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Fundamentals in Interventional Radiology

Type of images obtained in IR.

Digital Subtraction Agiography (DSA), and spot fluoro, etc.

2. Phase of contrast injection depends on timing of imaging. phases are generally classified as arterial, delayed, venous, dynamic, portal venousphase

3. Type of catheter. Flush, forward facing, reverse curve.

4. Catheter approach. Access can be obtained through the following vessels. Right or left common femoral artery, upper extremity vessels such as a radial artery approach, etc.

5. Catheter should be position at site where angiographic images are going to be obtained. For example the catheter can be placed in the celiac artery, SMA (superior mesenteric artery), aortic arch, etc. at this point images can be obtained such as “Fluoroscopic, arterial-phase image of a celiac artery injection using a forward-facing catheter through a right femoral approach.” “Digitally subtracted venogram of the IVC using a flush catheter through a right jugular approach.”

 

Vessel contrast Injection Rates

  • x mL/sec for y total volume.
  • Rule of thumb: size of vessel = x.
  • Aortic Arch 30cm 20cc/s 20-30cc (pigtail catheter)
  • Carotid (Selective) 20cm 4-6cc/s 7-9cc
  • Cerebral: AP 20cm 4-6cc/s 7-9cc
  • Cerebral: Lateral 30cm 4-6cc/s 7-9cc
  • Cerebral injections are generally done by hand. Alternate injection rates are as follows
    • (COMMON CAROTID: 8 for 10, INTERNAL CAROTID: 6 for 8, EXTERNAL CAROTID: 4 for 6, VERTEBRAL: 4 for 6, BASILAR: hand injection only through 1 cc syringe)
  • Abdominal aorta 20-40cm 16-20cc/s 16-25cc
  • Renal (Selective) 20cm 4-6cc/s (by hand) 4-6cc
  • Iliac (Selective) 20cm 6-10cc/s 8-10cc
  • Femoropopliteal-Tibial (Bolus) 30cm 4cc/s 16-20
  • SFA 30cm 4-6cc/s 10cc
  • SFA (Selective) 20—30cm 4-6cc/s 10cc
  • Below the knee (Bolus) 30cm 3cc/s 7-9cc
  • Tibial 20cm 3cc/s 5cc
  • Tibial (Selective) 20cm 1-2cc/s (by hand) 2-3cc

 

Medications used in IR

  • Heparin 5000-10,000 Units IV bolus, then 1000 units/hr, titrating PTT to 60-80 seconds.
  • NTG 50-100 mcg IV
  • tPA 1-2 mg bolus (graft/port declot or fibrin sheath) or 0.5-1.0 mg/hr continuous infusion. No longer than 48 hours total infusion.
  • Thrombin 1000 units in 1 mL, inject in 100 unit (0.1 mL) aliquots for pseudoaneurysms
  • Papaverine 30 mg bolus then 30-60 mg/hr continuous infusion
  • Vasopressin 0.2 U/min x20 minutes, increase to 0.3-0.4 U/min as needed
  • Flumazenil (for benzo reversal) = 0.2 mg IV
  • Adenosine 6 mg IV rapid push (for SVT)

 

Vessel Sizes

LARGE: aorta, pulmonary artery, subclavian arteries, common carotid arteries

MEDIUM: renal arteries, ICA (internal carotid artery), SMA (superior mesenteric artery)

SMALL: IMA (inferior mesenteric artery), tertiary and segmental branches

Renal artery= 6 mm

Common iliac artery= 10 mm

External iliac artery = 8 mm

SFA (Superficial femoral artery)= 6 mm

Popliteal artery = 5 mm

Tibial artery = 3-4 mm

 

Seldinger Technique

1. Small needle

2. Pass .018 wire

3. Exchange needle for transitional dilator

4. Switch over wire to and .035 wire and place sheath

 

Angioplasty balloons

Balloons can be compliant or noncompliant

o “Noncompliant” Balloon – inflates to a set diameter and no further.  Compliant balloons will inflate to larger diameters the more they are inflated.

o Balloon length: should span the lesion, but no more than 1 cm on either end.

o Balloon diameter: choose one that is 10% larger than the normal vessel.

 

Types of vascular Stents

(1) balloon-expandable (Palmaz®) – you have pinpoint accuracy for its deployment.

(2) self-expanding (Wallstent, Smart Stent) – flexible, so convenient for tortuous vessels but are less sure-footed as you deploy them.

Stent graft = metallic stent covered by fabric usually PTFE.

Main use for stent graft: infrarenal AAA o Zenith® stent – this is by far the most common. The proximal 2 cm portion is uncovered and should be placed SUPRArenal, over the ostia of the SMA and renal arteries for best stability.

