Search PubMed⌕ Search

Biomedical subjects

Peter C Austin

Publications and source records attributed to Peter C Austin.

At least 37 records · Page 2Linked to original sources
PubMed2005

Impact of the pravastatin or atorvastatin evaluation and infection therapy-thrombolysis in myocardial infarction 22/Reversal of Atherosclerosis with Aggressive Lipid Lowering trials on trends in intensive versus moderate statin therapy in Ontario, Canada.

BACKGROUND: In March 2004, the Reversal of Atherosclerosis with Aggressive Lipid Lowering (REVERSAL) trial demonstrated that intensive lipid-lowering therapy (atorvastatin 80 mg/d) reduced progression of coronary atherosclerosis compared with moderate lipid-lowering therapy (pravastatin 40 mg/d). The following month, the Pravastatin or Atorvastatin Evaluation and Infection Therapy-Thrombolysis In Myocardial Infarction 22 (PROVE IT-TIMI 22) study demonstrated the superiority of intensive (atorvastatin 80 mg/d) versus moderate (pravastatin 40 mg/d) lipid-lowering therapy for reducing death or cardiovascular events in patients suffering from an acute coronary syndrome. We sought to determine the impact of these 2 trials on trends in intensive versus moderate statin therapy in Ontario, Canada. METHODS AND RESULTS: This is a retrospective time-series analysis of statin prescribing between June 1997 and September 2004 in Ontario, Canada, for all residents age 65 years and older. The publication of the PROVE IT-TIMI 22 and REVERSAL trials was associated with a sustained and statistically significant increase in the number of prescriptions dispensed for atorvastatin 80 mg (range, 272 to 635 additional prescriptions per month), whereas the number of prescriptions filled for pravastatin 40 mg did not change. Similarly, it resulted in a temporal increase in the relative market share of atorvastatin at a dose of 80 mg versus that of atorvastatin at a dose of 40 mg. However, the proportion of simvastatin prescriptions for 80 mg relative to 40 mg did not change over time, implying a drug-specific effect rather than a class effect in prescribing practice. CONCLUSIONS: The publication of the PROVE IT-TIMI 22 and REVERSAL trials resulted in a significant sustained increase in the use of intensive compared with moderate statin therapy. This shift was evident primarily in an increased use of high-dose atorvastatin and did not appear to be generalizable to other statins.

Aged↗
PubMed2005

The use of the propensity score for estimating treatment effects: administrative versus clinical data.

There is an increasing interest in using administrative data to estimate the treatment effects of interventions. While administrative data are relatively inexpensive to obtain and provide population coverage, they are frequently characterized by lack of clinical detail, often leading to problematic confounding when they are used to conduct observational research. Propensity score methods are increasingly being used to address confounding in estimating the effects of interventions in such studies. Using data on patients discharged from hospital for whom both administrative data and detailed clinical data obtained from chart reviews were available, we examined the degree to which stratifying on the quintiles of propensity scores derived from administrative data was able to balance patient characteristics measured in clinical data. We also determined the extent to which measures of treatment effect obtained using propensity score methods were similar to those obtained using traditional regression methods. As a test case, we examined the treatment effects of ASA and beta-blockers following acute myocardial infarction. We demonstrated that propensity scores developed using administrative data do not necessarily balance patient characteristics contained in clinical data. Furthermore, measures of treatment effectiveness were attenuated when obtained using clinical data compared to when administrative data were used.

Adrenergic beta-Antagonists↗
PubMed2005

Effectiveness of statins for secondary prevention in elderly patients after acute myocardial infarction: an evaluation of class effect.

