Importance of electrode design, lead configuration and impedance for successful low energy transcatheter atrial defibrillation in dogs.

OBJECTIVES: We assessed the feasibility of low energy endocardial defibrillation in a canine model of atrial fibrillation, comparing catheters with large surface area electrodes and standard electrode catheters, and evaluated the effects of lead configuration and circuit impedance on defibrillation energy requirements. BACKGROUND: Although recent animal studies have demonstrated the feasibility of low energy endocardial atrial defibrillation, their results have been conflicting with regard to important methodologic aspects. METHODS: In 14 anesthetized greyhounds, atrial fibrillation was induced by rapid atrial pacing and maintained by vagal stimulation. Two large surface area braided electrode catheters and two standard electrode catheters were introduced percutaneously, one of each, in the right atrial appendage and right ventricular apex. A cutaneous patch electrode was placed on the left thorax. Biphasic shocks synchronized to the ventricular electrogram were used to terminate atrial fibrillation. Seven configurations were evaluated. Three used standard electrodes: proximal atrial cathode to distal atrial, ventricular or cutaneous anode. Four used braided electrodes: three with atrial cathode to ventricular, cutaneous or combined anode; one with ventricular cathode to atrial anode. RESULTS: Defibrillation with standard electrode catheters was associated with high impedance (576 +/- 112 omega) and low success rates for all configurations (28% success at < or = 40 J, no successes at 10 J). Low energy defibrillation was readily achieved with the braided electrodes with significantly lower impedance (75 +/- 13 omega, p < 0.0001). Ventricular fibrillation did not occur. The success rate of cardioversion increased in a dose-response manner, allowing fitting of a sigmoid curve and calculation of energy associated with 50% (ED50) and 90% (ED90) success. The most successful configuration was ventricular cathode/atrial anode (ED50 1.5 +/- 0.4 J), and the least successful was atrial anode/cutaneous patch (ED50 6.5 +/- 3.2 J, p = 0.0001). CONCLUSIONS: Low energy atrial defibrillation is feasible using large surface area electrodes but not with standard electrode catheters owing to high impedance. An intracardiac anode provides lower impedance and higher success rates than are provided by a cutaneous anode.

Passive ventricular constraint amends the course of heart failure: a study in an ovine model of dilated cardiomyopathy.

OBJECTIVE: Dilated cardiomyopathy (DCM) is associated with a progressive deterioration in cardiac function. We hypothesised that some of the deleterious effects of DCM could be reduced by mechanically limiting the degree of cardiac dilatation. METHODS: A Transonic 20A cardiac output (CO) flow-probe was implanted in the pulmonary artery of 12 adult (52 +/- 4 kg) sheep. Early heart failure was created by rapid right ventricular (RV) pacing for 21 days at a rate which resulted in an initial 10% decrease in CO (to a maximum of 190 bpm). A custom polyester jacket (Acorn Cardiovascular, St Paul, MN) was then placed, via a partial lower sternotomy, on the ventricular epicardium of all sheep. Animals were randomised either to jacket retention (wrap) or removal (sham). Pacing was recommenced at a higher rate (that initiated a further 10% decrease in CO) for 28 days. Haemodynamic and echocardiographic parameters were determined at baseline, implant and at termination. RESULTS: At termination, the left ventricular fractional shortening was significantly higher (p = 0.03), the degree of mitral valve regurgitation lower (scaled 0-3) (p = 0.03) and the left ventricular long axis area smaller (p = 0.02) in the wrap animals compared with sham. CONCLUSIONS: In this model of heart failure, ventricular constraint with a polyester jacket diminished the deterioration in cardiac function associated with progressive dilated cardiomyopathy. These results suggest that maintainance of a more normal cardiac size and shape may be beneficial in patients with dilated cardiomyopathy.

The use of 'spot' measurements in epidemiological studies of the health effects of magnetic field exposure.

