Is a heart rate of 170 beats per minute (bpm) indicative of sinus tachycardia or supraventricular tachycardia (SVT)?

Heart Rate of 170 bpm: Distinguishing Sinus Tachycardia from SVT

A heart rate of 170 bpm cannot be classified as sinus tachycardia or supraventricular tachycardia based on rate alone—the distinction requires ECG analysis of P-wave morphology, rhythm regularity, onset/offset characteristics, and clinical context. 1

Key Diagnostic Algorithm

Step 1: Obtain a 12-Lead ECG Immediately

• P-wave morphology is the critical distinguishing feature: Sinus tachycardia shows upright P waves in leads I, II, and aVF with a biphasic P wave in V1, while SVT typically shows abnormal P-wave morphology, hidden P waves within the QRS, or retrograde P waves 1
• Evaluate whether the rhythm is regular or irregular—sinus tachycardia is regular, while some SVTs (like atrial fibrillation with rapid ventricular response) are irregular 1
• Assess the QRS duration: narrow-complex (<120 ms) tachycardias are more likely supraventricular in origin 1

Step 2: Assess Onset and Termination Pattern

• Paroxysmal SVT has abrupt onset and termination, which is characteristic of AVNRT or AVRT 1
• Sinus tachycardia has gradual onset and offset, responding to physiologic stimuli 1
• If the patient describes sudden palpitations that start and stop abruptly, this strongly suggests SVT rather than sinus tachycardia 2

Step 3: Evaluate Clinical Context and Physiologic Appropriateness

• Sinus tachycardia is appropriate when it responds to physiologic stimuli such as fever, anemia, hypotension/shock, dehydration, pain, anxiety, or hyperthyroidism 1
• The upper limit of sinus tachycardia is age-related (approximately 220 minus patient's age in years)—a rate of 170 bpm may be within the expected range for younger patients during exercise or stress 1
• In adults without ventricular dysfunction, rates <150 bpm are more likely secondary to an underlying condition rather than a primary arrhythmia 1

Step 4: Compare with Baseline ECG in Sinus Rhythm

• If available, compare the tachycardia ECG with a baseline ECG in sinus rhythm 1
• In sinus tachycardia, the P-wave morphology during tachycardia should be identical to sinus rhythm (though amplitude may increase in inferior leads as rate increases) 1
• In SVT, the P-wave morphology will differ from sinus rhythm, or P waves may be hidden within or immediately after the QRS complex 1

Critical Distinguishing Features

Sinus Tachycardia Characteristics:

• Heart rate >100 bpm with P-wave morphology identical to normal sinus rhythm 1
• Gradual rate changes in response to activity, stress, or underlying conditions 1
• P waves precede each QRS with a normal PR interval 1
• Resolves when the underlying cause is treated 1, 3

SVT (Paroxysmal) Characteristics:

• Heart rate typically 150-250 bpm with abrupt onset and termination 1, 2
• P waves may be hidden within the QRS (typical AVNRT), appear as pseudo S waves in inferior leads, or show retrograde morphology 1
• In AVRT, P waves appear in the early ST-T segment with a "short RP" interval 1
• Does not respond to treatment of underlying physiologic stressors 1

Common Pitfalls to Avoid

Do not assume rate alone determines the diagnosis: A rate of 170 bpm can occur in both sinus tachycardia (especially in younger patients during exercise or severe physiologic stress) and SVT 1

Do not treat the rate without identifying the mechanism: If this is compensatory sinus tachycardia (e.g., in the setting of hypotension or shock), rate-controlling medications can precipitate cardiovascular collapse 4

Do not confuse irregular SVT with sinus tachycardia: Atrial fibrillation with rapid ventricular response at 170 bpm can be misdiagnosed as regular SVT if only a single lead is examined 1, 2

Do not delay cardioversion in unstable patients: If the patient shows signs of hemodynamic instability (altered mental status, chest pain, acute heart failure, hypotension, or shock), proceed immediately to synchronized cardioversion regardless of whether the rhythm is sinus tachycardia or SVT 1

When to Consider SVT Over Sinus Tachycardia

• Patient reports sudden onset of palpitations with abrupt termination 1
• Rate of 170 bpm persists despite resolution of physiologic stressors 1
• P waves are not clearly visible before each QRS or have abnormal morphology 1
• Patient has known history of paroxysmal SVT or accessory pathway (Wolff-Parkinson-White syndrome) 1, 5
• Vagal maneuvers or adenosine terminate the rhythm abruptly (diagnostic and therapeutic for SVT) 1