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Biomedical subjects

C D Naylor

Publications and source records attributed to C D Naylor.

At least 37 records · Page 2Linked to original sources
PubMed2000

Dealing with missing data in observational health care outcome analyses.

Observational outcome analyses appear frequently in the health research literature. For such analyses, clinical registries are preferred to administrative databases. Missing data are a common problem in any clinical registry, and pose a threat to the validity of observational outcomes analyses. Faced with missing data in a new clinical registry, we compared three possible responses: exclude cases with missing data; assume that the missing data indicated absence of risk; or merge the clinical database with an existing administrative database. The predictive model derived using the merged data showed a higher C statistic (C = 0.770), better model goodness-of-fit as measured in a decile-of-risk analysis, the largest gradient of risk across deciles (46.3), and the largest decrease in deviance (-2 log likelihood = 406.2). The superior performance of the enhanced data model supports the use of this "enhancement" methodology and bears consideration when researchers are faced with nonrandom missing data.

Adult↗
PubMed2000

Subgroups, treatment effects, and baseline risks: some lessons from major cardiovascular trials.

BACKGROUND: The objective of this study was to determine how subgroup analyses are performed in large randomized trials of cardiovascular pharmacotherapy. METHODS AND RESULTS: We reviewed 67 randomized, double-blind, controlled trials involving pharmacotherapy in at least 1000 patients with unstable angina, myocardial infarction, left ventricular dysfunction, or heart failure with clinical outcomes as primary end points, published between 1980 and 1997. Nine had no subgroup analyses but 43 reported on 5 or more subgroups and 31 reported subgroups without formal statistical tests for treatment-subgroup interactions. In most trials, a rationale for subgroup selection was missing. All but 6 focused on single-factor subgroups. CONCLUSIONS: Trial subgroups should ideally be defined a priori on 2 bases: single-factor subgroups with a strong rationale for biological response modification and multifactorial prognostic subgroups defined from baseline risks. However, single-factor subgroup analyses are often reported without a supporting rationale or formal statistical tests for interactions. We suggest that clinicians should interpret published subgroup-specific variations in treatment effects skeptically unless there is a prespecified rationale and a significant treatment-subgroup interaction.

Angina, Unstable↗
PubMed1999

Temporal changes in the outcomes of acute myocardial infarction in Ontario, 1992-1996.

BACKGROUND: There is relatively little information available on recent population-based trends in the outcomes of patients who have had an acute myocardial infarction (AMI). We, therefore, conducted a study of temporal trends in the outcomes of AMI patients in Ontario, Canada, between the 1992 and 1996 fiscal years. METHODS: 114,618 AMI patients were discharged from hospitals in Ontario between Apr. 1, 1992, and Mar. 31, 1997. After specific exclusion criteria were applied the final sample of 89,456 patients was divided into 5 cohorts according to the fiscal year of discharge. As part of the Ontario Myocardial Infarction Database project the linked administrative data pertaining to these patients were used to examine cohort characteristics, cardiac procedures used and mortality rates for each of the 5 cohorts over time. RESULTS: There was a significant increase in the percentage of patients in Ontario receiving coronary angiography, percutaneous transluminal coronary angioplasty and coronary artery bypass grafting surgery (p < 0.001) after an AMI between 1992 and 1996. In addition, the overall 30-day risk-adjusted mortality rate declined from 15.5% in 1992 to 14.0% in 1996 (p = 0.001) and the 1-year risk-adjusted mortality rate declined from 23.7% in 1992 to 22.3% in 1996 (p = 0.017). Virtually all of the improvement occurred within 30 days of admission. The absolute decline in 1-year mortality rates was significant for patients under the age of 65 (2.3%, 95% confidence interval [CI] 1.4% to 3.2%) and for males (1.2%, 95% CI 0.2% to 2.2%); absolute declines were not significant for patients 65 years of age or older (0.7%, 95% CI -0.6% to 2.0%) and for female patients (-0.1%, 95% CI -1.7% to 1.5%). Interestingly, post-infarction coronary angiography and coronary artery bypass grafting rates were consistently lower in the older and the female patients throughout the study period. INTERPRETATION: There was a modest improvement in the short- and long-term survival of patients in Ontario after an AMI between 1992 and 1996. The Ontario experience suggests that recent advances in AMI management have been of more benefit to younger and male AMI patients.

