Heart Rate Turbulence

Heart Rate Turbulence

Quantification of HRT

Turbulence Onset (TO) is the percentage difference between the heart rate immediately following PVC and the heart rate immediately preceding PVC. It is calculated using the equation

TO = ((RR1 + RR2) - (RR-2 + RR-1)) / (RR-2 + RR-1) * 100

with RR-2 and RR-1 being the first two normal intervals preceding the PVC and RR1 and RR2 the first two normal intervals following the PVC. Initially, TO is determined foreach individual PVC, followed by the determination of the average value of all individual measurements. Positive values for Turbulence Onset indicate deceleration, negative values indicate acceleration of the sinus rhythm.

The Turbulence Slope (TS) corresponds to the steepest slope of the linear regression line for each sequence of five consecutive normal intervals in the local tachogram. The Turbulence Slope calculations are based on the averaged tachogram and expressed in ms per RR interval.

Filters

The algorithm for HRT quantificationcan only deliver usable results if the triggering event was a true PVC (and not an artefact, T-wave or similar). In addition it must be ensured that the sinus rhythm immediately preceding and following the PVC is free from arrhythmia, artefacts and false classifications. In order to fulfill these requirements, we use filters which exclude RR intervals with the following characteristics from the HRT calculation:

• < 300 ms
• > 2000 ms
• > 200 ms difference to the preceding sinus interval
• > 20% difference to the reference interval (mean of the 5 last sinus intervals)

• a minimum prematurity of 20% and
• a post-extrasystole interval which is at least 20% longer than the normal interval.

For the calculation of the mean HRT-tachogram the HRT-algorithm requires at least 15 normal intervals after each single PVC.