Patrick S Parfrey

Health Canada, Ottawa, Ontario, Canada

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Publications (321)2347.51 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The calcimimetic cinacalcet reduced the risk of death or cardiovascular (CV) events in older, but not younger, patients with moderate to severe secondary hyperparathyroidism (HPT) who were receiving hemodialysis. To determine whether the lower risk in younger patients might be due to lower baseline CV risk and more frequent use of cointerventions that reduce parathyroid hormone (kidney transplantation, parathyroidectomy, and commercial cinacalcet use), this study examined the effects of cinacalcet in older (≥65 years, n=1005) and younger (<65 years, n=2878) patients. Evaluation of Cinacalcet HCl Therapy to Lower Cardiovascular Events (EVOLVE) was a global, multicenter, randomized placebo-controlled trial in 3883 prevalent patients on hemodialysis, whose outcomes included death, major CV events, and development of severe unremitting HPT. The age subgroup analysis was prespecified. Older patients had higher baseline prevalence of diabetes mellitus and CV comorbidity. Annualized rates of kidney transplantation and parathyroidectomy were >3-fold higher in younger relative to older patients and were more frequent in patients randomized to placebo. In older patients, the adjusted relative hazard (95% confidence interval) for the primary composite (CV) end point (cinacalcet versus placebo) was 0.70 (0.60 to 0.81); in younger patients, the relative hazard was 0.97 (0.86 to 1.09). Corresponding adjusted relative hazards for mortality were 0.68 (0.51 to 0.81) and 0.99 (0.86 to 1.13). Reduction in the risk of severe unremitting HPT was similar in both groups. In the EVOLVE trial, cinacalcet decreased the risk of death and of major CV events in older, but not younger, patients with moderate to severe HPT who were receiving hemodialysis. Effect modification by age may be partly explained by differences in underlying CV risk and differential application of cointerventions that reduce parathyroid hormone. Copyright © 2015 by the American Society of Nephrology.
    Clinical journal of the American Society of Nephrology : CJASN. 02/2015;
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    ABSTRACT: The relationship between major dietary patterns and colorectal cancer (CRC) in other populations largely remains consistent across studies. The objective of the present study is to assess if dietary patterns are associated with the risk of CRC in the population of Newfoundland and Labrador (NL). Data from a population based case-control study in the province of NL were analyzed, including 506 CRC patients (306 men and 200 women) and 673 controls (400 men and 273 women), aged 20-74 years. Dietary habits were assessed by a 169-item food frequency questionnaire (FFQ). Logistic regression analyses were performed to investigate the association between dietary patterns and the CRC risk. Three major dietary patterns were derived using factor analysis, namely a Meat-diet pattern, a Plant-based diet pattern and a Sugary-diet pattern. In combination the three dietary patterns explained 74% of the total variance in food intake. Results suggest that the Meat-diet and the Sugary-diet increased the risk of CRC with corresponding odds ratios (ORs) of 1.84 (95% CI: 1.19-2.86) and 2.26 (95% CI: 1.39-3.66) for people in the highest intake quintile compared to those in the lowest. Whereas plant-based diet pattern decreases the risk of CRC with a corresponding OR of 0.55 (95% CI: 0.35-0.87). Even though odds ratios (ORs) were not always statistically significant, largely similar associations across three cancer sites were found: the proximal colon, the distal colon, and the rectum. The finding that Meat-diet/Sugary-diet patterns increased and Plant-based diet pattern decreased the risk of CRC would guide the promotion of healthy eating for primary prevention of CRC in this population.
    Nutrition journal. 01/2015; 14(1):8.
  • Pietro Ravani, Brendan J Barrett, Patrick S Parfrey
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    ABSTRACT: In longitudinal studies the relationship between exposure and disease can be measured once or multiple times while participants are monitored over time. Traditional regression techniques are used to model outcome data when each epidemiological unit is observed once. These models include generalized linear models for quantitative continuous, discrete, or qualitative outcome responses, and models for time-to-event data. When data come from the same subjects or group of subjects, observations are not independent and the underlying correlation needs to be addressed in the analysis. In these circumstances extended models are necessary to handle complexities related to clustered data, and repeated measurements of time-varying predictors and/or outcomes.