In several countries, epidemiological studies are being planned, or are in progress, to test the hypothesis that a causal relation exists between exposure to extremely low frequency magnetic fields and cancer incidence. One of the major difficulties in these studies is the development of valid and efficient protocols to assess magnetic field exposure. In studies focusing on residential magnetic fields, many researchers are turning to recently developed stationary automated magnetic field monitors to characterize exposure. We argue that a relatively small number of manually collected 'spot' measurements may be an adequate alternative which has several advantages. We compared a dichotomous exposure classification based on continuous magnetic field monitoring of 40 houses with that obtained through 'spot' measurements randomly sampled from the continuous records. We found that a single spot measurement had at least an 80% chance of classifying houses correctly and that this probability did not increase significantly as the number of readings was increased. We also calculated the sensitivity and specificity of various simulated measurement protocols and, from these, the effect of misclassification on estimates of relative risk. Since relatively large spatial variations in background magnetic field exist in many homes, we suggest that a small number of readings collected manually at several points within a residence may characterize the magnetic field better than continuous monitoring at one fixed location.

A population-based study of assessed applicants to long-term nursing home care.

OBJECTIVE: To examine the characteristics of all individuals assessed as requiring nursing home care arising from a population living within a defined geographical region and to study the manner in which they presented for assessment. DESIGN: Clinical assessment by a physician in geriatric medicine with the assistance of other disciplines. SETTING: Regional Geriatric Assessment Service. SUBJECTS: All persons recommended for nursing home care within the study period. RESULTS: The major diseases contributing to the need for nursing home care were organic brain disorders (60%) and stroke (32%). Dementia was present in 64% of cases; significant behavioral disturbance in 18%; severe communication disorders were frequent. The majority (86%) had been ill for greater than 1 year. The mode of presentation was acute in 9%, acute-on-chronic in 46%, and chronic in 45%. It was associated with significant differences in case characteristics including the location at the time of assessment, diagnoses, duration of illness, physical dependency, communication disorders, behavioral disturbance, and skilled nursing care requirements. CONCLUSIONS: These observations suggest that progression to nursing home care varies considerably. Strategies directed toward the prevention of institutionalization should be organized in recognition of these variations.

Helicobacter pylori antibody titres in serum, plasma and successively thawed specimens: implications for epidemiological and clinical studies.

Agreement between Helicobacter pylori IgG antibodies measured using the Pylori-set EIA-G kit in serum, plasma and successively thawed specimens was studied and the implications for epidemiological and clinical studies assessed. Plasma titres may differ from serum titres by -6% to +8% and therefore may be substituted for serum. The change in titre around the cut off value was -0.31 (se = 5.7, p = 0.96) per thaw. The estimated maximum drop after three thawings, 34.5, would result in only a small decrease in sensitivity (1.3%). For qualitative epidemiological studies, this additional misclassification rate is relatively small. However, positive titres did reduce over successive thawings, with the estimated maximum drop being 11.4% per thaw. Therefore, thawing does need to be considered as a contributing factor when interpreting titre drops in eradication trials. Baseline and follow up specimens from clinical studies should be thawed once only and tested concurrently.

Discordance of mercury sphygmomanometer and ambulatory blood pressure measurements for the detection of untreated hypertension in a population study.

To evaluate the extent to which ambulatory blood pressure (ABP) measurements could redefine the prevalence of untreated hypertension in the general population, we studied a randomly selected subgroup of the National Heart Foundation of Australia's Risk Factor Prevalence Study 1989. Subjects taking blood pressure (BP) lowering medications were excluded, leaving 66 patients with 24h ABP recordings for analysis. Mean awake ABPs were generally lower than survey BPs and diminished with reduced activity (away from work and during sleep). The correlation of survey BP and daytime ABP (10.00-20.00 h) classification of untreated hypertension was moderate (Cohen's correlation coefficient 0.49-0.56). Untreated hypertension was identified in 20 subjects by the mercury sphygmomanometer technique (BP > or = 150/90 mmHg). Six (30%) of those subjects had a mean ABP < 135/85 mmHg suggesting 'normotension' on ambulatory criteria. Conversely, 19 subjects had a mean ABP of > or = 135/85 mmHg, five (26%) of whom had 'normal' survey BPs. We conclude that ambulatory and mercury sphygmomanometer methods of BP measurement in this population study defined a similar prevalence of untreated hypertension but were discordant for a substantial percentage of individuals. The prognostic significance of ABP levels and any discordance with survey or office mercury sphygmomanometer BP readings will remain uncertain until prospective studies using both forms of measurement are completed.

