On spatial conditional extremes for ocean storm severity.

We describe a model for the conditional dependence of a spatial process measured at one or more remote locations given extreme values of the process at a conditioning location, motivated by the conditional extremes methodology of Heffernan and Tawn. Compared to alternative descriptions in terms of max-stable spatial processes, the model is advantageous because it is conceptually straightforward and admits different forms of extremal dependence (including asymptotic dependence and asymptotic independence). We use the model within a Bayesian framework to estimate the extremal dependence of ocean storm severity (quantified using significant wave height, H S ) for locations on spatial transects with approximate east-west (E-W) and north-south (N-S) orientations in the northern North Sea (NNS) and central North Sea (CNS). For H S on the standard Laplace marginal scale, the conditional extremes "linear slope" parameter α decays approximately exponentially with distance for all transects. Furthermore, the decay of mean dependence with distance is found to be faster in CNS than NNS. The persistence of mean dependence is greatest for the E-W transect in NNS, potentially because this transect is approximately aligned with the direction of propagation of the most severe storms in the region.

The UK nephrostomy audit. Can a voluntary registry produce robust performance data?

AIM: To investigate the effectiveness of the Royal College of Radiologists Audit Sub-Committee's national prospective registry of percutaneous nephrostomy, which enables participants to audit their practice and compare performance with predetermined standards. METHODS: Following a limited retrospective audit, which permitted setting of achievable targets, a dataset was developed and all UK NHS acute hospitals were invited to participate in web-based prospective data collection. RESULTS: Eighty-five out of 285 (29.8%) hospitals contributed 3262 cases over a 29 month period. A satisfactory level of performance was achieved with an overall technical success rate of 98% and a complication rate of 6.3%. Significant risk factors for complications included rigors, anaemia, and impaired renal function. Low frequency operators were shown to have a lower technical success rate and a higher complication rate than high frequency operators; however, target thresholds were exceeded in all groups. Sepsis was identified as a risk factor in the majority of serious complications and all deaths. Some anomalous results were found due to unusual interpretation of the data entry form in two centres, but no evidence of under-performance was identified at any centre. CONCLUSIONS: Some weaknesses of the registry are discussed. In view of the low response rate, the possibility of significant bias cannot be excluded. In addition, there is no objective verification of the data; therefore, the results have limited credibility. However, individual centres that accurately completed a representative sample of cases can have confidence that their performance achieves an acceptable standard.

Role of subintimal angioplasty in the treatment of chronic lower limb ischaemia.

OBJECTIVES: To determine the clinical outcome of subintimal angioplasty (SA) and to assess impact on surgical workload. DESIGN: Retrospective review of a single radiologist's case series. MATERIALS: One hundred and twenty two patients with critical limb ischaemia and 26 with claudication. METHODS: One hundred and fifty eight limbs treated by SA. MAIN OUTCOME MEASURES: Technical success and complications; cumulative patency, limb salvage and survival; affect of SA on vascular workload. RESULTS: The technical success rate was 85%. There were 26 procedural complications (16%) but no patient required emergency surgery; 30-day mortality was 3%. Primary and secondary 12-month patency rates were 27 and 33%. Limb salvage rate was 88% at 12 months. SA initially reduced the number of patients needing arterial surgery, although this then increased due to late failure of SA and an increase in de novo bypass. CONCLUSIONS: SA carries a low risk of major complications and high immediate technical success. Poor long-term patency suggests that SA is not as durable as bypass surgery. However, failed SA did not compromise subsequent surgery, which only became necessary in a proportion of patients. Our data suggests that there is little to be lost by using SA as first-line treatment for patients with limb-threatening ischaemia who are poor operative risks or who have no autologous vein available.

Left ventricular aneurysm formation: an iatrogenic cause for the third mogul.

Two cases of left ventricular pseudoaneurysm formation developing post-operatively after mitral valve replacement are reported. The chest radiographs showed an abnormal protuberance on the left heart border at the site of the "third mogul". The definitive diagnosis of this protuberance, resulting from the development of a left ventricular aneurysm, was made on angiography in each case. This site is unusual for left ventricular aneurysm formation, with the exception of the annular subvalvular aneurysm described in the negro population. Relevant aetiological factors in the development of these post-operative left ventricular pseudoaneurysms are considered. Since pseudoaneurysms are more prone to rupture than true aneurysms, it is concluded that early diagnosis of development of these left ventricular pseudoaneurysms should be made.