†Deceased (see In Memoriam at the end of this document) *Representative of the Pediatric and Congenital Electrophysiology Society (PACES) ‡Representative of the European Heart Rhythm Association (EHRA) xRepresentative of the Society of Thoracic Surgeons (STS) {Representative of the American College of Cardiology (ACC) #Representative of the Latin American Heart Rhythm Society (LAHRS) **Representative of the Infectious Diseases Society of America (IDSA) ‡ ‡Representative of the American Heart Association (AHA) xxRepresentative of the American Society of Anesthesiologists (ASA) {{Representative of the Asia Pacific Heart Rhythm Society (APHRS)

Using a new method for long-term recording of monophasic action potentials from the human heart, we studied in 17 patients the effects on ventricular action potential duration (APD) of three clinically pertinent cycle length perturbations:(1) single extrastimuli, (2) abrupt sustained rate acceleration and deceleration, and (3) different steady-state cycle lengths. Results were: (a) APD after single extrastimuli at progressively longer cycle lengths were related to the extrastimulus cycle length with a biphasic electrical restitution curve which after an initial steep rise and a subsequent transient descent rose again more gradually to a plateau at cycle lengths above 800-1,000 ms. (b) After a sustained step decrease in cycle length, the first APD shortened abruptly while final steadystate adaptation required up to several minutes. The transition between the rapid and slow phase of APD change was characterized by a variable alternans of APD which correlated inversely with the preceding diastolic interval. (c) In the steady state, APD correlated linearly with cycle length, increasing an average of 23 ms per 100 ms cycle length increase (r = 0.995). The divergence between steady-state and non-steady-state APD, and the slowness of steady-state adaptation, are important factors to be considered in clinical electrophysiologic studies and in rate correction algorithms of APD or QT intervals, respectively.

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Background-The primary method for monitoring implantable cardioverter-defibrillator lead integrity is periodic measurement of impedance. Sprint Fidelis leads are prone to pace-sense lead fractures, which commonly present as inappropriate shocks caused by oversensing. Methods and Results-We developed and tested an algorithm to enhance early identification of lead fractures and to reduce inappropriate shocks. This lead-integrity algorithm, which can be downloaded into presently implanted implantable cardioverter-defibrillators, alerts the patient and/or physician when triggered by either oversensing or excessive increases in impedance. To reduce inappropriate shocks, the lead-integrity algorithm increases the number of intervals to detect (NID) ventricular fibrillation when triggered. The lead-integrity algorithm was tested on data from 15 970 patients with Fidelis leads (including 121 with clinically diagnosed fractures) and 95 other fractured leads confirmed by analysis of returned product.