Psychological aspects of nipple pain in lactating women.

The aim of the study was to assess the psychological impact of nipple pain in lactating women. Forty-eight lactating women with nipple pain completed mood scales at their first visit and following resolution of their pain, and 65 lactating women without nipple pain completed one set of mood scales. At the first visit, the mean score on the Edinburgh Postnatal Depression Scale (EPDS) in the nipple pain group was 12.4 and the control group was 7.6 (p < 0.0001). Eighteen women (38%) scored above the threshold for depression (> 12), compared to nine in the control group (14%): p < 0.01. Following pain resolution, the mean score on the EPDS decreased to 7.3 (p < 0.001); and six women (16%) scored 13 or over on the EPDS, significantly less than initially (p < 0.05). Similarly, on the Profile of Mood States (POMS), the nipple pain group scored significantly higher than control group on all mood factors (Tension, Depression, Fatigue, Confusion, Vigor [lower]), except Anger which did not reach a level of significance. After pain resolution, POMS scores returned to similar levels as the control group. In conclusion, both the EPDS and POMS indicated women with nipple pain were experiencing high levels of emotional distress. However, once the pain had resolved their distress also resolved.

Comparison of unsafe drinking between a rural and metropolitan area.

Factors associated with unsafe drinking in a rural area were identified and the prevalence of unsafe drinking and alcohol related mortality compared with a metropolitan area. Alcohol consumption data were collected from a random sample of adults in Greater Ballarat. Odds ratios of demographic factors associated with unsafe drinking were estimated by logistic regression. Compared with males and 20-29-year-olds, females and 30-59-year-olds had a significantly lower prevalence of 'intermediate' or higher risk drinking and binge-only drinking. Rural-metropolitan ratios for the prevalence of unsafe drinking and alcohol related mortality were also greatest in young adults. Young adults must adopt safer drinking habits if the rural excess in mortality is to be reduced.

An analysis of associations between social class and ambient magnetic fields in metropolitan Melbourne.

In the course of a study on residential magnetic-field exposure, some incidental data were obtained that bear on the issue of confounding of magnetic field exposure by social class. We have explored the possibility that the magnetic flux density of 50 Hz fields measured in Melbourne streets is correlated with a number of variables that index the socio-economic status of the neighborhood. We have examined also for a correlation between field-intensity levels and sums of some or all of the indicators, which were weighted to provide an overall score on socio-economic status. Although some of the indexes were weakly, but significantly, correlated with environmental levels of magnetic fields, the combined indices were not. These results indicate that socio-economic status is not likely to be a confounder in epidemiological studies of residential exposure to ELF magnetic fields in Melbourne.

Helicobacter pylori infection in an Australian regional city: prevalence and risk factors.

OBJECTIVE: To investigate the prevalence of Helicobacter pylori infection and potential risk factors for infection in an adult Australian population. DESIGN: Cross-sectional study. SETTING: Ballarat, a major regional city in Victoria (population, 78,000; 92% bom in Australia), November 1994 to July 1995. PARTICIPANTS: 217 adults randomly selected from the electoral roll. MAIN OUTCOME MEASURES: H. pylori IgG antibody status by enzyme immunoassay; amount of dental plaque; sociodemographic and other potential risk factors; odds ratios for risk factors determined by logistic regression analysis. RESULTS: Age-standardised prevalence of H. pylori infection was 30.6%. After adjustment for age, sex and socioeconomic index, positive H. pylori status was significantly associated with increasing number of tooth surfaces with a high plaque score (odds ratio [OR], 1.7; 95% confidence interval [CI], 1.1-2.7), increasing number of years in a job with public contact (OR, 1.7; 95% CI, 1.3-2.3), blood group B antigen (OR, 3.1; 95% CI, 1.1-9.1), and having lived in a household with more than six members during childhood (OR, 2.5; 95% CI, 1.1-5.5). Negative H. pylori status was significantly associated with increasing education, having ever lived on a farm, and having teeth scaled less than once a year. CONCLUSIONS: H. pylori infection is common. Dental plaque may be a reservoir for H. pylori, which is probably transmitted by person-to-person contact, and blood group B antigen may predispose to infection. Community education about effective oral hygiene and adoption of good hygiene practices by those with regular public contact may be important to prevent acquisition and transmission of H. pylori.