Age Factors↗
PubMed1999

Effects of socioeconomic status on access to invasive cardiac procedures and on mortality after acute myocardial infarction.

BACKGROUND: Universal health care systems seek to ensure access to care on the basis of need rather than income and to improve the health status of all citizens. We examined the performance of the Canadian health system with respect to these goals in the province of Ontario by assessing the effects of neighborhood income on access to invasive cardiac procedures and on mortality one year after acute myocardial infarction. METHODS: We linked claims for payment for physicians' services, hospital-discharge abstracts, and vital-status data for all patients with acute myocardial infarction who were admitted to hospitals in Ontario between April 1994 and March 1997. Patients' income levels were imputed from the median incomes of their residential neighborhoods as determined in Canada's 1996 census. We determined rates of use and waiting times for coronary angiography and revascularization procedures after the index admission for acute myocardial infarction and determined death rates at one year. In multivariate analyses, we controlled for the patient's age, sex, and severity of disease; the specialty of the attending physician; the volume of cases, teaching status, and on-site facilities for cardiac procedures at the admitting hospital; and the geographic proximity of the admitting hospital to tertiary care centers. RESULTS: The study cohort consisted of 51,591 patients. With respect to coronary angiography, increases in neighborhood income from the lowest to the highest quintile were associated with a 23 percent increase in rates of use and a 45 percent decrease in waiting times. There was a strong inverse relation between income and mortality at one year (P<0.001). Each $10,000 increase in the neighborhood median income was associated with a 10 percent reduction in the risk of death within one year (adjusted hazard ratio, 0.90; 95 percent confidence interval, 0.86 to 0.94). CONCLUSIONS: In the province of Ontario, despite Canada's universal health care system, socioeconomic status had pronounced effects on access to specialized cardiac services as well as on mortality one year after acute myocardial infarction.

Coronary Angiography↗
PubMed1999

Fairness in the coronary angiography queue.

BACKGROUND: Since waiting lists for coronary angiography are generally managed without explicit queuing criteria, patients may not receive priority on the basis of clinical acuity. The objective of this study was to examine clinical and nonclinical determinants of the length of time patients wait for coronary angiography. METHODS: In this single-centre prospective cohort study conducted in the autumn of 1997, 357 consecutive patients were followed from initial triage until a coronary angiography was performed or an adverse cardiac event occurred. The referring physicians' hospital affiliation (physicians at Sunnybrook & Women's College Health Sciences Centre, those who practice at another centre but perform angiography at Sunnybrook and those with no previous association with Sunnybrook) was used to compare processes of care. A clinical urgency rating scale was used to assign a recommended maximum waiting time (RMWT) to each patient retrospectively, but this was not used in the queuing process. RMWTs and actual waiting times for patients in the 3 referral groups were compared; the influence clinical and nonclinical variables had on the actual length of time patients waited for coronary angiography was assessed; and possible predictors of adverse events were examined. RESULTS: Of 357 patients referred to Sunnybrook, 22 (6.2%) experienced adverse events while in the queue. Among those who remained, 308 (91.9%) were in need of coronary angiography; 201 (60.0%) of those patients received one within the RMWT. The length of time to angiography was influenced by clinical characteristics similar to those specified on the urgency rating scale, leading to a moderate agreement between actual waiting times and RMWTs (kappa = 0.53). However, physician affiliation was a highly significant (p < 0.001) and independent predictor of waiting time. Whereas 45.6% of the variation in waiting time was explained by all clinical factors combined, 9.3% of the variation was explained by physician affiliation alone. INTERPRETATION: Informal queuing practices for coronary angiography do reflect clinical acuity, but they are also influenced by nonclinical factors, such as the nature of the physicians' association with the catheterization facility.

