What is the primary characteristic of sinus tachycardia?

The primary characteristic of sinus tachycardia is the increased rate of discharge from the sinoatrial (SA) node. In this condition, the heart rate exceeds the normal range, typically above 100 beats per minute in adults. This increase in heart rate occurs while maintaining the intrinsic rhythm that originates from the SA node, which is responsible for initiating each heartbeat in a healthy heart.

In sinus tachycardia, the regularity of the heart rhythm remains intact, meaning that despite the higher heart rate, the intervals between beats are consistent. P waves, which represent atrial depolarization, are present and have a normal morphology, indicating that the electrical activity still follows the usual pathway through the heart. Overall, sinus tachycardia is adaptive, often occurring in response to physiological or pathological factors such as exercise, anxiety, fever, or anemia, rather than a dysfunction of the heart's electrical system.