Modulation of QT interval during autonomic nervous system blockade in humans

Area of Science:

• Cardiology
• Autonomic Nervous System Research
• Clinical Electrophysiology

Background:

• The autonomic nervous system's role in modulating the QT interval is debated.
• Previous studies using combined propranolol and atropine yielded conflicting results.
• Ganglionic blockade offers an alternative method to assess autonomic influence on the QT interval.

Purpose of the Study:

• To investigate the effect of ganglionic blockade on the QT interval.
• To compare autonomic function and QT interval prolongation in normal subjects, multiple system atrophy (MSA) patients, and pure autonomic failure (PAF) patients.

Main Methods:

• Infusion of trimethaphan at increasing doses (0.5-10 mg/min IV) in 10 normal volunteers, 9 MSA patients, and 8 PAF patients.
• Monitoring of heart rate, heart rate variability (HRV) spectra, QT interval, and blood pressure.
• QT interval corrected for heart rate using Bazett's formula (QTc).

Main Results:

• PAF patients exhibited prolonged baseline QTc (465±8 ms) and very low HRV.
• Trimethaphan dose-dependently prolonged QTc in normal subjects (to 469±7 ms) and abolished HRV.
• MSA patients showed QTc prolongation (to 463±7 ms) and reduced HRV, with no significant change in RR interval.

Conclusions:

• Ganglionic blockade prolongs the QT interval in normal subjects to durations similar to those in PAF patients.
• Blocking residual autonomic tone in PAF patients further increases QT interval length.
• MSA patients demonstrate greater residual sympathetic tone and more significant QT interval prolongation during ganglionic blockade compared to PAF patients.