A abnormal SA node would primarily affect which aspect of cardiac function?

• A. Affects conduction through ventricles.
• B. Affects QRS duration.
• C. Affects T wave morphology.
• D. Affects initiation and rate of heartbeat.

Answer: (D)

The main concept is that the sinoatrial (SA) node is the heart’s natural pacemaker, responsible for initiating each heartbeat and setting the heart rate. If the SA node is abnormal, the timing and rate of impulses starting the cardiac cycle are affected, which directly alters how often the heart beats and its rhythm. The QRS duration reflects how quickly the ventricles depolarize after the impulse is generated, governed by the ventricular conduction system; this isn’t primarily about the rate at which impulses start. T wave morphology relates to ventricular repolarization, not the initiation of beats. So an abnormal SA node mainly changes initiation and rate, as the correct choice indicates. If another pacemaker takes over, the rate may slow or become irregular, but the ventricular conduction pathway and repolarization patterns remain controlled by their respective mechanisms.