Myocardial Infarction & Peripheral Vascular Diseases Q 46

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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 0.2 seconds.

    

Correct Answers: A & B

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(1) The consistency of the RR interval indicates a regular rhythm. (2) A normal P wave before each complex indicates the impulse originated in the SA node.

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Option A: Normal ECG values for waves and intervals include RR interval of 0.6-1.2 seconds. A well-planned approach to 12-lead ECG interpretation will prevent the interpreter from missing crucial information. Key aspects in the interpretation of the 12-lead ECG include the heart rate, the heart rhythm (both atrial and ventricular), the electrical axis (both the P-wave axis and the QRS axis), and knowledge of the normal intervals.

Option B: The P waves in leads I and II must be upright (positive) if the rhythm is coming from the sinus node. It is important to remember that the P wave represents the sequential activation of the right and left atria, and it is common to see notched or biphasic P waves of right and left atrial activation.

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. Next, determine the relationship of P waves to QRS complexes. Finally, analyze the QRS morphology and ST and T-wave segments.

Option D: Elevation of the ST segment is a sign of cardiac ischemia and is unrelated to the rhythm. More often the ST-T wave is a smooth, continuous waveform beginning with the J-point (end of QRS), slowly rising to the peak of the T, and followed by a rapid descent to the isoelectric baseline or the onset of the U wave. This gives rise to an asymmetrical T wave.

Option E: The QRS duration should be less than 0.12 seconds; the PR interval should be 0.12 to 0.2 seconds. The QRS represents the simultaneous activation of the right and left ventricles, although most of the QRS waveform is derived from the larger left ventricular musculature.

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