Initial experience with the implantable atrial and combined atrioventricular defibrillator

Abstract

The promising results achieved with internal atrial defibrillation have facilitated the development of an implantable atrial defibrillator. Methods: For any new therapy, it is imperative to demonstrate safety, efficacy, tolerability with improvement in quality of life, and cost-effectiveness compared to already available therapeutic options. Most importantly, the efficacy and safety rates with a new therapy should be better or at least as good than those observed with previously available means. Maintenance of sinus rhythm or prolonged duration in arrhythmia-free intervals should be clearly demonstrated with an implantable atrial defibrillator, the MetrixTM system. Recently, a new dual-chamber defibrillator (7250 Jewel AF AMD) has entered clinical evaluation. The most important new features of the 7250 AMD system include: dual-chamber pacing, a new dual-chamber detection criterion for rejection of supraventricular tachycardias, detection and treatment modalities of atrial arrhythmias, prevention strategies for atrial arrhythmias. The dual-chamber detection criterion is constantly monitoring the rhythm in the ventricle as well as in the atrium. This new dual-chamber detection algorithm is used to improve discrimination of ventricular tachycardia from supraventricular tachycardia by applying pattern recognition methods based on different P-wave positions within RR sequences. The detection algorithm can be used to withhold inappropriate ventricular therapies. Results: Initial clinical experience with the MetrixTM system indicates stable atrial defibrillation thresholds, appropriate R-wave synchronization markers, no shock induced ventricular proarrhythmia, and excellent detection of atrial fibrillation with a specificity of 100%. Ventricular proarrhythmia has not been reported for correctly R-wave synchronized low energy shocks when closely coupled RR intervals and long-short cycles are avoided. The first results with the 7250 Jewel AF device suggest a high sensitivity for induced ventricular tachyarrhythmias and an increased specificity for reduction of inappropriate therapies.