BACKGROUND: Clinical trials have shown the benefits of statins after acute myocardial infarction (AMI). However, it is unclear whether different statins exert a similar effect in reducing the incidence of recurrent AMI and death when used in clinical practice. METHODS: We conducted a retrospective cohort study (1997-2002) to compare 5 statins using data from medical administrative databases in 3 provinces (Quebec, Ontario and British Columbia). We included patients aged 65 years and over who were discharged alive after their first AMI-related hospital stay and who began statin treatment within 90 days after discharge. The primary end point was the combined outcome of recurrent AMI or death from any cause. The secondary end point was death from any cause. Adjusted hazard ratios (HRs) for each statin compared with atorvastatin as the reference drug were estimated using Cox proportional hazards regression analysis. RESULTS: A total of 18,637 patients were prescribed atorvastatin (n = 6420), pravastatin (n = 4480), simvastatin (n = 5518), lovastatin (n = 1736) or fluvastatin (n = 483). Users of different statins showed similar baseline characteristics and patterns of statin use. The adjusted HRs (and 95% confidence intervals) for the combined outcome of AMI or death showed that each statin had similar effects when compared with atorvastatin: pravastatin 1.00 (0.90-1.11), simvastatin 1.01 (0.91-1.12), lovastatin 1.09 (0.95-1.24) and fluvastatin 1.01 (0.80-1.27). The results did not change when death alone was the end point, nor did they change after adjustment for initial daily dose or after censoring of patients who switched or stopped the initial statin treatment. INTERPRETATION: Our results suggest that, under current usage, statins are equally effective for secondary prevention in elderly patients after AMI.

Aged↗
PubMed2005

Propensity score methods gave similar results to traditional regression modeling in observational studies: a systematic review.

OBJECTIVE: To determine whether adjusting for confounder bias in observational studies using propensity scores gives different results than using traditional regression modeling. METHODS: Medline and Embase were used to identify studies that described at least one association between an exposure and an outcome using both traditional regression and propensity score methods to control for confounding. From 43 studies, 78 exposure-outcome associations were found. Measures of the quality of propensity score implementation were determined. The statistical significance of each association using both analytical methods was compared. The odds or hazard ratios derived using both methods were compared quantitatively. RESULTS: Statistical significance differed between regression and propensity score methods for only 8 of the associations (10%), kappa = 0.79 (95% CI = 0.65-0.92). In all cases, the regression method gave a statistically significant association not observed with the propensity score method. The odds or hazard ratio derived using propensity scores was, on average, 6.4% closer to unity than that derived using traditional regression. CONCLUSIONS: Observational studies had similar results whether using traditional regression or propensity scores to adjust for confounding. Propensity scores gave slightly weaker associations; however, many of the reviewed studies did not implement propensity scores well.

Bias↗
PubMed2005

The use of quantile regression in health care research: a case study examining gender differences in the timeliness of thrombolytic therapy.

Investigators are frequently interested in determining patient and system characteristics associated with delays in the provision of essential medical treatment. Investigators have typically used either multiple linear regression or Cox proportional hazards models to assess the impact of patient and system characteristics on the timeliness of medical treatment. A drawback to the use of these two methods is that they allow, at best, a partial exploration of how a distribution of delays in treatment or of waiting times changes with patient characteristics. In contrast, quantile regression models allow one to assess how any quantile of a conditional distribution changes with patient characteristics. We illustrate the utility of quantile regression by examining gender differences in the delivery of thrombolysis in patients with an acute myocardial infarction. We demonstrate that richer inferences can be drawn through the use of quantile regression. Females were more likely to experience delays in treatment compared to males. Furthermore, gender had a greater impact upon those patients who had the greatest delays in treatment. Investigators who want to determine how a distribution of delays in treatment or of waiting times changes with patient or system characteristics should consider complementing their analyses with the use of quantile regression.

Aged↗
PubMed2005

Quality of care of international and Canadian medical graduates in acute myocardial infarction.

BACKGROUND: International medical graduates (IMGs) make up a substantial proportion of the physician workforce and play an important role in the care of patients with acute myocardial infarction (AMI). There are concerns that IMGs may provide inferior medical care compared with locally trained medical graduates, but that has not been established. METHODS: We performed a retrospective cohort study of linked administrative databases containing health care claims of physicians' service payments, hospital discharge abstracts, and patients' vital status. We included 127,275 AMI patients admitted between April 1, 1992, and March 31, 2000, to acute care hospitals in Ontario. We then compared the risk-adjusted mortality rates and adjusted use of secondary prevention medications and cardiac invasive procedures in patients treated by IMGs vs Canadian medical graduates. RESULTS: Of the 127,275 admitted AMI patients, 28,061 (22.0%) were treated by IMGs and 99,214 (78.0%) by Canadian medical graduates. The risk-adjusted mortality rates of IMG- and Canadian medical graduate-treated patients were not significantly different at 30 days (13.3% vs 13.4%, P = .57) and at 1 year (21.8% vs 21.9%, P = .63). Furthermore, AMI patients treated by both groups had similar adjusted likelihood of receiving secondary prevention medications at 90 days and cardiac invasive procedures at 1 year. CONCLUSIONS: The use of secondary prevention medications and cardiac procedures and the mortality of AMI patients were similar, regardless of the origin of medical education of the admitting physician. This information places the care provided by IMGs into perspective and supports the ability of well-selected IMGs in caring for AMI patients.

