Early Detection of Genetic Cardiomyopathies in Relatives | 159 Selection, Q3: Ascertainment of exposure (1p) Studies were awarded a point if it was reported that deformation imaging was performed blind for outcomes. Selection, Q4: Demonstration that outcome of interest was not present at start of the study (1p) A point was awarded if the outcome of interest was absent at the start of the study. Comparability, Q1: Comparability of cohorts (2p) Studies were awarded points if they reported data on comparability at baseline between the group with vs. the group without deformation imaging abnormalities. One point was awarded per variable that was comparable between the groups (with a significance level of p>0.05) or adjusted for confounding, with a maximum of two points Outcome, Q1: Assessment of outcome (1p) Studies were awarded points in case of independent or blind assessment of the outcome, or by confirmation of the outcome by reference to secure records. Outcome, Q2: Was follow-up long enough for outcomes to occur (1p) Since the outcomes of interest were different among the studies, we could not define one acceptable length of follow-up for all studies. This question was therefore assessed per study by two independent observers and disagreement was solved by consensus. Outcome, Q3: Adequacy of follow-up cohorts (1p) Studies were awarded a point if the follow-up rate was deemed high enough to avoid selection bias. In case of a low follow-up rate, we evaluated follow-up rates of the exposed and nonexposed cohort to assess the risk of bias (if needed we requested this data from the author). Supplementary results Quality assessment The Newcastle-Ottawa scale for case-control studies was used to assess the risk of bias in 24 studies (Supplementary table 1). The median score for case-control studies was 7 out of 9 points (ranging between 6 and 9 points). Most points were lost because the rate of echocardiogram exclusion due to insufficient image quality was not reported. Moreover, many studies investigating genotype-positive relatives lost points due to inclusion of healthy volunteers as control subjects instead of genotype-negative relatives. Last, more than half of the studies did not report whether analyses were performed blind for clinical data. The Newcastle-Ottawa scale for cohort studies was used in 10 studies (Supplementary table 2). The median score for cohort studies was 7 out of 9 points (ranging between 6 and 8 points). Most points were lost because it was not reported whether clinical characteristics of the two groups of relatives that were followed (often relatives with normal vs. abnormal strain) were comparable. Moreover, many studies lost points because follow-up was deemed not long enough for outcomes to occur 7
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