Prominent J wave and ST segment elevation: serial electrocardiographic changes in accidental hypothermia

J wave syndromes: What's new?

Among the inherited ion channelopathies associated with potentially life-threatening ventricular arrhythmia syndromes in nominally structurally normal hearts are the J wave syndromes, which include the Brugada (BrS) and early repolarization (ERS) syndromes. These ion channelopathies are responsible for sudden cardiac death (SCD), most often in young adults in the third and fourth decade of life. Our principal goal in this review is to briefly outline the clinical characteristics, as well as the molecular, ionic, cellular, and genetic mechanisms underlying these primary electrical diseases that have challenged the cardiology community over the past two decades. In addition, we discuss our recently developed whole-heart experimental model of BrS, providing compelling evidence in support of the repolarization hypothesis for the BrS phenotype as well as novel findings demonstrating that voltage-gated sodium and transient outward current channels can modulate each other's function via trafficking and gating mechanisms with implications for improved understanding of the genetics of both cardiac and neuronal syndromes.

J wave syndromes as a cause of malignant cardiac arrhythmias

The J wave syndromes, including the Brugada (BrS) and early repolarization (ERS) syndromes, are characterized by the manifestation of prominent J waves in the electrocardiogram appearing as an ST segment elevation and the development of life-threatening cardiac arrhythmias. BrS and ERS differ with respect to the magnitude and lead location of abnormal J waves and are thought to represent a continuous spectrum of phenotypic expression termed J wave syndromes. Despite over 25 years of intensive research, risk stratification and the approach to therapy of these two inherited cardiac arrhythmia syndromes are still rapidly evolving. Our objective in this review is to provide an integrated synopsis of the clinical characteristics, risk stratifiers, as well as the molecular, ionic, cellular, and genetic mechanisms underlying these two syndromes that have captured the interest and attention of the cardiology community over the past two decades.

Drug-induced fatal arrhythmias: Acquired long QT and Brugada syndromes

Since the early 1990s, the concept of primary "inherited" arrhythmia syndromes or ion channelopathies has evolved rapidly as a result of revolutionary progresses made in molecular genetics. Alterations in genes coding for membrane proteins such as ion channels or their associated proteins responsible for the generation of cardiac action potentials (AP) have been shown to cause specific malfunctions which eventually lead to cardiac arrhythmias. These arrhythmic disorders include congenital long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, short QT syndrome, progressive cardiac conduction disease, etc. Among these, long QT and Brugada syndromes are the most extensively studied, and drugs cause a phenocopy of these two diseases. To date, more than 10 different genes have been reported to be responsible for each syndrome. More recently, it was recognized that long QT syndrome can be latent, even in the presence of an unequivocally pathogenic mutation (silent mutation carrier). Co-existence of other pathological conditions in these silent mutation carriers may trigger a malignant form of ventricular arrhythmia, the so called torsade de pointes (TdP) that is most commonly brought about by drugs. In analogy to the drug-induced long QT syndrome, Brugada type 1 ECG can also be induced or unmasked by a wide variety of drugs and pathological conditions; so physicians may encounter patients with a latent form of Brugada syndrome. Of particular note, Brugada syndrome is frequently associated with atrial fibrillation whose therapeutic agents such as Vaughan Williams class IC drugs can unmask the dormant and asymptomatic Brugada syndrome. This review describes two types of drug-induced arrhythmias: the long QT and Brugada syndromes.

Unusual U wave induced by reconstructed retrosternal esophagus

The present case shows that a broad compression of the right ventricle by the reconstructed stomach tube after esophagus cancer surgery induced an abnormal U wave. When facing an abnormal ECG, we should keep in mind of the mechanical compression to the heart as a differential diagnosis.

Electrocardiographic changes in hypothermia: a review

Hypothermia is a common environmental emergency encountered by physicians and is associated with a variety of electrocardiographic (ECG) abnormalities. The classic and well-known ECG manifestations of hypothermia include the presence of J (Osborn) waves, interval (PR, QRS, QT) prolongation, and atrial and ventricular arrhythmias. There are less well defined and known ECG signs of hypothermia, which in fact may simulate findings of acute coronary ischemia, Brugada syndrome, or even pericarditis. Although classical ECG changes seen in hypothermia certainly serve as an important clinical clue for prompt identification and management of this easily curable life-threatening entity, physicians should, however, be able to maintain a high suspicion for recognition and differentiation of less common ECG abnormalities encountered in hypothermia. This article aims to provide a detailed review of all the potential ECG abnormalities that may be encountered in accidental and iatrogenic hypothermia.

