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Vidal Essebag

Publications and source records attributed to Vidal Essebag.

9 recordsLinked to original sources
PubMed2005

Comparison of nested case-control and survival analysis methodologies for analysis of time-dependent exposure.

BACKGROUND: Epidemiological studies of exposures that vary with time require an additional level of methodological complexity to account for the time-dependence of exposure. This study compares a nested case-control approach for the study of time-dependent exposure with cohort analysis using Cox regression including time-dependent covariates. METHODS: A cohort of 1340 subjects with four fixed and seven time-dependent covariates was used for this study. Nested case-control analyses were repeated 100 times for each of 4, 8, 16, 32, and 64 controls per case, and point estimates were compared to those obtained using Cox regression on the full cohort. Computational efficiencies were evaluated by comparing central processing unit times required for analysis of the cohort at sizes 1, 2, 4, 8, 16, and 32 times its initial size. RESULTS: Nested case-control analyses yielded results that were similar to results of Cox regression on the full cohort. Cox regression was found to be 125 times slower than the nested case-control approach (using four controls per case). CONCLUSIONS: The nested case-control approach is a useful alternative for cohort analysis when studying time-dependent exposures. Its superior computational efficiency may be particularly useful when studying rare outcomes in databases, where the ability to analyze larger sample sizes can improve the power of the study.

Aged↗
PubMed2004

Effect of amiodarone dose on the risk of permanent pacemaker insertion.

Bradyarrhythmia requiring permanent pacemaker insertion has been associated with amiodarone use but the effect of amiodarone dose has not been investigated. In order to determine the effect of amiodarone dose on the risk of requiring permanent pacemaker insertion, a cohort of 15,824 subjects with atrial fibrillation (AF) and prior myocardial infarction was established. This study included 1,340 subjects who received a first prescription of amiodarone at > 65 years of age. Cox regression with daily dose and cumulative dose (weighted for recency of exposure) represented by time dependent covariates was performed, adjusting for baseline risk factors and time dependent exposure to other cardiac medications. The incidence of pacemaker insertion was 2.2% per person-year during a mean of 1.8 +/- 1.5 years of follow-up, and 5.2% per person-year during the first 90 days of amiodarone exposure. Amiodarone daily doses > 200 mg were associated with an increased risk during the entire follow-up HR 2.0; 95% CI 1.0 to 4.1) as well as during the first 90 days (HR 3.1; 95% CI 1.1 to 9.0). Cumulative doses greater than the equivalent of continuous therapy with 200 mg per day were also associated with an increased risk (HR 2.8; 95% CI 1.4 to 5.5). Baseline conduction disorder or sinus node dysfunction was the only other significant predictor of pacemaker insertion. This study suggests that there is a dose dependent increased risk of permanent pacemaker insertion associated with amiodarone use that appears to be greatest during the initial months of treatment.

Age Factors↗
PubMed2003

Amiodarone and the risk of bradyarrhythmia requiring permanent pacemaker in elderly patients with atrial fibrillation and prior myocardial infarction.

OBJECTIVES: The aim of this study was to determine whether the use of amiodarone in patients with atrial fibrillation (AF) increases the risk of bradyarrhythmia requiring a permanent pacemaker. BACKGROUND: Reports of severe bradyarrhythmia during amiodarone therapy are infrequent and limited to studies assessing the therapy's use in the management of patients with ventricular arrhythmias. METHODS: A study cohort of 8,770 patients age > or =65 years with a new diagnosis of AF was identified from a provincewide database of Quebec residents with a myocardial infarction (MI) between 1991 and 1999. Using a nested case-control design, 477 cases of bradyarrhythmia requiring a permanent pacemaker were matched (1:4) to 1,908 controls. Multivariable logistic regression was used to estimate the odds ratio (OR) of pacemaker insertion associated with amiodarone use, controlling for baseline risk factors and exposure to sotalol, Class I antiarrhythmic agents, beta-blockers, calcium channel blockers, and digoxin. RESULTS: amiodarone use was associated with an increased risk of pacemaker insertion (OR: 2.14, 95% confidence interval [CI]: 1.30 to 3.54). This effect was modified by gender, with a greater risk in women versus men (OR: 3.86, 95% CI: 1.70 to 8.75 vs. OR: 1.52, 95% CI: 0.80 to 2.89). Digoxin was the only other medication associated with an increased risk of pacemaker insertion (OR: 1.78, 95% CI: 1.37 to 2.31). CONCLUSIONS: This study suggests that the use of amiodarone in elderly patients with AF and a previous MI increases the risk of bradyarrhythmia requiring a permanent pacemaker. The finding of an augmented risk of pacemaker insertion in elderly women receiving amiodarone requires further investigation.

Aged↗
PubMed2003

The nested case-control study in cardiology.

