摘要:

Identifying patients at high risk of sudden cardiac death is an important goal, given the magnitude of this problem. In this regard, T wave alternans (TWA) is a heart-rate–dependent measure of arrhythmia vulnerability. The predictive accuracy of this test is maximal at heart rates between 100 and 120 bpm, which are usually achieved with exercise or atrial pacing. TWA has been shown to predict inducibility of ventricular tachycardia with programmed stimulation and to predict spontaneous arrhythmic events. This test has been applied to diverse populations, including patients with coronary artery disease, nonischemic cardiomyopathy, congestive heart failure, and status post implantable defibrillators. Despite these encouraging results, the role of TWA to guide clinical therapy still must be better elucidated.

ISSN:0268-4705    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

ACE-inhibitors (ACE-I) represent effective drugs more and more widely used in acute myocardial infarction (AMI) patients, in post AMI patients and mainly, today, in CHF patients.A complete review of the scientific literature and of all the randomized controlled clinical trials (RCTs), where ACE-I have been tested directly or in association with other drugs, have been performed. ACE-I effects on total mortality (TM) and arrhythmic mortality (AM) and other composite clinical endpoints have been evaluated.It is well known that frequent ventricular arrhythmias (VA) and a high incidence of sudden death (SD) can be documented in CHF patients; nevertheless a direct relationship between VA, TM, and AM has not been clearly demonstrated; neither beneficial effects, on the same endpoints, of the treatment and suppression of ambient VA in CHF. Conversely, sometimes clear negative effects on both TM and AM have been observed.According to individual studies and two recent complete and large metanalysis, ACE-I were unable to reduce AM, but they reduced TM. Furthermore, they can affect and modify many, if not all, of the triggering factors of VA and SD in this context.Differently from ACE-I, betablockers (BB) have been clearly associated with a reduction in TM and AM, in the same context. Thus, at present time, ACE-I, with or without BB, should be considered the standard therapy in all patients with CHF, if not contraindicated.Angiotensin II antagonists (AII-a) probably represent a comparably effective treatment, in all CHF patients and mainly in those patients, suffering from side effects or showing intolerance to ACE-I, but we are still lacking definitive data from RCTs.In many RCTs, conducted with traditional antiarrhythmic drug therapy (ADT), these drugs have been widely used, contributing probably, in a consistent way, to some of the positive results of these studies. All primary and some secondary implantable defibrillators (ICD) RCTs, in the prevention of SD, have included these drugs as the standard treatment of the underlying cardiac disease, with or without CHF. The same therapeutical strategy is regularly applied in all biventricular pacing (BP) RCTs, with or without the ICD. These trials are supposed to assess the reduction in TM and AM, preventing deterioration or progression of CHF and improving the quality of the patients' s life.Finally, according to these clinical evidences, in the last part of the review, we stress the need for a more widespread implementation of ACE-I and AII-a in treating CHF patients.

ISSN:0268-4705    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

The Brugada syndrome describes a subgroup of patients at risk for the occurrence of ventricular fibrillation who have no definable structural heart disease associated with a right bundle branch block conduction pattern and ST-segment elevation in the right precordial leads. This syndrome is caused by genetic defects in the alpha subunit of the sodium channel. This defect causes a reduction in the sodium channel current, which accentuates the epicardial action potential notch leading to ST-segment elevation. Sodium channel blockers can potentiate these findings and screen for patients with intermittent baseline electrocardiographic findings. Because of the poor prognosis of such patients, symptomatic patients should be treated with an implantable cardioverter-defibrillator.

ISSN:0268-4705    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Implantable cardioverter defibrillators (ICDs) have become an important therapeutic modality for patients who have had a cardiac arrest or are at risk for life-threatening ventricular arrhythmias. Clinical trials have confirmed the role of the ICD for patients with sustained ventricular arrhythmias and have expanded the indications to include patients with coronary artery disease, left ventricular dysfunction, nonsustained ventricular tachycardia, and inducible ventricular tachycardia. Numerous technologic advances in ICDs have resulted in decreased size, greater ease of placement, and increased functionality. Important advancements have been made in the effectiveness of arrhythmia classification and electrogram storage. Dual-chamber ICDs have become increasingly sophisticated with rate-adaptive sensors. Biventricular pacing is being combined with ICD function in patients with heart failure, systolic dysfunction, and QRS widening. Future advances in devices will likely lead to improved arrhythmia classification, more advanced automated features, and additional features including more sophisticated sensors and biventricular pacing systems.