Hypothermia masquerading as pericarditis: an unusual electrocardiographic analogy

Hypothermia is one of the most common environmental emergencies encountered by physicians that can be associated with a variety of electrocardiographic (ECG) abnormalities. The classic and well-known ECG manifestations of hypothermia include the presence of J (Osborne) waves, interval (PR, QRS, QT) prolongation, varied T-wave abnormalities, and atrial and ventricular arrhythmias. There are less well-defined and known ECG signs of hypothermia that, in fact, may simulate findings of acute coronary ischemia. We describe a case of hypothermia with associated ECG findings mimicking pericarditis. Especially interesting was the challenging presentation and several associated important learning points. Herewith, we also discuss some important ECG and clinical factors that may be used in differentiating the genesis of ST elevations.

Diffuse ST segment depression from hypothermia

Hypothermia is known to cause specific electrocardiographic (EKG) changes such as Osborne waves and bradycardia. We report diffuse ST segment depression, an atypical EKG change, in a patient with a core temperature of 29.4°C (85°F). This patient had no previous cardiovascular pathology, and his EKG changes resolved gradually with aggressive warming. We also discuss the pathophysiology and clinical significance of ST depression in the general population and the typical EKG changes in hypothermia patients.

Hypothermia-induced Brugada-like electrocardiogram pattern

A patient in whom moderate hypothermia developed after prolonged cardiopulmonary resuscitation is described. Hypothermia was manifested by transient electrocardiogram changes, including long QT, precordial J waves, and downsloping ST-segment elevation ending in a negative T wave in leads V(1) and V(2) resembling the Brugada syndrome. The physiopathologic mechanisms of these electrocardiographic findings are discussed.

Brugada Syndrome Unmasked by Accidental Inhalation of Gasoline Vapors

Loss-of-function mutations in the gene SCN5A can cause Brugada syndrome (BrS), which is an inherited form of idiopathic ventricular fibrillation. We report the case of a 46-year-old patient, with no previous medical history, who had ventricular fibrillation after accidental inhalation of gasoline vapors. His electrocardiogram (ECG) showed a typical type-1 BrS pattern that persisted after the acute event. Genetic investigations allowed the identification of a novel SCN5A mutation leading to a frame-shift and early termination of the channel protein. Biochemical and cellular electrophysiology experiments confirmed the loss-of-function of the mutant allele. The patient was implanted with a cardioverter/defibrillator.

Brugada syndrome

First introduced as a new clinical entity in 1992, the Brugada syndrome is associated with a relatively high risk of sudden death in young adults, and occasionally in children and infants. Recent years have witnessed a striking proliferation of papers dealing with the clinical and basic aspects of the disease. Characterized by a coved-type ST-segment elevation in the right precordial leads of the electrocardiogram (ECG), the Brugada syndrome has a genetic basis that thus far has been linked only to mutations in SCN5A, the gene that encodes the alpha-subunit of the sodium channel. The Brugada ECG is often concealed, but can be unmasked or modulated by a number of drugs and pathophysiological states including sodium channel blockers, a febrile state, vagotonic agents, tricyclic antidepressants, as well as cocaine and propranolol intoxication. Average age at the time of initial diagnosis or sudden death is 40 +/- 22, with the youngest patient diagnosed at 2 days of age and the oldest at 84 years. This review provides an overview of the clinical, genetic, molecular, and cellular aspects of the Brugada syndrome, incorporating the results of two recent consensus conferences. Controversies with regard to risk stratification and newly proposed pharmacologic strategies are discussed.

Mechanisms of disease: current understanding and future challenges in Brugada syndrome

Brugada syndrome is a clinical entity characterized by ST-segment elevation in the right precordial leads (V1-V3) and an episode of ventricular fibrillation in the absence of structural heart disease. Data regarding genotype-phenotype relationships are limited, since SCN5A, the gene encoding the a subunit of the sodium channel, is as yet the only gene linked to Brugada syndrome. Studies of SCN5A mutations responsible for the Brugada phenotype have shown the presence of functional defects in the sodium-channel current. Experimental studies employing arterially perfused right-ventricular wedge preparations have elucidated cellular mechanisms for this phenotype. Data indicate that an accentuated action-potential notch, mediated by a prominent transient outward current and loss of the action-potential dome in the epicardium (but not in the endocardium) of the right ventricle give rise to a transmural voltage gradient, resulting in ST-segment elevation and the induction of ventricular fibrillation. On the basis of cellular mechanisms, it might be possible to normalize the Brugada phenotype by use of therapeutic agents or interventions that decrease net outward currents by decreasing the transient outward current or outward potassium currents, or increasing the L-type inward calcium current or fast sodium current. Interventions that increase net outward currents through raising the transient outward current or outward potassium currents or decreasing the L-type inward calcium current or fast sodium current might aggravate or unmask the Brugada phenotype, resulting in an acquired form of this syndrome. In this review, we discuss future challenges relating to risk stratification, genetic heterogeneity, sex and ethnic differences in Brugada syndrome.

