Abnormalities of the QT interval in primary disorders of autonomic failure

Experimental evidence shows that activation of the autonomic nervous system influences ventricular repolarization and, therefore, the QT interval on the ECG. To test the hypothesis that the QT interval is abnormal in autonomic dysfunction, we examined ECGs in patients with severe primary autonomic failure and in patients with congenital dopamine ß-hydroxylase (DßH) deficiency who are unable to synthesize norepinephrine and epinephrine. Subjects and Methods Maximal QT and rate-corrected QT (QTc) intervals and adjusted QTc dispersion [(maximal QTc – minimum QTc on 12 lead ECG)/vnumber of leads measured] were determined in blinded fashion from ECGs of 67 patients with primary autonomic failure (36 patients with multiple system atrophy [MSA], and 31 patients with pure autonomic failure [PAF]) and 17 age- and sex-matched healthy controls. ECGs of 5 patients with congenital DßH deficiency and 6 age- and sex-matched controls were also analyzed. Results Patients with MSA and PAF had significantly prolonged maximum QTc intervals (492 ± 58 ms1½ and 502 ± 61 ms1½ [mean ± SD]), respectively, compared with controls (450 ± 18 ms1½, P < .05 and P < .01, respectively). A similar but not significant trend was observed for QT. QTc dispersion was also increased in MSA (40 ± 20 ms1½, P < .05 vs controls) and PAF patients (32 ± 19 ms1½, NS) compared with controls (21 ± 5 ms1½). In contrast, patients with congenital DßH deficiency did not have significantly different RR, QT, QTc intervals, or QTc dispersion when compared with controls. Conclusions Patients with primary autonomic failure who have combined parasympathetic and sympathetic failure have abnormally prolonged QT interval and increased QT dispersion. However, QT interval in patients with congenital DßH deficiency was not significantly different from controls. It is possible, therefore, that QT abnormalities in patients with primary autonomic failure are not solely caused by lesions of the sympathetic nervous system, and that the parasympathetic nervous system is likely to have a modulatory role in ventricular repolarization. (Am Heart J 1998;136:664-71.)