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Biomedical subjects

E Dekker

Publications and source records attributed to E Dekker.

At least 19 recordsLinked to original sources
PubMed1995

Analysis of risk factors for excess mortality after aortic valve replacement.

OBJECTIVES: This study sought to identify risk factors for both late observed and late "excess" mortality after aortic valve replacement and to examine the causes of late mortality. BACKGROUND: Because operative mortality after aortic valve replacement is very low, the timing of surgical intervention should focus on maximizing long-term survival. However, to judge the effect of valve replacement on long-term survival in an elderly population, it is important to separate mortality resulting from extraneous causes (background mortality) from disease-related mortality (excess mortality). Background mortality can be estimated by calculating expected mortality on the basis of age and gender. METHODS: From 1966 to 1986, 643 patients (mean age 59.6 years, 138 [21%] > or = 70 years old) underwent aortic valve replacement, 129 of whom also underwent coronary bypass grafting; 594 patients survived > or = 30 days after the procedure. The overall operative mortality rate for isolated aortic valve replacement decreased over time from 25.5% (1966 to 1972) to 2.6% (1980 to 1986). Cumulative total follow-up after discharge was 3,603 patient-years. Multivariate analysis was performed for both observed and excess mortality. RESULTS: Risk factors for both observed and excess mortality were previous myocardial infarction, coronary artery disease, heart failure and atrial fibrillation. Although age > or = 70 years was a risk factor for observed mortality (hazard rate ratio [HRR] 2.4, 95% confidence interval [CI] 1.6 to 3.7), it was not a risk factor for excess mortality. In contrast, isolated aortic regurgitation was an important risk factor for excess mortality only (HRR 3.8, 95% CI 1.3 to 11.2). Late mortality was valve related in 22% of patients, including sudden death in 7% and cerebral vascular accidents in 7%. Congestive heart failure was an important cause of death (21%) irrespective of the time elapsed since aortic valve replacement. In patients with aortic regurgitation, congestive heart failure was the main cause of death (38%); in patients with aortic regurgitation and preoperative heart failure or severe left ventricular dysfunction, heart failure was the cause of death in 44% and 63%, respectively. CONCLUSIONS: Analysis of excess mortality revealed that older age in itself is not a risk factor for late mortality after aortic valve replacement. Aortic regurgitation carries a high risk, probably associated with left ventricular dysfunction at the time of operation. Earlier operation may be warranted in such patients.

Age Factors↗
PubMed1993

Background mortality in clinical survival studies.

In long-term follow-up studies of survival after an initial event (eg, an operation) mortality from causes other than the one under study obscures the results, especially in elderly patients. In the traditional approach to the calculation of expected mortality a fictitious cohort is drawn from the general population, being matched for age, sex, and calendar time at the time of the initial event. The membership of this cohort is then kept constant from the initial event until the closing date of the study. The survival and mortality of this static cohort is then compared with that of the dynamic patient cohort to throw light on mortality from extraneous causes. This method can lead to severe bias if there is a strong correlation between the duration of observation of the patients and their age. The analysis can be improved by applying rate adjustment when calculating the background component of mortality. In this approach mortality rates from the general population are adjusted (weighted) so that the age, sex, and calendar year are at all times identical with those of each of the patients still alive and under observation. This is illustrated by means of a simplified example and a real-life one from a study at survival after aortic valve replacement. Estimation of rate-adjusted background mortality provides a framework that may put long-term survival, especially of elderly patients, in proper perspective.

Adult↗
PubMed1992

Low-molecular-weight heparin versus standard heparin in general and orthopaedic surgery: a meta-analysis.

Low-molecular-weight heparins (LMWHs) have theoretical advantages over standard heparin as postoperative thromboprophylactic agents. We conducted a meta-analysis of studies reported between 1984 and April, 1991, in which LMWHs were compared with standard heparin for postoperative prophylaxis. We included only randomised studies (reported in English, French, or German) in which investigators compared currently recommended doses of the agents and used adequate screening techniques for deep vein thrombosis. For all surgical studies the relative risk (LMWH versus standard heparin) for deep vein thrombosis was 0.74 (95% Cl 0.65-0.86), for pulmonary embolism 0.43 (95% Cl 0.26-0.72), and for major bleeding 0.98 (95% Cl 0.69-1.40). Comparable relative risks were observed for the general and orthopaedic surgery studies separately. When the analysis for the general surgery studies was limited to those of strong methodology, assessed by eight criteria defined in advance, the benefit/risk ratio was less favourable--relative risk for deep vein thrombosis 0.91 (95% Cl 0.68-1.23), for major bleeding 1.32 (95% Cl 0.69-2.56). There is at present no convincing evidence that in general surgery patients LMWHs, compared with standard heparin, generate a clinically important improvement in the benefit to risk ratio. However, LMWHs may be preferable for orthopaedic surgery patients, in view of the larger absolute risk reduction for venous thrombosis.

