Event Rates with Transcervical Carotid Artery Stenting with Flow Reversal.

We thank Naazie et al1Naazie I.N. Osaghae I. Malas M.B. Regarding “An updated systematic review and meta-analysis of results of transcervical carotid artery stenting with flow reversal”.J Vasc Surg. 2021; 73: 1835-1838Abstract Full Text Full Text PDF Scopus (1) Google Scholar for their interest in our work.2Paraskevas K.I. Antonopoulos C.N. Kakisis J.D. Geroulakos G. An updated systematic review and meta-analysis of results of transcervical carotid artery stenting with flow reversal.J Vasc Surg. 2020; 72: 1489-1498Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar We had stated in the limitations of our systematic review that some patients might have been included in more than one study.2Paraskevas K.I. Antonopoulos C.N. Kakisis J.D. Geroulakos G. An updated systematic review and meta-analysis of results of transcervical carotid artery stenting with flow reversal.J Vasc Surg. 2020; 72: 1489-1498Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar As we stated, this issue could be better addressed by an individual patient meta-analysis; however, such an analysis would require access to the raw data from each study.2Paraskevas K.I. Antonopoulos C.N. Kakisis J.D. Geroulakos G. An updated systematic review and meta-analysis of results of transcervical carotid artery stenting with flow reversal.J Vasc Surg. 2020; 72: 1489-1498Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar Regarding the statistical method used, when conducting a meta-analysis of proportions, transformations are usually performed to achieve sampling distributions closer to normal and better approximations of the sampling variance. The Freeman-Tukey double-arcsine transformation has become increasingly popular in meta-analyses because it works particularly well for normalizing and variance-stabilizing the sampling distribution of proportions compared with other techniques.3Freeman M.F. Tukey J.W. Transformations related to the angular and the square root.Ann Math Stat. 1950; 21: 607-611Crossref Google Scholar Among the advantages of arcsine-based transformations is that the variances depend only on the sample sizes, which are typically fixed, known values. In contrast, the variances of the log and logit transformations also depend on the event counts, which are random variables.4Lin L. Xu C. Arcine-based transformations for meta-analysis of proportions: pros, cons, and alternatives.Health Sci Rep. 2020; 3: e178Crossref PubMed Scopus (54) Google Scholar In the meta-analysis by Naazie et al,5Naazie I.N. Cui C.L. Osaghae I. Murad M.H. Schermerhorn M. Malas M.B. A systematic review and meta-analysis of transcarotid artery revascularization with dynamic flow reversal versus transfemoral carotid artery stenting and carotid endarterectomy.Ann Vasc Surg. 2020; 69: 426-436Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar the overall event rates after transcarotid artery revascularization (TCAR) and corresponding Wald 95% confidence intervals were calculated using a logistic-normal random-effects model with logit transformation. As seen in the original studies included in both meta-analyses, many proportions of the outcomes with TCAR were close to zero.2Paraskevas K.I. Antonopoulos C.N. Kakisis J.D. Geroulakos G. An updated systematic review and meta-analysis of results of transcervical carotid artery stenting with flow reversal.J Vasc Surg. 2020; 72: 1489-1498Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar,5Naazie I.N. Cui C.L. Osaghae I. Murad M.H. Schermerhorn M. Malas M.B. A systematic review and meta-analysis of transcarotid artery revascularization with dynamic flow reversal versus transfemoral carotid artery stenting and carotid endarterectomy.Ann Vasc Surg. 2020; 69: 426-436Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar Thus, the estimate for the standard error is zero; therefore, the Wald 95% confidence intervals cannot be calculated, leading to the exclusion of studies with a zero standard error. However, excluding such studies could lead to biased results. This issue can be overcome using continuity correction. Although the use of continuity correction will ensure that the studies are retained, the 95% confidence intervals for the pooled estimate might yield inadmissible values. Also, continuity corrections of zero rates from studies with small numbers can lead to an artificial inflation of the corrected rate. This can have a considerable effect on the synthesized proportion of events.6Schwarzer G. Chemaitelly H. Abu-Raddad L.J. Rucker G. Seriously misleading results using inverse of Freeman-Tukey double arcsine transformation in meta-analysis of single proportions.Res Synth Methods. 2019; 10: 476-483Crossref PubMed Scopus (167) Google Scholar In such cases, it might be better to switch to a transformation that manages such proportions more gracefully, such as the Freeman-Tukey transformation, which does not require any adjustments to the observed data, even when proportions are equal to zero.6Schwarzer G. Chemaitelly H. Abu-Raddad L.J. Rucker G. Seriously misleading results using inverse of Freeman-Tukey double arcsine transformation in meta-analysis of single proportions.Res Synth Methods. 2019; 10: 476-483Crossref PubMed Scopus (167) Google Scholar Our transformations did not require the continuity correction for the zero counts. This might explain the higher rates in the meta-analysis reported by Naazie et al5Naazie I.N. Cui C.L. Osaghae I. Murad M.H. Schermerhorn M. Malas M.B. A systematic review and meta-analysis of transcarotid artery revascularization with dynamic flow reversal versus transfemoral carotid artery stenting and carotid endarterectomy.Ann Vasc Surg. 2020; 69: 426-436Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar compared with ours.2Paraskevas K.I. Antonopoulos C.N. Kakisis J.D. Geroulakos G. An updated systematic review and meta-analysis of results of transcervical carotid artery stenting with flow reversal.J Vasc Surg. 2020; 72: 1489-1498Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar Our meta-analysis also provided the crude (raw) rates.2Paraskevas K.I. Antonopoulos C.N. Kakisis J.D. Geroulakos G. An updated systematic review and meta-analysis of results of transcervical carotid artery stenting with flow reversal.J Vasc Surg. 2020; 72: 1489-1498Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar Therefore, readers can find the absolute measures of the studied outcomes. This is particularly useful and comprehensible from a clinical viewpoint and also normalizes the specific problems of low event frequencies, which can arise in terms of the use of different statistical methods for managing zero and the practical consequences of the adopted methodologic choice.7Messori A. Fadda V. Maratea D. Trippoli S. The need to know crude event rates in meta-analysis.Am J Heart. 2013; 166: e17Crossref PubMed Scopus (1) Google Scholar Overall, the issues raised are mainly methodologic. Both meta-analyses highlighted the high success rate and very low adverse event rates with TCAR and both agreed that this technique is safe and effective.2Paraskevas K.I. Antonopoulos C.N. Kakisis J.D. Geroulakos G. An updated systematic review and meta-analysis of results of transcervical carotid artery stenting with flow reversal.J Vasc Surg. 2020; 72: 1489-1498Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar,5Naazie I.N. Cui C.L. Osaghae I. Murad M.H. Schermerhorn M. Malas M.B. A systematic review and meta-analysis of transcarotid artery revascularization with dynamic flow reversal versus transfemoral carotid artery stenting and carotid endarterectomy.Ann Vasc Surg. 2020; 69: 426-436Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar This shared conclusion is especially important for clinicians and should be highly communicated.