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Normal cardiac
conduction occurs as:
- an impulse is generated
at the SA node and spreads
across both atria, causing them to contract. Note that the atrial
impulse correlates with the P wave in the EKG diagram above.
- The Fibro-fatty atrioventricular
groove insulates the ventricles from the atrial impulse. The AV
node is the only normal gateway of conduction to the ventricles.
- The impulse is delayed at
the AV node, travels down the AV bundle and it's branches and
reaches the Purkinje fibers. The ventricles are stimulated to
contract. Follow the red dots and note correlation with the QRS
wave in the EKG diagram above.
- The T wave correlates
with repolarization of the ventricles.
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Abnormal cardiac
conduction can occur in many ways. For example, in this diagram:
- The red dots follow the
normal conduction pathway.
- The yellow dot
represents conduction
via an abnormal "accessory" pathway back toward the
AV node. Typically, impulses travelling these abnormal pathways restimulate
the atria and/or ventricles and cause arrythmias.
- The abnormal EKG tracing
shown here represents a supraventricular tachycardia.
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