Retrospective and prospective study designs.

The labels "retrospective" and "prospective" strongly connote study quality, often favouring prospective studies. However, three definitions of these terms exist, each suggesting distinct methodological limitations. In this review, we summarize and evaluate these definitions. Caution is warranted when labeling a study "retrospective": This label should only be used when implying a risk of recall bias, which can only occur in retrospective data collection. Generally, assessing random and systematic errors is necessary to appraise study quality rather than relying on ambiguous labels.

Evaluation of Left Truncation and Censoring When Changing the Use of the International Classification of Diseases Eighth Revision Codes to Tenth Revision Codes in the Danish National Patient Registry.

Purpose: In the Danish National Patient Registry (DNPR), covering all Danish hospitals and widely used in research, diseases have been recorded using International Classification of Diseases (ICD) codes, transitioning from the Eighth to the Tenth revision in 1994. Uncertainty exists regarding whether including ICD-8 codes alongside ICD-10 is needed for complete disease identification. We assessed the extent of left-truncation and left-censoring in the DNPR arising from omitting ICD-8 codes. Patients and Methods: We sampled 500,000 Danes ≥40 years of age in 1995, 2010, and 2018. From the DNPR, we identified cardiovascular, endocrine, gastrointestinal, neurological, pulmonary, rheumatic, and urogenital diseases as well as fractures. We obtained the number of people with a disease recorded with ICD-8 codes only (ie, the ICD-8 record would be left-truncated by not using ICD-8 codes), ICD-8 plus ICD-10 codes (ie, the ICD-8 record would be left-censored by not using ICD-8 codes), and ICD-10 codes only. For each ICD group, we calculated the proportion of people with the disease relative to the total sample (ie, 500,000 people) and the total number of people with the disease across all ICD groups. Results: Overall, the left-truncation issue decreased over the years. Relative to all people with a disease, the left-truncated proportion was for example 59% in 1995 and <2% in 2018 for diabetes mellitus; 93% in 1995, and 54% in 2018 for appendicitis. The left-truncation issue increased with age group for most diseases. The proportion of disease records left-censored by not using ICD-8 codes was generally low but highest for chronic diseases. Conclusion: The left-truncation issue diminished over sample years, particularly for chronic diseases, yet remained rather high for selected surgical diseases. The left-truncation issue increased with age group for most diseases. Left-censoring was overall a minor issue that primarily concerned chronic diseases.

Preadmission Opioid Use and 1-Year Mortality Following Incident Myocardial Infarction: A Danish Population-Based Cohort Study (1997-2016).

Background Opioid use has been linked to an increased risk of myocardial infarction and cardiovascular mortality, but the prognostic impact of opioid use before an incident myocardial infarction is largely unknown. Methods and Results We conducted a nationwide population-based cohort study including all patients hospitalized for an incident myocardial infarction in Denmark (1997-2016). Based on their last redeemed opioid prescription before admission, patients were categorized as current users (0-30 days), recent users (31-365 days), former users (>365 days), and nonusers. One-year all-cause mortality was calculated using the Kaplan-Meier method. Hazard ratios (HRs) were computed using Cox proportional hazards regression analyses, adjusting for age, sex, comorbidity, any preceding surgery within 6 months before the myocardial infarction admission, and medication use before the myocardial infarction admission. We identified 162 861 patients with an incident myocardial infarction. Of these, 8% were current opioid users, 10% were recent opioid users, 24% were former opioid users, and 58% were nonusers of opioids. One-year mortality was highest among current users (42.5% [95% CI, 41.7%-43.3%]) and lowest among nonusers (20.5% [95% CI, 20.2%-20.7%]). Compared with nonusers, current users had an elevated 1-year all-cause mortality risk (adjusted HR, 1.26 [95% CI, 1.22-1.30]). Following adjustment, neither recent users nor former users of opioids were at elevated risk. Conclusions Preadmission opioid use was associated with an increased 1-year all-cause mortality risk following an incident myocardial infarction. Opioid users thus represent a high-risk subgroup of patients with myocardial infarction.

Long-Term Outcomes of Perioperative Versus Nonoperative Myocardial Infarction: A Danish Population-Based Cohort Study (2000-2016).

