Key result
Premature atrial excitation in young goats is conducted to the ventricles within ±10 msec of the expiration of the ventricular functional refractory period, without functional lateral bypass tracts.
Why the study?
Are there functional lateral accessory bypass tracts in young goats that explain differences in AV conduction of premature beats compared to adult goats?
Are there functional lateral accessory bypass tracts in young goats that explain differences in AV conduction of premature beats compared to adult goats?
The study demonstrates that young goats lack functional lateral accessory bypass tracts, and their AV node and specialized conduction system are capable of conducting premature atrial excitation very close to the ventricular functional refractory period.
No functional lateral bypass tracts in young goats; leaves open whether AV node properties explain pediatric conduction differences in humans.
Atrioventricular (AV) conduction was studied in anesthetized, open-chest, 1-35-day-old goats. Atrial, bundle of His, and ventricular bipolar electrograms were recorded, and the functional refractory periods of the AV conduction system and the ventricles were determined. Supraventricular premature excitation invaded the ventricles during their vulnerable period. This AV conduction property is different from that of the adult goat heart; thus, the existence of a lateral accessory bypass tract was investigated. Electrocardiographic leads I, aVF, and V10 revealed no delta waves indicative of ventricular preexcitation. Bundle of His electrograms showed that: (1) bundle of His excitation always preceded the onset of ventricular depolarization, (2) no shortening occurred in the bundle of His to ventricular activation time following early atrial premature beats, and (3) the functional refractory period of the AV node was less than that of the ventricle. The ventricular epicardial excitation sequence indicated no involvement of a lateral bypass tract in the AV conduction of basic or premature beats. Interruption of the bundle of His caused complete AV block. Therefore, no functional lateral accessory bypass tracts are present in the young goat heart, and the AV node and the ventricular specialized conduction system of the young goat are capable of conducting premature atrial excitation to the ventricles within plus or minus 10 msec of the expiration of the ventricular functional refractory period.
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Gough et al. (1975) studied Atrioventricular conduction. Premature atrial excitation vs. Basic beats / Adult goat heart was evaluated on Atrioventricular conduction properties and presence of lateral accessory bypass tract. Premature atrial excitation in young goats is conducted to the ventricles within ±10 msec of the expiration of the ventricular functional refractory period, without functional lateral bypass tracts.
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