Adult↗
PubMed1999

Will elderly patients stand aside for younger patients in the queue for cardiac services?

BACKGROUND: Fair management of queues for hospital-based services requires consideration of clinical need, but there is no information on public attitudes towards non-clinical factors such as age or work status as determinants of priority. METHODS: We asked elderly residents of Padova, Italy, whether, if they were awaiting cardiac surgery or an outpatient cardiology consultant, they would give up their place in line for a younger or self-employed individual. We also elicited responses from a convenience sample of younger health workers asked to imagine themselves as elderly persons facing the same choices. FINDINGS: The eligible response rate was 72% (443/616). About half deemed it right to give up their place in line for cardiac surgery to a 45-year-old (51%, 95% CI 46-56) or self-employed person (47%, 95% CI 42-51) Proportions were significantly higher for an outpatient consultation (68%, 95% CI 63-72). In multivariate analyses, married respondents, those closer to age 65, university graduates, and those who were formerly self-employed were significantly less likely to respond affirmatively. In significant contrast for all four scenarios (p<0.0001), the overwhelming majority of non-elderly respondents refused to give up their places in line. INTERPRETATION: The majority of elderly citizens were hypothetically willing to cede priority in accessing cardiac care to younger or self-employed persons, but this willingness was attenuated among the "young" elderly and more privileged respondents. Non-elderly respondents were much less self-sacrificing, suggesting that ageing baby-boomers may be more assertive about their continuing rights to health care.

Age Factors↗
PubMed1999

Use of vitamin B12 injections among elderly patients by primary care practitioners in Ontario.

BACKGROUND: Excess use of parenteral vitamin B12 has been reported from audits of clinical practices. The authors assessed the use of vitamin B12 injections in patients aged 65 years and over in Ontario. METHODS: A cross-sectional analysis was conducted that included all elderly people covered by the Ontario Health Insurance Plan who received insured services from general practitioners or family physicians (GP/FPs). For each practice the proportion of elderly patients who received regular vitamin B12 injections between July 1996 and June 1997 was calculated. The frequency of injections was determined for each patient receiving regular B12 replacement. RESULTS: Of the 1,196,748 elderly patients (mean age 74.8 [standard deviation 6.8], 58.0% female) treated by 14,177 GP/FPs, 23,651 (2.0%) received regular B12 injections. The rate of B12 injections per patient, standardized for age and sex, varied between practices (range 0%-48.6%). Although no authoritative sources support the practice, 3303 (19.8%) of the 16,707 patients receiving long-term parenteral therapy had, on average, overly frequent injections (more than 1 injection every 4 weeks). For 76 (12.3%) of the 617 practices with 10 or more patients receiving regular vitamin B12 injections, the mean injection frequency was greater than once every 4 weeks. The proportion of patients in these 617 practices who received overly frequent injections varied extensively (0%-100%). INTERPRETATION: Our findings indicate that some primary care physicians in Ontario administer unnecessary vitamin B12 injections to elderly patients.

Aged↗
PubMed1999

Ready-made, recalibrated, or Remodeled? Issues in the use of risk indexes for assessing mortality after coronary artery bypass graft surgery.

BACKGROUND: Risk indexes for operative mortality after cardiac surgery are used for comparative profiling of surgeons or centers. We examined whether clinicians and managers should use an existing index without modification, recalibrate it for their populations, or derive a new model altogether. METHODS AND RESULTS: Drawing on 7491 consecutive patients who underwent isolated CABG at 2 Toronto teaching hospitals between 1993 and 1996, we compared 3 strategies: (1) using a ready-made model originally derived and validated in our jurisdiction; (2) recalibrating the ready-made model to better fit the population; and (3) deriving a new model with additional risk factors. We assessed statistical accuracy, ie, area under a receiver-operator characteristic curve (ROC); precision, ie, statistical goodness-of-fit; and actual impact on both risk-adjusted operative mortalities (RAOM) and performance rankings for 14 surgeons. The new model was slightly more accurate than the ready-made model (ROC, 0.78 versus 0.76; P<0.05), albeit not different from the recalibrated model (ROC, 0.77). The ready-made model showed poor fit between the predicted and observed results (P<0.001), leading to significant underestimation of RAOM (1.6+/-0. 2%) compared with the other strategies (2.5+/-0.2%; P=0.048). Remodeling also changed the performance rankings among half the surgeons with higher RAOM. CONCLUSIONS: Poorly calibrated risk algorithms can bias the calculation of RAOM and alter the results of surgeon-specific profiles. Any existing index used for risk assessment in cardiac surgery should be episodically recalibrated or compared with new models derived from local subjects to ensure that its performance remains optimal.

