An unusual post mortem illustration of twiddler's syndrome.
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Aged, 80 and over↗
Biomedical subjects
B Thwaites
Publications and source records attributed to B Thwaites.
The strength-duration curve and its importance in pacing efficiency: a study of 325 pacing leads in 229 patients.
Pacemaker battery life is dependent on programmable parameters, principally pulse amplitude and pulse duration. High factory default settings cause excessive current drain. The strength-duration curve relates pacing threshold to pulse duration. The most energy efficient pacing occurs at chronaxie, a value of pulse duration derived from the curve. Strength-duration curves were calculated for 325 acutely implanted pacing leads. Chronaxie and rheobase were compared for atrial and ventricular leads. Chronaxie was compared with actual programmed pulse duration. There were 101 atrial and 224 ventricular leads, all passive fixation. The curve fit was good, (mean error +/- SD) 0.024 +/- 0.06 V for atrial curves and 0.008 +/- 0.034 V for ventricular curves. Mean (+/- SD) atrial and ventricular chronaxies were 0.24 +/- 0.07 ms and 0.25 +/- 0.07 ms, respectively. A "Z" value of 1.4 indicated that chronaxies might have been from the same population. Mean (+/- SD) atrial and ventricular rheobases were 0.51 +/- 0.2 V and 0.35 +/- 0.13 V, respectively. A "Z" value of 7.1 (P < 0.001) suggested atrial and ventricular rheobases were from differing populations. All patients had factory default pulse durations of 0.45 ms or 0.5 ms, exceeding acute chronaxie by a factor of two, thus, demonstrating suboptimal pacing. We conclude that understanding the strength-duration curve is critical. Sensible programming of other pacing functions optimizes longevity. Battery drain is reduced by programming pulse duration to chronaxie with a doubling of voltage threshold at this point to achieve a safety margin. Further study of chronaxie drift with time is required.
Adult↗
Prevalence of atrial fibrillation and eligibility for anticoagulants in the community.
BACKGROUND: Anticoagulants are effective in the prevention of stroke in atrial fibrillation and flutter (AF). We aimed to find out the prevalence of AF in the UK and to estimate the proportion of patients with AF who might benefit from anticoagulation. METHODS: We screened with electrocardiography a random sample of 4843 people from the community aged 65 years and older for AF. Participants with AF had further investigations to identify risk factors for stroke and contraindications to anticoagulants. We used three sets of criteria to assess risk and eligibility for anticoagulation. FINDINGS: 228 (4.7%) participants had AF. According to analyses derived from risk stratifications based on the Stroke Prevention in Atrial Fibrillation (SPAF) study 61% of these patients would have benefited from anticoagulation, 49% according to pooled analysis of trial results, and 41% according to the inclusion criteria for the SPAF 3 study. Anticoagulants were used by 1114 (23%) of all patients and were least used among elderly women, who may be the most likely to benefit. Echocardiography would be useful to assess the need for anticoagulation only in patients younger than 75 years with no contraindications to treatment and no clinical risk factors for stroke. INTERPRETATION: Anticoagulants seem to be underused and misdirected in treatment of AF, according to various criteria. Efforts to promote and support wider and more appropriate use of anticoagulants would seem to be justified, and should decrease the incidence of stroke amongst elderly patients.
Age Distribution↗
Prevalence and clinical significance of aortic valve prolapse.
The prevalence and clinical significance of aortic valve prolapse were determined prospectively in 2000 consecutive patients undergoing routine clinical cross sectional echocardiography. Two hundred and twelve patients were excluded because the aortic cusps were not adequately visualised. Aortic valve prolapse was defined as downward displacement of cuspal material below a line joining the points of attachment of the aortic valve leaflets. Twenty four cases of aortic valve prolapse (1.2%) were identified. The patients were aged 12-64 years and nine were women. All had underlying valvar heart disease and the commonest lesion (in 11 cases) was prolapse of the larger cusp in bicuspid valves. Aortic valve prolapse was seen in four patients with mitral valve prolapse (two with severe regurgitation), one of whom had marfanoid aortic root dilatation. The remaining examples of aortic prolapse were seen in patients with various disorders including one with pulmonary atresia, two with aortic root disease (one with dissection and one with idiopathic dilatation), and one case of severe mitral regurgitation. Valves destroyed by infective endocarditis were seen in two cases. Aortic valve prolapse may be detected in various cardiac disorders and does not imply the presence of aortic regurgitation, but when bicuspid aortic valves are present it may well be important in producing such regurgitation. Although aortic valve prolapse may be associated with severe forms of mitral valve prolapse, these patients rarely have aortic regurgitation.
Adolescent↗
A future with Griffiths.
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Administrative Personnel↗
Coronary care unit ST-trending system: interpreting complex output data.
Analysis of the ST segment is an accepted part of the assessment of coronary ischaemia. Traditionally, such analysis has been applied to 12-lead surface electrocardiograms, but it is increasingly applied to 24-hour Holter recordings and bedside monitoring systems, using complex computer algorithms. There is a potential for results to be misleading as a consequence of uncritical acceptance of complex medical data processing.
Bias↗