Effect of ischemic stroke on the dynamic beat-to-beat QT-RR relationship

The ECGs of 26 patients following ischemic stroke and 18 control patients with various orthopedic problems, all without primary heart disease, were examined to characterize the dynamic behavior of uncorrected QT interval in relation to changing RR interval during physiotherapy effort. ECG waveforms were analyzed to extract beat-to-bear QT and RR intervals. Based on performing multiple cross-correlations, the relationship between the RR and QT intervals was calculated using the following general formula QT(i) = c RRi-1b. Linear regression was performed on the logarithms of QT and RR measurements to estimate the constant (a = log c) and the slope (b) values, reflecting the dynamic change of QT during physiotherapy effort. Having these two values, the dynamic QT extrapolated to a heart period of 1 second (QTcd) was calculated. It was found that the mean slope (b) of the linear regression line in the ischemic stroke group was significantly lower than in the control group (0.26 +/- 0.08 vs 0.33 +/- 0.08, P < 0.02), and the constant (a) was significantly higher(1.83 <plus/minus> 0.21 for the ischemic stroke vs 1.61 +/- 0.23 for the controls, P < 0.002). No significant difference was found in QTcd values between the two groups (386 <plus/minus> 27 ms for the ischemic stroke vs 392 +/- 25 ms for the controls, P > 0.05). in conclusion, hemispheric brain infarction seems to result in alteration in the autonomic activity during exercise manifesting itself as distorted dynamic behavior of the QT interval.