A nurse is assessing an electrocardiogram rhythm strip. The P waves and QRS complexes are regular. The PR interval is 0.16 second, and QRS complexes measure 0.06 second. The overall heart rate is 64 beats per minute. The nurse assesses the cardiac rhythm as:
A. Normal sinus rhythm
B. Sinus bradycardia
C. Sick sinus syndrome
D. First-degree heart block
Correct Answer: A. Normal sinus rhythm
Measurements are normal, measuring 0.12 to 0.20 second and 0.4 to 0.10 second, respectively. Sinus rhythms originate in the SA node. The SA node is located in the right atrium and is the heart’s natural pacemaker. The normal rate of the SA node is between 60 and 100. On ECG, sinus rhythm is represented by monomorphic P waves before each QRS complex and is regular.
Option B: Sinus bradycardia is a cardiac rhythm with appropriate cardiac muscle depolarization initiating from the sinus node generating less than 60 beats per minute (bpm). The diagnosis of sinus bradycardia requires visualization of an electrocardiogram showing a normal sinus rhythm at a rate lower than 60 bpm.
Option C: Sick sinus syndrome, also known as sinus node dysfunction (SND), is a disorder of the sinoatrial (SA) node caused by impaired pacemaker function and impulse transmission producing a constellation of abnormal rhythms. These include atrial bradyarrhythmias, atrial tachyarrhythmias and, sometimes, bradycardia alternates with tachycardia often referred to as “tachy-brady syndrome.”
Option D: First-degree atrioventricular (AV) block is a condition of abnormally slow conduction through the AV node. It is defined by ECG changes that include a PR interval of greater than 0.20 without disruption of atrial to ventricular conduction.
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