SVT ECG Criteria (Supraventricular Tachycardia)

Interpreting a Supraventricular Tachycardia (SVT)

To interpret an SVT, remember the “S” stands for supra, connoting the complex’s origin above the ventricles. Most SVTs occur from a re-entry circuit somewhere around the AV node, and management should follow the ACLS tachycardia algorithm for appropriate intervention.

Re-entry circuits cause SVTs, leading to hidden P waves and a fast ventricular rate.

Step-by-Step ECG Interpretation Workflow

1. Rate

These re-entry circuits tend to be very quick. The overall ventricular rate for an SVT is typically greater than 150 bpm, frequently sitting between 150 and 250 bpm.

2. Rhythm Regularity

There is usually only one re-entry pathway used at a time, meaning the R-R intervals should be identical and march out in a highly regular rhythm.

3. QRS Width Assessment

Because the impulse originates above the ventricles and travels down the normal His-Purkinje system, it typically produces a narrow QRS complex (< 0.12 seconds).

4. P Wave Assessment

Since the complex originates around the AV node and the rate is so fast, normal P waves are not produced. P waves may be entirely absent, buried inside the QRS complex, or seen as a retrograde (inverted) wave just after the QRS.

ECG Example: Notice the highly regular R-R intervals, narrow QRS complexes, and absent P waves characteristic of SVT.

Criteria for SVT Interpretation Summary

The Wide-Complex Caveat

While SVT is classically a narrow-complex tachycardia, it can present with a wide QRS complex if the patient has a pre-existing Bundle Branch Block (BBB), rate-related aberrancy, or an accessory pathway (e.g., WPW syndrome). Wide-complex SVT can be diagnostically ambiguous and closely mimics Ventricular Tachycardia (VT). When in doubt, ACLS guidelines dictate treating undifferentiated wide-complex tachycardia as VT.

Differential Considerations: Common Pitfalls and Look-Alikes

Accurate diagnosis requires ruling out SVT mimics:

• Sinus Tachycardia Mistaken for SVT: Sinus tachycardia rarely exceeds 150 bpm at rest and will have visible P waves before every QRS.
• Atrial Flutter Hiding as SVT: Atrial flutter with a 2:1 conduction block often presents at exactly 150 bpm. You may need to look closely for hidden flutter (“sawtooth”) waves.
• Very Fast AFib: Rapid Atrial Fibrillation can appear almost regular to the naked eye. Always measure R-R intervals closely; AFib is inherently irregular, while SVT is strictly regular.

Comparison: Differentiating SVT from Sinus Tachycardia, AFib, and Atrial Flutter relies on rate, regularity, and P-wave morphology.

Read: Rhythm-based Management in Cardiac Arrest

Summary

Physicians and ACLS providers must know the specific criteria for Supraventricular Tachycardia to effectively guide treatment. Patients will typically exhibit a narrow QRS complex, an absent or hidden P wave, a heart rate greater than 150 bpm, and a highly regular rhythm. However, careful differentiation is crucial: always be aware of edge cases like atrial flutter with a 2:1 block, rapid atrial fibrillation, sinus tachycardia, or an SVT presenting with a wide QRS complex due to aberrancy.

To strengthen your foundational knowledge, review our ECG and Cardio Cycle Basics. For your next steps, continue practicing with real-world ECG strips and algorithms to master these subtle rhythm differences.