Can a rhythm on an electrocardiogram (EKG) with a heart rate of 135 beats per minute (bpm), no visible P waves, and regularity be consistent with Supraventricular Tachycardia (SVT)?

Supraventricular Tachycardia with HR 135 and No P Waves

Yes, a regular rhythm on ECG with heart rate of 135 bpm and no visible P waves can definitely be consistent with supraventricular tachycardia (SVT), specifically atrioventricular nodal reentrant tachycardia (AVNRT). 1

ECG Characteristics of SVT Without P Waves

In AVNRT, which is the most common form of SVT:

• The P waves are often hidden within the QRS complex due to nearly simultaneous atrial and ventricular activation
• The rhythm is characteristically regular
• Heart rates typically range from 150-250 bpm, but can be slower (135 bpm is within range)
• QRS complexes are typically narrow (<120 ms) unless there is aberrant conduction

When examining the ECG of suspected AVNRT:

• Look for subtle signs of hidden P waves:
  • A pseudo S wave in inferior leads (II, III, aVF)
  • A pseudo R' wave in lead V1
• The absence of visible P waves is actually characteristic of typical AVNRT 1

Differential Diagnosis

When evaluating a regular tachycardia at 135 bpm with no visible P waves, consider:

1. AVNRT (most likely) - Regular rhythm, no visible P waves or P waves hidden in QRS
2. Junctional tachycardia - Can mimic AVNRT pattern, may show AV dissociation
3. AVRT (accessory pathway) - Usually has visible P waves in early ST segment
4. Atrial flutter with fixed conduction - Usually has visible flutter waves
5. Ventricular tachycardia - Usually has wider QRS complexes

Diagnostic Approach

For a narrow QRS tachycardia with no visible P waves:

1. Confirm QRS duration is <120 ms
2. Examine for hidden P waves within the QRS complex
3. Look for the characteristic pseudo S wave in inferior leads and pseudo R' in V1 1

Management Considerations

For hemodynamically stable patients with suspected AVNRT:

1. First-line: Vagal maneuvers (Valsalva is preferred)
2. Second-line: Adenosine IV (6 mg rapid push, followed by 12 mg if needed)
3. Third-line: IV calcium channel blockers (diltiazem or verapamil) or beta blockers

For hemodynamically unstable patients:

• Immediate synchronized cardioversion

Common Pitfalls

1. Misdiagnosing VT as SVT: Always confirm narrow QRS complex on 12-lead ECG before treating as SVT
2. Missing atrial flutter: Look carefully for flutter waves that may be subtle
3. Inappropriate use of calcium channel blockers: Never use in wide-complex tachycardias of uncertain origin as this could precipitate cardiovascular collapse in VT 1
4. Overlooking WPW syndrome: Pre-excited tachycardias can have narrow QRS but require different management

Long-term Management

For recurrent episodes:

• Catheter ablation has >95% success rate for AVNRT with low complication rates 2, 3
• Pharmacologic options include beta blockers or calcium channel blockers for long-term suppression

Remember that SVT with a rate of 135 bpm is on the lower end of the typical range for SVT but is entirely consistent with the diagnosis, especially AVNRT where the P waves are characteristically hidden within the QRS complex.