What are the typical ECG (electrocardiogram) findings in patients with Paroxysmal Supraventricular Tachycardia (PSVT)?

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ECG Findings in Paroxysmal Supraventricular Tachycardia (PSVT)

The typical ECG findings in PSVT include a regular narrow QRS complex tachycardia (QRS duration <120 ms) with heart rates between 150-250 beats per minute, with P waves that are often hidden or abnormally positioned relative to the QRS complex. 1

Key ECG Characteristics by PSVT Mechanism

Atrioventricular Nodal Reentrant Tachycardia (AVNRT)

  • Regular narrow QRS tachycardia (most common form of PSVT)
  • Heart rate typically 150-250 bpm
  • P waves often hidden within the QRS complex due to simultaneous atrial and ventricular activation
  • When visible, P waves appear as:
    • Narrow negative deflection at the end of QRS in inferior leads (pseudo S wave)
    • Slightly positive deflection at the end of QRS in lead V1 (pseudo R') 1
  • Short RP interval (RP < PR)
  • RP interval typically <90 ms when measured from surface ECG 1

Atrioventricular Reentrant Tachycardia (AVRT)

  • Regular narrow QRS tachycardia
  • Heart rate typically 150-250 bpm
  • P waves visible in the early part of the ST-T segment
  • Short RP interval (RP < PR) but typically longer than in AVNRT
  • RP interval usually >90 ms 1
  • In orthodromic AVRT: narrow QRS unless pre-existing bundle branch block or aberrant conduction
  • In antidromic AVRT: wide QRS (maximally pre-excited) 1

Permanent Form of Junctional Reciprocating Tachycardia (PJRT)

  • Regular narrow QRS tachycardia
  • Long RP interval (RP > PR)
  • Involves a slowly conducting, concealed accessory pathway (usually posteroseptal) 1

Atrial Tachycardia

  • Regular narrow QRS tachycardia
  • Visible P waves with morphology different from sinus P waves
  • Long RP interval (RP > PR) 1

Differential Diagnosis Algorithm for Narrow QRS Tachycardia

  1. First step: Determine if the tachycardia is regular or irregular

    • Irregular → Consider atrial fibrillation, atrial flutter/tachycardia with variable AV conduction, or multifocal atrial tachycardia

  2. If regular: Look for visible P waves

    • No visible P waves → Likely AVNRT
    • Visible P waves → Proceed to next step

  3. If P waves visible: Assess the RP interval

    • Short RP interval (RP < PR)
      • RP <90 ms → Likely AVNRT
      • RP >90 ms → Likely AVRT
    • Long RP interval (RP > PR)
      • Likely atrial tachycardia or PJRT 1

Clinical Pearls for ECG Interpretation

  • The 12-lead ECG during tachycardia is crucial for accurate diagnosis 1
  • Vagal maneuvers or adenosine administration may help reveal the underlying mechanism by:
    • Terminating AVNRT/AVRT
    • Transiently blocking AV conduction to reveal atrial activity 2
  • In AVNRT, patients often describe "shirt flapping" or "neck pounding" sensations due to cannon a-waves (simultaneous atrial and ventricular contraction) 1
  • PSVT with aberrant conduction can present with wide QRS complexes, which must be differentiated from ventricular tachycardia 1, 2

Common Pitfalls in ECG Interpretation

  • Misdiagnosing PSVT with aberrancy as ventricular tachycardia
  • Failing to obtain a 12-lead ECG during tachycardia
  • Relying on automatic ECG analysis systems, which are often unreliable for arrhythmia diagnosis 1
  • Not recognizing pre-excitation on baseline ECG, which may indicate risk for potentially dangerous arrhythmias 1
  • Overlooking atrial activity that may be subtle but diagnostic 1

Clinical Implications

  • Accurate ECG diagnosis guides appropriate treatment strategy and risk stratification
  • Patients with WPW syndrome (pre-excitation pattern) require prompt evaluation due to risk of sudden cardiac death 1
  • The mechanism of PSVT affects response to therapy and suitability for catheter ablation 3
  • Regular documentation of 12-lead ECGs during symptomatic episodes is essential for definitive diagnosis 1

By systematically analyzing the ECG characteristics, particularly the relationship between P waves and QRS complexes, clinicians can accurately diagnose the specific mechanism of PSVT, which is crucial for appropriate management and treatment selection.

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

2
Guideline

Arrhythmia Diagnosis and Management

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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