Adult↗
PubMed2005

Mitral repair versus replacement for ischemic mitral regurgitation.

BACKGROUND: We compared mitral repair to replacement in patients with chronic ischemic mitral regurgitation (IMR), due to left ventricular dysfunction (LV-IMR) or papillary muscle infarction (PM-IMR). METHODS: Patients with IMR undergoing repair (n = 65) or replacement (n = 137) from 1990 to 2001 were evaluated. There were 87 patients with LV-IMR, and 115 patients with PM-IMR. Patients presenting in cardiogenic shock were excluded. Outcomes were evaluated by Cox survival analysis with propensity score adjustment and bootstrap validation. RESULTS: Survival at 3, 5, and 9 years was, respectively, 0.94, 0.79, and 0.63 in the repair group, and 0.73, 0.67, and 0.59 in the replacement group. The hazard ratio (HR) of death for mitral repair versus replacement was not constant over the period of follow-up. Repair was associated with better early survival in the PM-IMR group, with an adjusted HR of 0.25 (95% confidence interval: 0.09 to 0.71) at 1 year. In the LV-IMR group and in patients with PM-IMR with high acuity and comorbidity, there was no significant survival advantage associated with repair. The beneficial effect of repair was not evident at late follow-up in either group. These findings were independent of the surgeon. Need for reoperation was more common after repair than after replacement (14% versus 3%, p = 0.003). CONCLUSIONS: Patients with PM-IMR benefit from mitral repair with a significantly better early survival. However, the benefit of repair is not evident at longer follow-up. There was a nonsignificant trend toward greater early survival among patients with LV-IMR who underwent repair.

Aged↗
PubMed2005

Conventional models overestimate the statistical significance of volume-outcome associations, compared with multilevel models.

OBJECTIVE: To compare the use of conventional statistical models with multilevel regression models in volume-outcome analyses of surgical procedures in an empirical case study. STUDY DESIGN AND SETTING: Using conventional regression models and multilevel regression models, we estimated the effect of hospital volume and surgeon volume on 30-day mortality and length of postoperative hospital stay in persons who had an esophagectomy, pancreaticoduodenectomy, or major lung resection for cancer in Ontario, Canada, from 1994 to 1999. RESULTS: The point estimates of volume-outcome associations were similar using either method; however, the 95% confidence intervals estimated by multilevel models were wider than those estimated by conventional models. A significant association between volume and mortality was identified in 2 of 18 (11%) comparisons using conventional analysis but in none of the 18 (0%) comparisons using multilevel analysis, and between volume and length of stay in 15 of 18 (83%) comparisons using conventional analysis and in 1 of 18 (6%) comparisons using multilevel analysis. CONCLUSION: Conventional and multilevel statistical models can yield substantially different results in the analysis of volume-outcome associations for surgical procedures.

Age Factors↗
PubMed2005

Comparison of coding of heart failure and comorbidities in administrative and clinical data for use in outcomes research.

