Effect of atropine on the QT interval and T-wave amplitude in healthy volunteers.

Prolongation of the QT interval of the ECG represents an imbalance in cardiac autonomic function and may predict cardiac arrhythmia. Vagal activity protects against prolongation of the QT interval which may be associated with flattening of the T-wave of the ECG. The changes in QT interval, T-wave amplitude and respiratory sinus arrhythmia (RSA) were studied after i.v. administration of atropine 20 micrograms kg-1 or placebo to 10 healthy volunteers in a cross-over study. After atropine, a decrease in RSA occurred in all volunteers, but remained at baseline values after placebo. Corrected QT interval (QTc) increased from 410 (20) ms to 454 (11) ms (P < 0.001) 5 min after atropine and remained prolonged for the entire study period (60 min). The T-wave flattened significantly (measured as R:T ratio) up to 30 min, without any changes in the R-wave. No changes in the ECG occurred with placebo.