Electrocardiographic criteria for vagotonia-validation with pharmacological parasympathetic blockade in healthy subjects.
BACKGROUND
The importance of vagal tone on cardiac function and cardiovascular mortality is well established. Although the presence of an enhanced cardiac vagal tone (CVT) is frequently diagnosed using the 12-lead resting electrocardiogram (ECG) in daily practice, most of the proposed criteria have been determined on an empirical basis. Our objective was to evaluate the effects of pharmacological blockade of the parasympathetic component of the autonomic nervous system on resting ECG tracings.


METHODS
Nine healthy young adults (24+/-5 year-old) underwent parasympathetic blockade with atropine sulfate i.v. (0.04 mg kg(-1)) and resting ECGs were obtained before and 15 min thereafter. CVT was assessed by a dimensionless index, which measures the RR interval reduction caused by the vagal withdrawal induced by a 4-s exercise test performed on a cycle ergometer where the subjects pedal as fast as possible with no added resistance.


RESULTS
This index was 1.63+/-0.24 and 1.03+/-0.03, before and after atropine, respectively (P<0.0001). Atropine reduced the R-R intervals (P<0.0001), and the amplitude of T-waves in several leads (DII: P=0.03; V4: P=0.04; V5: P=0.03; V6: P=0.01), and abolished the appiculation of T-waves, J-point and ST-segment elevations (P<0.05), and U-waves (P<0.05), which were present in baseline ECG in all subjects in at least two leads. The R-wave amplitude in leads V4, V5, and V6 (all P>/=0.10) was not modified by atropine infusion.


CONCLUSIONS
The duration of the R-R intervals and the amplitude of T-waves in leads DII, V4, V5, and V6, and the presence of T-wave appiculation, U-waves, and elevation of J-point and ST-segment should be used to detect enhanced cardiac vagal tone in healthy subjects.
Lazzoli
José Kawazoe
JK
Department of Morphology, Universidade Federal Fluminense, Niterói, Brazil.
Soares
Pedro Paulo da Silva
PP
da Nóbrega
Antonio Claudio Lucas
AC
de Araújo
Claudio Gil Soares
CG
D000328:Adult; D001285:Atropine / Q000494:pharmacology*; D004562:Electrocardiography; D005260:Female; D006801:Humans; D008297:Male; D017764:Parasympathectomy / Q000379:methods*; D010275:Parasympathetic Nervous System / Q000187:drug effects* / Q000502:physiology; D011336:Probability; D011446:Prospective Studies; D012016:Reference Values; D012680:Sensitivity and Specificity; D014630:Vagus Nerve / Q000187:drug effects* / Q000502:physiology
D001285:Atropine