William H. K. Lee

Patterns of treatment for peripheral arterial disease in the United States: 1996-2005

OBJECTIVE Endovascular procedures are increasingly used in the treatment of peripheral arterial disease (PAD). Whether this new procedural approach translates to clinical outcomes equivalent or superior to open surgical revascularization is a subject of debate. We sought to analyze population-based rates of major amputations for PAD during a time period in which the use of endovascular surgical procedures increased dramatically. METHODS We used the 1996-2005 Nationwide Inpatient Sample (NIS) to analyze rates of amputations and vascular interventions, and also to characterize the treatment of patients admitted acutely for PAD. Vascular interventions were designated based on International Classification of Diseases (ICD) procedure codes as open bypass, endovascular intervention, or major amputation (disarticulation at ankle or higher amputation). Population-based age-adjusted incidence rates of treatment were calculated by combining procedure rates with census data. RESULTS Our analysis included 97,000 acute admissions for PAD, 83,000 major amputations, 77,500 endovascular procedures, and 171,000 open vascular bypass operations. Between 1996 and 2005, population-based rates of acute admissions for PAD decreased by 4.3% per year, open procedures by 6.6% per year, and major amputations by 6.4% per year, whereas endovascular procedures increased by 4.8% per year. Of patients acutely admitted for PAD, the likelihood of undergoing an amputation decreased (30.2% to 21.8%), the likelihood of undergoing an open vascular procedure decreased (34.5% to 26.3%), and the likelihood of undergoing an endovascular operation increased (12.7% to 28.3%). All of these changes were statistically significant at P < .05. CONCLUSION The last decade has seen a significant increase in the use of endovascular procedures and a decrease in rates of major amputation. These trends are seen both for patients admitted with acute PAD, as well as in the population in general. While our study was not designed to demonstrate a causal relationship, our findings suggest an association between increased application of endovascular technology and reduced rates of amputation in patients with PAD.

On the global variations of terrestrial heat-flow☆

Abstract Over 3 500 measurements of surface heat-flux have been catalogued and analyzed to study the large-scale variations of terrestrial heat-flow. It was found that heat-flow values are correlated with major geologic provinces: higher averages and scattered values in active tectonic regions, and lower averages and more uniform values in stable areas. Analyzing the data in the light of new global tectonics shows that the variations of heat-flow are consistent with the hypotheses of sea-floor spreading and plate tectonics. The observed heat-flow across the mid-oceanic ridges can be accounted for by a simple model of a spreading sea floor.

CWB Free-Field Strong-Motion Data from the 21 September Chi-Chi, Taiwan, Earthquake

The Chi-Chi earthquake occurred at 17:47 on 20 September 1999 and is the largest earthquake ( M W 7.6) to have occurred on land in Taiwan in the twentieth century. This earthquake caused considerable damage and was named the “921 Chi-Chi Great Earthquake” by the Taiwan government, as the local date was 21 September. Because an extensive strong-motion instrumentation program in Taiwan was completed by the Central Weather Bureau (CWB) in 1996, over 30,000 digital strong-motion records have been obtained from the Chi-Chi earthquake and thousands of its aftershocks. These records form the largest set of strong-motion data recorded from a major earthquake since strong-motion seismology studies began in the 1930s. This data set is important to seismology and earthquake engineering because it includes over 60 recording sites within 20 km of the fault ruptures, which provides a five-fold increase of such near-field records available for the entire world. A prepublication CD was made available in mid-December 1999, and the data on it have been used by many authors in dozens of articles published so far. Since then, we examined about 10,000 strong-motion records and conducted a first-order quality assurance procedure for all the records obtained on 20 September 1999, including the mainshock and hundreds of the early aftershocks. We performed extensive data processing for quality assurance and selected a total of 663 strong-motion data files from 441 accelerographs to construct strong-motion records up to 4-min long for the mainshock whenever possible. In this article, we present a brief description of the processed acceleration data from the Chi-Chi earthquake. The data set (about 500 megabytes) and an extensive 562-page report (documenting the data processing and results of the processed data) are archived on the attached CD in this Special Issue so that users can quickly access this valuable data set for their research. Manuscript received 7 April 2001.

