Doppler in transplant renal artery stenosis

Dr. Muhammad Bin Zulfiqar PGR FCPS SHL

Christian Doppler (1803 – 1853) Famous for what is called now “Doppler effect”

1841: Professor of mathematics & physics

Prague polytechnic

1842: Published his famous book

“ On the colored light of the binary stars

& some other stars of the heavens ”

1850: Head of institute of experimental physics

Vienna University

First reported case of transplant renal artery stenosis

Case records of the Massachusetts General Hospital

Case 43 – 1966. N Engl J Med 1966;275:721–729.

Transplant renal artery stenosis

• Potentially curable cause of refractory HTN

• 75% of all post-transplant vascular complications

• Incidence varies upon definition & diagnostic techniques

12% Routine Doppler in asymptomatic recipients

2% Doppler to confirm clinical suspicion

• Timing Can present at any time

Usually 3 mo – 2 yr after transplantation

Bruno S et al. J Am Soc Nephrol 2004 ; 15 : 134 – 141.

Clinical presentation of TRAS

• Severe HTN Difficult to treat

• Vascular murmur Not specific

• Graft dysfunctionSpecially after ACEi

• Erythrocytosis Found by some authors

• Asymptomatic Doppler done as routine screening

ACEI: Angiotensin-Converting Enzyme InhibitorsButurovic´-Ponikvar J. Nephrol Dial Transplant 2003 ; 18 : v74 – v77.

Causes of post-transplant HTN65 - 90% of patients

• Calcineurin inhibitors Cyclosporine - Tacrolimus

• Corticosteroids Largely depends on dosage

• Transplant RAS 2 – 10 %

• Post-biopsy AVF Rare cause

• Chronic graft rejection

• Native kidneys & pre-transplant HTN

Ponticelli C. Medical complications of kidney transplantation.Informa Healthcare, London, UK, 2007.

Locations for graft artery stenosisThree 3 main locations

• At the site of anastomosis

Probably a consequence of surgical technique

• Distal from the site of anastomosis

Cause is still ill-defined

• At the distal arterial branches

Multiple stenoses – Expression of chronic rejection

Diagnostic procedures of TRAS

Procedures Performance

Plasma renin activity Less informative than unilateral RAS of native kidneys

Serum potassium Normal or in patients on Cyc, tacrolimus or RI

Renal scintigraphy Good sensitivity 75% – Poor specificity 67%

CDUS Good sensitivity (87-94%) – Good specificity (86-100%)

Spiral or MSCT Contrast medium – High cost – Limited accessibility

MRI Gadolinium – High cost – More limited accessibility

Arteriography Gold standard test – Invasive – Contrast medium

Bruno S et al. J Am Soc Nephrol 2004 ;15 : 134 – 141.

Sonography of renal allograftRoutine exams

• 1 – 2 days after transplantation

Important standard to be compared with later changes

• 1 – 2 weeks after transplantation

• 3 months after transplantation

CDUS in transplant RASBest screening tool

• Main advantages Non-invasive

High sensitivity & specificity

Performed at bedside (ICU)

Follow-up• Main disadvantages Operator dependency

Time-consuming

Operator should consult the surgery report

Multiple arteries – Anastomotic problems

End-to-end arterial anastomosis

Artery

End-to-end anastomosis

to internal iliac artery

Vein

End-to-side anastomosis

to external iliac vein

Classical kidney transplantation surgery

Possibility of erectile dysfunction & TRAS

End-to-side arterial anastomosis

Artery

End-to-side anastomosis

to external iliac artery

Vein

End-to-side anastomosis

to external iliac vein

Possibilty of early obstruction, late stenosis

& steal phenomenon

Normal renal transplant End-to-side arterial anastomosis

Gaoa J et al. Clinical Imaging 2009 ; 33 : 116 – 122.

CDUS – 1st approachExtrarenal Doppler

• Scanning of RA from anastomosis to hilus

Pic Systolic Velocity around anastomosis

• Diagnosis severity of stenosis

• Diagnosis non-significant relative stenosis

• Possibility of localization

• High operator dependency

Normal Pic Systolic VelocityNear the anastomosis

PSV = 105 cm / sec

CDUS – 2nd approachIntrarenal Doppler

• Interlobar arteries (upper, middle, & lower poles)

Resistance index & Acceleration Time

• Can be amplified by use of captopril

• Not so operator dependent

• Only diagnose high grade stenosis (> 80 %)

• No possibility to localize stenosis along TRA

Resistance index or Pourcelot index

RI: S – ED / S

Normal: 50 – 70%

Abnormal: > 80 %

Normal resistance index

RI: 62%

RI & renal allograft survival601 patients – Follow-up 3 years

Radermacher J et al. N Engl J Med 2003 ; 349 : 115 – 24.

RI > 0.8 measured 3 months posttransplantation

has poor subsequent graft function & death

Accleration timeAT

• Length of time in seconds from

onset of systole to peak systole

• Normal value: < 0.07 second

Normal accleration time

AT: 0.05 sec

CDUS

Combined approach

Combine both extra- & intrarenal Doppler

examination as is suggested for native renal

artery stenosis

Doppler of transplant RAS

Clerbaux G et al. Nephrol Dial Transplant 2003 ; 18 : 1401 – 1404.