BACKGROUND: Despite the potential usefulness of administrative databases for evaluating outcomes, coding of heart failure and associated comorbidities have not been definitively compared with clinical data. OBJECTIVE: To compare the predictive value of heart failure diagnoses and secondary conditions identified in a large administrative database with chart-based records. METHODS: The authors studied 1808 patient records sampled from 14 acute care hospitals and compared clinically recorded data with administrative records from the Canadian Institute for Health Information. The impact of comorbidity coding in the administrative data set according to the Charlson classification was examined in models of 30-day mortality. RESULTS: The positive predictive value (PPV) of a primary diagnosis ICD-9 428 was 94.3% using the Framingham criteria and 88.6% using criteria previously validated with pulmonary capillary wedge pressure. There was reduced prevalence of secondary comorbid conditions in administrative data in comparison with clinical chart data. The specificities and PPV/negative predictive values of administratively identified index comorbidities were high. The sensitivities of index comorbidities were low, but were enhanced by examination of hospitalizations within 1 year prior to the index heart failure admission. Using information from prior hospitalizations modestly enhanced 30-day mortality model performance; however, the odds ratio point estimates of the index and enhanced administrative data sets were consistent with the clinical model. CONCLUSION: The ICD-9 428 primary diagnosis is highly predictive of heart failure using clinical criteria. Examination of hospitalization data up to 1 year prior to the index admission improves comorbidity detection and may provide enhancements to future studies of heart failure mortality.

Aged↗
PubMed2005

The impact of under coding of cardiac severity and comorbid diseases on the accuracy of hospital report cards.

CONTEXT: Hospital report cards usually are based on administrative discharge abstracts. However, cardiac severity and comorbidities generally are under-reported in administrative data. OBJECTIVE: We sought to determine how undercoding of cardiac severity and comorbidities affects the determination that some hospitals are high-mortality outliers. DESIGN: Simulations using retrospective data on 18,795 patients admitted with an acute myocardial infarction (AMI) to 109 acute care hospitals in Ontario. MAIN OUTCOME MEASURE: Change in the number of hospitals that remained high-mortality outliers after adjusting for potentially increased prevalence of as many as 9 separate measures of cardiac severity and comorbid conditions, individually or together. RESULTS: For most measures of cardiac severity and comorbidities, increasing the prevalence of each factor to the highest observed hospital-specific prevalence seldom altered the status of high-mortality outlier hospitals. Increases in the prevalence of cardiogenic shock or acute renal failure to even the median level led to reclassification of up to 4 of the 12 high-mortality outlier hospitals to nonoutlier status. Most high-mortality outlier hospitals were reclassified if the maximum prevalence was imputed for these 2 factors. Simultaneously increasing the prevalence of all comorbidities to the median level typically converted the status of about half the outlier hospitals. Not until the prevalence of all measures of cardiac severity and comorbidities were simultaneously increased to the maximum observed hospital-specific prevalence, did all hospitals initially classified as high-mortality outliers revert to nonoutlier status. CONCLUSIONS: Undercoding of severity and comorbidities in administrative data in itself is very unlikely to account for the outlier status of most hospitals. However, some potential for misclassification of individual institutions exists if influential factors are variably coded.

Comorbidity↗
PubMed2005

Measuring the effect of a large reduction in welfare payments on mental health service use in welfare-dependent neighborhoods.

BACKGROUND: Major social policy changes were implemented in Canada in the last decade with few efforts to examine their potential health effects. OBJECTIVES: We sought to determine the impact of a large reduction in welfare benefits on use of ambulatory physician mental health services in areas with high levels of welfare dependency relative to areas with low levels of welfare dependency. METHODS: The setting was Toronto, Canada. Data sources included census, provincial health insurance, and municipal welfare data. We used generalized estimating equations to compare ambulatory mental health service rates by neighborhood level of welfare dependency before and after a 21.6% reduction in welfare payments. RESULTS: There were no long-term relative differences by welfare dependency in mental health service use before compared with after the policy change. There was a very small short-term increase in mental health visits to generalists in the 6 months after the policy change. We demonstrated a marked gradient in psychiatric service use with low welfare dependency areas having significantly higher rates of use than high welfare dependency areas. CONCLUSIONS: We demonstrated a mismatch between known levels of need for care and levels of psychiatric use. We conclude that where use of services is not tightly linked to need for services, utilization data may be unsuitable for evaluating programs or policies. Social policy changes with potential health effects should have integrated evaluations planned at the time of policy implementation.

Community Mental Health Services↗
PubMed2005

Diabetic patients with prior specialist care have better glycaemic control than those with prior primary care.