    Methods in molecular biology (Clifton, N.J.) 01/2015; 1281:93-131. · 1.29 Impact Factor
  • Susan Stuckless, Patrick S Parfrey
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    ABSTRACT: Clinical epidemiological research in genetic diseases entails assessment of phenotypes, the burden and etiology of disease, and the efficacy of preventive measures or treatments in populations. In all areas, the main focus is to describe the relationship between exposure and outcome and to determine one of the following: prevalence, incidence, cause, prognosis, or effect of treatment. The accuracy of these conclusions is determined by the validity of the study. Validity is determined by addressing potential biases and possible confounders that may be responsible for the observed association. Therefore, it is important to understand the types of bias that exist and also to be able to assess their impact on the magnitude and direction of the observed effect. The following chapter reviews the epidemiological concepts of selection bias, information bias, and confounding and discusses ways in which these sources of bias can be minimized.
    Methods in molecular biology (Clifton, N.J.) 01/2015; 1281:333-48. · 1.29 Impact Factor
  • Patrick S Parfrey
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    ABSTRACT: The intention-to-treat analysis is the gold standard for evaluating efficacy in a randomized controlled trial. However, when non-adherence to randomized treatments is high, the actual treatment effect may be underestimated. The impact of drop-out from the intervention group or drop-in to the control group may be controlled by trial design, increasing the sample size, effective study execution, and a prespecified analytical plan to take contamination into account.These analyses may include censoring at time of co-interventions associated with stopping treatment, lag censoring which allows an additional period after discontinuation of study treatment to account for residual treatment effects, inverse probability of censoring weights (IPCW), accelerated failure time models, and contamination adjusted intent-to-treat analysis. These methods are particularly useful in assessing the "prescribed efficacy" of the study treatment, which can aid clinical decision-making.
    Methods in molecular biology (Clifton, N.J.) 01/2015; 1281:249-59. · 1.29 Impact Factor
  • Bryan M Curtis, Brendan J Barrett, Patrick S Parfrey
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    ABSTRACT: Today's clinical practice relies on the application of well-designed clinical research, the gold standard test of an intervention being the randomized controlled trial. Principles of the randomized control trial include emphasis on the principal research question, randomization, blinding; definitions of outcome measures, of inclusion and exclusion criteria, and of comorbid and confounding factors; enrolling an adequate sample size; planning data management and analysis; preventing challenges to trial integrity such as drop-out, drop-in, and bias. The application of pretrial planning is stressed to ensure the proper application of epidemiological principles resulting in clinical studies that are feasible and generalizable. In addition, funding strategies and trial team composition are discussed.
    Methods in molecular biology (Clifton, N.J.) 01/2015; 1281:159-75. · 1.29 Impact Factor
  • Pietro Ravani, Brendan J Barrett, Patrick S Parfrey
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    ABSTRACT: Statistical models are used to study the relationship between exposure and disease while accounting for the potential role of other factors impact upon outcomes. This adjustment is useful to obtain unbiased estimates of true effects or to predict future outcomes. Statistical models include a systematic and an error component. The systematic component explains the variability of the response variable as a function of the predictors and is summarized in the effect estimates (model coefficients). The error element of the model represents the variability in the data unexplained by the model and is used to build measures of precisions around the point estimates (Confidence Intervals).
    Methods in molecular biology (Clifton, N.J.) 01/2015; 1281:71-92. · 1.29 Impact Factor
  • Elizabeth Hatfield, Elizabeth Dicks, Patrick S Parfrey
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    ABSTRACT: Large integrated multidisciplinary teams have become recognized as an efficient means by which to drive innovation and discovery in clinical research. This chapter describes how to plan, budget and fund these large studies and execute the studies with well-designed governance and monitoring protocols in place, to efficiently manage the large, often dispersed teams involved. Sources of funding are identified, budget development, justification, reporting, financial governance and accountability are described, in addition to the creation and management of the multidisciplinary team that will implement the research plan.