Extra-renal Doppler

• PSV > 2 m/sec *

• Velocity gradient > 2

• Distal spectral broadening

* Generally accepted criteria

Values differs from 1.5–3m/sec

Intra-renal Doppler

• RI < 0.50

• AT > 0.07 sec

• AI < 3m/sec2

Only in severe stenosis

(> 80 % diameter reduction)

Severe transplant renal artery stenosisEnd-to-end-anastomosis

Stenotic anastomosis

PSV: 6.54 m/s

Proximal IIA

PSV: 0.78 m/s

Velocity ratio: 8

Severe transplant renal artery stenosisEnd-to-side-anastomosis

PSV: 3.74 m/s

Stenotic anastomosis

PSV: Proximal 1.29 m/sAnastomosis 1.77 m/sDistal 1.35 m/s

EIA

Velocity ratio: 2.3

PSV threshold for action

• 2.5 m/sec used by many centers

• One report use the value of 3 m/sec*

• Diagnosis of sub-clinical arterial stenosis may be

of no significance

• No evidence these lesions progress to clinical significance

* Patel U. Clinical Radiology 2003 ; 58 : 772 – 777.

Spectral broadeningPost-stenotic zone

• Proportional to severity of stenosis

• Cannot be precisely quantified: evaluated visually

• Fill-in of spectral window > 50% reduction

• Severely disturbed flow > 70% reduction

High amplitude

Low frequency Doppler signal

Flow reversal

Poor definition of spectral border

Spectral broadening

PSV = 5 m/sec

Pseudospectral broadening

• High gain setting

• Vessel wall motion

• Site of branching

• Abrupt change in vessel diameter

• Increase velocity: Athletes - high cardiac output - AVF

• Tortuous vessels

• Aneurysm, dissection, & FMD

‘Tardus-Parvus’ pattern

Intrarenal Doppler

Only severe stenosis (> 80%)

Decrease of PSV

Loss of early systolic peak

Prolongation of AT

Doppler of transplant RAS

Extrarenal Doppler Intrarenal Doppler

PSV > 2.5 m/sec * RI < 0.50

Velocity gradient > 2 AT > 0.07 sec

Marked distal spectral broadening AI < 3m/sec2

* Generally accepted criterion for diagnosis

Cut-off value differs from series to series (1.5 – 3.0 m/sec)

Nephrol Dial Transplant 2003 ; 18 : 1401 – 1404.

Doppler parameters between EE & ES TRASRetrospective – 38 patients – severe TRAS

End-to-End(n = 19)

End-to-Side(n = 19)

P value

PSV at stenosisPSV proximal to stenosisPSV ratio

4.62 ± 0.640.66 ± 0.197.61 ± 2.52

3.65 ± 1.331.18 ± 0.413.25 ± 1.37

< 0.01< 0.001< 0.001

AT in intrarenal artery 0.11 ± 0.04 0.12 ± 0.05 > 0.05

Gaoa J et al. Clinical Imaging 2009 ; 33 :116 – 122.

Different criteria need to be established depending

on type of arterial anastomosis in severe TRAS

Special forms of TRAS

• Intimal dissection of TRA

• Kinking of TRA

• Pseudo-TRAS

Intimal dissection of TRA

Rarely documented in literature

• Timing Within a week after transplantation

• Causes Artery traction: harvesting, cannulation, clamp

• Symptom Sudden onset of oligoanuria

• CDUS Severe perfusion failure - Flap not visualized

• Dx Angiography

• DD Acute rejection: rare in first few days

ATN - Cyclosporine toxicity - RV thrombosis

• Prognosis If not diagnosed: RA thrombosis - Graft loss

Takahashi M et al. AJR 2003;180:759 – 763.

Intimal dissection of TRA

Takahashi M et al. AJR 2003;180:759 – 763.

Severe TRA stricture Occlusion of IIA

Atherosclerosis of CIA

Angioplasty 1st stent placement

Remaining intimal flap

2nd stent placementNo residual stenosis

Kinking of transplant renal artery

Artery longer than vein

• Simulates hemodynamic & functional changes of TRAS

• Occasionally occurs when right kidney transplanted

RRA longer than RRV

Kinking of artery when anastomosis completed

Subsequent surgical revision if not recognized at surgery

Gray DW. Transplant Rev1994 ; 8 : 15 – 21.

Kinking of renal artery False-positive result of CDUS

Patel U et al. Clin Radiol 2003 ; 58 : 772 – 777.

Kink at anastomosis between TRA & IIAPSV 286 cm/s

Pseudo-TRAS

Should always be taken into consideration

• Iliac artery disease proximal to the anastomosis

Elderly patients or diabetic patients

• Low flow to transplanted kidney

• Signs & symptoms resembling those of TRAS

• Claudication or other signs of limbs hypoperfusion

• Treated by angioplasty or surgical revascularization

Aslam S et al. Transplantation 2001 ; 71 : 814 – 817.

Conclusion CDUS & TRAS

• CDUS is best screening tool for diagnosis of TRAS

• Need more precision in PSV for diagnosis of TRAS

• Need different criteria for diagnosis in EE or ES

• CDUS cannot diagnose intimal dissection

• CDUS cannot diagnose kinking

• Angiography remains the gold standard (MSCT?)

Thank You