How is sinus tachycardia differentiated from supraventricular tachycardia?

Sinus tachycardia is characterized by a normal sinus rhythm but at an increased heart rate, typically greater than 100 beats per minute. In this condition, each P wave is present and precedes each QRS complex, indicating that the electrical activity is originating from the sinus node as expected.

In contrast, supraventricular tachycardia (SVT) can arise from various sources above the ventricles, and this can sometimes result in the absence of identifiable P waves due to rapid rates that do not allow for clear differentiation of P waves from the QRS complexes. If P waves are present during SVT, they may appear obscured or merged with QRS complexes, making it difficult to establish a clear relationship between the P waves and QRS complexes.

Therefore, the presence of a P wave before each QRS complex serves as a critical distinguishing feature, indicating that the rhythm is sinus tachycardia rather than SVT, which may have a different origin for the electrical impulses leading to rapid heart rates. This differentiation is essential for appropriate diagnosis and management.