Analysis of Incomplete Data and an Intrinsic-Dimension Helly Theorem

The analysis of incomplete data is a long-standing challenge in practical statistics. When, as is typical, data objects are represented by points in R^d , incomplete data objects correspond to affine subspaces (lines or Δ-flats).With this motivation we study the problem of finding the minimum intersection radius r(L) of a set of lines or Δ-flats L: the least r such that there is a ball of radius r intersecting every flat in L. Known algorithms for finding the minimum enclosing ball for a point set (or clustering by several balls) do not easily extend to higher dimensional flats, primarily because “distances” between flats do not satisfy the triangle inequality. In this paper we show how to restore geometry (i.e., a substitute for the triangle inequality) to the problem, through a new analog of Helly’s theorem. This “intrinsic-dimension” Helly theorem states: for any family L of Δ-dimensional convex sets in a Hilbert space, there exist Δ + 2 sets L' ⊆ L such that r(L) ≤ 2r(L'). Based upon this we present an algorithm that computes a (1+ε)-core set L' ⊆ L, |L'| = O(Δ^4/ε), such that the ball centered at a point c with radius (1 +ε)r(L') intersects every element of L. The running time of the algorithm is O(n^(Δ+1)dpoly(Δ/ε)). For the case of lines or line segments (Δ = 1), the (expected) running time of the algorithm can be improved to O(ndpoly(1/ε)).We note that the size of the core set depends only on the dimension of the input objects and is independent of the input size n and the dimension d of the ambient space

Radiofrequency Catheter Ablation of AV Nodal Reentry: The Anterior Approach

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75131/1/j.1540-8159.1993.tb01633.x.pd

Aortic Leaflet Perforation During Radiofrequency Ablation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73537/1/j.1540-8159.1991.tb02732.x.pd

Safety, feasibility and cost of outpatient radiofrequency catheter ablation of accessory atrioventricular connections

AbstractObjectives. The purpose of this study was to evaluate prospectively the safety, feasibility and cost of performing radiofrequency catheter ablation of accessory atrioventricular (AV) connections on an outpatient basis in 137 cases.Background. The efficacy and low complication rate of radiofrequency ablation as performed in the hospital suggested that it might be feasible to perform it on an outpatient basis.Methods. In 100 cases (73%) performed between September 1, 1991 and April 20, 1992, patients met criteria for treatment as outpatients. Reasons for exclusion were age <13 or >70 years (4), anteroseptal location of the accessory AV connection (5 patients), obesity (>30% of ideal body weight) (4 patients) or clinical indication for hospitalization (24 patients). Patients with only venous punctures had a recovery period of 3 h and those with arterial punctures had a recovery period of 6 h. There were 63 men and 32 women (5 patients underwent two ablation procedures >1 month apart), with a mean age ± SD of 36 ± 13 years. The pathway was left-sided in 67 cases and right-sided or posteroseptal in 33.Results. The procedure was successful in 97 of 100 cases, with a mean procedure duration of 99 ± 42 min. In 70 cases the patient was discharged the day of ablation, and in 30 cases the patient required a short (≤18-h) overnight stay because the procedure was completed too late in the day for recovery in the outpatient facility. The mean duration of observation was 4.8 ± 1.5 h for outpatients and 15 ± 1.4 h for patients who underwent overnight hospitalization. At follow-up study, two patients had a clinically significant complication; both had a femoral artery pseudoaneurysm detected ≥1 week after the procedure and both required surgical repair. Thirty consecutive patients (22 outpatients and 8 hospitalized overnight) undergoing catheter ablation after January 1, 1992 were chosen for a cost analysis. The mean cost of the procedure was $10,183 ±$1,082.Conclusions. The majority of patients undergoing radiofrequency catheter ablation of an accessory AV connection can be treated safely on an outpatient basis

Comparison of Fixed Burst Versus Decremental Burst Pacing for Termination of Ventricular Tachycardia

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72440/1/j.1540-8159.1993.tb01531.x.pd

Using Passive Samplers to Track per and Polyfluoroalkyl Substances (PFAS) Emissions From the Paper Industry: Laboratory Calibration and Field Verification

Per and polyfluoroalkyl substances (PFAS) are becoming more stringently regulated and as such, a more diverse suite of environmental monitoring methods is needed. In this work a polar organic chemical integrative sampler (POCIS) with a nylon membrane and a combination of Oasis WAX and Fluoroflash® sorbents was calibrated in the laboratory and deployed in the field. A static renewal system was used to determine sampling rates for 12 PFAS which ranged between 0.69 ± 0.27 to 5.68 ± 1.80 L/day. POCIS devices were deployed for 10 days in lake Tyrifjorden, Norway which is known to be contaminated by a closed down factory producing paper products, in order to track the evolution of the PFAS contamination in a river system draining into the lake. Th sampling campaign enabled the stretch of the river which was responsible for the emissions of PFAS to lake Tyrifjorden to be identified. Freely dissolved concentrations determined with the POCIS were lowest at the site considered to reflect a diffuse PFAS contamination and highest at the site located downstream the factory. Perfluorooctanesulfonic acid (PFOS), perfluorohexanoic acid (PFHxA) and perfluorooctane sulfonamidoacetic acid (EtFOSAA) dominated the concentration profile at this site. Emissions of PFAS to lake Tyrifjorden were estimated to be 3.96 g/day for the sum of the 12 investigated PFAS.publishedVersio

