Reliability of the measurement of RT variability

The variability of the interval between the R peak and the apex of T wave has a power 2-3 orders of magnitude smaller than that of RR interval variability therefore, adequate recording, pre-processing and detection procedures are required to avoid artefacts. Emphasis is posed on the dramatic differences occurring between different leads, which are explained as artefacts induced by changes in the cardiac electrical axis. A satisfactory compensation appears to be provided by the modulus signal from three orthogonal leads. So, the low frequency (LF) and high frequency (HF) components were clearly recognised in 14 normal (N) subjects and in 12 patients 2 weeks after myocardial infarction (MI). This was confirmed by the cross-spectrum between the RT and the RR series. In N, HF (36.7/spl plusmn/23.1 nu.) was predominant over LF (25.4/spl plusmn/14.5), while in MI the ratio was inverted (LF=37.0/spl plusmn/23.3, HF=25.6/spl plusmn/13.9).<>