What does a biphasic wave on Doppler (Doppler ultrasound) indicate in a patient?

Biphasic Wave on Doppler Ultrasound

A biphasic waveform on Doppler ultrasound indicates a two-phase flow pattern with forward systolic flow followed by brief reverse flow, then absent or minimal diastolic forward flow—this pattern typically signifies either normal arterial flow in peripheral vessels, moderate arterial stenosis with increased downstream resistance, or normal venous flow patterns depending on the vessel examined. 1

Arterial Biphasic Waveforms

Normal Peripheral Arterial Flow

• Biphasic waveforms are the normal flow pattern in peripheral arteries (such as the femoral, radial, or tibial arteries) in healthy individuals, consisting of forward systolic flow, brief reverse flow, and minimal or absent diastolic forward flow 1, 2
• The triphasic pattern (systolic forward, reverse, diastolic forward) degrades to biphasic when arterial stiffness increases, peripheral wave reflection decreases, or pulse pressure amplification diminishes 2
• In the femoral artery specifically, biphasic flow (lacking the diastolic forward component) correlates with increased aortic pulse wave velocity, greater arterial stiffness, and reduced aorta-to-femoral pulse pressure amplification 2

Pathological Arterial Conditions

• In carotid arteries, biphasic flow with increased peak systolic velocity (>130 cm/s) combined with elevated end-diastolic velocity (>100 cm/s) indicates 70-99% stenosis 1
• Dampening of normal multiphasic waveforms to biphasic patterns with reduced pulsatility suggests proximal arterial obstruction or increased downstream resistance 1
• Loss of the normal triphasic pattern in lower extremity arteries, becoming biphasic, is associated with peripheral arterial disease, diabetes, increased age, and smaller vessel diameter 2

Venous Biphasic Waveforms

Normal Venous Flow Patterns

• In upper extremity veins, biphasic waveforms can represent normal respiratory variation superimposed on cardiac pulsations, with flow velocity increasing during expiration and decreasing during inspiration 1, 3
• Normal lower limb venous Doppler tracings demonstrate multiphasic cardiac waveforms that may become biphasic during certain respiratory phases (end of expiration) without indicating pathology 3
• Dampening of cardiac pulsatility or loss of respiratory variation in venous waveforms reliably indicates central venous obstruction 1

Distinguishing Normal from Abnormal

• Biphasic venous flow that maintains respiratory variation and cardiac pulsatility is normal; loss of phasicity suggests proximal obstruction 1, 3
• During breath-hold at end of expiration, normal venous waveforms may become biphasic in healthy individuals without indicating disease 3
• Complete loss of phasicity or continuous monophasic flow in veins indicates significant proximal obstruction or thrombosis 1

Cardiac and Fetal Applications

Fetal Circulation

• Biphasic waveforms in the fetal ductus venosus are normal, with peaks during ventricular systole and passive diastolic filling, followed by a nadir during atrial contraction 1, 4
• Abnormal ductus venosus flow shows decreased, absent, or reversed A-wave flow (not simply biphasic pattern), indicating myocardial impairment and linking to neonatal acidemia and perinatal mortality 1, 4

Cardiac Bypass Grafts

• In coronary artery bypass grafts (LITA or RGEA), biphasic velocity waveforms with predominant diastolic flow are typical and indicate patent grafts supplying blood primarily during diastole 5
• Systolic flow reversal near the anastomotic site in biphasic patterns occurs with less-occluded stenotic lesions or strong competitive backflow 5

Clinical Interpretation Algorithm

When encountering biphasic Doppler waveforms, follow this decision pathway:

1. Identify the vessel type (arterial vs. venous) and anatomic location
2. For peripheral arteries: Biphasic flow is normal; measure peak systolic velocity to exclude significant stenosis (PSV >130 cm/s warrants further evaluation) 1
3. For carotid arteries: Biphasic flow with elevated velocities (PSV >130 cm/s, EDV >100 cm/s) indicates 70-99% stenosis requiring intervention consideration 1
4. For veins: Assess whether respiratory variation and cardiac pulsatility are preserved; if present, biphasic pattern is normal 1, 3
5. For fetal vessels: Biphasic ductus venosus flow is normal; abnormality is defined by absent or reversed A-wave, not biphasic pattern 1, 4

Common Pitfalls

• Do not interpret normal biphasic peripheral arterial flow as pathological—this is the expected pattern in distal vessels like the femoral, radial, or tibial arteries 1, 2
• Avoid diagnosing venous obstruction based solely on biphasic flow during certain respiratory phases—confirm with loss of respiratory variation and assess for central obstruction 1, 3
• In carotid evaluation, biphasic waveforms alone are insufficient—velocity measurements are essential to quantify stenosis severity 1
• Respiratory factors can cause temporary loss of venous phasicity (breath-hold at end of inspiration) without indicating proximal obstruction 3
• Distinguish between normal biphasic ductus venosus waveforms and pathological absent/reversed A-wave flow in fetal assessment 1, 4