Time and frequency analysis of beat-to-beat R-T interval variability in XXXX with ischaemic left ventricular dysfunction providing evidence for non-neural control of ventricular repolarisation.

@entity1 @entity308 @entity301 @entity138 @entity10579 @entity583
BACKGROUND: Determinants of temporal lability in ventricular repolarisation are not fully recognised. We aimed to analyse the sources of @entity138 variability by comparing normal subjects and @entity1 after @entity583 ( @entity583 ) with either @entity308 or preserved left ventricular (LV) function. METHODS: One hundred and nine @entity1 (27 @entity1 , 82 @entity1 , aged 51 +/- 9 years) were divided into three groups: 24 @entity1 (pts) with an uncomplicated angiographically proven @entity301 (CHD-group), 59 post- @entity583 pts with preserved LV function (LVEF > 40%, PMI-N-group) and 26 post- @entity583 pts with @entity308 LV function (LVEF < 40%, PMI-L-group). An ECG signal of low-noise 512 heartbeats was recorded using a computer-assisted amplifier (16 bit, 2 kHz). The onset and offset of the R-wave and T-wave were determined automatically. The magnitude of R-R and R-T variability was measured as the standard deviation of all intervals (SD-RR and SD- @entity138 , ms, respectively). Their relationship was quantified by the correlation coefficient r( @entity138 /RR). Power spectral density of RR or @entity138 variability was estimated with the FFT (Welch's averaged periodogram, Hanning window) and frequency relation was quantified using a @entity10579 ( @entity10579 ). For all spectral and cross-spectral measurements two frequency ranges were considered: high (0.15-0.50 Hz, HF) and low (0.04-0.15 Hz, LF). Spectral power and @entity10579 of RR and @entity138 variability for both ranges (HF(RR), LF(RR), HF( @entity138 ), LF( @entity138 ), @entity10579 (HF), @entity10579 (LF)), and the ratios LF/HF(RR) and LF/HF( @entity138 ) were drawn for comparisons. The central frequency of HF(RR) was considered as the frequency of respiration (f(resp), Hz). RESULTS: In the PMI-L group the SD- @entity138 was significantly greater compared to the remaining groups and accounted for almost 10% of the SDRR. Also, the coefficient r( @entity138 /RR) was weakest in this group. The spectral indices of RR variability were similar in all groups, while the greatest value of the HFRT was observed in the PMI-L group. The @entity10579 (LF) was insignificant in this group, contrary to the CHD and PMI-N groups. Additionally, there were significant negative relationships between f(resp) and spectral indices of @entity138 variability in PMI- @entity1 with @entity308 LV function. CONCLUSION: A greater beat-to-beat variation in @entity138 interval duration along with increased power of its HF component indicates an important role of respiration in ventricular repolarisation control, while reduced time- and frequency @entity138 -RR relationships seem to relate to an impaired process of ventricular duration adaptation.
