What criteria should the nurse use to determine normal sinus rhythm for a client on a cardiac monitor? Select all that apply.
A. The RR intervals are relatively consistent.
B. One P wave precedes each QRS complex.
C. Four to eight complexes occur in a 6-second strip.
D. The ST segment is higher than the PR interval.
E. The QRS complex ranges from 0.12 to 0.20 second.
Correct Answers: A, B.
The consistency of the RR interval indicates regular rhythm. A normal P wave before each complex indicates the impulse originated in the SA node. Sinus arrhythmia is most typically present in young, healthy individuals. Studies have attempted to establish an increased prevalence in patients with underlying hypertension, obesity, and diabetes.
Option A: Sinus rhythm (a.k.a. normal sinus rhythm) refers to the normal heart beat originating from the sinoatrial node. This is manifested as an upright P wave in lead II of the ECG. Sinus arrhythmia is a common rhythm variation. It is seen more often in children and young adults. Respirations lead to vagal stimuli resulting in R-R interval variations.
Option B: Sinus arrhythmia is a commonly encountered variation of normal sinus rhythm. Sinus arrhythmia characteristically presents with an irregular rate in which the variation in the R-R interval is greater than 0.12 seconds. Additionally, P waves are typically monoform and in a pattern consistent with atrial activation originating from the sinus node.
Option C: The number of complexes in a 6-second strip is multiplied by 10 to approximate the heart rate; normal sinus rhythm is 60 to 100. On the EKG, sinus rhythm appears as a beat-to-beat variation in the P-P interval. Typically, this variation is greater than 120 msec: the P-P interval increases and decreases with inspiration and exhalation.
Option D: Elevation of the ST segment is a sign of cardiac ischemia and is unrelated to the rhythm. The ST Segment represents the interval between ventricular depolarization and repolarization. The most important cause of ST segment abnormality (elevation or depression) is myocardial ischaemia or infarction.
Option E: The QRS duration should be less than 0.12 second; the PR interval should be 0.12 to 0.20 second. The normal duration (interval) of the QRS complex is between 0.08 and 0.10 seconds — that is, 80 and 100 milliseconds. When the duration is between 0.10 and 0.12 seconds, it is intermediate or slightly prolonged. A QRS duration of greater than 0.12 seconds is considered abnormal.
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