Electrocardiograms (ECGs) captured by wearable ECG devices easily contain artifacts because of measurement faults. Since the frequency characteristics of artifacts are quite similar to those of R waves, it may result in R-R interval (RRI) miscalculations. To enable accurate heart rate variability (HRV) analysis in daily life, this paper proposes a method to reliably evaluate RRI measurement status, one that uses the electric potential characteristics of the QRS complex. Initial evaluation results show that it has the potential to distinguish miscalculated RRIs. Also proposed is a new RRI outlier exclusion method that uses the aforementioned method. Time domain measures of HRV derived from the proposed RRI outlier exclusion method are found to be more accurate than those derived from the conventional one.