Long and short term QT-RR interval co-variability in type 2 diabetes.

This paper examines the long and short term co-variability of QT and RR intervals for diabetic patients to explore if the QT-RR co-variability could yield a noble index for the stratification of clinical severity of the disease. Twenty four hour Holter ECG recordings are made for 19 type 2 diabetic (T2DM) patients and 25 normal subjects. RR and QT intervals are extracted from ECG signals sampled at 200 Hz and their co-variability has been examined. To see the long term QT-RR co-variability, correlation coefficients and mutual entropies between QT and RR intervals have been estimated for original beat to beat intervals and smoothed median interval series of successive one hundred beats. Mutual entropy for both beat-to-beat and smoothed median QT and RR interval series showed statistically significant differences between T2DM and control subjects whereas differences in correlation coefficients showed significant difference only for beat-to-beat intervals. Mutual entropy between both beat-to-beat and smoothed median QT-RR interval sequences showed the equally well separation between T2DM patients and control subjects: Mutual entropy and serial correlation coefficients for beat to beat intervals are respectively 1.42 ± 0.33 (bits), 0.856 ± 0.055 for control and 0.752 ± 0.23 (bits), 0.756 ± 0.10 for T2DM patients. Scatter diagram between RR and QT intervals show apparent nonlinearity which validate this result. Short term QT-RR co-variability has been examined by spline smoothed QTc series and sporadic changes have been observed for the control subjects whereas no such changes are found in diabetic patients. This new phenomenon could be a mean for the clinical characterization of diabetes.

T-wave alternans search over 24 hour holter ECG recordings based on singular value decomposition.

This paper proposes an efficient method to search for T-wave alternans (TWA) over 24 hour Holter ECG recordings. After appropriate pre-processing to remove baseline drift and artifact, data are segmented to 2 minute successive time intervals. For each beat in the segment, singular value decomposition is applied to derive orthogonal characteristic signals. Then two prominent orthogonal signals are used for the TWA search. A pair of alternans indices is defined for each beat as the orthogonal waveform distance between the target beat and the adjacent two beats. When alternans presents, the first index will be larger than the second index. The periodogram of the sequence of alternans indices in each segment yields a useful alternans measure named Alternans Ratio (AR). To show the effectiveness of the measure, the method is applied to 25 control and 24 data from patients with various cardio vascular disorders. AR distribution showed prominent differences among subject groups. It has been demonstrated that the measure AR is not only useful to detect the presence of TWA but the AR distribution can be used for the stratification of the TWA risk.

RR-QT interval trend covariability for sudden cardiac death risk stratification.

This paper examines the feasibility of the trend covariability between QT and RR Intervals (QTIs and RRIs) be a novel mean of the sudden cardiac death (SCD) risk stratification. Twenty four hour beat to beat QTIs and RRIs are measured from Holter ECG recordings of 25 normal control subjects (SCD-C), 14 low SCD risk patients (SCD-L) with high blood pressure or light cardiac arrhythmia and 11 SCD high risk patients (SCD-H) with heart attack history. The Kalman filtering technique has been applied to decompose 24 hour short term mean QTIs and RRIs sequences into trend components and additive random variations. The correlation coefficients (TC-QT/RR) and cross entropies (TE-QT/RR) between the QT and RR trend signals are estimated. Cross entropy TE-QT/RR achieved the best stratification of subject groups. TE-QT/RR distribution for SCD-C, -L -H subject groups were 1.697 ± 0.058, 1.160 ± 0.099, 0.920 ± 0.067. The differences in entropy values are statistically significant for all classes pairs (SCD-H and -C (p<0.00001); -L and -C (p<0.001); -H and -L (p<0.05) The result indicates that the TE-QT/RR could be a novel index for the SCD risk stratification.