CLINICAL RELEVANCE OF STORED ELECTROGRAMS FOR IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR (ICD) TROUBLESHOOTING AND UNDERSTANDING AT MECHANISMS FOR VENTRICULAR TACHYARRHYTHMIAS

A major problem in patients with cardioverter-defibrillators is to det ermine reliably the mechanism for spontaneous implantable cardioverter -defibrillator (ICD) discharges. Electrogram storage in ICD devices is comparable to that in permanent Holter monitors. Stored bipolar elect rograms obtained from the sensing or shocking lead system contain a wi de variety of different information. Intracardiac electrograms (EGMs) recorded from pace/sense electrodes (or ''near-field'' EGMs) show bipo lar signals that have a distinct absence of any atrial activity during ventricular tachycardia or sinus rhythm. in contrast, the EGMs record ing from the shocking electrodes, integrating a much larger area of my ocardium, provide a more global visualization of electrical activity, which includes both atrial and ventricular deflections. Improved diagn ostic capabilities available in the new generation ICD devices, in par ticular the stored intracardiac EGMs, facilitate sensing error diagnos is, permit a better evaluation of device function and ICD detection al gorithms, and are helpful for reprogramming in order to overcome or pr event errors. In addition, EGMs give us a unique opportunity to gather information about the arrhythmic mechanism of the sudden cardiac deat h syndrome. Information such as the day and time of the episode, the p receding heart rate, the influence of the coupling interval of precedi ng premature beats, and their morphology can be gained from the analys is of stored EGM recordings. Although the availability of stored intra cardiac EGMs are of enormous value in troubleshooting of ICD problems, they are occasionally not conclusive and must be complemented by addi tional techniques in order to complete the diagnosis. The information obtained by the analysis of stored intracardiac EGMs together with a d atabase of EGMs can be of great importance for further improvements in future devices and may provide insights as to which patients are like ly to benefit most from ICD therapy.