Page 202 - Critical Care Nursing Demystified

Chapter 4 CARE OF THE PATIENT WITH CRITICAL CARDIAC RHY THM DISTURBANCE NEEDS 187

doing reps. As the time gets longer and the muscle gets more and more fatigued,
the time to complete the rep gets longer until the will is there but the weight
cannot be moved. In Wenckebach, the PRI gets longer and longer with each
heartbeat until you get a P wave that does not conduct to the ventricles. We
often call this a nonconducted P wave.
• RATE: Depends on the underlying rhythm. There are missing P waves so
the ventricular rate is slower than the atrial due to blocked P waves.
• RHYTHM: Atrial is irregular; ventricular is irregular.
• CONDUCTION: PRI gets longer and longer until a P wave occurs but no
QRS or a nonconducted P wave (blocked P wave). The QRS and QTI
are normal.

Second-Degree AV Block—Type II (Mobitz II)
A second-degree heart block or Mobitz II involves some P waves that are con-
ducted and some that are not. These are usually in a 2:1, 3:1, or 4:1 conduction
where there are more Ps than Qs. So you need to mind your Ps and Qs here!
• RATE: Atrial rate is usually 60 to 100; ventricular rate is slow as not every
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• RHYTHM: Atrial is regular; ventricular is irregular.

• CONDUCTION: PRI is normal or prolonged but the P-to-P interval is
constant. In other words, you can march out the P waves as they fall on
time. The QRS is normal and the QT might be prolonged due to the
slow rate.

NURSING ALERT

Watch the ventricular response on this rhythm as a slow heart rate can cause a
dramatic drop in BP, causing decreased cardiac output. This can occur with ischemia
or MI. You might need to prepare for temporary or permanent cardiac pacing with a
sustained Mobitz II.

Third-Degree AV Block (Complete Heart Block)
This is the most severe of the four heart blocks, and it is now time to consider
a pacemaker as cardiac output falls with this one quickly. In this rhythm the SA
node pacemaker fires at its native rate and the ventricular pacer fires at its rate
as well, but there is no communication between the two.