Hypertension & Coronary Artery Disease Q 33

---

When assessing an ECG, the nurse knows that the P-R interval represents the time it takes for the:

  

     A. Impulse to begin atrial contraction.

     B. Impulse to transverse the atria to the AV node.

     C. SA node to discharge the impulse to begin atrial depolarization.

     D. Impulse to travel to the ventricles.

    

    

Correct Answer: D. Impulse to travel to the ventricles.

---

The P-R interval is measured on the ECG strip from the beginning of the P wave to the beginning of the QRS complex. It is the time it takes for the impulse to travel to the ventricle. The PR interval represents the time between atrial depolarization and ventricular depolarization. Abnormalities in the timing of the PR segment can indicate pathology. A PR interval of under 120 milliseconds (ms) may indicate that electrical impulses are traveling between the atria and ventricles too quickly.

---

Option A: Normal cardiac rhythm is established by the sinoatrial (SA) node, a specialized clump of myocardial conducting cells located in the superior and posterior walls of the right atrium in close proximity to the orifice of the superior vena cava. The SA node has the highest inherent rate of depolarization and is known as the pacemaker of the heart. It initiates the sinus rhythm, or normal electrical pattern followed by contraction of the heart.

Option B: The atrioventricular (AV) node is a second clump of specialized myocardial conductive cells, located in the inferior portion of the right atrium within the atrioventricular septum. The septum prevents the impulse from spreading directly to the ventricles without passing through the AV node. There is a critical pause before the AV node depolarizes and transmits the impulse to the atrioventricular bundle.

Option C: This impulse spreads from its initiation in the SA node throughout the atria through specialized internodal pathways, to the atrial myocardial contractile cells and the atrioventricular node. The internodal pathways consist of three bands (anterior, middle, and posterior) that lead directly from the SA node to the next node in the conduction system, the atrioventricular node. The impulse takes approximately 50 ms (milliseconds) to travel between these two nodes.

---