[Effects of vagal tone on Kent bundle conduction in patients with Wolff-Parkinson-White syndrome].
BACKGROUND
The influences of the sympathetic tone on the conduction in the Kent bundle have been widely investigated; on the contrary, very little is known about the effects of the vagal tone on such a bypass. Vagal influences on Kent bundle can be adequately investigated only after sympathetic blockade.


METHODS
An electrophysiological study was performed in 12 subjects with Wolff-Parkinson-White syndrome (7 F and 5 M, age: 30 +/- 17 years) during basal state, after beta-blockade (propranolol 0.2 mg/Kg iv) and after atropine (0.04 mg/Kg iv).


RESULTS
In no subject were signs of organic heart disease present. The anterograde effective refractory period of the bypass significantly lengthened after propranolol (291 +/- 65 ms vs 313 +/- 52 ms, p < .01), and shortened after atropine (313 +/- 52 ms vs 290 +/- 46 ms, p < .01). This parameter showed no significant differences in the basal state nor after complete autonomic blockade. The longest pacing atrial cycle length for a second degree atrio-ventricular block in the bypass significantly lengthened after propranolol (322 +/- 55 ms vs 383 +/- 44 ms, p < .01) and shortened after atropine, even if the variation was not statistically significant (383 +/- 44 ms vs 368 +/- 39 ms, p: NS); such a parameter was significantly more prolonged after complete autonomic blockade than in the basal state (p < .05). The retrograde conduction in the bypass showed a similar behaviour: the retrograde effective refractory period and the longest ventricular pacing cycle length for a second degree ventriculo-atrial block significantly lengthened after propranolol (434 +/- 133 ms vs 532 +/- 188 ms, p < .01 and 398 +/- 150 ms vs 492 +/- 179 ms, p < .01, respectively) and shortened after atropine (532 +/- 188 ms vs 464 +/- 157 ms, p < .01, and 492 +/- 179 ms vs 431 +/- 158 ms, p < .05, respectively). These parameters were more prolonged after complete autonomic blockade than in the basal state (p < .05).


CONCLUSIONS
These data evidence a vagal influence on the conduction in the resting Kent bundle; the vagal effect appears, however, less marked than the sympathetic one.
Divisione di Cardiologia, Ospedale Civile-Cento.
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N
Paparella
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R
Cappato
P
P
Alboni
D000293:Adolescent; D000328:Adult; D001285:Atropine / Q000494:pharmacology; D004594:Electrophysiology; D005260:Female; D006329:Heart Conduction System / Q000187:drug effects / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011433:Propranolol / Q000494:pharmacology; D014630:Vagus Nerve / Q000187:drug effects / Q000503:physiopathology*; D014927:Wolff-Parkinson-White Syndrome / Q000503:physiopathology*
D001285:Atropine; D011433:Propranolol
Effetti del tono vagale sulla conduzione nel fascio di Kent in soggetti con sindrome di Wolff-Parkinson-White.