Passive and active polymer coatings for intracoronary stents: novel devices to promote arterial healing

Coronary stent implantation is the second great advance in the treatment of obstructive coronary artery disease since the introduction of balloon catheter angioplasty. However, in-stent restenosis (ISR) caused by neointimal hyperplasia has been a major limitation of stents, occurring in up to 30% of cases. Advances in coronary stent technology both in terms of stent design and function and especially drug-eluting stents (DES) have significantly improved the safety and efficacy of percutaneous coronary intervention (PCI) with stenting, including marked reduction in ISR. This has led to use of DES for increasingly challenging clinical and lesional subsets, with potential for increased risk of stent-associated complications, especially late stent thrombosis (LST). Because restenosis and stent thrombosis are caused by multiple and often interrelated factors, ideal agents for stent coatings should inhibit thrombus formation, inflammatory reaction, and cellular proliferation, while supporting reendothelialization. To avoid undesirable effects of currently applied (durable) polymers, biocompatible, and bioabsorbable polymers as well as DES delivery systems that minimize polymer burden have been produced and tested. Bioabsorbable stents, both polymeric and metallic, have been developed to decrease potential late complications after stent implantation. Novel strategies to address some of these challenges are in various stages of research and development. In this article we outline developments in the field of passive and active stent coatings and evaluate the ongoing role of such coatings in the contemporary era of DES.

Impact of the definition utilized on the rate of contrast-induced nephropathy in percutaneous coronary intervention

Several definitions have been used to assess rates of contrast-induced nephropathy (CIN) in patients undergoing percutaneous coronary intervention (PCI). Whether the definition influences observed rates of CIN is unclear. The Oxilan Registry was the first-ever prospective analysis of the efficacy and safety of ioxilan (low-osmolar and low-viscosity contrast medium), including rates of CIN assessed by multiple definitions, in PCI. From July 2006 to June 2007, consecutive patients undergoing PCI using ioxilan were enrolled. Serum creatinine (SCr) and estimated glomerular filtration rate (eGFR) were assessed at baseline and 3 to 5 days after PCI. CIN was defined as SCr increase >or=0.5 mg/dl, eGFR decrease >or=25%, SCr increase >or=25%, or the composite. Of 400 patients (age 62 +/- 11 years), 19% were women, 37% were diabetic, 22% were anemic, and 8% had a history of congestive heart failure. Baseline SCr was 1.12 +/- 0.3 mg/dl and 24% had an eGFR <60 ml/min. CIN rates were 3.3% (SCr increase >or=0.5 mg/dl), 7.6% (eGFR decrease >or=25%), 10.2% (SCr increase >or=25%), and 10.5% (composite). Hospitalization was prolonged in 3.4% of patients with CIN and none required dialysis. There were no deaths or severe allergic reactions. Non-ST-elevation myocardial infarction and repeat revascularization each occurred in 0.8%. In conclusion, in this unselected population undergoing PCI, CIN ranged in frequency from 3.3% to 10.5% depending on the definition used and was not associated with in-hospital mortality or substantial morbidity, such as dialysis. The wide variation in CIN and its lack of association with adverse outcomes underscore the need for a standardized, clinically relevant definition.

Abnormal vasomotor function of porcine coronary arteries distal to sirolimus-eluting stents

OBJECTIVES

This study sought to determine vasomotor functional responses of conduit coronary artery distal to bare-metal stents (BMS), polymer-only stents (POLY), and sirolimus-eluting stents (SES) in a clinically relevant animal model.

BACKGROUND

Drug-eluting stents (DES) reduce in-stent restenosis, and also affect neointima formation and vascular remodeling in downstream coronary segments. Whether distal artery vasomotor function is also influenced by DES has not been determined.

METHODS

Pigs (n = 12) received coronary stent implants, and hearts were harvested at 1 month. Arterial segments >or=15 mm distal to stents were excised and studied in an organ-chamber apparatus. Endothelium-dependent and endothelium-independent relaxation and contraction to classical agonists were measured.

RESULTS

The SES showed increased lumen area and reduced neointima; abnormal vasomotor function of conduit arteries distal to SES also was observed. Contraction to endothelin-1 was significantly enhanced for SES compared with both BMS and POLY. Endothelium-dependent relaxation to a maximal dose of substance P was attenuated for SES compared with both BMS and POLY (46 +/- 6% vs. 71 +/- 3% and 78 +/- 3%, respectively, p < 0.001). Endothelium-independent relaxation to sodium nitroprusside was potentiated for SES, compared with BMS and POLY (100 +/- 5% vs. 69 +/- 7% and 77 +/- 5%, respectively, p = 0.02).

CONCLUSIONS

Stent-based local delivery of sirolimus profoundly inhibited neointima formation but caused vasomotor dysfunction in distal conduit vessel segments. These observations suggest that distal coronary vasospasm may be more readily evoked in the presence of DES and contribute to pathophysiological sequela.