OBJECTIVE: To compare glycaemic control, as reflected in the A1c level, of diabetic patients with primary care vs. with specialist care. METHODS: The study used administrative data from eastern Ontario, Canada, and a database containing the results of all A1c tests from this region between 1 September 1999 and 1 September 2000. To avoid referral bias, diabetic patients with an index specialist visit were selected and separated into those with exclusively primary care previously (n = 974) and those with prior specialist care (n = 3533). We compared A1c levels measured within 30 days of the index visit and hence attributable to the prior care. To control for confounding between the groups, both multiple linear regression and propensity score-based matching were used. RESULTS: After controlling for confounders, patients with prior specialist care had significantly lower A1c levels (P < 0.0001). Other predictors of lower A1c included older age, shorter diabetes duration, rural residence and higher neighbourhood income. In propensity score-matched cohorts, the A1c level was 8.3 +/- 2.0% with prior primary care vs. 7.9 +/- 1.6% with prior specialist care (P < 0.0001). CONCLUSIONS: Specialist care prior to the index visit was associated with a lower A1c level than prior primary care. This difference would result in reductions in diabetes complications for patients with ongoing specialist care.

Aged↗
PubMed2005

Community factors, hospital characteristics and inter-regional outcome variations following acute myocardial infarction in Canada.

BACKGROUND: While various community and hospital characteristics have been demonstrated to have an impact on individual cardiovascular outcomes, the extent to which such factors account for inter-regional and interhospital outcome variations following acute myocardial infarction (AMI) remains unknown. OBJECTIVES: To examine the impact of community and hospital factors on individual AMI outcomes and procedure use, and to determine the extent to which such characteristics account for inter-regional and interinstitutional AMI outcome and procedure variations across Canada. METHODS: Patients hospitalized with AMI between April 1, 1997, and March 31, 2000, across Canada were examined. The community and hospital characteristics studied included three indicators of socioeconomic status, two indicators of ethnicity, rural-urban status of residence, hospital academic affiliation, and the presence or absence of on-site angiography or revascularization capabilities at the admitting institution. Outcomes included in-hospital mortality, one-year cardiac readmissions and 30-day revascularization rates post-AMI. All analyses were adjusted for age, sex and age-sex interaction. The relationships between community/hospital factors and individual outcomes were examined using random-effects hierarchical logistic regression analysis, while the relationships between community/hospital characteristics and inter-regional/hospital risk-adjusted outcomes were examined using least squares regression and the coefficient of determination (r2). RESULTS: After adjusting for demographic factors, a patient's neighbourhood socioeconomic status was inversely correlated with the likelihood of death and downstream cardiac readmissions (P<0.001); patients residing in lower educated regions were less likely to receive revascularization post-AMI (P<0.001). Patients living in regions with higher concentrations of new immigrants and/or visible minorities, as well as those admitted to academically affiliated hospitals or hospitals with on-site procedural capacity, had fewer cardiac readmissions (P<0.001) and greater use of revascularization post-AMI (P<0.001) after adjusting for age and sex. Despite their associations with outcomes on an individual patient level, community and hospital factors explained no more than 7% of the variation in the risk-adjusted outcomes across hospitals or regions. Finally, adjustments for community and hospital factors and procedure use, beyond adjustments for age and sex alone, had marginal impact on a province's risk-adjusted outcomes. CONCLUSIONS: While community and hospital factors are important determinants of individual outcomes after AMI, they account for only a minimal degree of outcome variation across regions. Further studies are required to examine whether AMI outcome variations in Canada are explained by differences in patient clinical profiles and/or by differences in the decision-making behaviours of providers across jurisdictions.

Adult↗
PubMed2004

The impact of the Women's Health Initiative study on incident clonidine use in Ontario, Canada.

BACKGROUND: Following publication of the Women's Health Initiative (WHI) study, many women discontinued use of estrogen replacement therapy. There is some evidence that the antihypertensive agent clonidine can reduce the frequency of hot flashes associated with menopause. OBJECTIVES: To determine the impact of the WHI study on incident use of clonidine in elderly women in Ontario, Canada. METHODS: Retrospective, population-based administrative database design. Data on all residents of Ontario over the age of 65 years were included. Time series methods were used to analyze change in incident clonidine use following publication of the WHI study. RESULTS: Following publication of the WHI study, incident use of clonidine increased substantially among elderly women in Ontario, Canada. Similar trends were not observed for incident use of other antihypertensive medications. CONCLUSION: During a period of time in which a large proportion of women discontinued estrogen replacement therapy, incident use of clonidine increased. There is some evidence that a small number of women may have sought alternative relief from menopausal symptoms using other pharmacological therapies.

