Assessment of Autonomic Function by Phase Rectification of RRInterval Histogram Analysis in Chagas Disease

Background

In chronic Chagas disease (ChD), impairment of cardiac autonomic function bearsprognostic implications. Phase‑rectification of RR-interval series isolates thesympathetic, acceleration phase (AC) and parasympathetic, deceleration phase (DC)influences on cardiac autonomic modulation.

Objective

This study investigated heart rate variability (HRV) as a function of RR-intervalto assess autonomic function in healthy and ChD subjects.

Methods

Control (n = 20) and ChD (n = 20) groups were studied. All underwent 60-minhead-up tilt table test under ECG recording. Histogram of RR-interval series wascalculated, with 100 ms class, ranging from 600–1100 ms. In each class, meanRR-intervals (MNN) and root-mean-squared difference (RMSNN) of consecutive normalRR-intervals that suited a particular class were calculated. Average of all RMSNNvalues in each class was analyzed as function of MNN, in the whole series(RMSNN_T), and in AC (RMSNN_AC) and DC (RMSNN_DC)phases. Slopes of linear regression lines were compared between groups usingStudent t-test. Correlation coefficients were tested before comparisons. RMSNN waslog-transformed. (α < 0.05).

Results

Correlation coefficient was significant in all regressions (p < 0.05). In thecontrol group, RMSNN_T, RMSNN_AC, and RMSNN_DCsignificantly increased linearly with MNN (p < 0.05). In ChD, onlyRMSNN_AC showed significant increase as a function of MNN, whereasRMSNN_T and RMSNN_DC did not.

Conclusion

HRV increases in proportion with the RR-interval in healthy subjects. Thisbehavior is lost in ChD, particularly in the DC phase, indicating cardiac vagalincompetence.