Local gene transfer and expression following intramuscular administration of FGF-1 plasmid DNA in patients with critical limb ischemia

NV1FGF is an expression plasmid encoding sp.FGF-1(21-154) currently under investigation for therapeutic angiogenesis in clinical trials. NV1FGF plasmid distribution and transgene expression following intramuscular (IM) injection in patients is unknown. The study involved six patients with chronic critical limb ischemia (CLI) planned to undergo amputation. A total dose of 0.5, 2, or 4 mg NV1FGF was administered as eight IM injections (0.006, 0.25, or 0.5 mg per injection) 3-5 days before amputation. Injected sites (30 cm(3)) were divided into equally sized smaller pieces to assess spatial distribution of NV1FGF sequences (PCR), NV1FGF mRNA (reverse transcriptase-PCR), and fibroblast growth factor-1 (FGF-1)-expressing cells (immunohistochemistry). Data indicated gene expression at all doses. The distribution area was within 5-12 cm for NV1FGF sequences containing the expression cassette, up to 5 cm for NV1FGF mRNA, and up to 3 cm for FGF-1-expressing myofibers. All FGF receptors were detected indicating robust potential for bioactivity after NV1FGF gene transfer. Circulating levels of NV1FGF sequences were shown to decrease within days after injection. Data support demonstration of plasmid-mediated gene transfer and expression in muscles from patients with CLI. FGF-1 expression was shown to be limited to injection sites, which supports the concept of multiple-site injection for therapeutic use.

Comparison of the clinical characteristics of apical and non-apical variants of "broken heart" (takotsubo) syndrome in the United States

OBJECTIVES

The present study was designed to delineate and compare the clinical characteristics of patients with apical and non-apical takotsubo syndrome in a high-volume U.S. hospital.

BACKGROUND

A comparison between apical and non-apical variants of the "broken heart," or takotsubo syndrome, has not been performed in the United States.

METHODS

From 2004 through 2007, patients with takotsubo syndrome were identified according to the following criteria: acute chest pain with electrocardiographic changes or elevation of cardiac enzymes, absence of significant coronary narrowing, left ventricular (LV) segmental akinesia ("ballooning"), with or without antecedent stressful events. Based upon the location of LV ballooning, the patients were divided into two subgroups: apical and non-apical.

RESULTS

Of 38 patients (age 64 +/- 12 years) fulfilling the inclusion criteria, 84% were women, 79% had documented stressors, 76% had apical and 24% non-apical LV ballooning. When compared to non-apical subjects, apical patients presented predominantly with ST-elevation, had a higher incidence of hypertension, had significantly higher levels of Troponin T (8.5 +/- 6.7 ng/ml vs. 3.4 +/- 2.1 ng/ml, respectively; p = 0.032), and lower ejection fraction (31 +/- 9% vs. 43 +/- 5%, respectively; p < 0.001). Severe complications occurred only in apical subjects: pulmonary edema (10.3%), ventricular tachycardia (6.9%), cardiogenic shock (6.9%), LV apical thrombus (3.4%), transient LV outflow tract obstruction (3.4%), and death (3.4%).

CONCLUSIONS

Apical and non-apical ballooning subgroups may represent different manifestations of a single syndrome. When compared with non-apical ballooning, the apical ballooning group may represent a more severe subset characterized by more heart failure and an increased rate of cardiac complications.

Exercise-induced myocardial ischemia detected by cardiopulmonary exercise testing

Cardiopulmonary exercise testing (CPET) is a well-accepted physiologic evaluation technique in patients diagnosed with heart failure and in patients presenting with unexplained dyspnea on exertion. Several variables obtained during CPET, including oxygen consumption relative to heart rate and work rate provide consistent, quantitative patterns of abnormal physiologic responses to graded exercise when left ventricular dysfunction is caused by myocardial ischemia. This concept report describes both the methodology and clinical application of CPET associated with myocardial ischemia. Initial evidence indicates left ventricular dysfunction induced by myocardial ischemia may be accurately detected by an abnormal CPET response. CPET testing may complement current noninvasive testing modalities that elicit inducible ischemia. It provides a physiologic quantification of the work rate, heart rate, and O(2) uptake at which myocardial ischemia develops. In conclusion, adding CPET with gas exchange measurements is likely to be of value in diagnosing and quantifying both overt and occult myocardial ischemia and its reversibility with treatment.

Ambulatory discharge after transradial coronary intervention: Preliminary US single-center experience (Same-day TransRadial Intervention and Discharge Evaluation, the STRIDE Study)

BACKGROUND

Although the safety and cost-effectiveness of same-day discharge after uncomplicated transradial percutaneous coronary intervention (TR-PCI) is well established in Europe and Asia, such data are not available for US patients.

METHODS

All patients who underwent TR-PCI at our high-volume US medical center between 2004 and 2007 were included in this study. The primary end point was in-hospital adverse clinical outcomes between 6 and 24 hours postprocedure.