    Methods in molecular biology (Clifton, N.J.) 01/2015; 1281:273-86. · 1.29 Impact Factor
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    ABSTRACT: Fractures are frequent in patients receiving hemodialysis. We tested the hypothesis that cinacalcet would reduce the rate of clinical fractures in patients receiving hemodialysis using data from the Evaluation of Cinacalcet HCl Therapy to Lower Cardiovascular Events trial, a placebo-controlled trial that randomized 3883 hemodialysis patients with secondary hyperparathyroidism to receive cinacalcet or placebo for ≤64 months. This study was a prespecified secondary analysis of the trial whose primary end point was all-cause mortality and non-fatal cardiovascular events, and one of the secondary end points was first clinical fracture event. Clinical fractures were observed in 255 of 1935 (13.2%) patients randomized to placebo and 238 of 1948 (12.2%) patients randomized to cinacalcet. In an unadjusted intention-to-treat analysis, the relative hazard for fracture (cinacalcet versus placebo) was 0.89 (95% confidence interval [95% CI], 0.75 to 1.07). After adjustment for baseline characteristics and multiple fractures, the relative hazard was 0.83 (95% CI, 0.72 to 0.98). Using a prespecified lag-censoring analysis (a measure of actual drug exposure), the relative hazard for fracture was 0.72 (95% CI, 0.58 to 0.90). When participants were censored at the time of cointerventions (parathyroidectomy, transplant, or provision of commercial cinacalcet), the relative hazard was 0.71 (95% CI, 0.58 to 0.87). Fracture rates were higher in older compared with younger patients and the effect of cinacalcet appeared more pronounced in older patients. In conclusion, using an unadjusted intention-to-treat analysis, cinacalcet did not reduce the rate of clinical fracture. However, when accounting for differences in baseline characteristics, multiple fractures, and/or events prompting discontinuation of study drug, cinacalcet reduced the rate of clinical fracture by 16%-29%. Copyright © 2014 by the American Society of Nephrology.
    Journal of the American Society of Nephrology 12/2014; · 9.47 Impact Factor
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    ABSTRACT: Colorectal cancer is a common malignancy. Identification of genetic prognostic markers may help prognostic estimations in colorectal cancer. Genes that regulate response to hypoxia and other genes that are regulated under the hypoxic conditions have been shown to play roles in cancer progression. In this study, we hypothesized that genetic variations in the hypoxia pathway genes were associated with the risk of outcome in colorectal cancer patients. This study was performed in two phases. In the first phase, 49 SNPs from six hypoxia pathway genes (HIF1A, HIF1B, HIF2A, LOX, MIF and CXCL12) in 272 colorectal cancer patients were analyzed. In the second phase, 77 SNPs from seven hypoxia pathway genes (HIF1A, HIF1B, HIF2A, HIF2B, HIF3A, LOX and CXCL12) were analyzed in an additional cohort of 535 patients. Kaplan Meier, Cox univariate and multivariable regression analyses were performed to analyze the relationship between the SNPs and overall survival (OS), disease free survival (DFS) or disease specific survival (DSS). Since this was a hypothesis-generating study, no correction for multiple testing was applied. In phase I, one SNP (HIF2A rs11125070) was found to be associated with DFS in multivariable analysis; yet association of a proxy polymorphism (HIF2A rs4953342) was not detected in the phase II patient cohort. In phase II, associations of two SNPs (HIF2A rs4953352 and HIF2B rs12593988) were significant in both OS and DFS multivariable analyses. However, association of HIF2A rs4953352 was not replicated in the phase I cohort using a proxy SNP (HIF2A rs6706003). Overall, our study did not find a convincing evidence of association of the investigated polymorphisms with the disease outcomes in colorectal cancer.
