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QT & RR variability spots the earliest autonomic deregulation in diabetes

Domenii publicaţii > Ştiinţe medicale + Tipuri publicaţii > Articol în revistã ştiinţificã

Autori: Negoescu R, Istrãtescu O., Dincã-Panaitescu M., Dinca-Panaitescu Ş., Achim A.

Editorial: Transactions Publisher, Integrative Physiological and Behavioral Science, 37, p.151-162, 2002.


27 consecutive insulin-dependent diabetic patients (pts), under 50 years, with blood glu-cose
controlled within normal limits and no significant or multiple cardiovascular/neuro-logical
complications in the lights of clinical tests, went through a protocol as follows: laid-down
at relaxed rest for 10 min, then stood-up quietly for 7 min, and finally experienced a
stress-interview for 10 min while supine. A thoracic ECG lead was digitized at 1 ms
(Codas, Dataq Instr.), RR and QT intervals were software-detected, resampled at 500 ms,
and Fourier-transformed over 3 min epochs to get auto—or cross—spectra. RR-by-QT
mean square coherence detached the RR-independent fraction of QT low fequency (LF)
spectral power, called idioventricular QT-LF. We detected autonomic impairment of three
types (discriminant score = 92.31%), presumably differentiated upon the locus of lesion,
using RR’s basal variance and mean RR shortening when standing as follows: (I) RR
shortening > 200 ms in 10 pts; (II) normal RR shortening but no RR variance in 4 pts; (III)
stiff RR around 600 ms and no RR variance in 2 pts. The above pts have been excluded
from further analysis. The remaining 11 pts with no such impairments (5M and 6F, 36.4 y
± 4.4 SD, history of 6.0 y ± 5.2) have been compared with 11 normal subjects in an age
and gender-paired control group in two steps.
Step 1: Preliminary MANOVA/ANOVA showed significant effects on the ensemble
of spectral variables of every single factor (status: normal or patient group; intervention;
gender) with no significant factor interactions. Significant effects of intervention or status
on main RR spectral variables and on a few QT spectral variables were also documented.
Step 2: Non-parametric tests showed that diabetics had (mildly to moderately) shorter
mean RR, while their RR-LF was always significantly lower than those found in normals—
a difference propagated to QT-LF but not to idioventricular QT-LF. In the intra-group there
were similar responses to interventions except stress with respect to mean RR. Consistent
reduction in RR-LF under moderate or no change in mean RR suggests vagal down-regulation that, judging by idioventricular QT-LF showing, goes perhaps before a similar
process with sympathetic control of ventricles. This phase delay may introduce an early
arrhythmic risk worth dealing with in secondary prevention.