Helicobacter pylori infection is not a correlate of plasma fibrinogen in the Australian population.

Plasma fibrinogen concentration is an important independent risk factor for cardiovascular disease. Studies into whether Helicobacter pylori infection and fibrinogen are associated have yielded inconsistent results. Despite the geographical variation in fibrinogen and prevalence of H. pylori infection, all studies to date have been undertaken in the United Kingdom or Italy. The association between H. pylori infection and fibrinogen was investigated in 324 adults, 65% of a random sample, in an Australian regional city. The mean plasma fibrinogen concentration in 98 infected participants (2.52 g/l) was similar to that in 226 non-infected subjects (2.58 g/l, P = 0.51); 95% confidence interval on the difference was -0.23-0.11 g/l. After including all potential confounding factors in a backward multiple linear regression analysis, H. pylori was still not associated with fibrinogen (P = 0.084). Any association between H. pylori and cardiovascular disease in Australia is not mediated through fibrinogen.

Age-standardised mortality and proportional mortality analyses of aboriginal and non-aboriginal deaths in metropolitan, rural and remote areas.

The study's aim was to assess how much of the variation in disease-specific mortality between metropolitan, rural and remote areas is specific to those diseases or reflects the all-cause mortality pattern. The ranges and variances of disease-specific standardised proportional mortality ratios between geographical areas were compared to those of the corresponding standardised mortality ratios. For most chapters in the International Classification of Diseases, the ranges and variances of the standardised proportional mortality ratios were less than 40% of those of the corresponding standardised mortality ratios. Only a small proportion of the variation in mortality can therefore be attributed to a specific disease component; the remainder must be attributed to an underlying 'force of mortality'. Research, programs and policies addressing the socio-economic disadvantages of living in remote areas may lead to a greater improvement in mortality than those targeting specific diseases.

Helicobacter pylori infection: an added stressor on iron status of women in the community.

OBJECTIVE: To explore a possible association between Helicobacter pylori infection and iron status. DESIGN: Cross-sectional study. SETTING: Ballarat (a major regional city in Victoria), population 78000, October November 1997. PARTICIPANTS: 160 women and 152 men, a subsample of participants in a cardiovascular disease risk factor prevalence survey for whom frozen plasma was available. MAIN OUTCOME MEASURES: H. pylori IgG antibody status by enzyme immunoassay; iron intake; plasma iron, transferrin and ferritin concentrations. RESULTS: 28% of women and 33% of men were infected with H. pylori. The mean (SEM) plasma ferritin concentration of infected women (59.3 [7.6] microg/L) was significantly lower than for non-infected women (88.8 [7.9] microg/L; P=0.002), after adjusting for age. Mean daily dietary iron intakes were similar in infected and non-infected women. CONCLUSIONS: H. pylori infection appears to be an additional stressor on women's iron status, but the mechanism remains to be determined.

Candida albicans: is it associated with nipple pain in lactating women?

Persistent nipple pain in lactating women, burning in nature, and associated with radiating breast pain, has been claimed by some authorities to be due to 'thrush' (candida) infection. Yet, scientific proof has been lacking. This study compared microbiological assessment of 61 women with nipple pain, 64 women without nipple pain, and 31 non-lactating women. Swabs of the nipple and baby's mouth, and expressed breast milk were collected for culture. Growth of Candida albicans (nipple and milk) was found more often in the women with nipple pain (19%) than in the control group (3%, p < 0.01). In addition, Staphylococcus aureus was also associated with nipple pain (p < 0.0001), and independently associated with nipple fissures (p < 0.0001). Neither C. albicans nor S. aureus was found on the nipples of the non-lactating group.

Complementary therapies: have they become accepted in general practice?