    PLoS ONE 11/2014; 9(11):e113513. · 3.53 Impact Factor
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    ABSTRACT: Premature cardiovascular disease limits the duration and quality of life on long-term hemodialysis. The objective of this study was to define the frequency of fatal and nonfatal cardiovascular events attributable to atherosclerotic and nonatherosclerotic mechanisms, risk factors for these events, and the effects of cinacalcet, using adjudicated data collected during the EValuation of Cinacalcet HCl Therapy to Lower CardioVascular Events (EVOLVE) Trial. EVOLVE was a randomized, double-blind, placebo-controlled clinical trial that randomized 3883 hemodialysis patients with moderate to severe secondary hyperparathyroidism to cinacalcet or matched placebo for up to 64 months. For this post hoc analysis, the outcome measure was fatal and nonfatal cardiovascular events reflecting atherosclerotic and nonatherosclerotic cardiovascular diseases. During the trial, 1518 patients experienced an adjudicated cardiovascular event, including 958 attributable to nonatherosclerotic disease. Of 1421 deaths during the trial, 768 (54%) were due to cardiovascular disease. Sudden death was the most frequent fatal cardiovascular event, accounting for 24.5% of overall mortality. Combining fatal and nonfatal cardiovascular events, randomization to cinacalcet reduced the rates of sudden death and heart failure. Patients randomized to cinacalcet experienced fewer nonatherosclerotic cardiovascular events (adjusted relative hazard 0.84, 95% CI 0.74 to 0.96), while the effect of cinacalcet on atherosclerotic events did not reach statistical significance. Accepting the limitations of post hoc analysis, any benefits of cinacalcet on cardiovascular disease in the context of hemodialysis may result from attenuation of nonatherosclerotic processes. Unique identifier: NCT00345839. URL: © 2014 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell.
    Journal of the American Heart Association 10/2014; 3(6).
  • 05/2014; 29 Suppl 3:iii47-iii48.
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    ABSTRACT: To assess hemodialysis (HD) patients' physical health, social supports, psychosocial well-being and the interrelationship among patients' experiences, demographics, illness characteristics, and biochemical indicators of health. To determine responsiveness of the Patient's Perception of Hemodialysis Scale (PPHS) to change in health status and critical events.
    04/2014; 24(2):33-44.
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    ABSTRACT: Background:Smoking is a risk factor for incident colorectal cancer (CRC); however, it is unclear about its influence on survival after CRC diagnosis.Methods:A cohort of 706 CRC patients diagnosed from 1999 to 2003 in Newfoundland and Labrador, Canada, was followed for mortality and recurrence until April 2010. Smoking and other relevant data were collected by questionnaire after cancer diagnosis, using a referent period of '2 years before diagnosis' to capture pre-diagnosis information. Molecular analyses of microsatellite instability (MSI) status and BRAF V600E mutation status were performed in tumour tissue using standard techniques. Multivariate hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated with Cox proportional hazards regression, controlling for major prognostic factors.Results:Compared with never smokers, all-cause mortality (overall survival, OS) was higher for current (HR: 1.78; 95% CI: 1.04-3.06), but not for former (HR: 1.06; 95% CI: 0.71-1.59) smokers. The associations of cigarette smoking with the study outcomes were higher among patients with 40 pack-years of smoking (OS: HR: 1.72; 95% CI: 1.03-2.85; disease-free survival (DFS: HR: 1.99; 95% CI: 1.25-3.19), those who smoked 30 cigarettes per day (DFS: HR: 1.80; 95% CI: 1.22-2.67), and those with microsatellite stable (MSS) or MSI-low tumours (OS: HR: 1.38; 95% CI: 1.04-1.82 and DFS: HR: 1.32; 95% CI: 1.01-1.72). Potential heterogeneity was noted for sex (DFS HR: 1.68 for men and 1.01 for women: P for heterogeneity=0.04), and age at diagnosis (OS: HR: 1.11 for patients aged <60 and 1.69 for patients aged 60: P for heterogeneity=0.03).Conclusions:Pre-diagnosis cigarette smoking is associated with worsened prognosis among patients with CRC.British Journal of Cancer advance online publication, 21 January 2014; doi:10.1038/bjc.2014.6
    British Journal of Cancer 01/2014; · 5.08 Impact Factor
  • Canadian Journal of Kidney Health and Disease. 01/2014; 1(1):2.
