Objectives: The electrically evoked compound action potential (eCAP) is widely used in the clinic as an objective measure to assess cochlear implant functionality. During the past decade, there has been increasing interest in applying eCAPs for fitting of cochlear implants. Several studies have shown that eCAP-based fitting can potentially replace time-consuming behavioral fitting procedures, especially in young children. However, a closer look to all available literature revealed that there is no clear consensus on the validity of this fitting procedure. This study evaluated the validity of eCAP-based fitting of cochlear implant recipients based on a systematic review of the recent literature.
Design: The Preferred Reporting Items for Systematic Reviews and Meta-Analyses were used to search the PubMed, Web of Science, and Cochrane Library databases. The term "eCAP" was combined with "cochlear implants," "thresholds," and "levels," in addition to a range of related terms. Finally, 32 studies met the inclusion criteria. These studies were evaluated on the risk of bias and, when possible, compared by meta-analysis.
Results: Almost all assessed studies suffered from some form of risk of bias. Twenty-nine of the studies based their conclusion on a group correlation instead of individual subject correlations (analytical bias); 14 studies were unclear about randomization or blinding (outcome assessment bias); 9 studies provided no clear description of the populations used, for example, prelingually or postlingually implanted subjects (selection bias); and 4 studies had a high rate of loss (>10%) for patients or electrodes (attrition bias). Meta-analysis of these studies revealed a weak pooled correlation between eCAP thresholds and both behavioral T- and C-levels (r = 0.58 and r = 0.61, respectively).
Conclusions: This review shows that the majority of the assessed studies suffered from substantial shortcomings in study design and statistical analysis. Meta-analysis showed that there is only weak evidence to support the use of eCAP data for cochlear implant fitting purposes; eCAP thresholds are an equally weak predictor for both T- and C-levels. Based on this review, it can be concluded that research on eCAP-based fitting needs a profound reflection on study design and analysis to draw well-grounded conclusions about the validity of eCAP-based fitting of cochlear implant recipients.