OBJECTIVES: To describe Victorian general practitioners' attitudes towards and use of a range of complementary therapies. DESIGN: A self-administered postal survey sent to a random sample of 800 general practitioners (GPs) in Victoria in July 1997. PARTICIPANTS: 488 GPs (response rate, 64%). MAIN OUTCOME MEASURES: GPs' knowledge; opinions about harmfulness and effectiveness; appropriateness for GPs to practise; perceived patient demand; need for undergraduate education; referral rates to complementary practitioners; and training in and practice of each therapy. RESULTS: Acupuncture, hypnosis and meditation are well accepted by the surveyed GPs, as over 80% have referred patients patients to practitioners of these therapies and nearly half have considered using them. General practitioners have trained in various therapies--meditation (34%), acupuncture (23%), vitamin and mineral therapy (23%), hypnosis (20%), herbal medicine (12%), chiropractic (8%), naturopathy (6%), homoeopathy (5%), spiritual healing (5%), osteopathy (4%), aroma-therapy (4%), and reflexology (2%). A quarter to a third were interested in training in chiropractic, herbal medicine, naturopathy and vitamin and mineral therapy. General practitioners appear to underestimate their patients' use of complementary therapies. CONCLUSIONS: There is evidence in Australia of widespread acceptance of acupuncture, meditation, hypnosis and chiropractic by GPs and lesser acceptance of the other therapies. These findings generate an urgent need for evidence of these therapies' effectiveness.

The reliability and validity of work measurement in Australian general practice consultations.

OBJECTIVES: To examine the reliability of relative work value assessment in general practice consultations and to determine whether different methods of assessing work produce consistent rankings. DESIGN: Cross-sectional observational assessment of general practice consulations. SETTING: General practices in Victoria between October 1991 and October 1992. PARTICIPANTS: 686 patients attending one of 58 general practitioners (GPs) drawn from a random, stratified sample. METHODS: Each participating GP had one day of consultations videotaped. They rated the work value of each consultation by using a magnitude estimation scale relative to a reference vignette. Three GP observers independently applied the same scale to the videotaped consultations. After three months, the observers applied a second measurement of work value, a compensation scale (also relative to the reference vignette), to the videotaped consultations. Duration of consultation was the third rating method. MAIN OUTCOME MEASURES: The reliability of work value assessment for each scale. Consultation rank order correlation coefficients among all rating methods. RESULTS: Observer reliability was high for both scales. Practising GPs showed lower levels of reliability in assessing the work value of their consultations. Strong positive correlations were found for consultation rankings among the observer scales and duration of the consultation. The duration of the consultation emerged as an important predictor of consultation work value. CONCLUSIONS: Scaling methods appear to be of little value to the practising GP in reliably assessing the relative work value of their consultations; training in the use of these scales may improve their reliability. However, the duration of consultation may be a reasonable proxy for relative work value assessment in general practice consultations.

The influence of age on atrial fibrillation as a risk factor for stroke.

To determine the influence of age on atrial fibrillation as a risk factor for cerebral infarction, the Austin Hospital Stroke Unit Register from 1977 to 1990 was reviewed. There were 2279 patients with cerebral infarction (excluding lacunar infarction syndromes) with a mean age of 68.3 years who were identified as subjects, and 800 patients with pseudostroke and lacunar infarction syndromes with a mean age of 64.7 years who were identified as controls. Data concerning potential risk factors for stroke (including sex, age, atrial fibrillation, cardiac disease, hypertension, diabetes, peripheral vascular disease and smoking) were analyzed using multivariate regression techniques. It was found that atrial fibrillation was a significant risk factor for cerebral infarction (excluding lacunar infarction) for all age groups, after adjusting for the effects of other risk factors (P less than .001). However, when age was stratified into four groups, the age-specific odds ratios for atrial fibrillation were not significantly different and no significant interactions between atrial fibrillation and age or other risk factors were found (P greater than 0.1). It was concluded that, although with increasing age atrial fibrillation becomes a more frequent cause of stroke, its potency as a risk factor does not increase correspondingly. There was no significant influence of age on the relationship between atrial fibrillation and cerebral infarction.

Effects of left atrial dilatation on the endocardial atrial defibrillation threshold: a study in an ovine model of pacing induced dilated cardiomyopathy.

