Nomenclature Purpose: to clarify and standardize essential definitions and descriptors in the analysis of arterial Doppler waveforms.

Reference baseline for spectral Doppler waveforms universally defined as the zero-flow baseline.

Reporting arterial spectral Doppler involves key descriptors (flow direction, phasicity, resistance) and optional modifier terms for additional insights.

The normal peripheral arterial waveform includes a sharp systolic peak, an early diastolic notch or early diastolic reversal, and a positive end diastole.

WAVEFORM MAJOR DESCRIPTORS

BASED ON FLOW DIRECTION:

1. ANTEGRADE FLOW (OLD TERM: FORWARD FLOW)

Blood moves in the normal direction within the assessed artery.

2. RETROGRADE (OLD TERM: REVERSE FLOW)

Blood moves in a opposite direction within the assessed artery.

3. BIDIRECTIONAL FLOW (OLD TERM: TO-FRO FLOW)

Blood enters and exits a confined sac through a single orifice.

4. ABSENT FLOW

No flow is detected with absent color and spectral signal.

BASED ON PHASICITY

1. MULTIPHASIC (OLD TERM: TRIPHASIC. BIPHASIC)

The waveform crosses the zero-flow baseline and incorporates both forward and reverse velocity elements.

2. MONOPHASIC

The waveform doesn’t cross the zero-flow baseline throughout the entire cardiac cycle.

BASED ON RESISTANCE

1. HIGH RESISTANCE

Sharp upstroke followed by a rapid downstroke, with or without the reversal of diastolic flow.

2. INTERMEDIATE RESISTANCE

Sharp upstroke, rapid downstroke, clear end systolic notch, and continuous forward flow throughout diastole above the zero-flow baseline.

3. LOW RESISTANCE

Prolonged downstroke during late systole with continuous forward flow throughout the diastole. towards the end of systole and ongoing forward flow throughout diastole.

(Unlike intermediate resistance, the low-resistive waveform shows a prolonged and continuous forward flow during diastole without an end systolic notch)

WAVEFORM MODIFIERS:

1. RAPID UPSTROKE

A nearly vertical slope or rapid ascent to the peak of systole with less acceleration time (measured from the beginning of systole to mid-systole). For example, The acceleration time for the common femoral artery, is less than 140 ms.

2. PROLONGED UPSTROKE (OLD TERMS: TARDUS, DELAYED, DAMPED)

Abnormal gradual incline to the peak systole with increased acceleration time.

3. SHARP PEAK

A sharp singular, and well-defined peak, often with the highest velocity falling within the artery's specified range.

4. SPECTRAL BROADENING (OLD TERMS: NON-LAMINAR, TURBULENT, DISORDERED, CHAOTIC)

Broadening of the velocity range in the waveform; like filling in the clear space under the systolic peak.

Note: Broadening is often seen in turbulent flow but can also occur without turbulence.

5. STACCATO

A very high resistance spectrum with a short "spike" of velocity acceleration and deceleration, followed by a short and less amplitude diastole which indicates low antegrade flow.

6. DAMPENED (OLD TERMS: PARVUS ET TARDUS, ATTENUATED, BLUNTED)

A combination of an abnormal delayed upstroke and a broad peak, often accompanied by reduced velocity.

7. FLOW REVERSAL

Flow changes its direction, not as a typical part of normal diastolic flow reversal (which may be temporary (position-related) or consistent with each cardiac cycle)

Fig 19: pan diastolic flow reversal in subclavian artery in a case of aortic insufficiency Image courtesy : Reference(4)

PHYSIOLOGIC STATE OF NORMAL PERIPHERAL ARTERIAL WAVEFORMS

At rest, the normal pattern of all peripheral arteries is multiphasic with rapid acceleration during systole, a sharp peak in systole, reversal flow during diastole, and minimal or absent flow at the end of diastole.

