pva: don't forget about me

Polyvinyl Alcohol:

Don’t Forget About Me!

Keigo Osuga, MD, PhD

Department of Diagnostic and Interventional Radiology,

Osaka University Graduate School of Medicine

Keigo Osuga, M.D., Ph.D.

• No relevant financial relationship reported

Drying towel

PVA Products in Our Life

Cleaning sponges

Textile fiber

Synthetic polymer

Biocompatible

Chemical resistant

Elastic and tensile

Water-soluble

Glue

Chemical Structure

Acetate group (Hydrophobic)

Hydroxyl group (Hydrophilic)

• n+m = Degree of polymelization

• n/n+m = Degree of saponification

PVA is obtained by first polymerizing vinyl acetate, and

second by saponification of polyvinyl acetate.

The extent of hydroxylation determines the physical,

chemical and mechanical properties of PVA.

Formalized PVA

Most PVA embolic particles undergo formalization to bridge

between hydroxyl groups to give insolubility, and can be used

as a permanent embolic material.

Contour® PVA, Contour SE™, Cook Medical® PVA

PVA for Medical Applications

Non-implant devices

Surgical sponges

Soft contact lenses

Eye drops

Implantable devices

Artificial cartilage

Patch grafts in cardiac surgery

Skin grafts in burns

Embolic agents

Early History of PVA as Embolic

Compressed PVA plug as a closure of PDAPorstmann W, et al. Radiol Clin North Am 1971

Early History of PVA as Embolic

Compressed PVA plug as a closure of PDAPorstmann W, et al. Radiol Clin North Am 1971

Compressed PVA sponge for postsurgical pelvic

bleeding, vascular tumors and spinal AVMTadavarthy SM, et al. Radiology 1974

Tadavarthy SM, et al. AJR 1975

PVA plug in pre-loaded polyethylene tubes for gas sterilization

Early History of PVA as Embolic

Compressed PVA plug as a closure of PDAPorstmann W, et al. Radiol Clin North Am 1971

Compressed PVA sponge for postsurgical pelvic

bleeding, vascular tumors and spinal AVMTadavarthy SM, et al. Radiology 1974

Tadavarthy SM, et al. AJR 1975

PVA shavings for hypervascular tumors and AVMsHerrera M, et al. Radiology 1982

Rotating rasp to prepare shavings from PVA block

Vibrating sieve for separating shavings into different sizes

Non-spherical PVA Products

Ready-to-use dry particles

Contained in a sterilized vial

Color-coded vials according to size (50-1,200 μm)

PVA

Bearing nsPVA

Contour

A PVA Particle in Microscope

Derdeyn,CP et al. AJNR 1995;16:1335–43

Dry In contrast

Irregular shape Size increases in contrast by 20-40% Rarely, small fragments <50 μm Long & short axis diameter in best-fitting ellipse

Inhomogeneous in size distribution

Calibration improved in the newer product

PVA: Size Distribution

Newer 71%

Older 51%Newer

Older

Newer 72%

Older 38%

www.merit.com

355-500 μm 500-710 μm

PVA: Microcatheter Compatibility

<500 μm

<700 μm

0.027 inch ID

0.021 inch ID

Microcatheter passage <700 μm

PVA: Preparation & Injection

Preparation

Suspension in contrast media for radio-opacity

Albumin, dextran, or ethanol helps decreasing clumping

Injection techniques:

Flow-directed technique

Fluoroscopic guidance

Frequent catheter flushing to avoid its occlusion

Endpoint:

- Slowing of the antegrade flow

- Occlusion faster than expected due to clumping

Irregular shaped particles aggregate and adhere to the

vessel wall ---> blood flow stagnation

Vessel occlusion completed with thrombus among particles.

Recanalization may occur due to resorption of the thrombi

and/or angiogenesis inside the organized thrombus

PVA foam® 180-300 μm

Rabbit kidney 1w (EVx100)

PVA: Mechanism of Action

Preoperative embolization for meningioma

Hemoptysis

TACE/TAE for liver tumors

UFE or post-partum hemorrhage

GI bleeding

Prostate embolization for BPH

etc.

Today, overtaken by microspheres…

PVA: Clinical Applications

Spies JB, et al. JVIR 2004; 15:793-800

PVA vs. Microspheres

Advantages:

Less particle volume

Less contrast volume

Less procedure time (radiation exposure)

Less cost

Disadvantages:

Harder to inject through a microcatheter

Proximal aggregation -- unpredictable occlusion level

PVA vs. Microsphere:

Microcatheter Passage

PVA 355-500 μm Microsphere 400 μm

Aggregation in the hub

PVA(S) 45-150 μm (n=15)

PVA(L) 150-250 μm (n=15)

TGMs 150-300 μm (n=30)

Efficacy of trisacryl gelatin microspheres versus polyvinyl

alcohol particles in the preoperative embolization of

meningiomas.Bendszus M, et al. AJNR2000;21:255-261

PVA vs. Microspheres: Meningioma

• Interval to surgery 6-7 days

TGMs significantly reduced blood loss(mL) at surgery

- PVA mean 886 or 917 vs. TGMS 621 (p<0.05)

TGMs occluded more distal vessels, and induced more

extensive tumor necrosis.

TGMs 500-900 @ “limited” endpoint (n=54)

PVA 355-710 @ “near-stasis” endpoint (n=46)

PVA smaller volume (3.0mL vs. 9.4mL, p=0.0001)

PVA more catheter occlusion (28% vs. 4%, p=0.001)

No difference in VAS pain score (3.1 vs. 3.0, p=0.87)

No difference in fibroid infarction (76% vs. 77%, p=0.89),

symptom relief, patient satisfaction, complications

Spies JB, et al. JVIR 2004; 15:793-800

Polyvinyl alcohol particles and tris-acryl gelatin microspheres

for uterine artery embolization for leiomyomas: Results of

randomized comparative study.Spies JB, et al. JVIR2004; 15:793-800

PVA is as safe and effective as

microspheres in clinical and imaging

outcomes.

PVA vs. Microspheres: UAE

PVA: Conclusion

Safety and effects proven in long-history >40 years

Drawbacks from irregular size/shape

Use diminished by prevalence of microspheres with

deeper penetration

In most regular practice, PVA still contributes to

achieve faster procedure with lower cost.

(Like gelatin sponge in Japan…)

Thank you for your kind attention!

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