Provided is an ECG image of sinus tachycardia. Identify the wave pattern and describe its characteristics.

Choice A rationale Sinus tachycardia is defined by a heart rate exceeding 100 beats per minute, originating from the sinoatrial node. The rhythm remains regular because the electrical impulses follow the normal conduction pathway through the atria and ventricles. Each QRS complex is preceded by a visible P wave, and the PR interval remains within the normal range of 0.12 to 0.20 seconds. This rhythm is often a physiological response to stress, fever, exercise, or pain. Choice B rationale A heart rate between 60 and 100 beats per minute with a regular rhythm defines normal sinus rhythm. In this state, the sinoatrial node fires at a standard physiological pace, and the electrical conduction through the heart is unimpeded. Because sinus tachycardia specifically refers to a rate that is faster than this normal range, this choice does not accurately describe the wave pattern in question. It represents a healthy cardiac electrical state rather than a tachycardic one. Choice C rationale An irregular rhythm with changing P wave morphology is characteristic of rhythms like wandering atrial pacemaker or multifocal atrial tachycardia. These conditions involve multiple ectopic foci within the atria competing for dominance, rather than a single impulse from the sinoatrial node. In true sinus tachycardia, the P waves should look identical to one another because they are all generated from the same location. Therefore, this description is inconsistent with the diagnostic criteria for sinus tachycardia. Choice D rationale A rapid rate without visible P waves and narrow QRS complexes is typical of supraventricular tachycardia or atrial fibrillation, depending on the regularity of the rhythm. In sinus tachycardia, the P wave must be present and clearly associated with the QRS complex because the rhythm originates from the sinus node. The absence of P waves suggests that the rhythm is originating from a different part of the atrium or the atrioventricular junction, which is incorrect.