INFLOW ARTERIES:

Lower Extremity: Common, External, and Internal Iliac Artery

Upper Extremity: Innominate and Subclavian Artery

The spectral bandwidth is narrow throughout the cardiac cycle consistent with laminar flow.

Minimally increased spectral broadening may be seen in the internal iliac artery secondary to the size of the sample volume and the smaller vessel diameter.

OUTFLOW ARTERIES:

Lower Extremity: Common Femoral, Profunda Femoris (Deep Femoral) Superficial Femoral (SFA) and Popliteal Artery

Upper Extrimity: Axillary and Brachial Artery

There may be a slight decrease in PSV compared with the peak systolic velocities in the normal inflow arteries.

RUN -OFF ARTERIES:

Lower extremity: Anterior Tibial, Posterior Tibial, Peroneal Artery

Upper Extremity: Radial, Ulnar Artery

The spectral bandwidth in pulsed-wave Doppler stays steady with smooth flow, although there might be a slight spectral broadening seen due to the sample volume and the smaller vessel sizes. However, there's no notable difference in peak systolic velocity (PSV) among the three calf arteries or two forearm arteries.

PALMER, PLANTER & DIGITAL ARTERIES:

The flow remains laminar, but there's a small rise in the spectral bandwidth due to the size of the sample volume and the smaller diameter of the plantar and digital arteries.

CHANGES IN VASCULAR RESISTANCE WITH EXERCISE:

Situations that lead to heightened blood flow to the limb muscles, like exercising, rise in limb temperature, or having an arteriovenous fistula, achieve this by widening the arterioles in the muscle bed, enabling continuous forward flow throughout diastole.

And the Doppler waveform may show a rise in spectral broadening, influenced by the size of the arterial segment and the Doppler sample volume.

PATHOLOGIC STATE OF ABNORMAL PERIPHERAL ARTERIAL WAVEFORMS.

< 50% diameter stenosis:

Slight increase in peak systolic velocity (PSV), but it remains less than double that in the normal adjacent proximal segment (velocity ratio <2).

Multiphasic waveform is observed with a quick upstroke and no significant rise in diastolic velocity.

The spectral broadening is spread throughout the systolic phase.

Fig 21: Image courtesy : Reference(1)

50% to 74% stenosis:

Pressure-flow gradient emerges at the narrowed site.

Peak systolic velocity (PSV) increases by over 100% (velocity ratio >2) when compared to the normal adjacent proximal segment.

The early diastolic reverse flow component is mostly not seen

Thus continuous forward flow throughout diastole due to reduced vascular resistance in the distal tissue bed.

Spectral broadening is evident.

Fig 22: Image courtesy : Reference(1)

> 75% stenosis:

Severe constriction leads to a minimum 4-fold surge in peak systolic velocity (PSV),

velocity ratio surpassing 4 when compared to the normal proximal adjacent segment.

The waveform becomes monophasic, showcasing increased diastolic velocity,

often accompanied by the presence of a spectral bruit adjacent to the zero-flow baseline.

Fig 23: Image courtesy : Reference(1)

Distal to a hemodynamically significant stenosis:

The waveform exhibits a monophasic pattern characterized by an extended upstroke.

There is a decrease in peak systolic velocity (PSV).

Spectral broadening is evident.

Distal to occlusion:

monophasic and dampened waveform

Proximal to occlusion:

In cases where there is no flow-limiting stenosis

The waveform displays a rapid upstroke and there can be either high resistance or intermediate resistance.

Pseudoaneurysm:

there is bidirectional flow through the neck or tract of the sac.

The waveform demonstrates a quick systolic upstroke with pronounced deceleration, along with an elongated and prominent reverse flow component.

Arteriovenous fistula:

the movement of blood from a high-pressure artery to a low-pressure vein leads to an increase in spectral broadening and higher systolic and diastolic velocities.

Continuous forward flow is observed throughout the cardiac cycle.

Fig 26: Image courtesy : Reference(5)