Effects of thermal exposure on binding of heparin in vitro to the arterial wall and to clot and on the chronic angiographic luminal response to local application of a heparin film during angioplasty in an in vivo rabbit model

Angiographic observations 10 years following coronary laser balloon angioplasty

A patient underwent laser balloon angioplasty (LBA) combined with local intracoronary heparin therapy for treatment of a high grade stenosis of the mid-portion of the left anterior descending (LAD) coronary artery. Sustained patency of the LBA-treated lesion and no new coronary stenoses were found in a 10-year angiographic follow-up study.

In vivo quantitative assessment of catheter patency in rats

Formation of fibrin sleeves around catheter tips is a central factor in catheter failure during chronic implantation, and such tissue growth can occur despite administration of anticoagulants. We developed a novel method for monitoring catheter patency. This method recognizes the progressive nature of catheter occlusion, and tracks this process over time through measurement of changes in catheter resistance to a standardized 1 mL bolus infusion from a pressurized reservoir. Two indirect measures of catheter patency were used: (a) reservoir residual pressure and (b) reservoir discharge time. This method was applied to the study of catheter patency in rats comparing the effect of catheter material (silastic, polyurethane, Microrenathanetrade mark), lock solution (heparin, heparin/dexamethasone) and two different cannulation sites (superior vena cava via the external jugular vein, inferior vena cava via the femoral vein). Our findings reveal that application of flexible smaller-size silastic catheters and a dexamethasone lock solution resulted in prolonged catheter patency. Patency could be maintained over nine weeks with the femoral vein catheters, compared with five weeks with the external jugular vein catheters. The current method for measuring catheter patency provides a useful index for the assessment of tissue growth around the catheter tip. The method also provides an objective and quantitative way of comparing changes in catheter patency for different surgical methods and catheter types. Our method improves on the conventional method of assessing catheter occlusion by judging the ability to aspirate from the catheter.

Improved microvessel repair: laser welding with an anti-thrombotic solder

BACKGROUND AND OBJECTIVES

Concentrated protein solutions can be used as thermally polymerized solders in laser welding. Solders supplemented with biologically active chemicals may provide in situ drug delivery for localized therapeutics. These studies characterize a serum albumin (SA) solder containing heparin, designed to reduce microvascular thrombosis rates.

STUDY DESIGN/MATERIALS AND METHODS

Samples of heparin added to 30% SA to obtain heparin-to-albumin molar ratios (HAMR) of 4:1 and 2:1 were thermally polymerized, and heparin release into saline was measured. Using a rat thrombosis model, patency was determined for suture, and 0 U/ml (control), 2.5 U/ml, 50 U/ml heparin solder repairs.

RESULTS

Heparin release was five times higher for 4:1 than 2:1 HAMR solder acutely, but was equivalent after 2 days. Animal patency rates were: 50% suture, 0% control, 50% low heparin, 66% high heparin (P < 0.05 vs. control).

CONCLUSIONS

Solders incorporating heparin should provide in situ anti-thrombotic therapy reducing the risk of microvascular thromboses.

Laser balloon angioplasty combined with local intracoronary heparin therapy: immediate and short-term follow-up results

Laser balloon angioplasty (LBA) has been shown to acutely increase angiographic luminal dimensions after conventional balloon angioplasty (PTCA) without a favorable impact on chronic restenosis. Experimentally, laser and thermal energy enhance binding of heparin to the injured arterial wall and to the thrombus. In view of the anticoagulant, antiproliferative, and antifibrotic activities of the drug, a pilot study was performed to evaluate the potential safety and efficacy of LBA combined with local heparin therapy. Ten patients scheduled for elective PTCA were entered in the study. In each patient, a single lesion was treated with a laser balloon and coated with a heparin film (3000 I.U. at a concentration > 100,000 I.U./gm) immediately after optimal PTCA. The mean minimum luminal diameter and mean percent stenosis of the 10 treated lesions after PTCA were 1.62 +/- 0.39 mm and 37% +/- 9%, respectively. After LBA and local heparin therapy, the mean minimal lumen diameter increased to 2.01 +/- 0.34 mm (p < 0.01) and the mean percent stenosis decreased to 20% +/- 10% (p < 0.01). Systemic heparin was discontinued immediately after the procedure in all patients. Acute or inhospital complications, either major or minor, occurred in none (0%) of the 10 patients (95% confidence interval 0% to 31%); all were discharged home on the day after the procedure. All patients remained well and free of cardiac symptoms for at least 2 months after the procedure. However, restenosis developed in six (60%) of the 10 patients (95% confidence interval 26% to 88%) 2 to 6 months after the procedure. The results suggest that LBA and local heparin therapy, with discontinuation of systemic heparin immediately after angioplasty, is a safe treatment modality that yields favorable acute angiographic results.

Prevention of Restenosis by Local Drug Delivery

Local drug therapy for preventing restenosis after angioplasty has been investigated for over a decade. Biologically active agents ranging from drugs to genes can be delivered locally using a wide variety of catheters. Microspheres, liposomes, and polymers have been used to enhance drug retention at the delivery site. More recently stents have been investigated as devices to attain local drug delivery, either by coating with polymers, seeding with genetically modified cells or by using them as a source of local radiation. Though the best method of delivering agents locally remains undefined, this approach is likely to emerge as an essential mode of therapy in the near future.