Introduction to the Special Issue on Rotational Seismology and Engineering Applications

Rotational seismology is an emerging field for studying all aspects of ro- tational ground motions induced by earthquakes, explosions, and ambient vibrations. It is of interest to a wide range of geophysical disciplines, including strong-motion seismology, broadband seismology, earthquake engineering, earthquake physics, seis- mic instrumentation, seismic hazards, seismotectonics, and geodesy, as well as to physicists using Earth-based observatories for detecting gravitational waves generated by astronomical sources (predicted by Einstein in 1916). In this introduction to the BSSA special issue on rotational seismology and engineering applications, we will include (1) some background information, (2) a summary of the recent events that led to this special issue, and (3) an overview of its 51 papers—27 articles, 11 short notes, 4 reviews, 6 tutorials, and 3 supplementary articles. Our comments on these 51 papers are very brief and give just a hint of what the papers are about. Papers in this special issue demonstrate that earthquake monitoring cannot be limited to measuring only the three components of translational motion. We also need to simultaneously measure the three components of rotational motion and the many components of strains. A golden opportunity to improve our understanding of earth- quakes lies in the near field of large earthquakes (within about 25 km of the earthquake ruptures), where nonlinear rock and soil response influences ground motions in a com- plicated way.

Use of microearthquakes in the study of the mechanics of earthquake generation along the San Andreas fault in central California

Abstract A small, dense network of independently recording portable seismograph stations was used to delineate the slip surface associated with the 1966 Parkfield-Cholame earthquake by precise three dimensional mapping of the hypocenters of its aftershocks. The aftershocks were concentrated in a very narrow vertical zone beneath or immediately adjacent to the zone of surf ace fracturing that accompanied the main shock. Focal depths ranged from less than 1 km to a maximum of 15 km. The same type of portable network was used to study microearthquakes associated with an actively creeping section of the San Andreas fault south of Hollister during the summer of 1967. Microearthquake activity during the 6-week operation of this network was dominated by aftershocks of a magnitude-4 earthquake that occurred within the network near Bear Valley on July 23. Most of the aftershocks were concentrated in an equidimensional region about 2 1 2 km across that contained the hypocenter of the main shock. The zone of the concentrated aftershocks was centered near the middle of the rift zone at a depth of about 3 1 2 km . Hypocenters of other aftershocks outlined a 25 km long zone of activity beneath the actively creeping strand of the fault and extending from the surface to a depth of about 13 km. A continuing study of microearthquakes along the San Andreas, Hayward, and Calaveras faults between Hollister and San Francisco has been under way for about 2 years. The permanent telemetered network constructed for this purpose has grown from about 30 stations in early 1968 to about 45 stations in late 1969. Microearthquakes between Hollister and San Francisco are heavily concentrated in narrow, nearly vertical zones along sections of the Sargent, San Andreas, and Calaveras faults. Focal depths range from less than 1 km to about 14 km.

Review: Progress in Rotational Ground-Motion Observations from Explosions and Local Earthquakes in Taiwan

Rotational motions generated by large earthquakes in the far field have been successfully measured, and observations agree well with the classical elasticity theory. However, recent rotational measurements in the near field of earthquakes in Japan and in Taiwan indicate that rotational ground motions are 10 to 100 times larger than expected from the classical elasticity theory. The near-field strong-motion records of the 1999 Mw 7:6 Chi-Chi, Taiwan, earthquake suggest that the ground motions along the 100 km rupture are complex. Some rather arbitrary baseline corrections are necessary in order to obtain reasonable displacement values from double integra- tion of the acceleration data. Because rotational motions can contaminate acceleration observations due to the induced perturbation of the Earths gravitational field, we started a modest program to observe rotational ground motions in Taiwan. Three papers have reported the rotational observations in Taiwan: (1) at the HGSD station (Liu et al., 2009), (2) at the N3 site from two TAiwan Integrated GEodynamics Research (TAIGER) explosions (Lin et al., 2009), and (3) at the Taiwan campus of the National Chung-Cheng University (NCCU )( Wuet al., 2009). In addition, Langston et al. (2009) reported the results of analyzing the TAIGER explosion data. As noted by several authors before, we found a linear relationship between peak rotational rate (PRR in mrad=sec) and peak ground acceleration (PGA in m=sec 2 ) from local earthquakes in Taiwan, PRR 0:002 1:301 PGA, with a correlation coefficient of 0.988.

