with unipolar electrograms and a transmural ECG. Loss of the action potential dome in epicardium but not endocardium after exposure to pinacidil (2 to 5 mol/L), a K ϩ channel opener, or the combination of a Na ϩ channel blocker (flecainide, 7 mol/L) and acetylcholine (ACh, 2 to 3 mol/L) resulted in an abbreviation of epicardial response and a transmural dispersion of repolarization, which caused an ST-segment elevation in the ECG. ACh facilitated loss of the action potential dome, whereas isoproterenol (0.1 to 1 mol/L) restored the epicardial dome, thus reducing or eliminating the ST-segment elevation. Heterogeneous loss of the dome caused a marked dispersion of repolarization within the epicardium and transmurally, thus giving rise to phase 2 reentrant extrasystole, which precipitated ventricular tachycardia (VT) and ventricular fibrillation (VF). Transient outward current (I to ) block with 4-aminopyridine (1 to 2 mmol/L) or quinidine (5 mol/L) restored the dome, normalized the ST segment, and prevented VT/VF. Conclusions-Depression or loss of the action potential dome in RV epicardium creates a transmural voltage gradient that may be responsible for the ST-segment elevation observed in the Brugada syndrome and other syndromes exhibiting similar ECG manifestations. Our results also demonstrate that extrasystolic activity due to phase 2 reentry can arise in the intact wall of the canine RV and serve as the trigger for VT/VF. Our data point to I to block (4-aminopyridine, quinidine) as an effective pharmacological treatment. (Circulation. 1999;100:1660-1666.)

Abstract-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, ␣-adrenergic agonists, ␤-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.

Background-Cardiac ion channelopathies are responsible for an ever-increasing number and diversity of familial cardiac arrhythmia syndromes. We describe a new clinical entity that consists of an ST-segment elevation in the right precordial ECG leads, a shorter-than-normal QT interval, and a history of sudden cardiac death. Methods and Results-Eighty-two consecutive probands with Brugada syndrome were screened for ion channel gene mutations with direct sequencing. Site-directed mutagenesis was performed, and CHO-K1 cells were cotransfected with cDNAs encoding wild-type or mutant CACNB2b (Ca v␤2b ), CACNA2D1 (Ca v␣2␦1 ), and CACNA1C tagged with enhanced yellow fluorescent protein (Ca v 1.2). Whole-cell patch-clamp studies were performed after 48 to 72 hours. Three probands displaying ST-segment elevation and corrected QT intervals Յ360 ms had mutations in genes encoding the cardiac L-type calcium channel. Corrected QT ranged from 330 to 370 ms among probands and clinically affected family members. Rate adaptation of QT interval was reduced. Quinidine normalized the QT interval and prevented stimulation-induced ventricular tachycardia. Genetic and heterologous expression studies revealed loss-of-function missense mutations in CACNA1C (A39V and G490R) and CACNB2 (S481L) encoding the ␣ 1 -and ␤ 2b -subunits of the L-type calcium channel. Confocal microscopy revealed a defect in trafficking of A39V Ca v 1.2 channels but normal trafficking of channels containing G490R Ca v 1.2 or S481L Ca v␤2b -subunits. Conclusions-This is the first report of loss-of-function mutations in genes encoding the cardiac L-type calcium channel to be associated with a familial sudden cardiac death syndrome in which a Brugada syndrome phenotype is combined with shorter-than-normal QT intervals. Key Words: arrhythmia Ⅲ genetics Ⅲ electrophysiology Ⅲ tachycardia Ⅲ fibrillation C ardiac arrhythmias are responsible for an estimated 1 million cases of syncope and sudden cardiac death (SCD) among Europeans and Americans each year. 1 Cardiac arrhythmias can be acquired as a consequence of coronary heart disease or may be secondary to familial or inherited syndromes. The past decade has witnessed an explosion of information linking cardiac ion channel mutations with a wide variety of inherited arrhythmia syndromes. 2 The long-QT syndrome has been associated with 10 different Clinical Perspective p 449genes, in large part owing to the pioneering studies of Keating and coworkers. The LQT8 form of long-QT syndrome, also known as Timothy syndrome, is associated with gain-offunction mutations in cardiac calcium channel activity. 3,4 The cardiac L-type calcium channel is a protein complex formed by at least 3 subunits, ␣ 1 , ␤, and ␣ 2␦ . The pore-forming Ca v 1. subunit, encoded by CACNB2b, modulates calcium channel activity in the human heart and enables trafficking by suppressing an endoplasmic reticulum retention signal in the I-II loop of the ␣ 1 -subunit. 5 The short-QT syndrome (SQTS), a clinical entity first described in 2000,6 has been associated ...