ISSN:0268-4705    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

The implantable cardioverter defibrillator (ICD) has been in clinical use for 20 years and its clinical role is becoming increasingly clear. A number of well-designed trials demonstrated its effectiveness in high-risk patients who have already experienced a malignant arrhythmia. A more controversial role for the ICD is in patients who are at high risk but have not yet had an arrhythmic event. Randomized clinical trials published in the late 1990s demonstrated survival benefit with the ICD in narrowly defined high-risk populations. These populations are presently defined by a low ejection fraction and inducible ventricular tachyarrhythmia. Clinical trials still in progress will determine whether broader populations will benefit from prophylactic ICD implantation. These trials will have broad clinical importance.

ISSN:0268-4705    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Recent studies of the molecular basis of the long QT syndrome (LQTS) have advanced our understanding of the mechanisms responsible for the abnormal prolongation of ventricular repolarization and revealed associations between LQTS and other primary electrical diseases of the heart such as Brugada syndrome. The role of DNA single nucleotide polymorphisms in acquired LQTS and differences between the Romano-Ward and Jervell-Lange-Nielsen forms of congenital LQTS are gradually coming into focus. In this brief review, our goal is to summarize the molecular mechanisms proposed to underlie the susceptibility to arrhythmias in LQTS and discuss the direction of current and future research.

ISSN:0268-4705    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

QT prolongation is commonly associated with life-threatening torsade de pointes arrhythmias that develop as a consequence of the amplification of electrical heterogeneities intrinsic to the ventricular myocardium. These heterogeneities exist because of differences in the time course of repolarization of the three predominant cell types that make up the ventricular myocardium, giving rise to transmural voltage gradients and a dispersion of repolarization responsible for the inscription of the electrocardiographic T wave. Agents and conditions that reduce net repolarizing current amplify the intrinsic spatial dispersion of repolarization, thus creating the substrate for the development of re-entry. The result is a prolongation of the QT interval, abnormal T waves, and development of polymorphic re-entrant ventricular tachycardia displaying characteristics of torsades de pointes. These conditions also predispose M cells and Purkinje fibers to develop early afterdepolarization–induced extrasystoles, which are thought to trigger episodes of torsades de pointes. Agents that prolong the QT interval but do not increase transmural dispersion of repolarization are not capable of inducing torsades de pointes. The available data suggest that that the principal problem with the long QT syndrome is not long QT intervals but rather the dispersion of repolarization that often accompanies prolongation of the QT interval.

ISSN:0268-4705    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Atrial fibrillation (AF) is a heterogeneous disorder; its management must be individualized depending upon the mode of presentation, underlying substrate, and need for either rate or rhythm control. In hemodynamically unstable patients with new onset AF, conversion by electrical cardioversion is the preferred approach; however, in stable patients pharmacological options may be considered. Recurrence rate after conversion is high in the majority of patients, necessitating the use of antiarrhythmic agents. Because of modest efficacy and potential for untoward effects, various nonpharmacologic approaches are being explored. Some of these modalities are considered curative in the short-term but techniques are still being refined.

ISSN:0268-4705    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Catheter ablation has evolved from an experimental technique to first-line therapy for the treatment of atrial flutter. Atrial flutter is characterized by a macroreentrant atrial tachycardia circuit. Successful ablation of atrial flutter involves (1) mapping the atrial flutter to define the conduction zones within the re-entrant circuit to determine whether the atrial flutter is isthmus-dependent, non–isthmus-dependent, or atypical; (2) interrupting the atrial flutter macroreentrant circuit with an ablation catheter by creating either focal or linear lesions within a critical zone of slow conduction that extends to anatomical borders; and (3) terminating the tachycardia and demonstrating conduction block within the atrial flutter circuit after ablation. This update discusses the classification schemes of atrial flutter and macroreentrant atrial tachycardias, reviews the technique of radiofrequency catheter ablation, and highlights recent ablation approaches for atrial flutters and macroreentrant atrial tachycardias.

ISSN:0268-4705    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Assessment of the timing of electrical activation recorded by multiple electrodes positioned in various locations within the heart has been the conventional method for mapping cardiac arrhythmias. This technique requires fluoroscopy for catheter manipulation, which in addition to being harmful (ionizing radiation), is inadequate for visualizing the complex three-dimensional cardiac anatomy and lacks reproducibility regarding localization of sites of interest. Because of these limitations, several new mapping systems that can function in a complimentary role to the conventional mapping technique, or can be used independently, have been developed. These new mapping strategies have unique advantages. They overcome the limitations of fluoroscopy by creating accurate three-dimensional intracardiac maps. The ability to localize and accurately display intracardiac catheter positioning and ablation lesion sites facilitate increasingly complex catheter ablation procedures.

ISSN:0268-4705    

出版商:OVID    

年代:2002

数据来源: OVID