Which one of the following is known as the pacemaker of the heart?

Appeared in: SCTIMST Staff Nurse - 2015 (Set-A)

Explanation

The Sinoatrial (SA) node is correctly identified as the heart's natural pacemaker.
It is located in the upper part of the right atrium, near the entry of the superior vena cava.
The SA node possesses the highest intrinsic rate of automaticity, generating electrical impulses at 60-100 beats per minute in a resting adult.
This inherent speed allows it to override other potential pacemaker sites in the heart, thereby setting the normal sinus rhythm.

Option B: The Atrioventricular (AV) node has a slower intrinsic rate (40-60 bpm) than the SA node. It primarily functions to delay the impulse before it reaches the ventricles.
Option C: The Bundle of His is part of the conduction pathway that transmits impulses from the AV node to the ventricles. It does not typically initiate impulses.
Option D: Purkinje fibers are specialized to rapidly conduct impulses to the ventricular muscle, ensuring a coordinated contraction. Their intrinsic pacemaker rate is the slowest (20-40 bpm).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Cardiac Conduction System and Primary Pacemaker Identification as background academic context rather than a clinical decision trigger.
Understanding the hierarchy of the heart's conduction system is fundamental for interpreting electrocardiograms (ECGs) and diagnosing arrhythmias.
Dysfunction of the SA node, known as Sick Sinus Syndrome, can lead to symptomatic bradycardia (slow heart rate), requiring the implantation of an artificial pacemaker.
What if? If a patient's ECG shows a regular rhythm at 45 bpm with no visible P waves but a narrow QRS complex, the pacemaker is likely the AV node (a junctional escape rhythm), indicating SA node failure.

How to Approach the Question

Identify the key term in the question: 'pacemaker of the heart'.
Recall the definition of a cardiac pacemaker: the structure that initiates the heartbeat and has the fastest intrinsic rate.
Mentally review the components of the heart's electrical conduction system: SA node, AV node, Bundle of His, and Purkinje fibers.
Compare the intrinsic firing rates of these components. The SA node is the fastest (60-100 bpm), followed by the AV node (40-60 bpm), and finally the Purkinje fibers (20-40 bpm).
Conclude that the structure with the highest intrinsic rate, the SA node, is the primary pacemaker.
Select the option that matches this conclusion.

Concept Tested & Keywords

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E6 Pharmacology Nursing Lilley 11e Part 2 p. 84-86

E6 Physiology Essentials Sembulingam 10e Part 2 p. 168-170

E6 Medicine Harrison 22e Part 1 p. 1958-1960

Practise the full SCTIMST Staff Nurse - 2015 (Set-A)

Attempt every question from this paper in a timed mock, then review the full solution for each one.