What is the significance of monophasic waveforms in the subclavian and ulnar arteries?

Monophasic Waveforms in Subclavian and Ulnar Arteries: Diagnostic Significance

Monophasic waveforms detected in the right ulnar, left proximal, and mid subclavian arteries indicate significant arterial stenosis or obstruction proximal to the site of measurement, requiring urgent vascular imaging to identify the location and severity of occlusive disease. 1

Understanding Monophasic Waveforms

Monophasic waveforms represent a pathologic dampening of normal arterial flow patterns and serve as a critical indirect marker of upstream obstruction:

• Normal arterial waveforms are triphasic or biphasic, reflecting the pulsatile nature of arterial flow with distinct systolic forward flow, early diastolic flow reversal, and late diastolic forward flow 1

• Monophasic waveforms appear as continuous, flattened flow patterns without the normal phasic variations, indicating hemodynamically significant stenosis (typically ≥50-70%) proximal to the measurement site 1

• In subclavian arteries specifically, the 2024 ESC Guidelines state that monophasic post-stenotic waveforms detected by duplex ultrasound indicate significant subclavian stenosis, with 50% stenosis corresponding to peak systolic velocity ≥230 cm/s and 70% stenosis to PSV ≥340 cm/s 1

Clinical Implications by Location

Subclavian Artery Involvement

Your finding of monophasic waveforms in the left proximal and mid subclavian artery suggests:

• Proximal subclavian stenosis or occlusion, most commonly atherosclerotic in origin 1

• Risk of subclavian steal syndrome, where >90% of patients with at least 50% proximal subclavian stenosis demonstrate vertebral artery flow reversal, though not all become symptomatic 1

• Potential for neurological symptoms including visual disturbances, syncope, ataxia, vertigo, dysphasia, dysarthria, and facial sensory deficits during arm movements 1

• Upper extremity claudication, exercise-induced fatigue, and in severe cases with distal disease involvement, rest pain and digital ischemia with necrosis 1

Ulnar Artery Involvement

The right ulnar artery monophasic waveform indicates:

• Proximal obstruction in the subclavian, axillary, or brachial arteries affecting downstream flow to the ulnar artery 1

• Potential for hand ischemia, particularly if combined with radial artery disease, as the hand depends on dual arterial supply through the palmar arches 1

Diagnostic Algorithm

Immediate next steps should follow this sequence:

1. Bilateral arm blood pressure measurement is mandatory for all patients with suspected peripheral arterial disease, as recommended by ESC Guidelines (Class I, Level B) 1

   • An inter-arm systolic blood pressure difference >10-15 mmHg suggests subclavian stenosis 1
   • A difference >25 mmHg doubles the prevalence and independently predicts mortality 1

2. Complete duplex ultrasound assessment should evaluate:

   • Peak systolic velocities and velocity ratios at stenotic sites 1
   • Vertebral artery flow direction (assess for flow reversal indicating subclavian steal) 1
   • Hyperemia testing if subclavian steal syndrome is suspected 1

3. Advanced vascular imaging with CT angiography or MR angiography of the aortic arch and upper extremity vessels to:

   • Define the exact location and severity of stenoses 1
   • Identify the underlying etiology (atherosclerosis, Takayasu arteritis, giant cell arteritis, fibromuscular dysplasia, or radiation-induced arteriopathy) 1
   • Plan revascularization strategy if indicated 1

Treatment Considerations

Revascularization should be considered (Class IIa, Level B) in symptomatic patients with:

• TIA/stroke related to subclavian disease 1
• Coronary subclavian steal syndrome 1
• Ipsilateral hemodialysis access dysfunction 1
• Severe upper extremity ischemia 1
• Planned coronary artery bypass grafting using the ipsilateral internal mammary artery (Class IIa, Level C) 1

Endovascular revascularization may be considered over surgery (Class IIb, Level B) due to lower complication rates, despite similar long-term outcomes 1

Routine revascularization in asymptomatic patients is not recommended (Class III, Level C), as many patients with high-grade stenosis and mild claudication become asymptomatic as collateral circulation develops 1

Critical Pitfalls to Avoid

• Do not assume monophasic waveforms are benign - they always indicate hemodynamically significant proximal disease requiring investigation 1, 2

• Do not rely solely on pulse palpation - palpable pulses may be present despite significant ischemia, particularly in patients with good collateral circulation 1

• Do not miss bilateral disease - blood pressure measurements may appear symmetrical when bilateral subclavian disease or aortic arch syndrome compromises perfusion of both upper limbs equally 1

• Assess for vertebral artery involvement - the combination of subclavian stenosis with vertebral flow reversal significantly increases stroke risk, particularly if the dominant vertebral artery is affected 1

Cardiovascular Risk Stratification

All patients with upper extremity arterial disease require aggressive cardiovascular risk modification, as subclavian stenosis prevalence is 11.4% in patients with peripheral arterial disease and indicates systemic atherosclerosis 1

• Dual antiplatelet therapy should be initiated if revascularization is planned 1
• Statin therapy, blood pressure control, and smoking cessation are essential 1
• Follow-up is required to ensure optimal cardiovascular prevention and early detection of procedural failure after revascularization 1