Supraventricular Tachycardia (SVT) and ECG Interpretation

Introduction

Supraventricular Tachycardia (SVT) is a rapid heart rhythm originating above the ventricles, usually in the atria or the atrioventricular (AV) node. It can cause palpitations, dizziness, shortness of breath, and even fainting in severe cases.

Understanding the ECG of SVT

An ECG (Electrocardiogram) is the primary tool used to diagnose SVT. Here are the key ECG characteristics of SVT:

• Heart Rate : Usually between 150-250 beats per minute (bpm).
• Rhythm : Regular (though exceptions exist).
• P Waves : May be absent, hidden in the preceding T wave, or appear as retrograde P waves.
• QRS Complex : Narrow (<120 ms) if there is no underlying bundle branch block or pre-excitation.
• Sudden Onset and Termination : SVT typically starts and stops abruptly (often recorded as 'paroxysmal' SVT).

Types of SVT Based on ECG Findings

• Atrioventricular Nodal Reentry Tachycardia (AVNRT):

  • Most common type.
  • Regular narrow QRS tachycardia.
  • P wave often hidden within the QRS complex.

• Atrioventricular Reentrant Tachycardia (AVRT):

  • Seen in Wolff-Parkinson-White (WPW) syndrome.
  • Delta waves and a short PR interval on baseline ECG.
  • Can show orthodromic (narrow QRS) or antidromic (wide QRS) tachycardia.

• Atrial Tachycardia:

  • P waves seen before each QRS but with an unusual morphology.
  • Heart rate is usually between 100-250 bpm.

Management of SVT

• Acute Episode :

  • Vagal maneuvers (e.g., Valsalva maneuver, carotid massage).
  • Adenosine (first-line pharmacologic treatment for narrow-complex SVT).
  • Beta-blockers or calcium channel blockers (for rate control if adenosine is ineffective).
  • Cardioversion (if the patient is unstable).

• Long-term Management :

  • Lifestyle modifications (avoidance of caffeine, nicotine, alcohol).
  • Medications (beta-blockers, calcium channel blockers, or antiarrhythmic drugs).
  • Catheter ablation (curative in many cases for AVNRT and AVRT).

When to Seek Medical Attention?

If you experience frequent or prolonged episodes of rapid heartbeat, feel faint, or have chest pain, seek medical attention immediately.

Conclusion

SVT is a common arrhythmia with specific ECG features. Diagnosis is essential for effective management, and in many cases, treatment options like ablation can provide a long-term cure.

Source recommendations

1. American College of Cardiology/American Heart Association/Heart Rhythm Society Guidelines for the Management of Patients with Supraventricular Tachycardia

1. https://www.ahajournals.org/doi/10.1161/cir.0000000000000311
2. https://pubmed.ncbi.nlm.nih.gov/26399662/
3. https://www.acc.org/Latest-in-Cardiology/ten-points-to-remember/2015/09/23/09/13/2015-ACC-AHA-HRS-Guideline-for-the-Management-of-Adult-Patients-With-SVT
4. https://www.heartrhythmjournal.com/article/s1547-5271(15)01189-3/fulltext
5. https://www.hrsonline.org/guidance/clinical-resources/2015-accahahrs-guideline-management-adult-patients-supraventricular-tachycardia

2. European Society of Cardiology Guidelines on Supraventricular Tachycardia

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Supraventricular-Tachycardia
2. https://academic.oup.com/eurheartj/article/41/5/655/5556821
3. https://pubmed.ncbi.nlm.nih.gov/31504425/
4. https://www.acc.org/Latest-in-Cardiology/ten-points-to-remember/2019/09/10/12/36/2019-ESC-Guidelines-for-Supraventricular-Tachycardia
5. https://www.ahajournals.org/doi/10.1161/cir.0000000000000311