Page 375 - Cardiac Nursing

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C HAPTER 1 6 / Arrhythmias and Conduction Disturbances 351
partially refractory and unable to conduct at a normal rate, re- PR interval: May vary depending on proximity of the pacemaker
sulting in a prolonged PR interval. to the AV node
QRS complex: May be normal, aberrant (wide), or absent, de- QRS complex: Usually normal
pending on the prematurity of the beat. If the bundle branches Conduction: Conduction through the atria varies as it is depo-
have repolarized completely, they are able to conduct the early larized from different spots. Conduction through the bundle
impulse normally, resulting in a normal QRS. If the PAC occurs branches and ventricles is usually normal.
during the relative refractory period of the bundle branches or Example: WAP
ventricles, the impulse conducts aberrantly and the QRS is
wide. If the PAC occurs very early during the complete refrac-
tory period of the AV node or both bundle branches, the im- II II I
pulse does not conduct to the ventricles and the QRS is absent.
Conduction: PACs travel through the atria differently from sinus
impulses because they originate from a different spot.
Conduction through the AV node, bundle branches, and ven-
tricles is usually normal unless the PAC is very early (see pre- Treatment of WAP is not usually necessary. If the heart rate is
vious discussion of PR interval and QRS complex). slow enough to be symptomatic, atropine can be given.
Examples: (A) Sinus rhythm with PAC. (B) Sinus rhythm with a
nonconducted PAC.
Multifocal Atrial Tachycardia (MAT)
MAT (also known as chaotic AT) is rapid firing of several ectopic
atrial foci at a rate faster than 100 beats per minute. MAT is most
V 1
commonly seen in elderly patients and is associated with chronic
pulmonary disease but can also occur in the presence of HF, hy-
pokalemia, hypomagnesemia, hypoxia, acute MI, and mitral
stenosis. 5,18,19 MAT is often misdiagnosed as AF because it shares
A
many of the ECG features of AF.
V 1 The ECG characteristics of MAT include the following:
Rate: Usually 100 to 130 beats per minute
Rhythm: Usually irregular
B P waves: Vary in shape because they originate in different spots in
the atria. At least three different P waves are seen. They usually
Treatment of PACs is rarely necessary because they do not precede each QRS complex, but some may be blocked in the
cause hemodynamic compromise. If they result in symptoms such AV node.
as “skipped beats” that are bothersome, the patient should be ad-
vised to avoid precipitating factors such as smoking, alcohol in-
take, and coffee consumption. Frequent PACs may precede more
serious arrhythmias such as AF and can initiate SVT, especially V 1
AV nodal reentry or tachycardias associated with accessory path-
ways. Drugs such as -blockers; or type IA, IB, or III antiar-
rhythmics can be used to suppress atrial activity if necessary.
Wandering Atrial Pacemaker (WAP)
WAP refers to rhythms that exhibit varying P-wave morphology as
the site of impulse formation shifts from the SA node to various
sites in the atria to the AV junction and back. 18 This arrhythmia PR interval: May vary depending on proximity of each ectopic atrial
occurs when two (usually sinus and junctional) or more supraven- focus to the AV node and the prematurity of atrial impulses
tricular pacemakers compete with each other for control of the QRS complex: Usually normal
heart. Because the rates of these competing pacemakers are almost Conduction: Usually normal through the AV node and ventricles.
identical, it is common to have atrial fusion occur as the atria are Aberrant ventricular conduction may occur if an impulse is
activated by more than one wave of depolarization at a time, re- conducted into the ventricles while they are partially refractory.
sulting in varying P-wave morphology. WAP can be due to in- Example: MAT
creased vagal tone that slows the sinus pacemaker or due to en-
Treatment of MAT is directed toward eliminating the causes,
hanced automaticity in atrial or junctional pacemaker cells,
including hypoxia and electrolyte imbalances. Antiarrhythmic
causing them to compete with the SA node for control.
therapy is often ineffective. -Blockers, verapamil, flecainide,
WAP is characterized as follows:
amiodarone, and magnesium have been reported to be successful
Rate: 60 to 100 beats per minute in the treatment of MAT. 5,18,19 -Blockers seem to work best but
Rhythm: May be slightly irregular must be used with caution because pulmonary disease is usually as-
P waves: Exhibit varying shapes (upright, flat, inverted, notched) sociated with MAT. Theophylline may need to be discontinued. If
y
y
as impulses originate in different parts of the atria or junction MAT is chronic and unresponsive to drug therapy, radiofrequency
and as atrial fusion occurs. At least three different P-wave con- ablation of the AV node and insertion of a permanent pacemaker
figurations should be seen. may be necessary to control the ventricular rate. 20