ISSN:0268-4705    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The properties of cardiac impulse propagation are governed largely by the interplay of cellular depolarization, repolarization, cellular excitability, and myocardial tissue anisotropy. During the last decade, the introduction of the patch-clamp technique, which allows recording of ionic current flow through a single ion channel, provided insight into the mechanism of depolarization and repolarization in various cardiac cell types. The culmination of work in the field of molecular biology led to the cloning and functional expression of ion channel proteins. It is now possible to introduce systematic changes in ion channel protein structure to study the structure-function relationship and antiarrhythmic drug-binding sites on the ion channel. Such specific alterations in ion channel protein structure may help in the design of drugs with specific binding properties to suit a given clinical goal (arrhythmia management or suppression or both). However, it must be remembered that the phenomenon of arrhythmia suppression must ultimately be studied at the tissue (multicellular) level, because tissue models are the only practical means to evaluate and appreciate the interaction of depolarization and repolarization in impulse propagation. Hopefully, during the next decade, information coming from the two different approaches (molecular versus tissue) can be integrated to provide insight to various mechanisms of arrhythmia suppression or arrhythmia aggravation (proarrythmia) or both.

ISSN:0268-4705    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Pharmacologic therapy of cardiac arrhythmias remains in a state of considerable flux. New findings from relevant experimental models, controlled clinical trials, and meta-analyses of randomized clinical trials need to be integrated into appropriate algorithms for the control of ventricular and supraventricular tachyarrhythmias. The Cardiac Arrhythmia Suppression Trial I drew attention to the fact that certain sodium-channel blockers (class Ic agents) were powerful premature ventricular contraction suppressants but produced an excess mortality in survivors of acute infarction, raising the issue whether the premature ventricular contraction hypothesis was valid. Its validity is further challenged by the results of the Cardiac Arrhythmia Suppression Trial II with moricizine, which also increased mortality although it differs electrophysiologically from class Ic agents. From meta-analytic studies, it has become clear that most, if not all, sodium-channel blockers increase mortality given the appropriate clinical milieu. In contrast, controlled and uncontrolled clinical trials have indicated that in different subsets of patients, β-blockers reduce sudden death and total cardiac mortality. Data also suggest that a reduction in sudden death might be effected by amiodarone and possibly by sotalol, both of which act by lengthening repolarization and refractoriness, properties modified by, sympathetic modulation. The role of sympathetic modulation may now be determined with studies involving pure class III agents. Preliminary data from the Electrophysiologic Study versus Electrocardiographic Monitoring trial in manifest ventricular tachycardia and aborted sudden death indicated that the two techniques were statistically indistinguishable in predicting drug responses and that sotalol was significantly-superior to class I agents in reducing arrhythmia recurrence in responders. The emerging data again emphasize the need for a major reorientation in our approach to antiarrhythmic therapy, taking cognizance of sudden death and mortality as endpoints and not merely surrogate endpoints and risk markers for guiding treatment. Such a reorientation of antiarrhythmic therapy with drugs should shift attention away from the concept of delaying conduction to that of prolonging refractoriness, with a focus on β-blockers and class III agents that have antiadrenergic properties, such as sotalol and amiodarone.

ISSN:0268-4705    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The symptom most frequently requiring investigation and consideration for cardiac pacing is syncope. This symptom is now receiving more attention than ever, mainly because of the advent of tilt table testing—a simple noninvasive procedure that has substantially reduced the number of syncopal patients remaining undiagnosed. The first part of this review addresses developments in the understanding of syncope, and the latter part covers developments in the understanding and therapy of atrioventricular block and sinus node disease, the management of carotid sinus syndrome, and two possible new indications for pacemaker therapy.

ISSN:0268-4705    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Technology for pacemakers and automatic implantable defibrillators continues to evolve. Emphasis is placed not only on preventing cardiac death, but also on improving symptoms and quality of life. The basic antibradycardia function of pacemakers is complemented by highly sophisticated rate-responsive capabilities. The search for the perfect physiologic sensor has not ended; potential limitations of the systems currently available are considered in this review. Reports on outcome with pacing in different populations are also discussed. There have been two important advances in automatic implantable defibrillators. One is the introduction of the third generation defibrillator in clinical investigation. A tiered therapy (including antitachycardia pacing, cardioversion, and defibrillation) can now be programmed in the same device, with the protection of back-up antibradycardia pacing. The other remarkable innovation is the expanding use of nonthoracotomy techniques for implantable cardioverter-defibrillator placement. This approach permits the avoidance of a subcutaneous patch electrode in some cases, the system being entirely transvenous. Finally, recent insights on external cardioversion for atrial arrhythmias are briefly reviewed.

