Hemoglobin spectroscopy to evaluate hemodynamic function during tachycardias: The future of ICD discrimination algorithms?

Abstract

m s w Inappropriate shocks remain an important problem associated with implantable cardioverter-defibrillator (ICD) therapy. Results from multicenter trials show that about one third of shocks are inappropriate, and this proportion has been stubbornly stable over the years. The concern regarding inappropriate therapies was heightened by studies showing increased mortality associated with shocks, including inappropriate ones. Although a causative effect of shocks n mortality has not been demonstrated, there is a clear onsensus that avoiding unnecessary and painful shocks is n important goal of ICD therapy. A number of strategies have been employed to reduce nappropriate ICD shocks, including higher programmed ates for ventricular tachycardia (VT)/ventricular fibrillation VF) detection, prolonged detection times, antitachycardia acing for VTs at rates as high as 250 beats/min, and dvanced discrimination algorithms. Prospective, multienter studies have shown that these strategies can signifcantly reduce shock rates. 6 Morphology algorithms to detect differences between ventricular and supraventricular arrhythmias are now commonplace. Although conceptually similar, comparative effectiveness studies have shown some important differences between these algorithms. Despite these differences, all discriminators currently in use rely on analysis of electrograms, through either timing or morphology. There has long been interest in identifying non–electrogram-based metrics that could be incorporated into arrhythmia discrimination algorithms. Recent data suggest that digital heart sounds, for example, could potentially be useful for arrhythmia classification. The hemodynamic response during an arrhythmia could be of even greater value both for discrimination and for therapy selection. Early pacemaker lead studies showed high failure rates with the use of blood-borne sensors such as pH or O2 saturation.