Radiofrequency Ablation for Post Infarction--论文代写范文精选

射频消融术(RFA)治疗选择的症状患者是缺乏结构性心脏病。RFA住院病人与VT慢性缺血性心脏病患者是不太好定义的。室性心动过速(VT)是一种常见的缺血性心脏病的并发症,有着显著相关的发病率和死亡率。下面的essay代写范文进行详述。

Abstract 
Radiofrequency ablation has an important role in the management of post infarction ventricular tachycardia. The mapping and ablation of ventricular tachycardia (VT) is complex and technically challenging. In the era of implantable cardioverter defibrillators, the role of radiofrequency ablation is most commonly reserved as an adjunctive treatment for patients with frequent, symptomatic episodes of ventricular tachycardia. In this setting the procedure has a success rate of around 70-80% and a low complication rate. With improved ability to predict recurrent VT and improvements in mapping and ablation techniques and technologies, the role of radiofrequency ablation should expand further.

Introduction 
Radiofrequency ablation (RFA) is the treatment of choice in the management of symptomatic patients with ventricular tachycardia (VT) in the absence of structural heart disease. The role of RFA in-patients with VT in the setting of chronic ischemic heart disease is less well defined. Ventricular tachycardia (VT) is a common complication of ischemic heart disease, with significant associated morbidity and mortality. 1,2 Traditionally, anti-arrhythmic medications have formed the mainstay of treatment, despite the low efficacy, the risk of pro-arrhythmia and long term adverse effects.3 Anti-arrhythmic surgery is successful in abolishing VT, however, the operative mortality in most series was unacceptably high.4 Over the past 10 years, implantable cardioverter defibrillators (ICDs) have become the treatment of choice for all but incessant VT. This treatment is based on the evidence of a number of studies which have shown that ICDs reduce overall mortality in certain subgroups of patients with ischemic heart disease with documented VT5, 6 , or even in the absence of previously documented VT7 . 

The development of anti-tachycardia pacing algorithms has significantly reduced the need for cardioversion8 and resulted in much improved patient acceptance of such devices. Whilst ICDs are associated with significant mortality benefits in-patients with ischemic heart disease and VT, they do not actually prevent the onset of arrhythmia and remain relatively contraindicated in-patients with frequent arrhythmic episodes. In addition the implantation and function of an ICD can contribute to pathological anxiety and depression in some patients.9 Furthermore, ICD therapy is relatively expensive, when considered over the expected lifetime of particularly younger patients. In-patients with ischemic heart disease RFA has developed predominantly an adjunctive role in patients with incessant or highly symptomatic, drug refractory VT.

Defining the Substrate for ventricular tachycardia in ischemic heart disease 
VT in the setting of ischemic heart disease is predominantly manifest as monomorphic VT, caused by stable reentrant circuits.10,11 Whilst polymorphic VT and primary ventricular fibrillation are seen in patients with ischemic heart disease these more often relate to acute biochemical, ischemic or pharmacological insults; whilst ablation has been proposed for these arrhythmias 12, correction of the underlying abnormalities form the first line of treatment. In simple terms the mechanism of reentry in ischemic heart disease relates to zones of heterogeneous conduction, typically at the edge of myocardial scars. 

Residual functioning myocytes at the edge of, or interspersed within, myocardial fibrous scar create zones of slow conduction and conduction block.13 When appropriately located and with appropriate electrophysiological properties, these slow conduction zones can take the form of a discrete electrical channel or isthmus critical to the initiation and continuation of VT. The re-entrant VT circuit utilizes the slow conduction properties of the critical isthmus. (Fig 1) The electrical activity propagates relatively slowly along the isthmus during diastole and forms a silent zone on the surface ECG. When electrical activity reaches the exit zone it rapidly propagates throughout the ventricular myocardium, giving rise to mechanical systole and the QRS complex on the surface ECG. 

The electrical wavefront courses a loop through the myocardium before returning to the entrance zone and repeating the isthmus passage. 14 The diagrammatic representation of re-entry in Fig 1 is a simplistic description of a process, which can be highly complex. The reentry circuits can be multiple with shared and separate components; the circuits can be located in the endocardium, epicardium, transmuraly or throughout each of these zones. The isthmuses can vary significantly in length and electrophysiological properties. The regions of conduction block can be formed by scar tissue or by anatomical boundaries (typically mitral annulus) and can manifest absolute conduction block or functional conduction block developing only during VT. A comprehensive knowledge of the anatomy and electrophysiology is fundamental to approaching ablation of VT in ischemic heart disease.

Patient selection 
At one end of the spectrum, the patient with incessant or intractable ventricular tachycardia, resistant to pharmacotherapy and overdrive pacing and requiring frequent cardioversion is an obvious candidate for ablation of ventricular tachycardia. At the other end of the spectrum there is presently no role for ablation in the sense of primary prevention. Patients with frequent episodes of VT should be considered for ablation. The threshold for deciding to undergo ablation should consider the local expertise, the frequency of episodes, patient and economic factors. Comprehensive data has shown a substantial mortality benefit supporting the use of ICDs in-patients with post infarction VT. At present ablation should ideally be considered to have a role as an adjunct to an ICD in-patients with highly symptomatic VT. As mapping and ablation techniques develop and the accuracy of predicting the long-term outcome improves, the role of RFA may expand, making it the therapy of first choice in a growing proportion of patients. Perhaps with time ICDs may be reserved as the treatment for failed ablation procedures or for prophylactic indications, particularly in parts of the world where widespread implantation of ICDs is financially impractical. Even if ICDs remain justified on the basis of residual uncertainty, the quality of life is likely to be improved by the reduction in discharges resulting from catheter ablation. 

Conclusions 
Radiofrequency catheter ablation of patients with highly symptomatic, sustained, monomorphic post infarction VT can be performed with high success rate and acceptable procedural complication rate. The procedure can be successfully applied to a wide spectrum of patients including those with multiple morphologies of VT and hemodynamically unstable VT. The procedure at present requires extensive understanding of anatomical and electrophysiological principles and is prolonged and technically demanding. Its application beyond a few expert centers is dependent upon electrophysiological and technological advances.

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