BACKGROUND: Perioperative myocardial infarction is a serious cardiovascular complication of noncardiac surgery. The clinical course of perioperative myocardial infarction, other than all-cause mortality, is largely unknown. We examined long-term fatal and nonfatal outcomes of perioperative myocardial infarction compared with nonoperative myocardial infarction. METHODS: We conducted a population-based cohort study of first-time myocardial infarction in Denmark from 2000 to 2016. We calculated cumulative incidence of all-cause mortality, cardiac mortality, recurrent myocardial infarction, heart failure, stroke, venous thromboembolism, acute kidney injury, and kidney failure with replacement therapy. We computed 5-year risk ratios adjusted for age, sex, year of diagnosis, educational level, and comorbidities. RESULTS: We identified 5068 patients with perioperative myocardial infarction and 137 862 patients with nonoperative myocardial infarction. The 5-year risk of all-cause mortality was 67.5% (95% CI, 66.1%-69.0%) for perioperative myocardial infarction patients and 38.0% (95% CI, 37.7%-38.3%) for nonoperative myocardial infarction patients. The adjusted risk ratio of all-cause mortality was 1.13 (95% CI, 1.11-1.16) at 5 years. After adjustment, we found no association between patients with perioperative myocardial infarction and 5-year cardiac mortality, recurrent myocardial infarction, heart failure, stroke, or kidney failure with replacement therapy when compared with nonoperative myocardial infarction patients. Perioperative myocardial infarction patients had a higher relative risk of venous thromboembolism (5-year risk ratio, 1.21 [95% CI, 1.01-1.46]) and acute kidney injury (5-year risk ratio, 1.37 [95% CI, 1.22-1.53]). CONCLUSIONS: Compared with nonoperative myocardial infarction patients, perioperative myocardial infarction patients had elevated risk of all-cause mortality, venous thromboembolism, and acute kidney failure. In addition to the myocardial infarction component of perioperative myocardial infarction, this poor prognosis seemed associated with the surgery or underlying comorbidities. These findings warrant further research on strategies to reduce the risk of perioperative myocardial infarction and on strategies to manage perioperative myocardial infarction.

Impact of the Look-Back Period on Identifying Recurrent Myocardial Infarctions in the Danish National Patient Registry.

PURPOSE: Studies examining myocardial infarction (MI) often seek to include only incident MIs by excluding recurrent MIs. When based on historical data, identification of previous MI depends on the length of the look-back period. However, international registries often cover a short time period, consequently containing left-censored data, making it impossible to determine if a first MI in a period is truly an incident MI. We evaluated whether the proportion of MIs identified as recurrent MIs depends on the look-back period, and how including recurrent MIs in a planned incident MI cohort impacts survival estimates. PATIENTS AND METHODS: We used the Danish National Patient Registry, covering all Danish hospitals since 1977 to identify first MIs during 2010-2016 (index events). The hospital registry history preceding the index event was then searched for previous MIs. We plotted the proportion of index events identified as recurrent MIs as a function of the look-back period. Moreover, we calculated 5-year all-cause mortality and confidence intervals (CIs) using the 1-Kaplan-Meier method for five cohorts based on the index events and defined by look-back periods of 0, 5, 10, 20, and up to 39 years. RESULTS: Among 63,885 index events, 3.4% were identified as recurrent MIs with 5 years of look-back, 7.9% with 10 years, 14% with 24 years, and 15% with up to 39 years. All-cause mortality risk was 36% (95% CI: 36-37%) with 0 years of look-back, 35% (95% CI: 35-36%) with 5 years, 35% (95% CI: 35-36%) with 10 years, 34% (95% CI: 34-35%) with 20 years, and 34% (95% CI: 33-34%) with up to 39 years. CONCLUSION: Most recurrent MIs were identified with a look-back period of 24 years. Including recurrent MIs in a planned incident MI cohort, due to shorter look-back periods, overestimated the mortality risk.

Breaking Point Toward Decreasing Prevalence of Myocardial Infarction Owing to Relative Stronger Decrease in Incidence Than Increase in Survival Rate (A Danish Cohort Study [1994-2016]).

The aim of this study was to examine whether myocardial infarction (MI) incidence rate continues to decrease and to determine whether the relative magnitude of a potentially decreasing incidence rate has surpassed increasing survival, demasking a breaking point in trends of MI prevalence proportion. This was a nationwide population-based cohort study using medical registries covering all hospitals in Denmark (1994 to 2016). We identified 193,870 persons with a first-time hospitalization for MI. Age-standardized incidence rates (per 100,000 persons) decreased from 154 (95% confidence interval [CI] 149 to 159) in 1994 to 90 (95% CI 86 to 93) in 2016 for females, and from 335 (95% CI 326 to 344) in 1994 to 205 (95% CI 199 to 211) in 2016 for males. Age-standardized prevalence proportion increased overall from 1994 to 2004 with a subsequent plateau. From 2006 to 2016, age-standardized prevalence proportion decreased by 0.09% (95% CI 0.07% to 0.11%) for females (from 1.07% to 0.98%) and by 0.20% (95% CI 0.17% to 0.23%) for males (from 2.85% to 2.65%). The age-standardized prevalence proportion decreased solely among persons aged 55 to 84 years. It remained stable among persons aged <55 years and increased among persons aged ≥85 years until 2012 with subsequent stable trends. We conclude that the continuous decreasing age-standardized incidence rate of MI over decades has, although with increasing survival, led to an overall breaking point toward a decreasing age-standardized prevalence proportion of MI since 2006.