Acquired forms of the Brugada syndrome

The Brugada syndrome is characterized by ST-segment elevation in the right precordial leads (V1 through V3) and an episode of ventricular fibrillation in the absence of structural heart disease. SCN5A, the gene encoding the alpha subunit of the sodium channel, is the only gene thus far linked to the Brugada syndrome but is identified in only 18% to 30% of patients with clinically diagnosed Brugada syndrome. On the other hand, experimental studies have suggested that an intrinsically prominent transient outward current-mediated action potential (AP) notch and a subsequent loss of the AP dome in the epicardium but not in the endocardium of the right ventricular outflow tract give rise to a transmural voltage gradient, resulting in ST-segment elevation and phase 2 reentry-induced ventricular fibrillation. Therefore, any intervention that increases outward currents (eg, transient outward current, adenosine triphosphate-sensitive potassium current, delayed modifier potassium current) or decreases inward currents (eg, L-type calcium current, fast sodium current) at the end of phase 1 of the AP can accentuate or unmask ST-segment elevation, similar to that found in the Brugada syndrome, thus producing acquired forms of the Brugada syndrome. In this review, several drugs in addition to sodium-channel blockers and conditions that induce transient ST-segment elevation such as that in the Brugada syndrome, developing acquired forms of the Brugada syndrome, are discussed.

Heritability and a genome-wide linkage scan for arterial stiffness, wave reflection, and mean arterial pressure: the Framingham Heart Study

BACKGROUND

Arterial stiffness and mean arterial pressure variably contribute to systolic hypertension and increased cardiovascular risk. However, few prior community-based studies have evaluated the genetics of arterial stiffness and separate mean and pulsatile components of blood pressure.

METHODS AND RESULTS

Using arterial tonometry, we evaluated heritability and linkage of forward and reflected wave amplitude, mean arterial pressure, and carotid-femoral pulse wave velocity (CFPWV) in 1480 participants representing 817 pedigrees in the Framingham Study offspring cohort. In 204 families with tonometry data, a genome-wide scan was performed with microsatellite markers that covered the genome at 10-cM intervals. Heritability estimates were moderate for reflected wave amplitude (h2=0.48), forward wave amplitude (h2=0.21), CFPWV (h2=0.40), and mean arterial pressure (h2=0.33). Variance components linkage analysis identified 2 regions of linkage for reflected wave amplitude: chromosome 4 at 181 cM (logarithm of odds [LOD]=4.93, permuted P=0.002) and chromosome 8 at 33 cM (LOD=3.27, permuted P=0.058). There was 1 region of linkage for forward wave amplitude on chromosome 7 at 174 cM (LOD=2.88, permuted P=0.017). There were several regions of suggestive linkage for CFPWV: chromosome 2 at 94 cM (LOD=2.46), chromosome 7 at 29 cM (LOD=2.50), chromosome 13 at 108 cm (LOD=2.10), and chromosome 15 at 108 cM (LOD=2.48). There was 1 region of suggestive linkage for mean arterial pressure on chromosome 1 at 192 cM (LOD=2.18).

CONCLUSIONS

Arterial stiffness measures and mean and pulsatile components of blood pressure are heritable and appear to have genetic determinants that may be linked to separate genetic loci in humans.

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.

Brugada syndrome: from cell to bedside

Since its introduction as a new clinical entity in 1992, the Brugada syndrome has attracted great interest because of its high incidence in many parts of the world and its association with high risk for sudden death in infants, children, and young adults. Recent years have witnessed an exponential rise in the number of reported cases and a striking proliferation of articles serving to define the clinical, genetic, cellular, ionic, and molecular aspects of the disease. A consensus report published in 2002 delineated diagnostic criteria for the syndrome. A second consensus conference was held in September 2003. This review provides an in-depth overview of the clinical, genetic, molecular, and cellular aspects of the Brugada syndrome, incorporating the results of the two consensus conferences, and the numerous clinical and basic publications on the subject. The proposed terminology, diagnostic criteria, risk stratification schemes, and device and pharmacologic approach to therapy discussed are based on available clinical and basic studies and should be considered a work-in-progress that will without doubt require fine-tuning as confirmatory data from molecular studies and prospective trials become available.