Clinical Outcomes and Implications of Failed Infrainguinal Endovascular Stents

OBJECTIVE While the influence of initial TransAtlantic InterSociety Consensus (TASC) II classification has been clearly shown to influence the primary patency of infrainguinal stenting procedures, its effect on outcomes once stent failure has occurred is less well documented. It is the objective of this paper to determine whether clinical outcomes and implications of anatomic stent failure vary according to initial TASC II classification. METHODS Results were analyzed by TASC II classification. Kaplan-Meier survival curves were plotted and differences between groups tested by log-rank method. A Cox proportional hazards regression model was used to perform the multivariate analysis. RESULTS During a 5-year period, 239 angioplasties and stents were performed in 192 patients. Primary patency was lost in 69 stented arteries. Failure was due to one or more hemodynamically significant stenoses in 43 patients, and occlusion in 26 patients. After primary stenting, limbs initially classified as TASC C and D were more likely to fail with occlusion (P < .0001), require open operation (P = .032), or lose run-off vessels (P = .0034) than those classified as TASC A or B. In two patients initially classified as TASC C, stent failure changed the level of open operation to a more distal site. Percutaneous reintervention was performed on 35 limbs. Successful reintervention improved the patency of TASC A and B lesions to 92%, 85%, and 64% and TASC C and D lesions to 78%, 72%, and 50% at 12, 24, and 36 months, respectively. Initial TASC classification was highly predictive of first anatomic failure (P < .0001), but it did not predict the durability of subsequent catheter based reintervention (P = .32). Ten patients with stent failure required operation, and five underwent amputation; all had failed with occlusion. Overall limb salvage was 89% and peri-procedural mortality was 0.4%. CONCLUSIONS Following primary stenting of the superficial femoral artery (SFA) and popliteal artery, lesions classified as TASC C or D are more likely to fail with occlusion, lose run-off vessels, and alter the site of subsequent open operation than their TASC A and B counterparts. Although these complications are infrequent, they may negatively impact later attempts at revascularization, and this must be considered when deciding upon the proper treatment strategy for patients with infrainguinal occlusive disease.

Observing Rotational and Translational Ground Motions at the HGSD Station in Taiwan from 2007 to 2008

Because of a lack of suitable instruments, rotational ground motions have not been observed until the last decade. Rotational measurements in the near field of earthquakes in Japan (Takeo, 1998) indicate that rotational ground motions are many times larger than expected from the classical elasticity theory. After failing to obtain useful rotational ground motions (using similar rotational sensors as Takeo did), we deployed a far more sensitive rotational velocity sensor (R-1) at the HGSD station in eastern Taiwan. From 7 December 2004 to 12 November 2006, several hundreds of earthquakes were recorded during our Phase 1 operation. This was mostly a learning exercise to solve field operation problems; Phase 1 operations ended when our two R-1 sensors ceased to operate. A K2 R1 instrument was deployed in the spring of 2007 to start our Phase 2 operation. From 8 May 2007 to 17 February 2008, we ob- served 52 local earthquakes with good rotational velocity signals (with signal-to-noise ratio >∼5), together with excellent translational acceleration signals (with signal-to- noise ratio >∼10). Unfortunately, field operation was interrupted due to flooding of the HGSD station site in mid-February 2008; we just resumed normal operation in June 2008. This article reports our observations of rotational and translational ground motions made at the HGSD station so far. We concentrate on describing our instru- mentation and the data obtained from 52 local earthquakes during our Phase 2 opera- tion and present some very preliminary results.

Preface to the 1999 Chi-Chi, Taiwan, Earthquake Dedicated Issue

The 1999 Chi-Chi, Taiwan, earthquake ( M w 7.6) struck central western Taiwan at 1:47 a.m. local time (on 21 September or at UTC 17:47 20 September). The causal fault was immediately identified to be the mapped active Chelungpu thrust fault as it produced a remarkable 100-km-long surface break, with fault scarps as high as 8 m in places. The nucleation point of this long rupture was defined by an epicenter at 120.82 °E and 23.85 °N, with a focal depth of 8 km. A first-motion solution was reported to be striking N20 °E, dipping 30 °SE with an average rake of 85° (Chang et al., 2000). The event was officially named after the nearest town Chi-Chi by the Central Weather Bureau (CWB) (Shin, 2000). This was the most devastating earthquake to hit Taiwan in modern times. The Chi-Chi earthquake and its energetic aftershock sequence inflicted a casualty toll of 2435 and an estimated US

Seismic-Wave Strain, Rotation, and Gradiometry for the 4 March 2008 TAIGER Explosions

4 billion property loss (Tsai et al., this issue). This catastrophe was nonetheless fortunate in several aspects. The mainshock struck when schools were not in session; the loss of student lives would have been unthinkable in view of the total collapse of hundreds of school buildings. In emergency response, it was fortunate that the CWB completed in 1995 the Taiwan Rapid Earthquake Information Release System that was capable of electronically releasing pertinent information within a couple minutes of an earthquake occurrence. Rapid earthquake information greatly facilitated the disaster relief missions, and it mitigated further secondary losses. Scientifically, because of the completion of the Taiwan Strong-Motion Instrumentation Program (TSMIP), the occurrence of the Chi-Chi earthquake sequence has resulted in the richest seismological data recovery in the world to date, in both quality and quantity. These data were open to the world with a data CD of the …