ISSN:0268-4705    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Low-amplitude, high frequency components in the terminal QRS-complex (so-called late potentials) are thought to arise from diseased myocardial tissue that forms the “electrophysiologic substrate” for ventricular tachyarrhythmias. Recording of late potentials is now commercially available in several systems and may possibly become clinically routine in the near future. Increased attention has been given recently to heart rate variability as an indicator of conditions of the autonomic nervous system that might trigger ventricular tachyarrhythmias. The value of late potentials and heart rate variability for identification of patients at risk for developing life-threatening ventricular tachyarrhythmias is discussed, as are the other applications and limitations of both methods.

ISSN:0268-4705    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

With recent advances in transcatheter ablation of reentrant atrioventricular junctional tachycardias, these arrhythmias are now considered curable, whereas other forms of supraventricular tachycardias,ie,atrial fibrillation and flutter, the two oldest known clinical arrhythmias, remain a challenge to clinicians and basic scientists. New observations that have been made in experimental models of atrial fibrillation and flutter further improved our understanding of their mechanism and the effects of pharmacologic agents on them. The final results of several trials on the role of anticoagulation in the prevention of thromboembolism were recently published and indicate the beneficial effects of anticoagulation in patients with nonrheumatic atrial fibrillation. Although class Ic antiarrhythmic agents are very effective in maintaining sinus rhythm, the recognition and emergence of proarrhythmic effects have raised some concerns on the long-term use of these agents. Experience with the long-term efficacy of sotalol is limited. Low-dose amiodarone has been used for both ventricular rate control and maintenance of sinus rhythm. Catheter ablation by radiofrequency current of atrioventricular junctional tachycardias in drug refractory cases is more frequently used now and, indeed, no longer considered the last resort approach, but the therapy of first choice. Surgery for atrial fibrillation is very limited and long-term results and efficacy have to be determined.

ISSN:0268-4705    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

There is substantial interest in the association of ventricular tachyarrhythmias with the autonomic nervous system. Long QT syndrome has been proposed as a “Rosetta Stone” for the association between sympathetic nervous activity and genesis of ventricular tachyarrhythmias. Early afterdepolarizations, which can now be recorded in the clinical electrophysiology laboratory, may play an important role in repolarization abnormalities and the development of associated ventricular tachyarrhythmias. The response of the QT interval to exercise and other physical maneuvers is disturbed in congenital long QT syndrome and in patients who develop polymorphic ventricular tachycardia from class la antiarrhythmic drugs. Therefore it may be more important clinically to the dynamic rather than the resting behavior of the QT interval. Automatic analysis of the QT interval from ambulatory ECG recordings will provide new perspective. Patients with left ventricular dysfunction and a recent history of ventricular tachyarrhythmias have excessive cardiac norepinephrine spillover, and sympathetic nerve traffic is higher at the onset of a ventricular tachyarrhythmia. Excess catecholamine may induce the arrhythmia but may also help to preserve hemodynamic stability during the tachycardia by buffering the sudden fall of arterial pressure at the onset of arrhythmia. Antiadrenergic therapy prevents sudden death in post-myocardial infarction patients and in patients with prolonged ventricular depolarization. Other therapies have been disappointing. The combination of several low-dosage antiarrhythmic agents, particularly with amiodarone, may be worth considering for ventricular arrhythmias and poor left ventricular function. Full revascularization is known to reduce the incidence of sudden cardiac death. Coronary angioplasty may confer an antiarrhythmic benefit in selected cases, but more information is needed. Electric ablation using low-energy capacitor discharges has achieved some success in patients unsuited for surgery. This year there has been movement toward clinical modification of ventricular repolarization rather than conduction, the therapeutic modulation of the autonomic nervous system, and further refinement of nonpharmaceutical techniques.

ISSN:0268-4705    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

With the introduction of radiofrequency energy, catheter ablation has become an established technique for managing many cardiac rhythm disturbances. High efficacy and safety have been reported for accessory pathway ablation, selective fast and slow atrioventricular nodal pathway ablation to eliminate atrioventricular nodal reentrant tachycardia (while preserving atrioventricular conduction), atrioventricular junctional ablation to control the ventricular response to atrial tachyarrhythmias, ablation of the right bundle branch to eliminate bundle branch reentrant ventricular tachycardia, and ablation of the site of tachycardia origin in patients with ventricular tachycardia unassociated with structural heart disease. In addition, there has been active investigation into ablation techniques for more complex arrhythmias such as atrial tachycardia, atrial flutter, and ventricular tachycardia associated with structural heart disease.

ISSN:0268-4705    

出版商:OVID    

年代:1993

数据来源: OVID

ISSN:0268-4705    

出版商:OVID    

年代:1993

数据来源: OVID