No abstract

The possibility of using implantable cardioverter-defibrillators (ICDs) for primary prevention of sudden death in selected highrisk patients has prompted a series of prospective controlled studies. Recently, the MADIT II study highlighted the possibility of effective primary prevention of sudden death in patients with coronary artery disease selected by straightforward clinical data and without expensive screening (electrophysiological study). For patients with previous myocardial infarction and low left ventricular ejection fraction ((30%), ICD implantation may reduce mortality risk by approximately 31% in the following 2 years. Implementation of this therapeutic strategy threatens to impact on public health-care spending. Possible cost-limiting mechanisms include price cuts because of increasing usage (market forces); identification of subgroups at higher risk of sudden death and use of cheaper devices with limited diagnostic and therapeutic options. Further long-term evaluation of the cost-effectiveness and cost-utility of ICDs should identify subgroups of patients for whom implantation is affordable despite current economic constraints. For heart failure patients, randomized controlled trials are currently evaluating the effects on overall survival of both conventional ICDs and devices with biventricular pacing capabilities. In this perspective, data from the COMPANION trial are expected to stimulate the use of devices with defibrillation back-up in candidates for biventricular pacing.

BORIANI, G., et al.: Transvenous Low Energy Internal Cardioversion for Atrial Fibrillation: A Review of Clinical Applications and Future Developments. Low energy internal atrial cardioversion can be performed by delivering biphasic shocks between transvenous catheters positioned within the cardiac chambers or great vessels. Delivery of shocks results in effective cardioversion at energies < 6–10 J and the procedure can be effective even when external cardioversion has failed. Shock induced discomfort varies from patient to patient, but the procedure can be usually performed without general anesthesia and eventually under mild sedation. Nevertheless, tolerability has to be improved by obtaining a substantial reduction in defibrillating thresholds. With regard to safety, delivery of shocks for defibrillating the atria implies a potential risk of inducing ventricular fibrillation; to minimize this risk, shock delivery must be synchronous to the QRS and should be avoided during rapid RR cycles (< 300 ms). Presently, transvenous low energy cardioversion is an investigational procedure, but a widening of indications is expected in the near future. The cost of the procedure, which remains invasive and requires a brief hospital stay, must be balanced with the benefit of restoring sinus rhythm and the possibility of maintaining sinus rhythm for the medium‐ to long‐term. Experimental and clinical investigations of low energy internal cardioversion have resulted in the development of devices for atrial defibrillation whose clinical role and cost‐benefit ratio is currently under evaluation.

Sustained AF reinduced after cardioversion of chronic AF is comparable with baseline AF in terms of atrial defibrillation threshold, atrial cycle length, and pattern of organization. Therefore, a clinical model based on reinduction of sustained AF after cardioversion is suitable for studying the effects of a series of interventions on atrial defibrillation threshold. However, because this model does not yield a form of AF with comparable indices of local refractoriness (e.g., P5), it is not recommended when analyzing local electrophysiologic properties.