The normal heartbeat triggered by the SA node is termed the

The normal heartbeat triggered by the SA node is termed the

• A. Sinus rhythm
• B. Atrial fibrillation
• C. Ventricular tachycardia
• D. Junctional rhythm

Answer: (A)

The key idea is that normal rhythm is driven by the sinoatrial (SA) node, producing a sinus rhythm when the impulse travels in a normal sequence from atria to ventricles. On an ECG, sinus rhythm means a P wave precedes every QRS complex with the same shape, a constant PR interval (about 0.12–0.20 seconds), a regular rhythm, and a heart rate in the normal range (roughly 60–100 beats per minute). The QRS complex is narrow because the ventricle depolarizes through the normal His-Purkinje pathway. This distinguishes it from atrial fibrillation, where there are no distinct P waves and the rhythm is irregularly irregular with variable R-R intervals. It also differs from ventricular tachycardia, which presents as a rapid, wide-complex rhythm often with no organized atrial activity, and from junctional rhythm, which arises from the AV junction and may show absent or retrograde P waves with a slower rate. Therefore, the description that matches these features points to sinus rhythm as the normal heartbeat triggered by the SA node.

The key idea is that normal rhythm is driven by the sinoatrial (SA) node, producing a sinus rhythm when the impulse travels in a normal sequence from atria to ventricles. On an ECG, sinus rhythm means a P wave precedes every QRS complex with the same shape, a constant PR interval (about 0.12–0.20 seconds), a regular rhythm, and a heart rate in the normal range (roughly 60–100 beats per minute). The QRS complex is narrow because the ventricle depolarizes through the normal His-Purkinje pathway.

This distinguishes it from atrial fibrillation, where there are no distinct P waves and the rhythm is irregularly irregular with variable R-R intervals. It also differs from ventricular tachycardia, which presents as a rapid, wide-complex rhythm often with no organized atrial activity, and from junctional rhythm, which arises from the AV junction and may show absent or retrograde P waves with a slower rate. Therefore, the description that matches these features points to sinus rhythm as the normal heartbeat triggered by the SA node.