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Automated blood pressure measurement in atrial fibrillation: a systematic review and meta-analysis

Cheng, Hao-Mina,b,c; Tufanaru, Catalina; Pearson, Alana; Chen, Chen-Huana,b,c,d

doi: 10.1097/HJH.0b013e32835ae9a3
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aThe Joanna Briggs Institute, Faculty of Health Sciences, The University of Adelaide, Adelaide, Australia

bDepartment of Medical Research and Education, Taipei Veterans General Hospital

cDepartment of Medicine, National Yang-Ming University

dInstitute of Public Health and Community Medicine Research Center, National Yang-Ming University, Taipei, Taiwan

Correspondence to Hao-Min Cheng, MD, The Joanna Briggs Institute, Faculty of Health Sciences, The University of Adelaide, Adelaide 5005, Australia. Tel: +61 8 8410 4809; fax: +61 8 8410 4809; e-mail: hao-min.cheng@adelaide.edu.au

We read with interest the article by Stergiou et al.[1] on the ‘Automated blood pressure measurement in atrial fibrillation: a systematic review and meta-analysis’. Although appreciative of the contribution this article makes to the field, we wish to comment on the method used in the meta-analysis related to the measurement comparison of a tested technique with an established one [2]. Bland and Altman, the methodological leaders in this field, proposed methods to investigate agreement that have become the validation standards for the measurement accuracy of blood pressure monitors [2–4]. They have pointed out more than once that the use of a correlation coefficient is inappropriate in the analysis of measurement method comparison data [3,5]. To describe agreement, it is necessary to emphasize not only the mean difference between two measurements but also the 95% limits of agreement, which can be calculated by the equation: (mean difference) ± 1.96 × (standard deviation of differences) [3]. It is insufficient to present only the mean difference because if the two methods agree on average, the mean difference is small regardless of the agreement for individuals [5]. In this regard, there should be two outcome measures that the meta-analysis of method comparison studies should synthesize: the pooled estimates of systematic bias (mean differences) and random error (standard deviation of differences) [6]. Williamson et al.[6] have developed a concise methodology for the meta-analysis of method comparison studies, which had been utilized in previous systematic reviews with meta-analysis [7–9]. The outcome measures for meta-analysis in the present article [1] are correlation coefficients and averaged blood pressure difference, and the random error was only evaluated with the variability of individual studies as presented in its Table 2 [1]. The 95% confidence interval shown in the article is actually the pooled estimate of the mean differences and has nothing to do with the limits of agreement (random error). We think that the limits of agreement is an important measure for this study to describe the extent of agreement between blood pressure measurements, which should also be meta-analysed on the basis of the previously established methodology [6–9]. Through the presentation of pooled estimates of random errors (the 95% limits of agreement), readers can have a better understanding and assessment on the accuracy of automated blood pressure monitors in atrial fibrillation.

On the basis of the data provided in Figures 5 and 6 [1] and the random effect model of meta-analysis for method comparison studies established by Williamson et al.[6], the pooled estimates of agreement for SBP and DBP (Table 1) were 0.04 ± 5.5 mmHg (95% limits of agreement −10.7∼10.8) and 2.5 ± 8.5 mmHg (95% limits of agreement −14.1∼19.2), respectively. However, after excluding the study by Farsky et al.[10], which used a dual control device with both Korotkov and oscillometric methods, the pooled estimates of agreement for SBP and DBP are 1.0 ± 11.3 mmHg (95% limits of agreement −21.1∼23.1) and 3.0 ± 9.7 mmHg (95% limits of agreement −16.0∼22.0), respectively. Both exceed the recommended range for agreement on the basis of the international standard of 5.0 ± 8.0 mmHg [4]. Thus, the accuracy of the automatic blood pressure monitors in measuring SBP needs to be improved.

TABLE 1

TABLE 1

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ACKNOWLEDGEMENTS

Conflicts of interest

There are no conflicts of interest.

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REFERENCES

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