Aged↗
PubMed2004

Rates of hyperkalemia after publication of the Randomized Aldactone Evaluation Study.

BACKGROUND: The Randomized Aldactone Evaluation Study (RALES) demonstrated that spironolactone significantly improves outcomes in patients with severe heart failure. Use of angiotensin-converting-enzyme (ACE) inhibitors is also indicated in these patients. However, life-threatening hyperkalemia can occur when these drugs are used together. METHODS: We conducted a population-based time-series analysis to examine trends in the rate of spironolactone prescriptions and the rate of hospitalization for hyperkalemia in ambulatory patients before and after the publication of RALES. We linked prescription-claims data and hospital-admission records for more than 1.3 million adults 66 years of age or older in Ontario, Canada, for the period from 1994 through 2001. RESULTS: Among patients treated with ACE inhibitors who had recently been hospitalized for heart failure, the spironolactone-prescription rate was 34 per 1000 patients in 1994, and it increased immediately after the publication of RALES, to 149 per 1000 patients by late 2001 (P<0.001). The rate of hospitalization for hyperkalemia rose from 2.4 per 1000 patients in 1994 to 11.0 per 1000 patients in 2001 (P<0.001), and the associated mortality rose from 0.3 per 1000 to 2.0 per 1000 patients (P<0.001). As compared with expected numbers of events, there were 560 (95 percent confidence interval, 285 to 754) additional hyperkalemia-related hospitalizations and 73 (95 percent confidence interval, 27 to 120) additional hospital deaths during 2001 among older patients with heart failure who were treated with ACE inhibitors in Ontario. Publication of RALES was not associated with significant decreases in the rates of readmission for heart failure or death from all causes. CONCLUSIONS: The publication of RALES was associated with abrupt increases in the rate of prescriptions for spironolactone and in hyperkalemia-associated morbidity and mortality. Closer laboratory monitoring and more judicious use of spironolactone may reduce the occurrence of this complication.

Adrenergic beta-Antagonists↗
PubMed2004

Cyclo-oxygenase-2 inhibitors versus non-selective non-steroidal anti-inflammatory drugs and congestive heart failure outcomes in elderly patients: a population-based cohort study.

BACKGROUND: Non-selective, non-steroidal anti-inflammatory drugs (NSAIDs) are associated with an increased risk of congestive heart failure, but little is known about the cardiovascular effects of a newer group of NSAIDS called selective cyclo-oxygenase (COX)-2 inhibitors. We aimed to compare rates of admission for congestive heart failure in elderly patients who were newly dispensed COX-2 inhibitors or non-selective NSAIDs. METHODS: In this population-based retrospective cohort study we identified NSAID-naive individuals aged 66 years or older, who were started on rofecoxib (n=14,583), celecoxib (n=18,908), and non-selective NSAIDs (n=5,391), and randomly selected non-NSAID users as controls (n=100,000). FINDINGS: Relative to non-NSAID users, patients on rofecoxib and non-selective NSAIDS had an increased risk of admission for congestive heart failure (adjusted rate ratio 1.8, 95% CI 1.5-2.2, and 1.4, 1.0-1.9, respectively), but not celecoxib (1.0, 0.8-1.3). Compared with celecoxib users, admission was significantly more likely in users of non-selective NSAIDs (1.4, 1.0-1.9) and rofecoxib (1.8, 1.4-2.4). Risk of admission for rofecoxib users was higher than that for non-selective NSAID users (1.5, 1.1-2.1). Of patients with no admission in the past 3 years, only rofecoxib users were at increased risk of subsequent admission relative to controls (1.8, 1.4-2.3). INTERPRETATION: These findings suggest a higher risk of admission for congestive heart failure in users of rofecoxib and non-selective NSAIDs, but not celecoxib, relative to non-NSAID controls.

Aged↗