Aged↗
PubMed1999

No impact from active dissemination of the Ottawa Ankle Rules: further evidence of the need for local implementation of practice guidelines.

BACKGROUND: Local implementation strategies are often required to promote consistent adherence to clinical guidelines, but they are time consuming and expensive. The authors tested an educational intervention designed to increase use of the Ottawa Ankle Rules, a widely publicized set of clinical guidelines previously shown to reduce the use of radiography for diagnosis of acute ankle injuries. METHODS: The study consisted of a quasi-experimental, before-and-after comparative analysis. Trained experts provided 1-hour educational sessions and supplied resource materials on the Ottawa Ankle Rules to health care professionals from 63 Ontario hospitals. Participants were asked to evaluate the intervention. The authors then compared, for periods before and after the educational sessions, the use of ankle radiography for adults with acute ankle injury in 10 hospitals that received the educational intervention and reported no (n = 5) or some (n = 5) prior use of the rules and in 5 control hospitals, which declined the educational intervention because they were already implementing the rules. RESULTS: Although participants gave highly positive appraisals of the Ottawa Ankle Rules and the educational sessions, there was no reduction in the use of ankle radiography for the 10 hospitals that received the educational sessions (73% before and 78% after the intervention, p = 0.11). In contrast, use of radiography decreased significantly, from 75% to 65%, in the 5 control hospitals (p = 0.022). INTERPRETATION: Even when a dissemination strategy is well received and involves a widely accepted clinical guideline, the impact on behaviour in clinical practice may be small. In addition to broad dissemination, an active local implementation strategy is necessary to encourage physicians to adopt clinical guidelines.

Acute Disease↗
PubMed1999

Trends in clinical and economic outcomes of coronary angioplasty from 1992 to 1995: a population-based analysis.

BACKGROUND: The impact of recent developments in coronary angioplasty on the broad spectrum of patients treated in routine practice is largely undefined. Analysis of population-based data can provide insight into trends in clinical outcomes and associated costs of coronary angioplasty procedures. METHODS AND RESULTS: With the use of a comprehensive hospital discharge database covering more than 11 million Canadians, we analyzed 12,748 first-time angioplasty procedures performed from 1992 to 1995 inclusive. Patient demographics and major adverse events were recorded. With the use of forward linkage, readmissions within 12 months were classified according to procedure performed and/or most responsible diagnosis. The proportion of patients readmitted, the number of readmissions per index procedure, and diagnosis-specific readmission costs were compared by calendar year. Over the 4-year study period, there was a 21% increase in the annual volume of index procedures. There were no statistically significant differences between 1992 and 1995 in sex distribution, mean age, comorbid conditions, length of stay, or need for coronary bypass surgery related to the index procedure. The all-cause readmission rate declined from 51.6% to 47.2% between 1992 and 1995 (P <.001), primarily because of a decline in the admission rate for repeat revascularization from 24.8% to 19.6% (P <.001). The 12-month readmission cost declined by $435 (1994 Canadian dollars) per patient. CONCLUSIONS: The clinical outcomes of coronary angioplasty in a broad cohort of patients have improved in recent years. Although readmissions within 1 year of an angioplasty procedure remain common, the number related to repeat revascularization has declined, with an associated decline in downstream costs.

