Atrial threshold variability: implications for automatic atrial stimulation algorithms.

BACKGROUND: Automatic management of atrial stimulation by verification of atrial threshold (ACM) has recently been made feasible. We investigated circadian atrial threshold variability over the long term and the predictors of successful automatic atrial threshold measurement, in order to provide practical clues for programming ACM features, in such a way as to achieve daily threshold verification and > 99% effective atrial stimulation. METHODS: Six daily attempts to measure atrial threshold were programmed in patients receiving an EnPulse pacemaker (Medtronic Inc., Minneapolis, MN, USA). Atrioventricular (AV) conduction was maximized by programming Search AV+ (SAV+) to a resting Paced AV delay = 400 ms in the first month, and 600 ms thereafter. RESULTS: Seventy-six patients had a median follow-up of 12 months. Median ACM success was 77%. Concordance between automatically and manually measured thresholds was observed during the entire follow-up (Rho = 0.82, P < 0.001). Daily variability in atrial threshold was < 0.5 V in > 94% of measurements in the first trimester after implantation, and < 0.5 V in > 99% of measurements thereafter, as well as any time after pacemaker replacement. Atrial threshold was measured on 86% of days: the predictors of ACM failure were AV block (AVB), high%Atrial pacing, and atrial fibrillation. Programming SAV+ to achieve 600 ms resting Paced AV decreased%Vpacing in patients with normal AV conduction and first-degree AVB, improving the ability to detect atrial threshold. CONCLUSIONS: The reliability of ACM is high over a long follow-up. On the basis of atrial threshold variability, a practical approach to ACM programming should be two daily atrial threshold measurements in patients with normal AV conduction and%Ap < or = 40%, or with normal sinus activity and AVB, whereas 3-4 measurements should be recommended in patients with first-degree AVB and%Ap > 40% or with recurrent atrial fibrillation and AVB. The lowest adapted stimulation output should achieve at least threshold +1 V in the first trimester after implantation, then threshold +0.5 V thereafter, in order to achieve > 99.5% effective atrial stimulation.

Monitored atrial fibrillation duration predicts arterial embolic events in patients suffering from bradycardia and atrial fibrillation implanted with antitachycardia pacemakers.

OBJECTIVES: The aim of our study was to evaluate arterial embolism (AE) occurrence rates and predictors in patients suffering from bradycardia and wearing a pacemaker with antitachycardia pacing therapies. BACKGROUND: Atrial fibrillation (AF) is associated with a high incidence of AE. METHODS: A total of 725 patients (360 men, age 71 +/- 11 years) were implanted with a DDDRP pacemaker (Medtronic AT500, Medtronic Inc., Minneapolis, Minnesota). At baseline 225 (31.0%) patients received antiplatelet therapy and 264 (36.4%) patients received anticoagulation agents. RESULTS: Over a median 22-month follow-up (25th to 75th interquartile range 16 to 30 months), AE occurred in 14 (1.9%) patients: 7 patients suffered a nonfatal ischemic stroke (0.6% per year), 4 patients had transient ischemic attack (0.34% per year), and 3 patients had embolic complications. Among baseline patients' characteristics, multivariate logistic analysis showed that embolic events are independently associated to ischemic heart disease (7.0 odds ratio [OR], 95% confidence interval [CI] 2.3 to 21.3, p = 0.001), prior embolic event (7.3 OR, 95% CI 1.2 to 43.9, p = 0.029), diabetes (5.0 OR, 95% CI 1.2 to 15.7, p = 0.032), and hypertension (4.1 OR, 95% CI 1.1 to 15.6, p = 0.036). The risk of embolism, adjusted for known risk factors, was 3.1 times increased (95% CI 1.1 to 10.5, p = 0.044) in patients with device-detected atrial fibrillation episodes longer than one day during follow-up. CONCLUSIONS: In a cohort of patients with bradycardia and AF, arterial embolism was common in patients with ischemic cardiopathy, hypertension, diabetes mellitus, and in patients with known stroke risk factors. Atrial fibrillation occurrences longer than one day were independently associated with embolic events.

Maximum likelihood segmentation of ultrasound images with Rayleigh distribution.

This study presents a geometric model and a computational algorithm for segmentation of ultrasound images. A partial differential equation (PDE)-based flow is designed in order to achieve a maximum likelihood segmentation of the target in the scene. The flow is derived as the steepest descent of an energy functional taking into account the density probability distribution of the gray levels of the image as well as smoothness constraints. To model gray level behavior of ultrasound images, the classic Rayleigh probability distribution is considered. The steady state of the flow presents a maximum likelihood segmentation of the target. A finite difference approximation of the flow is derived, and numerical experiments are provided. Results are presented on ultrasound medical images as fetal echography and echocardiography.