Failure
of the Conduction System of the Heart
The sinuatrial node is the spontaneous source of the cardiac
impulse. The atrioventricular node is responsible for picking up the cardiac
impulse from the atria. The atrioventricular bundle is the only route by which
the cardiac impulse can spread from the atria to the ventricles. Failure of the
bundle to conduct the normal impulses results in alteration in the rhythmic contraction
of the ventricles (arrhythmias) or, if complete bundle block occurs, complete dissociation
between the atria and ventricular rates of contraction. The common cause of defective
conduction through the bundle or its branches is atherosclerosis of the
coronary arteries, which results in a diminished blood supply to the conducting
system
Commotio
Cordis
This condition results in ventricular fibrillation and
sudden death and is caused by a blunt nonpenetrating blow to the anterior chest
wall over the heart. It occurs most commonly in the young and adolescents and
is often sports-related. The sudden blow is frequently produced by a baseball,
baseball bat, lacrosse ball, or fist or elbow. The common incidence in the
young is most likely due to the compliant chest wall due to the flexible ribs
and costal cartilages and the thin undeveloped chest muscles. Apparently,
timing of the blow relative to the cardiac cycle is critical; ventricular
fibrillation is most likely to occur if the blow occurs during the upstroke of
the T wave of the electrical activity of the cardiac muscle.
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