Published on March 20, 2014
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 dysfunction Specially after ACEi • Erythrocytosis Found by some authors • Asymptomatic Doppler done as routine screening ACEI: Angiotensin-Converting Enzyme Inhibitors Buturovic -Ponikvar J. Nephrol Dial Transplant 2003 ; 18 : v74 – v77.
Causes of post-transplant HTN 65 - 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 stenosis Three 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 allograft Routine 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 RAS Best 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 approach Extrarenal 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 Velocity Near the anastomosis PSV = 105 cm / sec
CDUS – 2nd approach Intrarenal 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 survival 601 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 time AT • 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 stenosis End-to-end-anastomosis Stenotic anastomosis PSV: 6.54 m/s Proximal IIA PSV: 0.78 m/s Velocity ratio: 8
Severe transplant renal artery stenosis End-to-side-anastomosis PSV: 3.74 m/s Stenotic anastomosis PSV: Proximal 1.29 m/s Anastomosis 1.77 m/s Distal 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 broadening Post-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 TRAS Retrospective – 38 patients – severe TRAS End-to-End (n = 19) End-to-Side (n = 19) P value PSV at stenosis PSV proximal to stenosis PSV ratio 4.62 ± 0.64 0.66 ± 0.19 7.61 ± 2.52 3.65 ± 1.33 1.18 ± 0.41 3.25 ± 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 placement No 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?)
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