Wires used in IR

  • Small size (for coronary arteries, etc) = 0.018” guidewire.
  • Standard size = 0.035” guidewire.
  • Bentsen – atraumatic blunt tip wire.
  • Glidewire – hydrophilic slippery.

MED STOPPAGE – rule of thumb…. All home meds should be stopped (aspirin/Plavix/Coumadin) for 1 week. Lovenox for 24 hours. Heparin overnight.

  • Aspirin/NSAID 7-14 days
  • Plavix 5 days
  • Lovenox 12-24 hours
  • Heparin <6 hrs (half-life = 1 hr)
  • Coumadin 7 days

Broad Vascular Complications

o Vessel Rupture

o Vessel Dissection

Complications in Interventional Radiology

  • For all vascular procedures, you have puncture site complications: hematoma & pseudoaneurysms.
  • For any angioplasty/stent procedure, you run the risk of vessel rupture and iatrogenic pseudoaneurysm.
  • Pseudoaneurysms management options…
  • A small PSA (<1 cm) may thrombose on its own.
  • Compression – U/S guided compression is often successful (up to 90%) for small PSA, but may be painful and occasionally time consuming
  • Thrombin – U/S guided thrombin injection may be considered when there is a distinct, narrow neck. You mix up 1000 Units thrombin in 1 cc of NS. Inject at 100-Unit aliquots. Check pre- and post-thrombin distal pulses.
  • Coil – Endovascular embolization with coils (or detachable balloons).
  • Surgery – may ultimately be required in many cases.

 

Catheter Basics

“French” size is the circumference in mm.

π * Diameter = Circumference

3-mm ≈ 9-French.

TYPE OF CATHETERS

{1) flush, (2) forward facing, (3) reverse curve

FIBRINOLYSIS/THROMBOLYSIS

INDICATIONS

Thrombosis of native vessel or vascular graft. Embolic occlusion – these may undergo IR thrombolysis.

CONTRAINDICATIONS TO THROMBOLYSIS

BRAIN: Recent stroke, brain metastasis, recent neurosurgery

ABDOMEN: Recent surgery, active GI bleed

Pregnancy

LIMB: Threatened limb……..this generally goes to surgery.

PROTOCOL FOR THROMBOLYSIS:

Dose of TPA is 1 mg/hr through an infusion catheter (multiple side holes) spanning the entire length of the clot. Treatment time is overnight. Bring the patient back at 24 hours and inject…. See if you need another 24hours of thrombolysis of if thrombus has resolved. You can continue treatment for another 24 hours.

MONITORING: Check coags q 6 hours: fibrinogen (keep > 150), PTT, INR. If fibrinogen falls < 150, then half dose of tPA. If fibrinogen falls < 100, stop infusion.

 

COMPLICATIONS OF THROMBOLYSIS

Reperfusion Syndrome = when necrotic tissue is reperfused, toxic waste is released (lactic acid and myoglobin).

Distal clot embolization

Bleeding (10% incidence)

 

EMBOLIZATION MATERIALS

Glue – occasionally used for AVM’s.

Absolute Alcohol – produces complete infarction of the target tumor or organ. It is sometimes used for renal tumor ablation, but has major problems if non-target embolization, so you use a balloon occlusion catheter to lower that risk.

Detachable Balloons – limited applications similar to coils, such as varicoceles.

PARTICULATES

Gelfoam – used for temporary occlusion, plugs vessels by soaking up fluid and blood, rapidly creating a clot, and holds for 4 weeks. Resorbs after 5-6 weeks. USES: bleeding! – for example, visceral bleeding from blunt trauma, liver/spleen lacerations, bronchial arteries.

Polyvinyl Alcohol (PVA) Spheres – permanent occlusion. One limitation is that they are not perfect spheres, so they may aggregate proximal to the target and thus fail.

Embospheres – these are perfect spheres!

Coils

Covered with wool/Dacron threads that produce the thrombotic effect.

USES: most AVM’s and AVF’s, post-biopsy renal pseudoaneurysm/AVF, GI bleeders, brain aneurysms, visceral aneurysms/pseudoaneurysms

 

TUMOR FEATURES ON ANGIO = BEDPAN

  • Blush
  • Encasement of vessels
  • Displacement of vessels
  • Puddling of contrast
  • AV or arterioportal shunting
  • Neovascularity Air Embolism
  • Trendelenburg & left lateral decubitus. (They’re not shown to work but we do it anyway.)
  • Best treatment is hyperbaric 100% O2.

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