Beat-to-beat QT interval variability is primarily affected by the autonomic nervous system.
BACKGROUND
Beat-to-beat QT interval variability is associated with life-threatening arrhythmias and sudden death, however, its precious mechanism and the autonomic modulation on it remains unclear. The purpose of this study was to determine the effect of drugs that modulate the autonomic nervous system on beat-to-beat QT interval.


METHODS
RR and QT intervals were determined for 512 consecutive beats during fixed atrial pacing with and without propranolol and automatic blockade (propranolol plus atropine) in 11 patients without structural heart disease. Studied parameters included: RR, QTpeak (QRS onset to the peak of T wave), QTend (QRS onset to the end of T wave) interval, standard deviation (SD) of the RR, QTpeak, and QTend (RR-SD, QTpeak-SD, and QTend-SD), coefficients of variation (RR- CV, QTpeak-CV, and QTend-CV) from time domain analysis, total power (TP; RR-TP, QTpeak-TP, and QTend-TP), and power spectral density of the low-frequency band (LF; RR-LF, QTpeak-LF, and QTend-LF) and the high-frequency band (HF; RR-HF, QTpeak-HF and QTend-HF).


RESULTS
Administration of propranolol and infusion of atropine resulted in the reduction of SD, CV, TP, and HF of the QTend interval when compared to controlled atrial pacing (3.7 +/- 0.6 and 3.5 +/- 0.5 vs 4.8 +/- 1.4 ms, 0.9 +/- 0.1 and 0.9 +/- 0.1 vs 1.2 +/- 0.3%, 7.0 +/- 2.2 and 7.0 +/- 2.2 vs 13.4 +/- 8.1 ms(2), 4.2 +/- 1.4 and 4.2 +/- 1.2 vs 8.4 +/- 4.9 ms(2), respectively). Administration of propranolol and atropine did not affect RR interval or QTpeak interval indices during controlled atrial pacing.


CONCLUSIONS
Beat-to-beat QT interval variability is affected by drugs that modulate the autonomic nervous system.
Mine
Takanao
T
Department of Internal Medicine, Cardiovascular Division, Hyogo College of Medicine, Nishinomiya, Japan. mine@hyo-med.ac.jp
Shimizu
Hiroki
H
Hiromoto
Kenji
K
Furukawa
Yoshio
Y
Kanemori
Tetsuzou
T
Nakamura
Hiroaki
H
Masuyama
Tohru
T
Ohyanagi
Mitsumasa
M
D000368:Aged; D000889:Anti-Arrhythmia Agents / Q000008:administration & dosage*; D001145:Arrhythmias, Cardiac / Q000175:diagnosis / Q000188:drug therapy / Q000401:mortality; D001282:Atrial Flutter / Q000175:diagnosis / Q000188:drug therapy / Q000401:mortality; D001285:Atropine / Q000008:administration & dosage; D001341:Autonomic Nervous System / Q000187:drug effects* / Q000503:physiopathology; D015331:Cohort Studies; D004562:Electrocardiography / Q000379:methods; D005260:Female; D006801:Humans; D008133:Long QT Syndrome / Q000175:diagnosis* / Q000188:drug therapy*; D008297:Male; D008875:Middle Aged; D011433:Propranolol / Q000008:administration & dosage; D015203:Reproducibility of Results; D018570:Risk Assessment; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D012804:Sick Sinus Syndrome / Q000175:diagnosis / Q000188:drug therapy / Q000401:mortality; D015996:Survival Rate; D013617:Tachycardia, Supraventricular / Q000175:diagnosis / Q000188:drug therapy / Q000401:mortality
D000889:Anti-Arrhythmia Agents; D001285:Atropine; D011433:Propranolol