Cross-Stimulation: The Unexpected Stimulation of the Unpaced Chamber

The ability to stimulate one chamber through a lead or output circuit to the opposite cardiac chamber is termed cross-stimulation. Three examples of this phenomenon are presented. The first involves the close proximity of the atrial lead to the ventricular myocardium with ventricular capture occurring at sufficiently high outputs; the second is due to the basic design of dual unipolar pacing systems which have output circuits that share a common anode; the third is a self-limited eccentricity of one device that occurs only during the first phase of magnet-induced asynchronous pacing. The mechanism and clinical significance of these observations are discussed.     

Clinical Benefits of Telemetered Electrograms in Assessment of DDD Function

La télémétrie de l'ECG endocavitaire est une nouvelle téchnique pour la stimulation DDD. L'expérience initiale confirme que les données transmises par cette méthode sont comparables à celles que Ton pouvait avoir seuiement par des techniques invasives. La valeur de cette technologie est mise en évidence dans cette présentation. A notre avis elle va continuer à prendre de l'importance au fur et à mesure que les stimulateurs sophistiqués prolifèrerant.     

A New Advancement in Noninvasive Electrophysiology: A Standard Laboratory Stimulator Pulse Coupled with an Implanted Pacemaker

A new device for coupling the pulse from a standard laboratory stimulator to commercially available implanted pacemakers for use in noninvasive electrophysiology testing has been developed. When programmed to an electrophysiology mode, a 37 kHz carrier wave, generated by the programmer, maintains communication with the implanted pacemaker. Stimuli generated from a standard lab stimulator cause a break in the carrier wave and an output from the pacemaker. Cycle lengths as short as 127 msec can be attained. In addition to standard electrophysiology testing, this noninvasive electrophysiological technique can be used to fibrillate the heart to test the efficacy of automatic implantable cardioverter/defibrillators.     

The Effects of Extracorporeal Shock Wave Lithotripsy on Pacemaker Function

Twenty-two pacemaker pulse generators were exposed to shock waves of an extracorporeal shock wave lithotripter to assess the effects of the extremely high pressure transients on pacemaker function. The pulse generator and distal aspect of the lead were positioned 5 cm from the focal point of the lithotripter and 10 cm from each other. Pulse generator function was analyzed during shock wave delivery synchronized with pulse generator output, during shock waves at a rate faster than the escape rate, and after exposure to lithotripsy. During shock waves delivered synchronously with pulse generator output, only one of 22 pulse generators malfunctioned by intermittently reverting to the magnet rate. When subjected to shock waves at a rate greater than the escape rate, 50% of the pulse generators were inhibited by electromechanical interference from the lithotripter. Both bipolar and unipolar devices were affected. However, analysis after exposure to shock waves showed that none of the pacemakers was damaged or spuriously reprogrammed. In conclusion, cardiac pacemakers do not appear to be damaged or reprogrammed by exposure to extracorporeal shock wave lithotripsy. The likelihood of false inhibition appears to be very low if shock waves are delivered synchronously with the QRS.     

UPPER TRACT RECURRENCES FOLLOWING RADICAL CYSTECTOMY: AN ANALYSIS OF PROGNOSTIC FACTORS, RECURRENCE PATTERN AND STAGE AT PRESENTATION

PURPOSE: We study the incidence and pattern of upper tract recurrences following radical cystectomy for bladder cancer, and analyze the prognostic factors. MATERIALS AND METHODS: A retrospective study was performed on 529 patients who underwent radical cystectomy and urinary diversion at Memorial Sloan-Kettering Cancer Center between July 1989 and June 1997. Data related to upper tract recurrence were analyzed. RESULTS: Of the 529 patients 16 (3%) had upper tract recurrence. Median followup was 16.9 months for the entire group and 49.1 months for patients with upper tract recurrence, with a median time to recurrence of 37.2 months. Of 12 upper tract recurrences 7 (58%) were locally advanced at surgery (p3a or greater with or without lymph node metastasis) and 5 of 16 patients with recurrence (31.3%) had bilateral tumors (2 synchronous and 3 metachronous). Overall survival from the time of diagnosis of upper tract recurrence after radical cystectomy was poor, with a median of 10 months (confidence interval 1 to 19). CONCLUSIONS: The incidence of upper tract recurrence following radical cystectomy is low (3%). However, the incidence of bilateral tumors (31.3%) and locally advanced stage at the time of operation (58%) is higher than expected for upper tract tumors in the general population. Survival of patients with upper tract recurrence is poor, with a median of 10 months.