Autonomic and electrocardiographic findings in Parkinson's disease

Parkinson disease (PD) is a progressive neurodegenerative disorder characterized by motor and non-motor symptoms and signs. Many reports suggest that diminished heart rate variability occurs early, even prior to the cardinal signs of PD. In a longitudinal study of PD, we evaluated whether heart rate variability (HRV) obtained using a 10-second ECG tracing, and the electrocardiographic QT-interval would be associated with PD severity and progression. Subjects were derived from a longitudinal study of 1741 individuals with early, stable PD. The severity of PD was measured using the global statistical test (GST). In a subset, the heart rate corrected QT-interval (QTcB) was calculated for each electrocardiogram (ECG). The HRV was measured for each ECG and then transformed to fit a normal distribution. The baseline analysis included 653 subjects, with 256 completing the 5-year follow up study. There was an association (P < 0.05) between QTcB and PD severity in individuals that were taking QT-interval affecting drugs. A longer QT-interval at baseline was associated with more advanced PD at 5 years (P < 0.05), and greater disease progression over 5 years (P < 0.05). There was an association between diminished HRV and an orthostatic decrease in standing blood pressure at baseline in individuals with PD (P < 0.05). HRV was not associated with PD severity or progression. In conclusion, we were able to detect measurable associations between the QTcB interval and PD severity, PD severity 5 years later, and the change in disease over time. However, routine ECG tracings appear inadequate for the evaluation of autonomic function in PD.