Sinus Tachycardia vs SVT: How to Tell the Difference on the Monitor

Sinus tach and SVT both show narrow-complex tachycardia on the monitor. Learn how onset, P waves, rate behavior, and clinical context help you tell them apart.

Two Fast Rhythms, Very Different Meanings You are watching a patient on the monitoring wall. The heart rate reads 148 bpm. The QRS complexes are narrow. The rhythm is regular. Is it sinus tachycardia or SVT? This is one of the most common judgment calls you will face at the central station. Both rhythms produce narrow-complex tachycardia. Both can push rates into the 140 to 160 range. And the difference matters enormously — sinus tachycardia is the heart doing exactly what it should in response to a physiologic stressor, while SVT is an electrical short circuit that may need immediate intervention. Getting this call right is not about memorizing a chart. It is about understanding the handful of reliable clues the monitor gives you and knowing when to pick up the phone. Sinus Tachycardia: The Heart Doing Its Job Sinus tachycardia is not an arrhythmia. It is a normal response to increased demand. The sinus node, which is the heart's natural pacemaker, fires faster because something is telling it to — the sympathetic nervous system is activated, and the heart rate rises accordingly. Common causes you will see in monitored patients: - Fever (one of the most common drivers — the heart rate rises roughly 10 bpm for every degree Fahrenheit above normal) - Pain or anxiety - Hypovolemia (blood loss, dehydration) - Anemia - Medications (albuterol, dopamine, dobutamine) - Post-surgical stress response - Pulmonary embolism - Sepsis and infection The key point is that sinus tachycardia always has a reason. The heart is responding to something. When the stimulus resolves — the fever breaks, the pain is treated, the fluids are given — the rate comes back down. What it looks like on the monitor - P waves visible before every QRS. This is the most important feature. In sinus tachycardia, the sinus node is driving the rhythm, so every beat starts with a P wave followed by a QRS complex. At higher rates, the P wave may merge with the preceding T wave, making it harder to see — but it is there. - Gradual onset and offset. The rate does not jump from 80 to 150 in one beat. It climbs over minutes to hours as the underlying cause worsens, and it descends gradually as the cause improves. If you scroll back through the trend, you will see a smooth acceleration, not a step change. - Rate typically under 150 bpm at rest. In a resting adult, sinus tachycardia usually maxes out around 140 to 150 bpm. It can go higher in young patients, during extreme physiologic stress, or with certain medications, but a resting rate above 150 in a typical hospitalized adult should make you look twice. - Rate varies with activity and stimulation. Sinus tachycardia responds to the patient's state. You may notice the rate climb when the patient is being turned for a bath, then settle when they rest. This variability is normal and expected. SVT: An Electrical Short Circuit SVT — supraventricular tachycardia