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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: Basic rhythm regular; irregular with nonconducted PAC


Rate: Basic rhythm rate 60 beats/minute; rate slows following nonconducted PAC; rate suppression can occur following a pause in the basic rhythm. After several cycles, the rate will return to the basic rhythm rate.


P waves: Sinus P waves with basic rhythm; premature, abnormal P wave with nonconducted PAC


PR interval: 0.20 second with basic rhythm


QRS complex: 0.06 to 0.08 second with basic rhythm


Comment: U wave is present


Interpretation: Normal sinus rhythm with nonconducted premature atrial contraction (PAC)


A nonconducted PAC results when an ectopic atrial focus occurs so early that it finds the AV node refractory and the impulse is not conducted to the ventricles. This results in a premature, abnormal P wave not accompanied by a QRS complex, but followed by a pause. Like the conducted PAC, the P wave associated with the nonconducted PAC will be premature and abnormal in size, shape, or direction. The P wave is commonly found hidden in the preceding T wave, distorting the T-wave contour, and the pause that follows is usually noncompensatory. The nonconducted PAC is the most common cause of unexpected pauses in a regular sinus rhythm.


The nonconducted PAC can be confused with sinus arrest or block (especially if the P wave of the PAC occurs early enough to be hidden in the preceding T wave). All three rhythms produce a sudden pause in the rhythm without QRS complexes. To differentiate between these rhythms, examine and compare the T-wave contours. The early, abnormal P wave of the nonconducted PAC will distort the preceding T wave. In sinus arrest or sinus block, no P wave is produced and the T-wave contour remains unchanged.


Nonconducted PACs: Identifying ECG features

Rhythm: Underlying rhythm usually regular; irregular with nonconducted PACs


Rate: That of underlying rhythm


P waves: P wave associated with the nonconducted PAC is premature, and abnormal in size, shape, or direction; often found hidden in preceding T wave, distorting the T-wave contour


PR interval: Absent with nonconducted PAC


QRS complex: Absent with nonconducted PAC