What does a normal pulsed wave (PW) Doppler waveform of the radial vein look like on ultrasound?

Normal Pulsed Wave Doppler Waveform of Radial Vein on Ultrasound

A normal pulsed wave (PW) Doppler waveform of the radial vein typically displays multiphasic flow with both cardiac and respiratory phasicity, characterized by continuous forward flow throughout the cardiac cycle with variations in velocity that correspond to cardiac phases and respiratory movements.

Normal Characteristics of Radial Vein PW Doppler

Cardiac Phasicity Components

When examining the radial vein during breath-hold in mid-respiration (to isolate cardiac components), the normal waveform includes:

• Multiphasic pattern with frequency similar to heart rate 1

• Four distinct components in each cardiac cycle:

  • Systolic wave (S wave) - Antegrade flow occurring approximately 0.4 seconds after the QRS complex
  • v wave - Small retrograde component without flow reversal
  • Diastolic wave (D wave) - Antegrade flow during ventricular diastole
  • a wave - Retrograde component during atrial contraction that may show minimal flow reversal

• Normal velocity ratios:

  • Systolic:diastolic velocity ratio typically ranges from 0.9 to 1.5 (mean 1.1)
  • Minimum:maximum velocity ratio ranges from -0.4 to 0.2 (mean -0.15) 1

Respiratory Influence

During normal breathing, the basic cardiac pattern is modulated by respiratory phases:

• Flow velocity increases during expiration
• Flow velocity decreases during inspiration
• During quiet respiration, both cardiac and respiratory waveforms are present 1
• With deep breathing, respiratory waves increase in amplitude while cardiac components decrease

Clinical Significance and Pitfalls

Important Diagnostic Considerations

• Loss of phasicity in radial vein waveforms may indicate venous obstruction proximal to the site of examination, even when the vein appears compressible 2
• Monophasic waveforms in a compressible vein should raise suspicion for proximal venous obstruction, which may be intrinsic (thrombosis) or extrinsic (compression) 2

Common Pitfalls

• Misinterpreting respiratory variations: Loss of phasicity can be caused by respiratory factors and doesn't always indicate obstruction 1
• Overinterpreting minimal retrograde flow: Small cyclic retrograde flow (≤5 cm/sec) is normal and doesn't necessarily indicate cardiac disease 1
• Failing to correlate with respiratory phase: Waveforms should be assessed during different respiratory maneuvers to fully understand their significance

Technique for Optimal Assessment

• Use color flow imaging for optimal alignment of PW Doppler with blood flow
• Position sample volume (1-3 mm axial size) in the center of the vessel
• Use low wall filter settings (100-200 MHz) and low signal gain
• Obtain measurements during different respiratory phases:
  • Mid-respiration (baseline)
  • End-expiration
  • End-inspiration
  • During Valsalva maneuver
  • During quiet and deep breathing

Clinical Applications

Abnormal radial vein waveforms may indicate:

• Proximal venous obstruction
• Right heart dysfunction (particularly when pulsatility fraction ≥100%) 3
• Tricuspid regurgitation (sensitivity 54%, specificity 78%) 4

By understanding normal radial vein Doppler patterns, clinicians can better identify pathological conditions affecting venous return and right heart function, potentially uncovering significant clinical issues before they become symptomatic.