Clinical Trials as Topic↗
PubMed1991

Transesophageal atrial pacing--stimulation and discomfort thresholds: the role of electrode configuration and pulse width.

A balloon catheter with six electrodes has been developed for transesophageal atrial stimulation of the human heart. Introduction is easy and its positioning is simple with the help of six unipolar atrial electrograms. In a group of 20 healthy volunteers, stimulation and discomfort thresholds (intolerable discomfort) were measured for three levels of pulse widths (12, 16, and 20 msec) and for five electrode configurations. Stimulation thresholds were below discomfort thresholds in each case. The stimulation threshold depended on pulse width and not on electrode configuration. The discomfort threshold, however, depended on the electrode configuration and not on the pulse width. A moderate but potentially important increase of the ratio between stimulation threshold and discomfort threshold could be achieved by combining a long pulse width (20 msec) and avoiding the largest distance between the active (cathode) and the passive (anode) electrode. Transesophageal atrial stimulation promises to be a practical noninvasive tool for the termination of regular supraventricular tachycardias, basal electrophysiological studies, and controlled acceleration of the heart rate in the study of myocardial ischemia.

Adult↗
PubMed1989

[HIV occupational risk of surgical specialists and operating room personnel in the Saint Lucas Hospital in Amsterdam].

All instrument and needle accidents, and mucosal exposure to blood involving surgical specialists and operating room personnel were recorded for a seven-month period in a middle-sized Amsterdam hospital, the St. Lucas. Fifty-four accidents were reported, of which 42 were percutaneous wounds and 12, blood splatters in the eyes. The frequency of percutaneous wounds per operation per person ranged from 0 to 0.013. In the same period 3098 patients who had to be operated on were asked to participate in an anonymous study for HIV antibody. One hundred and twenty patients refused participation (3.9%). Of the 2978 participating patients seven were seropositive for anti-HIV (0.23%). The observed percutaneous accident frequency and HIV prevalence were used in combination with reports from the literature on the risk of infection after a single exposure to HIV infected material, to calculate the HIV professional risk for operating room personnel in this hospital. For general surgeons the risk of infection (based on 500 operations per year) was calculated as 0.0012 for an occupational lifespan of 30 years. For the other specialists and functions the risk was the same or less. Considering the low risk our conclusion is that screening of preoperative patients is not necessary in this hospital. The observance of general protective measures provides sufficient protection for the professional group examined.

Accidents↗
PubMed1982

Practical considerations in the positioning of EEG electrodes.

Although the 10-20 system of the International Federation was originally proposed as a basis for discussion, there has been little published comment on its strengths and weaknesses or suggestions for its improvement. There are inherent ambiguities in the system, which cannot be applied strictly in accordance with the published specification unless the 4 measurements between the right and left preauricular points and the nasion and the inion are all equal. A study of the cranial measurements of 20 normal adults showed that this criterion was fulfilled to within a margin of 10% in less than half. Further, the standard placements of the 10-20 system cover less than 3/4 of the cerebral convexity. A study of fronto-temporal epileptiform phenomena in 100 subjects indicated that in the majority these were of maximum amplitude over the anterior temporal region, some 20 mm below the typical positions of F7 and F8. In the light of these and previous studies, modifications of the 10-20 system are suggested.

Adult↗
PubMed1980

[Improved care for the aphasic patient: introduction to the central theme of aphasia].

The Dutch Hart Foundation has as one of its major goals the furthering of revalidation of hart patients as well as patients with cerebrovascular illnesses. Since many of these latter patients suffer from aphasic disturbances, the CVD-committee of the above mentioned foundation has, in co-operation with the Dutch Society for Neurology, investigated the possibilities of improving the treatment of these disturbances. A systematic improvement of this treatment depends on the ability to measure it. Therefore, the foundation has invited a number of prominent researchers in this area for a workshop in August 1979 posing the question whether and if so how the severity of aphasia can be measured. The lectures of this meeting, including the discussion, are published in this issue.

Aged↗