How to differentiate between supraventricular tachycardia (SVT) and sinus tachycardia on an electrocardiogram (EKG)?

How to Differentiate SVT from Sinus Tachycardia on ECG

The most reliable way to differentiate supraventricular tachycardia (SVT) from sinus tachycardia on ECG is by examining the rate, regularity, P wave morphology, and R-R interval variation patterns. 1, 2

Key Differentiating Features

Rate

• Sinus tachycardia is almost always <230 beats/min 1
• SVT typically has rates of 260-300 beats/min, especially in infants 1
• In adults, SVT rates are typically >150 beats/min, while sinus tachycardia rarely exceeds 180 beats/min 2

R-R Interval Variation

• Sinus tachycardia shows gradual acceleration and deceleration over several seconds 1
• SVT demonstrates extreme regularity after the first 10-20 beats 1
• Cycle length alternans (alternating R-R intervals) may be present in certain types of SVT 3

P Wave Characteristics

• Sinus tachycardia: P waves are always visible and have the same morphology as during normal sinus rhythm 1
• SVT: P waves are visible in only about 60% of cases and have different morphology from sinus P waves 1
• SVT may show:
  • Hidden P waves within QRS complexes (creating pseudo-r' in V1 and/or pseudo-S waves in inferior leads) in AVNRT 2
  • P waves in the ST segment separated from QRS by ≥70 ms in AVRT 2
  • RP/PR interval ratio >1 in atrial tachycardia 4

QRS Morphology

• Sinus tachycardia: QRS complex is the same as in slower sinus rhythm 1
• SVT: QRS complex is typically the same as sinus after the first 10-20 beats 1
• QRS alternans (alternating QRS amplitude) is more common in AVRT (27%) than other SVT types 4

Clinical Context

• Sinus tachycardia is typically associated with an identifiable cause: fever, sepsis, hypovolemia, pain, anxiety, or medications 1
• SVT often occurs in patients who are otherwise healthy 1
• When in doubt, vagal maneuvers or adenosine administration can help differentiate, as sinus tachycardia will gradually slow while SVT will either abruptly terminate or transiently slow revealing underlying atrial activity 2

Diagnostic Algorithm

1. Check heart rate:

   • <150 bpm: Likely sinus tachycardia 2

   • 150 bpm: Could be either, proceed to next steps 2

2. Examine R-R interval pattern:

   • Gradually varying: Suggests sinus tachycardia 1
   • Extremely regular: Suggests SVT 1

3. Analyze P wave morphology:

   • Visible, normal axis P waves before each QRS: Sinus tachycardia 1
   • Absent, abnormal, or retrograde P waves: SVT 1, 2

4. Consider clinical context:

   • Identifiable physiologic trigger: Favors sinus tachycardia 1
   • Sudden onset/offset: Favors SVT 2

Common Pitfalls to Avoid

• Relying solely on heart rate for diagnosis - overlap exists between the two conditions 2
• Failing to look for P waves - they may be hidden in the T wave or QRS complex in SVT 2
• Not considering the clinical context - sinus tachycardia typically has an identifiable cause 1
• Missing QRS alternans, which is more common in AVRT than other tachycardias 4

Advanced Diagnostic Techniques

• If available, compare with previous ECGs during normal sinus rhythm to assess P wave morphology 2
• Consider recording a 12-lead ECG during vagal maneuvers or adenosine administration to reveal the underlying mechanism 1
• In difficult cases, smartphone-based single-lead ECG monitors can differentiate SVT from inappropriate sinus tachycardia with approximately 90% sensitivity and specificity 5