Evidence in crisis: a closer look into the quality of published systematic reviews in the cardiology literature

Background

Systematic reviews are usually considered as the highest level of evidence and are increasingly used in shaping cardiology policies and guidelines. However, as the rate of publishing systematic reviews increases annually, there are rising concerns regarding their quality and reporting standards.

Purpose

The current analysis provides an insight into the quality of published systematic reviews in cardiology and provides recommendations for researchers, clinicians, and stakeholders in this regard.

Methods

Using a comprehensive Medline/PubMed search, we retrieved all systematic reviews, published between 2009 and 2019 in five general cardiology journals with the highest impact factor as per the Clarivate Analytics 2019 Journal Impact Factor List (Circulation, European Heart Journal, Journal of the American College of Cardiology, Circulation Research, and JAMA Cardiology). We assessed the methodological characteristics, eligibility criteria, reporting standards, as well as review quality scores according to the AMSTAR tool.

Results

Among 352 retrieved reviews, 275 (75.3%) performed direct head-to-head analysis and 164 (46.6%) included only clinical trials. The median numbers of searched databases and included studies were 3 (IQR: 2, 3) and 13 (IQR: 7, 30). The primary outcomes were often hard clinical endpoints as mortality (39.2%) and stroke (11.9%). 64 (18.2%) registered their protocol, 208 (58.4%) used validated tools for risk of bias assessment, 177 (52.3%) assessed for publication bias, and 221 (62.8%) adhered to the PRISMA checklist. Thirty-five reviews detected significant publication bias, which was significantly associated with heterogeneity of the primary outcome. The AMSTAR quality scores were low or critically low in 71% of evaluated reviews. Further, 87 (24.7%) did not report on whether they received funding or not, 33 (9.4%) reported receiving no funding, and 232 adequately reported on their funding sources [70 (19.9%) from governmental/academic sources, 120 (34.1%) from pharmaceutical companies, and 42 (11.9%) from both sources]. analysis showed that reviews with advanced statistical analysis, those that included RCTs, adhered to the PRISMA checklist, or had higher AMSTAR quality scores had significantly higher citation metrics (p<0.05).

Conclusion

Due to the widespread low quality and poor reporting in cardiovascular systematic reviews, clinicians should be educated on the value of methodological quality in interpreting systematic review findings. In addition, academic societies and guideline writing groups should implement rigorous critical appraisal and peer review policies to improve the synthesis and utilization of systematic reviews in evidence-based cardiovascular medicine.

Funding Acknowledgement

Type of funding sources: None.

Association between type 1, type 2 cytokines, diabetic autoantibodies and 25-hydroxyvitamin D in children with type 1 diabetes

PURPOSE

Vitamin D may play a role in the pathogenesis of type 1 diabetes (T1D). The aim of the current study was to determine the possible association between 25-hydroxyvitamin D [25(OH)D] levels and circulating levels of type 1 and type 2 cytokines, as well as the pathophysiology of T1D in children.

METHODS

A total of 250 T1D patients and 250 sex- and age-matched T1D-free controls were screened for 25(OH)D, hemoglobin A1c (HbA1c), type 1 and type 2 cytokines, C-reactive protein (CRP) and bone mineral metabolism, as well as antibodies against insulin, glutamic acid decarboxylase (anti-GAD 65) and islet cells.

RESULTS

Our data showed that the plasma level of 25(OH)D was significantly lower in T1D patients and that there was a significant negative correlation between 25(OH)D levels and HbA1c values. There was a significant association between deficient levels of 25(OH)D and higher levels of cytokines (IFN-γ, TNF-α, IL-6, IL-1β, IL-4 and IL-10) and CRP. Total blood hemoglobin, the hematocrit percentage, body mass index SDS values, phosphate and magnesium levels were significantly lower in T1D patients than in T1D-free subjects. The levels of parathyroid hormone and alkaline phosphatase were significantly higher in T1D patients. Higher levels of cytokines were significantly associated with deficient levels of 25(OH)D. Moreover, in T1D patients, higher levels of islet antibodies, anti-GAD antibodies and anti-insulin antibodies were significantly associated with deficient levels of 25(OH)D.

CONCLUSIONS

In type 1 diabetic children, deficient levels of 25(OH)D are associated with high levels of HbA1c, circulatory cytokines and antibody markers.