14th International Congress
THE "NEW FRONTIERS"
OF ARRHYTHMIAS 2000

Jan. 29 - Feb. 5, 2000
Marilleva, Trento, Italy

RT-28

Heart-rate turbulence

Marek Malik, Dan Wichterle, Georg Schmidt.
Department of Cardiological Sciences, St. George’s Hospital Medical School, London, UK, Third Department of Medicine, First Medical School, Charles University, Prague, Czech Republic, Deutsches Herzzentrum and 1.Medizinische Klinik der Technischen Universität München, Germany

Expression of heart rate turbulence

A number of different numerical descriptors and quantifiers expressing both phases of heart rate turbulence were previously investigated⁶. During these investigations, a particular attention was paid to the goal of finding descriptors which were independent of each other, at a strong predictive power in terms of identifying post-infarction patients at higher risk, and were predictors of mortality independent of age, parameters of ventricular performance such as left ventricular ejection fraction, and of other established Holter based risk predictors.

Based on these pilot studies, the seminal publication on heart rate turbulence eventually proposed two numerical expressions termed turbulence onset (TO) and the turbulence slope (TS). TO is a difference between the mean of the first two sinus RR intervals following a VPB and the last two sinus rhythm RR intervals before the VPB expressed as a relative number of the mean of the two sinus RR intervals before the VPB. In precise numerical terms, the following formula is used:

        (RR₁+RR₂) – (RR_–2+RR_–1)
TO = ------------------------- * 100
              (RR_–2+RR_–1)


where RR_–1 and RR_–2 are the first and second sinus rhythm intervals preceding the coupling interval of the VPB, and RR₁ and RR₂ are the first and second sinus rhythm interval following the compensatory pause of the VPB.

TS expresses the subsequent deceleration of heart rate and is quantified by the steepest regression between the RR interval count (relative to the VPB occurrence) and cycle duration. In precise terms, the following approach for the computation of turbulence slope was proposed: TS is the maximum positive slope of a regression line assessed over any sequence of 5 subsequent sinus rhythm RR intervals within the first 20 sinus rhythm RR intervals after a VPB. The value of TS is expressed in milliseconds per RR interval. It was obtained from the tachogram RR₁, RR₂, RR₁, ..., RR₂₀ for each recording, with RR_i being the average of i-th sinus rhythm RR intervals after the compensatory pause of a single VPB.

The computation of heart rate turbulence clearly depends on the precision with which the individual RR intervals are measured. In the original publication, the patterns of sinus rhythm RR intervals surrounding single VPBs were firstly averaged over 24 hr recordings and only subsequently processed using the above expressions.