Pacemaker of heart is?

ESIC Nursing Officer 2016 (Shift -2)

Applied Anatomy

Easy

Appeared in: ESIC Nursing Officer 2016 (Shift -2)

Explanation

The sinoatrial (SA) node is designated as the heart's primary pacemaker.
This is because it has the highest intrinsic rate of spontaneous depolarization (automaticity) compared to other parts of the cardiac conduction system.
Located in the superior wall of the right atrium, it normally generates electrical impulses at a rate of 60 to 100 beats per minute, establishing the normal sinus rhythm.

Option B: The atrioventricular (AV) node has a slower intrinsic firing rate (40-60 bpm) than the SA node, so it only takes over as the pacemaker if the SA node fails.
Option C: The atrium is one of the upper chambers of the heart. While the SA node is located within the right atrium, the atrial muscle tissue itself is not the primary pacemaker.
Option D: The ventricle is one of the lower, main pumping chambers of the heart. The specialized Purkinje fibers within the ventricular walls have a very slow intrinsic rate (20-40 bpm) and only act as a last-resort pacemaker.

Visual 1: Diagram - An illustration of the heart's electrical conduction system. This visual should clearly label the Sinoatrial (SA) node, Atrioventricular (AV) node, Bundle of His, and Purkinje fibers to show their locations and the pathway of the electrical impulse.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Cardiac Conduction System as background academic context rather than a clinical decision trigger.
Understanding the heart's pacemaker is fundamental for interpreting an electrocardiogram (ECG). The P wave on an ECG represents the electrical activity of the SA node and atrial depolarization.
Dysfunction of the SA node, known as Sick Sinus Syndrome, can cause severe bradycardia (a very slow heart rate), fatigue, or syncope (fainting). The primary treatment for symptomatic SA node dysfunction is the implantation of a permanent artificial pacemaker.
What if? If a patient's ECG shows a regular heart rate of 45 bpm with no visible P waves but a normal QRS complex, the nurse should suspect that the AV node has taken over as the pacemaker (a junctional escape rhythm), indicating a problem with the SA node.

How to Approach the Question

First, identify the key term in the question: 'Pacemaker of heart'. This is asking for the primary structure that initiates the heartbeat.
Recall the components of the heart's electrical conduction system: SA node, AV node, Bundle of His, and Purkinje fibers.
Remember the principle of automaticity: the cardiac tissue with the fastest intrinsic firing rate will be the dominant pacemaker.
Compare the intrinsic rates of the potential pacemakers: SA node (60-100 bpm) is the fastest, followed by the AV node (40-60 bpm), and then the ventricular Purkinje fibers (20-40 bpm).
Based on this hierarchy, conclude that the SA node is the primary pacemaker of the heart.

Concept Tested & Keywords

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