Second Degree Blocks - Mobitz I (Wenckebach)
Second Degree heart
block occurs in cycles caused by
progressive electrical interruptions in the conduction system.
When the electrical impulse leaves the atria, it is interrupted
at the AV junction or node. This interruption becomes
progressively longer with each electrical impulse (the P-R
interval lengthens with every beat) until a non-conductive event
occurs (i.e. the depolarization stops at the AV node) causing the
QRS complex to be dropped completely from the rhythm strip. This
is not a life threatening dysrythymia unless the patient is
medically unstable. Causes for 
Mobitz I include toxicity to
certain drugs, MI and infection.
Second Degree heart
block occurs in cycles caused by
progressive electrical interruptions in the conduction system.
When the electrical impulse leaves the atria, it is interrupted
at the AV junction or node. This interruption becomes
progressively longer with each electrical impulse (the P-R
interval lengthens with every beat) until a non-conductive event
occurs (i.e. the depolarization stops at the AV node) causing the
QRS complex to be dropped completely from the rhythm strip. This
is not a life threatening dysrythymia unless the patient is
medically unstable. Causes for 
Mobitz I include toxicity to
certain drugs, MI and infection.