Aged↗
PubMed1999

Coronary bypass and carotid endarterectomy: does a combined approach increase risk? A metaanalysis.

BACKGROUND: Patients with concomitant carotid and coronary artery disease present a surgical dilemma. We compared the stroke and mortality rates for combined coronary artery bypass grafting and carotid endarterectomy in which both procedures were performed under a single anesthetic, versus a staged approach, in which coronary artery bypass grafting and carotid endarterectomy were performed separately. METHODS: A computerized MEDLINE search supplemented with a manual bibliographic review was performed for all peer-reviewed English language publications that contained both combined and staged coronary artery bypass grafting/carotid endarterectomy patient cohorts. Outcomes of interest were stroke, death, and stroke or death; aggregation of outcome rates was performed with the Mantel-Haenszel method. RESULTS: Sixteen studies were identified with a total of 844 combined patients and 920 staged patients. None of the studies was completely randomized. The combined surgical group had a higher prevalence of unstable angina; the two groups had a similar prevalence of symptomatic carotid disease and severe carotid stenosis. Meta-analysis revealed a significantly increased risk of the composite end point, stroke or death, for patients undergoing combined procedures (relative risk 1.49; 95% confidence interval 1.03-2.15; p = 0.034). There was also a trend toward increased risk during combined procedures for the end points of stroke (relative risk 1.50; 95% confidence interval 0.97-2.32; p = 0.068) and death (relative risk 1.55; 95% confidence interval 0.94-2.53; p = 0.084) considered separately. The crude event rates for stroke were 6.0% versus 3.2% for combined versus staged procedure, 4.7% versus 2.9% for death, and 9.5% versus 5.7% for stroke or death. Two of the 16 individual studies showed a statistically significant increase in the risk of stroke or death for combined procedure (p < 0.05). CONCLUSIONS: Combined coronary artery bypass grafting and carotid endarterectomy may be associated with a higher risk of stroke or death than staged procedures. A randomized trial needs to be performed to determine the optimal management of patients with concomitant carotid and coronary artery disease.

Cerebrovascular Disorders↗
PubMed1998

Phase 2 studies of adenosine cardioplegia.

BACKGROUND: Laboratory evidence supports the use of adenosine-supplemented cardioplegia. An initial phase 1 dose-ranging clinical evaluation demonstrated that an adenosine concentration of 15 mumol/L could be safely administered with warm blood cardioplegia and suggested that phase 2 studies were warranted. METHODS AND RESULTS: Two separate double-blind, randomized, placebo-controlled trials were performed in patients undergoing primary, isolated, nonemergent coronary artery bypass graft surgery. Patients were randomized to receive adenosine 15 mumol/L versus placebo in the first study (n = 200) and adenosine 50 or 100 mumol/L versus placebo in the second study (n = 128). Adenosine was infused with both initial and final doses of warm antegrade blood cardioplegia. The data from the 2 trials were combined using the methods of Mantel and Haenszel, and the results of the meta-analysis are presented as the relative risk with their associated 95% confidence intervals (CI). The different study groups were comparable with respect to all preoperative clinical characteristics, angiographic findings, and intraoperative variables. In both trials 1 and 2, no differences were found between groups in the incidence of the individual primary or secondary outcomes. Similarly, when both studies were combined, there was no significant evidence of any consistent treatment benefit (primary: death: relative risk [RR] = 1.02, 95% CI = 0.06, 16.6; myocardial infarction by CK-MB: RR = 0.84, CI = 0.54, 1.31; low output syndrome: RR = 1.38, CI = 0.29, 6.42; any of the above: RR = 0.98, CI = 0.78, 1.25; secondary: Q-wave myocardial infarction: RR = 1.30, CI = 0.41, 4.13; myocardial infarction by troponin T: RR = 0.7, CI = 0.40, 1.21; inotrope requirement: RR = 0.9, CI = 0.46, 1.79; intra-aortic balloon pump requirement: RR = 0.6, CI = 0.07, 4.81; P > 0.20). CONCLUSIONS: Despite promising experimental data, adenosine supplementation of warm blood cardioplegia did not demonstrate any statistically significant benefit in patients undergoing elective coronary artery bypass graft surgery. Although sample sizes were relatively small, based on our interim analyses, it is unlikely that increased patient enrollment would reveal any substantive clinical differences between groups.