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    ABSTRACT: Several N-nitroso compounds (NOC) have been shown to be carcinogenic in a variety of laboratory animals, but evidence of their carcinogenicity in humans is lacking. We aimed to examine the association between NOC intake and colorectal cancer (CRC) risk and possible effect modification by vitamins C and E and protein in a large case-control study carried out in Newfoundland and Labrador and Ontario, Canada. A total of 1760 case patients with pathologically confirmed adenocarcinoma and 2481 population controls were asked to complete a self-administered FFQ to evaluate their dietary intakes 1 year before diagnosis (for cases) or interview (for controls). Adjusted OR and 95 % CI were calculated across the quintiles of NOC (measured by N-nitrosodimethylamine (NDMA)) intake and relevant food items using unconditional logistic regression. NDMA intake was found to be associated with a higher risk of CRC (highest v. lowest quintiles: OR 1·42, 95 % CI 1·03, 1·96; P for trend = 0·005), specifically for rectal carcinoma (OR 1·61, 95 % CI 1·11, 2·35; P for trend = 0·01). CRC risk also increased with the consumption of NDMA-containing meats when the highest tertile was compared with the lowest tertile (OR 1·47, 95 % CI 1·03, 2·10; P for trend = 0·20). There was evidence of effect modification between dietary vitamin E and NDMA. Individuals with high NDMA and low vitamin E intakes had a significantly increased risk than those with both low NDMA and low vitamin E intakes (OR 3·01, 95 % CI 1·43, 6·51; P for interaction = 0·017). The present results support the hypothesis that NOC intake may be positively associated with CRC risk in humans. Vitamin E, which inhibits nitrosation, could modify the effect of NDMA on CRC risk.
    The British journal of nutrition 10/2013; · 3.45 Impact Factor
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    ABSTRACT: Context:The clinical course of secondary hyperparathyroidism (sHPT) in patients on hemodialysis is not well described, and the effect of the calcimimetic cinacalcet on disease progression is uncertain.Objective:To describe (a) the clinical course of sHPT in patients treated with phosphate binders and/or vitamin D sterols and (b) the impact of cinacalcet on occurrence of severe unremitting HPT, defined by the persistence of markedly elevated parathyroid hormone (PTH) concentrations together with hypercalcemia or parathyroidectomy (PTX).Design:Randomized, double-blind, placebo-controlled clinical trial.Setting:Global, multicenter.Patients:3883 patients on hemodialysis of 5755 screened with moderate to severe sHPT.Main outcome measures:Parathyroidectomy, severe, unremitting HPT and use of commercial cinacalcet (a protocol violation).Intervention:Cinacalcet (30 to 180 mg daily) or placebo for up to 64 months.Results:In the 1935 patients randomized to placebo, 278 (14%) patients underwent PTX (median PTH 1872 pg/mL within prior 12 weeks of surgery). Age, sex, geographic region, co-morbidity, calcium-containing phosphate binder use, and baseline serum calcium, phosphorus and PTH concentrations were associated with PTX. Commercial cinacalcet was started in 443 (23%) patients (median PTH 1108 pg/mL before treatment began). Severe unremitting HPT developed in 470 (24%) patients. In a multivariable Cox model, the relative hazard (comparing patients randomized to cinacalcet versus placebo) of severe unremitting HPT was 0.31 (95% CI 0.26 to 0.37). The relative hazard differed little when adjusted by baseline clinical characteristics.Conclusions:Severe unremitting HPT develops frequently in patients on hemodialysis despite conventional therapy, and cinacalcet substantially reduces its occurrence.
    The Journal of Clinical Endocrinology and Metabolism 10/2013; · 6.31 Impact Factor
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    ABSTRACT: Knowledge of molecular biology and genomics continues to expand rapidly, promising numerous opportunities for improving health. However, a key aspect of the success of genomic medicine is related to public understanding and acceptance. Using community consultations and an online survey, we explored public attitudes and expectations about genomics research. Thirty-three members of the general public in Newfoundland, Canada, took part in the community sessions, while 1024 Atlantic Canadians completed the online survey. Overall, many participants noted they lacked knowledge about genetics and associated research and took the opportunity to ask numerous questions throughout sessions. Participants were largely hopeful about genomics research in its capacity to improve health, not only for current residents, but also for future generations. However, they did not accept such research uncritically, and a variety of complex issues and questions arose during the community consultations and were reflected in survey responses. With the proliferation of biobanks and the rapid pace of discoveries in genomics research, public support will be crucial to realize health improvements. If researchers can engage the public in regular, transparent dialogue, this two-way communication could allow greater understanding of the research process and the design of efficient and effective genetic health services, informed by the public that will use them.