Local biochemical and morphological differences in human Achilles tendinopathy: a case control study

<p>Abstract</p> <p>Background</p> <p>The incidence of Achilles tendinopathy is high and underlying etiology as well as biochemical and morphological pathology associated with the disease is largely unknown. The aim of the present study was to describe biochemical and morphological differences in chronic Achilles tendinopathy. The expressions of growth factors, inflammatory mediators and tendon morphology were determined in both chronically diseased and healthy tendon parts.</p> <p>Methods</p> <p>Thirty Achilles tendinopathy patients were randomized to an expression-study (<it>n </it>= 16) or a structural-study (<it>n </it>= 14). Biopsies from two areas in the Achilles tendon were taken and structural parameters: fibril density, fibril size, volume fraction of cells and the nucleus/cytoplasm ratio of cells were determined. Further gene expressions of various genes were analyzed.</p> <p>Results</p> <p>Significantly smaller collagen fibrils and a higher volume fraction of cells were observed in the tendinopathic region of the tendon. Markers for collagen and its synthesis collagen 1, collagen 3, fibronectin, tenascin-c, transforming growth factor-β fibromodulin, and markers of collagen breakdown matrix metalloproteinase-2, matrix metalloproteinase-9 and metallopeptidase inhibitor-2 were significantly increased in the tendinopathic region. No altered expressions of markers for fibrillogenesis, inflammation or wound healing were observed.</p> <p>Conclusion</p> <p>The present study indicates that an increased expression of factors stimulating the turnover of connective tissue is present in the diseased part of tendinopathic tendons, associated with an increased number of cells in the injured area as well as an increased number of smaller and thinner fibrils in the diseased tendon region. As no fibrillogenesis, inflammation or wound healing could be detected, the present data supports the notion that tendinopathy is an ongoing degenerative process.</p> <p>Trial registration</p> <p>Current Controlled Trials <a href="http://www.controlled-trials.com/ISRCTN20896880">ISRCTN20896880</a></p

Delayed Effects of Radiofrequency Energy on Accessory Atrioventricular Connections

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74618/1/j.1540-8159.1993.tb04574.x.pd

Recurrence of conduction in accessory atrioventricular connections after initially successful radiofrequency catheter ablation

AbstractThe purpose of this study was to characterize the incidence and clinical features of accessory pathway recurrence after initially successful radiofrequency catheter ablation and to identify variables correlated with recurrence. Radiofrequency ablation was performed with a 7F deflectable tip catheter with a large (4 mm in length) distal electrode. Left-sided accessory patthways were approached through the left ventricle and right-sided pathways by way of the right atrium. Patients were included in the study if 1) they had an initially successful procedure, defined as the absence of accessory pathway conduction immediately after ablation, and 2) had undergone a 3-month follow-up electrophysiologic test or had documented recurrence of accessory pathway conduction.Accessory pathway conduction recurred after initially successful ablation in 16 (12%) of 130 patients. Almost half (7 of 16) of these recurrences were in the 1st 12 h after ablation, and the last occurred after 106 days. Return of delta waves on the electrocardiogram (ECG) or spontaneous paroxysmal supraventricular tachycardia was the initial indication of recurrence in 15 of the 16 patients. Two patients with manifest accessory pathways exhibited recurrence with exclusively concealed accessory pathway conduction.Accessory pathways ablated from the tricuspid anulus (right free wall or septal accessory pathways) had a much higher recurrence rate (24%) than did those on the mitral anulus (6%). Fourteen of 15 patients have had successful repeat accessory pathway ablation after the initial recurrence. After a mean follow-up period of 4 ± 3 months, there have been no repeat recurrences of any of these accessory pathways.It is concluded that accessory pathway recurrence is infrequent after successful radiofrequency catheter ablation. All but one episode of recurrence was diagnosed clinically, suggesting that routine follow-up electrophysiologic testing in asymptomatic patients is not warranted. Because manifest accessory pathways may recur with retrograde conduction only, patients with palpitation after ablation should have electrophysiologic testing even if no delta waves are seen on the ECG. The success rate of ablation after recurrence (93%) is comparable to that achieved at the initial session, suggesting that return of accessory pathway function should not be a contraindication to a repeat attempt

A Time-Domain Analysis of Intracardiac Electrograms for Arrhythmia Detection

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73045/1/j.1540-8159.1991.tb05116.x.pd