Adenosine↗
PubMed1998

A survey of provider experiences and perceptions of preferential access to cardiovascular care in Ontario, Canada.

BACKGROUND: The public health insurance system in Canada is predicated on equal access to care for persons in need. OBJECTIVE: To determine the views and experiences of Ontario physicians and hospital administrators in providing patients with preferential access to specialized cardiovascular care on the basis of nonclinical factors. DESIGN: Survey with self-administered questionnaire. SETTING: Ontario, Canada. PARTICIPANTS: All Ontario cardiologists (n = 268), cardiac surgeons (n = 68), and hospital chief executives (n = 218) and random samples of internists (n = 300) and family physicians (n = 300). MEASUREMENTS: Elicited responses (yes or no) to questions on whether and why preferential access occurred and whether the respondents had been personally involved in such a situation. RESULTS: After undeliverable surveys and respondents no longer involved with acute care were excluded, the eligible response rate was 71.3% (788 of 1105 respondents). More than 80% of physicians and 53% of hospital chief executives had been personally involved in managing a patient who had received preferential access on the basis of factors other than medical need. Patients deemed most likely to receive such treatment were those with personal ties to the treating physicians (93% [95% CI, 91% to 95%]), high-profile public figures (85% [CI, 82% to 87%]), and politicians (83% [CI, 80% to 86%]). Physicians were significantly more likely than chief executives to indicate that hospital board members (81% and 68%; P < 0.001) and donors to hospital foundations (63% and 42%; P < 0.001) would receive preferential access. Most respondents indicated that preferential access was more likely to be provided if patients or families were well informed, aggressive, or potentially litigious. The survey did not permit estimation of the frequency of episodes of preferential access. CONCLUSIONS: Although equality of access is a cornerstone principle of Canada's universal health care system, some access to specialized cardiovascular services occurs preferentially on the basis of factors other than clinical need. The actual magnitude and consequences of this phenomenon remain unknown.

Attitude of Health Personnel↗
PubMed1998

Do we know what inappropriate laboratory utilization is? A systematic review of laboratory clinical audits.

OBJECTIVE: Laboratory utilization has steadily increased, and some studies suggest inappropriate utilization. Therefore, we wished to assess studies that measure inappropriate laboratory use in light of methodological criteria. DESIGN: Systematic review of published studies. DATA SOURCES: MEDLINE, HEALTHSTAR, and EMBASE databases were searched from 1966 to September 1997 using a broad and inclusive strategy with no language restriction. In addition, the references of all retrieved studies and 3 textbooks on diagnostic testing were hand-searched. STUDY SELECTION: All studies that provided and applied criteria for inappropriate laboratory use. DATA EXTRACTION: Studies were categorized based on whether the criteria were implicit (objective criteria for inappropriate utilization not provided or very broad) or explicit. Guidelines for evaluation were applied to each study by a single reviewer. DATA SYNTHESIS: Forty-four eligible studies were identified. Eleven studies used implicit criteria for inappropriate laboratory utilization and contained small numbers of patients or physicians. Most did not adequately assess the reliability of the implicit criteria. Thirty-three studies used explicit criteria based on the appropriateness of test choice, frequency, and timing, as well as the probability of a positive result. There were large variations in the estimates of inappropriate laboratory use (4.5%-95%). Evidence supporting the explicit criteria was frequently weak by the standards suggested for therapeutic maneuvers, but was nonetheless compelling based on principles of physiology, pharmacology, and probability. CONCLUSIONS: Many studies identify inappropriate laboratory use based on implicit or explicit criteria that do not meet methodological standards suggested for audits of therapeutic maneuvers. Researchers should develop alternative evidentiary standards for measuring inappropriateness of laboratory test use.

Clinical Laboratory Techniques↗