What kind of disturbance causes the heart blocks?
conduction disturbances in the AV node
Which heart block is not a true block?
First-Degree Heart Block is not a true block; it is a delay in conduction
Which of the wave patterns on the EKG will yield information about the AV node?
the PR interval (specifically, the PR segment), since it will tell you the relationship between the atria and the ventricles
What will the PRI be like in a First-Degree Heart Block?
It will be longer than normal, greater than 0.20 second
What is the rate of a First-Degree Heart Block?
First-Degree Heart Block is not a rhythm in itself; thus, it cannot have a rate. The rate of the rhythm will depend on the underlying rhythm
Is a First-Degree Heart Block regular or irregular?
depends on the regularity of the underlying rhythm
In addition to identifying a First-Degree Heart Block, what other information must you provide in order for you interpretation to be complete?
the identity of the underlying rhythm
Does the PRI in First-Degree Heart Block vary from one beat to the next?
No, it remains constant across the strip
In First-Degree Heart Block, how many P waves will you see for every complex?
One; all beats are eventually conducted QRS through to the ventricles, even though each one encounters a delay at the AV node
Is the QRS measurement also prolonged in First-Degree Heart Block?
No; once the impulse passes through the AV node, conduction through the ventricles in normal
In Wenckebach, do any of the sinus impulses get through the AV node to depolarize the ventricles?
Yes, most of them do; but the AV node holds each one a little longer than the preceding one, until one is blocked completely. Then the cycle starts over again
What is the ventricular rate of a Wenckebach?
It's usually just a little bit slower than normal, since most of the impulses are conducted
Is the R-R interval regular in a Wenkebach?
No; it is irregular in a pattern of grouped beating
Does a Wenckebach have a regular P-P interval?
Yes; even though the PRIs and the R-Rs change, the P-P remains regular
Is the R-R interval grossly irregular in a Wenckebach?
No; it has a distinctive cyclic pattern of grouped beating
Does a Wenckebach produce one P wave for every QRS complex?
No; most P waves are followed by QRS complexes, but some P waves are not conducted through to the ventricles
What is the key feature of a Wenckebach?
progressively lengthening PRIs with eventual blocked impulses
Does Type II Second-Degree Heart Block have an equal number of P waves and QRS complexes?
No; a Type II Second-Degree Heart Block will always have more P waves than QRS complexes
Is the PRI of a Type II Second-Degree Heart Block constant, or does it vary between beats?
It's constant. This is a key diagnostic feature that helps distinguish it from Wenckebach and CHB
Is the PRI measurement normal in Type II Second-Degree Heart Block?
It can be normal or it can be prolonged. Whatever that measurement, however, it will always be constant
What is the usual rate for a Type II Second-Degree Heart Block?
Because most of the P waves are being blocked, it will be in the bradycardia range; usually one-half to one-third the normal rate
What is meant by a variable conduction ratio?
It means that the AV node is varying the pattern in which sinus impulses are being conducted to the ventricles. It changes from one beat to the next (e.g., 4:3, 5:4, 4:3, 5:4, etc.)
Is the R-R interval regular or irregular in a Type II Second-Degree Heart Block?
It will be regular unless the conduction ratio is variable, in which case the rhythm will be irregular
Is the QRS measurement normal or abnormal in a Type II Second-Degree Heart Block?
It should be normal because those impulses that are allowed to pass through the AV node are expected to continue on through the ventricles in a normal way
In Third-Degree Heart Block (CHB), do any of the impulses from the SA node penetrate the AV node to depolarize the ventricles?
No. In CHB, the block at the AV node is complete. None of the sinus impulses passes through to the ventricles
In CHB, will there be more P waves or more QRS complexes on the EKG?
There will be more P waves
If none of the sinus impulses are able to depolarize the ventricles, what focus is producing the QRS complexes?
A lower site will take over at an escape rate. This rhythm can be either junctional or ventricular in origin
How would you differentiate between a junctional focus and a ventricular focus in a CHB?
Junctional focus - QRS complex is less than 0.12 second; rate 40-60 bpm.
Ventricular focus - QRS is 0.12 second or more; rate 20-40 bpm
Is CHB regular or irregular?
Regular; this will help you distinguish it from Wenckebach
What will the PRI be in CHB?
There is no PRI, as atria and ventricles are dissociated. The P waves have no relationship to the QRS complexes