    Health expectations: an international journal of public participation in health care and health policy 08/2013; · 1.80 Impact Factor
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    ABSTRACT: Lynch Syndrome (LS) families harbor mutated mismatch repair genes,which predispose them to specific types of cancer. Because individuals within LS families can experience multiple cancers over their lifetime, we developed a progressive three-state model to estimate the disease risk from a healthy (state 0) to a first cancer (state 1) and then to a second cancer (state 2). Ascertainment correction of the likelihood was made to adjust for complex sampling designs with carrier probabilities for family members with missing genotype information estimated using their family's observed genotype and phenotype information in a one-step expectation-maximization algorithm. A sandwich variance estimator was employed to overcome possible model misspecification. The main objective of this paper is to estimate the disease risk (penetrance) for age at a second cancer after someone has experienced a first cancer that is also associated with a mutated gene. Simulation study results indicate that our approach generally provides unbiased risk estimates and low root mean squared errors across different family study designs, proportions of missing genotypes, and risk heterogeneities. An application to 12 large LS families from Newfoundland demonstrates that the risk for a second cancer was substantial and that the age at a first colorectal cancer significantly impacted the age at any LS subsequent cancer. This study provides new insights for developing more effective management of mutation carriers in LS families by providing more accurate multiple cancer risk estimates. Copyright © 2013 John Wiley & Sons, Ltd.
    Statistics in Medicine 08/2013; 33(4). · 2.04 Impact Factor
  • Patrick S Parfrey, Geoff Warden, Brendan J Barrett
    American Journal of Kidney Diseases 06/2013; · 5.76 Impact Factor

Publication Stats

19k Citations
2,347.51 Total Impact Points


  • 2014
    • Health Canada
      • Health Sciences Center
      Ottawa, Ontario, Canada
  • 1988–2014
    • Memorial University of Newfoundland
      • • Faculty of Medicine
      • • Division of Community Health and Humanities
      • • Division of Nephrology
      Saint John's, Newfoundland and Labrador, Canada
  • 2012
    • Stanford University
      Palo Alto, California, United States
  • 2010–2012
    • University of Toronto
      • Department of Laboratory Medicine and Pathobiology
      Toronto, Ontario, Canada
    • The University of Calgary
      • Department of Medicine
      Calgary, Alberta, Canada
    • SickKids
      • Program in Genetics and Genome Biology
      Toronto, Ontario, Canada
  • 2010–2011
    • Brigham and Women's Hospital
      • • Center for Brain Mind Medicine
      • • Department of Medicine
      Boston, MA, United States
  • 2009–2010
    • University of Minnesota Duluth
      Duluth, Minnesota, United States
    • McMaster University
      • Department of Clinical Epidemiology and Biostatistics
      Hamilton, Ontario, Canada
    • Azienda Ospedaliera di Cremona
      Cremona, Lombardy, Italy
  • 2003–2009
    • University Health Network
      • • Department of Medicine
      • • Division of Nephrology
      Toronto, Ontario, Canada
  • 2008
    • Mount Sinai Hospital, Toronto
      • Department of Pathology and Laboratory Medicine
      Toronto, Ontario, Canada
  • 2007
    • Samuel Lunenfeld Research Institute
      Toronto, Ontario, Canada
    • University of California, San Francisco
      • Division of Hospital Medicine
      San Francisco, CA, United States
  • 2003–2006
    • University of Manitoba
      Winnipeg, Manitoba, Canada
  • 2005
    • Newfoundland and Labrador Centre for Health Information
      St. John's, Newfoundland and Labrador, Canada
    • Simon Fraser University
      • Department of Molecular Biology and Biochemistry
      Burnaby, British Columbia, Canada
  • 2004
    • Washington University in St. Louis
      • Department of Genetics
      Saint Louis, MO, United States
  • 2002
    • University of Birmingham
      Birmingham, England, United Kingdom
  • 1999–2000
    • National Heart, Lung, and Blood Institute
      • Division of Cardiovascular Sciences (DCVS)
      Maryland, United States
  • 1996
    • Florida Memorial University
      Saint John, Indiana, United States
  • 1995
    • The University of Western Ontario
      • Department of Medicine
      London, Ontario, Canada
  • 1992
    • St. John's Hospital
      Springfield, Illinois, United States