BACKGROUND: The nested case-control study is an efficient epidemiological design whereby a case-control approach is employed within an established cohort. The large number of recent prospective studies and randomized trials conducted in cardiology provide cohorts within which the nested case-control approach is increasingly used. METHODS: This paper describes the design of the nested case-control study, and evaluates its role in cardiology by reviewing all such studies indexed in Medline from 1966 to 2000. The example of homocysteine is used to illustrate how discrepancies between results of nested case-control and case-control studies played an important role in the decisions and recommendations of national and international organizations. RESULTS: Seventy-seven nested case-control studies in cardiology were reviewed. The number of studies per year has been increasing since the first publication in 1987. The majority (96%) of studies evaluated potential risk factors for cardiovascular disease while the remainder evaluated drugs with cardiac adverse effects. In studies of homocysteine and coronary artery disease, nested case-control studies did not confirm the strong association suggested by early case-control studies that may have been influenced by bias (eg, selection, publication, or reverse causality). This led national and international organizations to advise against routine screening. CONCLUSIONS: The nested case-control study is increasingly used to study causal relationships in cardiology. The large cohorts of cardiac patients created by prospective studies, clinical trials, and administrative databases should be exploited using this methodology to assess potential cardiac risk factors and other causal relationships that cannot be studied in randomized trials.

Biomarkers↗
PubMed2003

Expanding indications for defibrillators after myocardial infarction: risk stratification and cost effectiveness.

Practice guidelines have expanded to include a new Class IIa recommendation for implantable cardiac defibrillator (ICD) use in patients post-myocardial infarction (MI) with a left ventricular ejection fraction (LVEF) </=30% on the basis of the results of the Multicenter Automatic Defibrillator Implantation Trial II (MADIT II). Given that over 3 million patients in North America meet these criteria and over 400,000 additional patients will meet these criteria every year, the potential costs to the healthcare system are substantial and possibly prohibitive. The results of MADIT II must be interpreted in the context of other studies. The benefits of ICD therapy may vary substantially across subgroups of MADIT II patients. Studies of amiodarone suggest that it may be useful if used in addition to beta-blockers, and the relative value of this therapy compared to ICD therapy remains to be elucidated. Subgroups of MADIT II patients with QRS duration >0.12 seconds or LVEF </=25% appear to derive the greatest benefit from ICD therapy. Cost-effectiveness depends on the magnitude of benefit expected and will differ across subgroups of patients with different levels of risk. Better risk stratification strategies are needed to predict which patients will benefit most. Results of ongoing studies will be crucial in determining the relative effectiveness of ICD compared to optimal medical therapy including the use of amiodarone and beta-blockers. Predictors of subsets of MADIT II patients most likely to benefit from ICD therapy are urgently needed in order to prioritize allocation of healthcare resources.

Canada↗
PubMed2003

Air medical transport of cardiac patients.

The air medical transport of cardiac patients is a rapidly expanding practice. For various medical, social, and economic indications, patients are being flown longer distances at commercial altitudes, including international and intercontinental flights. There are data supporting the use of short-distance helicopter flights early in the course of a cardiac event for patients needing emergent transfer for percutaneous coronary intervention or aortocoronary bypass. When considering elective long-distance air medical transport of cardiac patients for social or economic reasons, it is necessary to weigh the benefits against the potential risks of flight. A few recent studies suggest that long-distance air medical transport is safe under certain circumstances. Current guidelines for air travel after myocardial infarction do not address the use of medical escorts or air ambulances equipped with intensive care facilities. Further research using larger prospective studies is needed to better define criteria for safe long-distance air medical transport of cardiac patients.

Aerospace Medicine↗
PubMed2002

Routine advance directive and organ donation questioning on admission to hospital.

OBJECTIVE: The purpose of this study is to determine whether routine questioning on admission to hospital can identify patients who do not want cardiopulmonary resuscitation (CPR) or intensive-care unit (ICU) admission. We also determined whether routine questioning can identify patients interested in organ donation. Finally, we determined whether routine questioning helps train housestaff to discuss end-of-life issues with patients. METHODS: The housestaff of an internal-medicine ward questioned admitted patients about previous discussions regarding resuscitation or organ donation, and about preferences regarding CPR, ICU, and organ donation. RESULTS: Of 40 patients who had never discussed CPR and ICU issues, 25 per cent preferred no CPR, and 18 per cent preferred no ICU. Of 24 patients who had never discussed organ-donation issues, 67 per cent were interested in being donors. All housestaff felt more comfortable discussing end-of-life issues by the end of the study. CONCLUSION: Routine questioning of patients on admission identifies a significant number who prefer no CPR or ICU. This information may help to avoid inappropriate resuscitation efforts and ICU admissions. Routine questioning also reveals many patients who are interested in organ donation. Encouraging these patients to identify themselves and to discuss their wishes with family members may increase the number of procurable organs. Housestaff benefit from the experience of discussing end-of-life issues.

Advance Care Planning↗