Left atrial (LA) dilation is a common finding in patients with chronic atrial fibrillation (AF). Progressive dilatation may alter the atrial defibrillation threshold (ADFT). In our study, epicardial electrodes were implanted on the LA free wall and right ventricular apex of eight adult sheep. Large surface area, coiled endocardial electrodes were positioned in the coronary sinus and right atrium (RA). LA dilatation was induced by rapid ventricular pacing (190 beats/min) for 6 weeks and echocardiographically assessed weekly along with the ADFT (under propofol anesthesia). LA effective refractory period (ERP) was measured every 2-3 days using a standard extra stimulus technique and 400 ms drive. The AF cycle length (AFCL) was assessed from LA electrograms. During the 6 weeks of pacing the mean LA area increased from 6.1 +/- 1.5 to 21.3 +/- 2.4 cm2. There were no significant changes in the mean ADFT (122 +/- 15 V), circuit impedance (46 +/- 5 omega), or LA AFCL (136 +/- 23 ms). There was a significant increase in the mean LA ERP (106 +/- 10 ms at day 0, and 120 +/- 13 ms at day 42 of pacing). In this study, using chronically implanted defibrillation leads, the minimal energy requirements for successful AF were not significantly altered by ongoing left atrial dilatation. This finding is a further endorsement of the efficiency of the coronary sinus/RA shock vector. Furthermore, the apparent stability of the AF present may be a further indication of a link between the type of AF and the ADFT.

Smoking as a risk factor for cortical ischaemia presumably due to carotid occlusive disease.

Smoking is now a well established risk factor for ischaemic stroke. However, the risk associated with smoking may differ between subgroups of ischaemic stroke. To test the hypothesis that cortical ischaemia due to carotid artery occlusive disease, the latter of which has previously been linked to smoking, may have a higher smoking risk compared to other forms of cerebral ischaemia, we identified 178 cases of cortical ischaemia presumably due to carotid occlusive disease in our previous case-control population and compared the odds ratios (OR) for smoking risk in this group with that in group of 244 cases of other forms of cerebral ischaemia combined. All cases were individually matched for age (+/- 5 years) and sex with neighbourhood controls. Multiple conditional logistic regression was used to adjust for potentially confounding factors. The OR for current smokers in the cortical group was higher than that in the non-cortical group [OR 4.4, 95% confidence interval 2.2, 8.9 vs. 2.1 (1.1, 4.1)], particularly for those who smoked more than 60 pack-years [5.5 (2.2, 14.0) vs. 1.5 (0.6, 3.8)] and those who currently smoked more than one pack per day [20.2 (3.3, 122.3) vs. 2.6 (0.8, 8.2)], but not significantly. Overall, there is some evidence to suggest that smoking may be a more potent risk factor for cortical than for other forms of cerebral ischaemia, particularly at high smoking rates. Further studies are needed to substantiate this finding.

A case-control study of the androgen receptor gene CAG repeat polymorphism in Australian prostate carcinoma subjects.

BACKGROUND: The development of prostate carcinoma is androgen-dependent. The coding sequence of the androgen receptor (AR) gene contains a CAG repeat polymorphism that has been shown to influence AR activity in vitro. Studies of this polymorphism as a prostate carcinoma risk factor have been conflicting. METHODS: A matched case-control design was used in a clinic-based multicenter study of Australian prostate carcinoma subjects. Cancer subjects were matched by age and locality with controls, all of whom had a serum prostate specific antigen (PSA) level of less than 4 mg/L. Conditional logistic regression was used to determine the relative risk of prostate carcinoma dependent on AR gene CAG number. The association of disease characteristics at diagnosis with the polymorphism also was assessed. RESULTS: Five hundred forty-five cases of prostate carcinoma and 456 matched case-control pairs were recruited. Association studies of disease characteristics at diagnosis showed age at diagnosis to be associated with AR CAG number by univariate (P = 0.004) and multivariate (adjusting for PSA, stage, and grade) linear regression (P = 0.018). No association was observed between the polymorphism and disease stage (TNM-based categories; P = 0.277), histologic grade (P = 0.41), or PSA level at diagnosis (P = 0.48). In the pairwise case-control analysis, the odds ratio of prostate carcinoma for a change of 5 CAG repeats gave an odds ratio of 0.9821 (95% confidence interval, 0.84-1.15). CONCLUSIONS: In this Australian study population, the AR CAG repeat polymorphism was not a risk factor for prostate carcinoma, but a shorter repeat sequence was associated with earlier age at diagnosis.