Check whether a peak is a qrs complex. It is classified as qrs
        if it:
        - Comes after the refractory period
        - Passes qrs threshold
        - Is not a t-wave (check it if the peak is close to the previous
          qrs).

        Parameters
        ----------
        peak_num : int
            The peak number of the mwi signal to be inspected
        backsearch: bool, optional
            Whether the peak is being inspected during backsearch

def _is_qrs(self, peak_num, backsearch=False):
        """
        Check whether a peak is a qrs complex. It is classified as qrs
        if it:
        - Comes after the refractory period
        - Passes qrs threshold
        - Is not a t-wave (check it if the peak is close to the previous
          qrs).

        Parameters
        ----------
        peak_num : int
            The peak number of the mwi signal to be inspected
        backsearch: bool, optional
            Whether the peak is being inspected during backsearch

        """
        i = self.peak_inds_i[peak_num]
        if backsearch:
            qrs_thr = self.qrs_thr / 2
        else:
            qrs_thr = self.qrs_thr

        if (i-self.last_qrs_ind > self.ref_period
           and self.sig_i[i] > qrs_thr):
            if i-self.last_qrs_ind < self.t_inspect_period:
                if self._is_twave(peak_num):
                    return False
            return True

        return False