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WAVEFORMS
WAVEFORMS
Three components to carotid artery exam:
Plaque morphology
Hemodynamic evaluation
Waveform analysis
Bilateral extracranial cerebral vessels include CC, EC, IC and vertebral arteries.
Inflow depends on Ao valve, Ao arch, brachiocephalic, and subclavian arteries. When normal, waveform reflects the resistance of the distal vascular bed.
Outflow depends on status of basal cerebral arteries (CoW) and rest of intracranial cerebral circulation.
PLAQUE MORPHOLOGY
Evaluated on grayscale w/o Doppler and described in terms of absolute percent stenosis
<50%: no hemodynamic significant
>50%: luminal plaque expected to show increased PSV
Morphology:
Residual lumen: concentric, eccentric, irregular
Echogenicity: uniformly echolucent, predominantly echolucent (>50% plaque), predominantly echogenic (>50% of plaque), uniformly echogenic
+/- ulceration
HEMODYNAMICS
Normal PSV in large arteries is 60-100 cm/sec
<125 cm/s normal
>125 cm/sec ~>50% stenosis
>230 cm/sec ~>70% stenosis
Occluded or nearly occluded artery can have no detectable flow
End diastolic velocity >100 cm/sec suggests >70% stenosis
PSVR ratio (ICA stenosis: normal distal CCA) is more useful than absolute PSV in high and low flow states (poor cardiac function or tandem stenosis underestimates, crossover collateralization in contralateral arteries overestimates).
<2 normal
>2 suggests >50% ICA stenosis
>4 suggests >70% ICA stenosis
WAVEFORM ANALYSIS
Normal flow:
Rapid systolic upstroke, reflecting normal prox vessels and cardiac function
Diastolic portion is determined by resistance of distal vascular bed.
Waveform changes can occur w/ proximal occlusive lesions, focal lesions in specific arterial segments and changes in the resistance of the distal vascular bed.
Brain tissue normally has a low vascular resistance, a normal ICA waveform shows a low resistive pattern with relatively high diastolic velocities and forward flow throughout the cardiac cycle. In contrast, the EC supplies a high resistive vascular bed (skin, mm, bone) similar to that of peripheral arteries
Parvus tardus waveforms: diminished and delayed arterial pulsations characterized by increased systolic acceleration time (longer intervals b/n the bringing of systolic upstroke and the systolic peak. Observed distal to locations of severe stenosis.
COMMON CAROTID ARTERY
COMMON CAROTID ARTERY
NORMAL
AORTIC VALVE / CARDIAC DISEASE
AoV STENOSIS
Bilateral parvus tardus waveforms seen throughout the carotid and vertebral arteries
Ao REGURGITATION
Pulsus bisferiens: two prominent systolic peaks w an interposed mid-systolic retraction.
First sytolic peak may represent initial high volume ejection of blood followed by abrupt midsystolic flow deceleration caused by the regurgitant valve; second peak may be related to relaxation of the distended aorta.
AVS & REGURG
DEVICES
Monophasic parvus tardus waveforms w slow systolic upstroke and rounded systolic peak (thought to be 2/2 intrinsic residual myocardial reserve pumping some of the blood.
Constant antegrade flow w no flow reversal
Reduced PSVs. Be cautious in pts w LVAD as they may have carotid stenosis w/o elevated PSV
IABP alters doppler waveforms due to sequential inflation and deflation of balloon which can lead to over/underestimation of true flow velocities.
A second peak of forward flow during systole corresponds to balloon inflation.
Transient reversal of flow corresponds to balloon deflation at end of diastole immediately preceding the next hearbeat.
INTERNAL CAROTID ARTERY
INTERNAL CAROTID ARTERY
NORMAL
ABNORMAL
EXTERNAL CAROTID ARTERY (ECA)
EXTERNAL CAROTID ARTERY (ECA)
NORMAL
ABNORMAL
VERTEBRAL ARTERY (VA)
VERTEBRAL ARTERY (VA)
SUBCLAVIAN STEAL SYNDROME
VA provides collateral BF to upper extremity bc of vascular blockage 2/2 stenosis/occlusion of prox subclavian or brachiocephalic artery.
Leads to reverse flow in VA to perfuse SCA distal to stenosis/occlusion
Exacerbated by demand for increased arterial BF in affected arm.
SCA obstruction is most likely 2/2 atherosclerosis tho must exclude vasculitis, dissection, adjacent neoplasm.
Findings:
Normal waveform of one VA w signal systolic peak followed by a diastolic component.
Contralateral VA demonstrates 2 systolic peaks: Initial systolic peak followed by sharp deceleration and second systolic peak (bunny rabbit sign)
Evocation maneuvers can be performed to accentuate steal
BP cuff inflated: minimal restoration toward normal waveform
Sudden BP cuff deflation: accentuation of steal w/ flow reversal during mid systole.
Subclavian steal is likely if cerebral sx are exacerbated w arm exercise.
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