**Quantification of HRT**
(1) Turbulence Onset: percentage difference between the average
value of the first two normal intervals following the PVC and of
the last two normal intervals preceding the PVC. Initially, TO is
determined for each individual PVC, followed by the determination
of the average value of all individual measurements.

(2) Turbulence Slope: steepest slope of a linear regression line
through five consecutive measurement points in the averaged
tachogram. The Turbulence Slope calculations are based on the
averaged tachogram and expressed in ms per RR interval.