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Determine the following:

Figure. No caption a... - Click to enlarge in new windowFigure. No caption available.

Rhythm: _______________________________________


Rate: ___________________________________________


P waves: _______________________________________


PR interval: ____________________________________


QRS complex: __________________________________


What's your interpretation?


(Answers on next page)


Name that strip: Answers

Rhythm: Irregular


Rate: 60 beats/minute


P waves: Vary in size and shape


PR interval: 0.08 to 0.12 second


QRS complex: 0.04 to 0.08 second


Interpretation: Wandering atrial pacemaker


Wandering atrial pacemaker (WAP) occurs when the pacemaker site shifts back and forth between the sinus node and ectopic atrial sites. The P-wave morphology will vary as the pacemaker "wanders" between the multiple sites. Generally, at least three different P-wave morphologies should be identified before making the diagnosis of WAP.


The heart rate is usually normal, but may be slow. The rhythm may be regular or irregular, as each impulse travels through the atria via a slightly different route. The PR interval is usually normal, but may be abnormal because of the different sites of impulse formation. The QRS complex is usually normal in duration. The distinguishing feature of this rhythm is the changing P-wave morphology. WAP is usually a result of increased vagal effect on the SA node, slowing the sinus rate and allowing other pacemaker sites an opportunity to compete for control of the heart rate.


WAP is seen in the very young, in the very old, and in athletes, and can manifest itself during a person's normal sleep cycle. It may also be caused by the administration of digitalis. WAP isn't clinically significant, and treatment is not indicated. If the heart rate is slow, medications should be reviewed and those affecting heart rate discontinued, if possible. If the heart rate is slow and the patient is symptomatic, treatment of the rhythm is the same as for symptomatic sinus bradycardia with a pulse. When WAP is associated with a heart rate greater than 100 beats/minute, the rhythm is called multifocal atrial tachycardia (MAT). MAT is a relatively infrequent dysrhythmia and is most commonly observed in patients with lung disorders such as chronic obstructive pulmonary disease.


WAP: Identifying ECG features

Rhythm: Regular or irregular


Rate: Usually normal (60 to 100 beats/minute) but may be slow (less than 60 beats/minute)


P waves: Vary in size, shape, and direction; one P wave precedes each QRS complex


PR interval: Usually normal duration, but may be abnormal depending on changing pacemaker location


QRS complex: Usually normal (less than 0.12 second)