Name That Strip

Source: Huff J. ECG Workout: Exercises in Arrhythmia Interpretation. 7th ed. Philadelphia, PA: Wolters Kluwer; 2016.

Determine the following: Rhythm: ______Rate: ______P waves: ______PR interval: ______What’s your interpretation? QRS complex: ______(Answers on next page)

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Name that strip: Answers

Rhythm: Basic rhythm regular; irregular with premature Premature junctional contraction: Identifying junctional contraction (PJC) ECG features Rate: 75 beats/minute Rhythm: Underlying rhythm usually regular; irregular with PJC P waves: Sinus P waves with Rate: That of the underlying rhythm basic rhythm; inverted P wave P waves: P waves associated with the PJC will be premature, will be before PJC inverted in lead II, will occur immediately before or after the QRS complex, PR interval: 0.16 second or are hidden within the QRS complex (basic rhythm); 0.08 to 0.10 PR interval: Short (0.10 second or less) second (PJC) QRS complex: Premature; normal duration (0.10 second or less) QRS complex: 0.06 to 0.08 second (basic rhythm and PJC) tive lead). The inverted P waves or tobacco; electrolyte imbal- Comment: ST segment will occur immediately before or ances; hypoxemia; heart failure; depression is present after the QRS complex or will be coronary artery disease; and Interpretation: Normal sinus hidden within the QRS complex. enhanced automaticity of the AV rhythm with one PJC. The PR interval will be short junction caused by digitalis toxic- (0.10 second or less). ity (the most common cause). A PJC is an early beat that origi- PACs are much more common PJCs may also occur without nates in an ectopic pacemaker than PJCs. As a result, narrow apparent cause. Frequent PJCs site in the atrioventricular (AV) complex premature beats are (more than 6 per minute) are junction, interrupting the regu- more likely to be PACs. PJCs best treated by correcting the larity of the basic rhythm, which occur in the same pattern as underlying etiology. is usually a sinus rhythm. Like PACs: as a single beat; in bigemi- Frequent PJCs may precede the premature atrial contrac- nal, trigeminal, or quadrigeminal the development of a more seri- tion (PAC), the PJC is character- patterns; or in pairs. A series ous junctional dysrhythmia, ized by a premature, abnormal of three or more consecutive such as junctional tachycardia. P wave followed by a normal junctional beats is considered Occasionally, an ectopic beat duration QRS complex and a a rhythm (junctional rhythm, will occur late instead of early. pause that is usually noncom- accelerated junctional rhythm, or These junctional escape beats pensatory. The premature beat junctional tachycardia). Differen- usually occur during a pause in occurs in addition to an under- tiation of the rhythm depends on the underlying rhythm (follow- lying rhythm. Therefore, both the heart rate. Like PACs, the pre- ing sinus arrest or block, after the underlying rhythm and the mature junctional impulse may premature beats or nonconduct- premature beat must be identi- be conducted to the ventricles ed PACs, or during the pause fied (for example, normal sinus abnormally (aberrantly). This associated with second-degree rhythm with a PJC). Some differ- results in a wide QRS complex. AV block Type I ). The pause in ences exist, however, between Because of the wide QRS com- the rhythm allows a focus in the two premature beats. plex, PJCs with aberrancy must the AV junction to “escape” and Because atrial depolarization be differentiated from premature pace the heart. Escape beats act occurs in a retrograde fashion ventricular contractions (PVCs). as an electrical backup to main- with the PJC, the P wave associ- Conditions associated with tain the heart rate and require ated with the premature beat PJCs include ingestion of sub- no treatment. ■ will be negative in lead II (a posi- stances such as caffeine, alcohol, DOI-10.1097/01.CCN.0000554835.64412.05

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