RESULTS

A total of 450 patients were included in this study (aged 59 +/- 11 years). Of these, 13% were female, 27% were diabetic, 6% had peripheral vascular disease, and 5% had chronic kidney disease. Procedural indications included stable angina (49%), unstable angina (31%), non-ST elevation myocardial infarction (NSTEMI) (17%), and ST elevation myocardial infarction (STEMI) (3%). All patients received an intra-arterial cocktail of heparin, verapamil, and nitroglycerin, and 13% of patients received glycoprotein IIb/IIIa inhibitors. Seven percent of patients had 3-vessel disease, 3% had bypass grafts stenoses, and 20% had class B(2)/C lesions. Procedural success rate was 96%. A total of 24 (5.3%) postprocedural complications were observed; however, none occurred between hours 6 to 24, the time differential between same-day and next-day discharge. Thirteen patients (2.9%) experienced significant complications within the first 6 hours (MI, urgent repeat revascularization, and ventricular tachycardia). Eleven (2.4%) spontaneously resolved minor access complications developed. There were 12 same-day discharges according to the operators' discretion; none required readmission.

CONCLUSIONS

Although a low incidence of complications did occur, none would have been impacted by same-day discharge. Those observed before 6 hours would have prevented early discharge, and those occurring after 24 hours would have been unaffected by routine next-day discharge. This observational study demonstrated the safety and feasibility for a prospective evaluation of ambulatory TR-PCI in an American practice setting.

Drug-eluting stents: present and future

In-stent restenosis (ISR) caused by neointimal hyperplasia is the major drawback after percutaneous coronary intervention (PCI) for obstructive coronary disease, occurring in up to 40% of lesions. Recently, one of the most intriguing new therapies developed is drug-eluting stents (DES) that target the central phenomenon of cellular proliferation that causes ISR. The benefits of stent-based drug delivery include maximizing the local tissue levels of therapeutic agents while minimizing systemic toxicity. Numerous DES using different thin-film polymeric drug carrier have been developed and tested, those eluting either antimitotic or antimicrotublar agents such as sirolimus and paclitaxel have been shown effective in clinical trials. Two DES, the J&J Cypher (sirolimus-eluting) and the Boston Scientific Taxus (paclitaxel-eluting) stents, are commercially available in the U.S. after a number of randomized trials demonstrated reductions in late lumen loss, binary restenosis rate, and need for repeat revascularization compared with bare-metal stents (BMS). Because ISR is multifactorial, ideal agents for DES should inhibit thrombus formation, inflammation and cellular proliferation as well as enhance re-endothelialization. The next generation of DES currently undergoing preclinical studies includes new technology, new stent designs and materials, biological polymers, bioabsorbable stents coated with new drugs including stent based gene, as well as cell delivery. The current paper will review and discuss the current and future status of DES.

Review of percutaneous therapy for bifurcation lesions in the era of drug-eluting stents

Although recent advances in percutaneous coronary interventions (PCI) have led to dramatic expansions in procedural complexity, bifurcation lesions (BL) remain a serious challenge for the interventionalist. Turbulent flow dynamics and high shear stress likely predispose coronary bifurcations to development of atherosclerotic plaques. These lesions comprise 15% to 20% of the total number of coronary interventions. When compared with non-BL interventions, BL interventions demonstrate lower procedural success rates, higher procedural costs, longer hospitalizations, and higher clinical and angiographic restenosis rates. The recent introduction of drug-eluting stents (DES) has resulted in lower incidences of target lesion/ vessel revascularization and reduction of main branch restenosis in this anatomic subset, when compared to historical bare metal stent (BMS) controls. Nonetheless, DES have not resolved the bifurcation PCI problem; and several techniques employing either 1 or 2 stents have emerged. Stenting of the main vessel with provisional side branch stenting seems to be the prevailing approach. While no definitive single BL-PCI technique has been identified, the optimal approach is likely lesion-specific. This paper reviews different treatment modalities for this complex lesion subset, with particular emphasis on the use of DES, as well as new potential therapeutic approaches.

Comparison of multidetector 64-slice computed tomographic angiography to coronary angiography to assess the patency of coronary artery bypass grafts

This study prospectively evaluated the diagnostic accuracy of 64-slice computed tomographic angiography (CTA) in assessing the patency of coronary artery bypass grafts compared with invasive coronary angiography. In total 147 bypass grafts (100 venous grafts and 47 mammary artery grafts) were evaluated in 50 consecutive patients. Contrast-enhanced 64-slice CTA was performed and compared with invasive angiography. The computed tomographic angiographic scan protocol used 64- x 0.5-mm slice collimation and 0.33-second gantry rotation time during simultaneous electrocardiographic gating. Patients with a heart rate >65 beats/min received beta blockers. Overall 145 of 147 bypass grafts (98.6%) were detected by CTA; 2 nonvisualized grafts were occluded at the time of invasive angiography. Of the grafts visualized, 28 were totally occluded, 103 were patent, and 14 had significant stenoses that were confirmed by invasive angiography. Ninety-five percent (111 of 117) of patent grafts demonstrated good run-off distal to anastomoses but without an ability to accurately evaluate the presence of retrograde flow; 83% (97 of 117) of distal anastomoses were adequately evaluated, whereas the remaining 17% (20 of 117) were not well visualized due to vascular clips and/or calcification artifacts. Two grafts were not demonstrated by invasive angiography but were detected by CTA and found to be widely patent. In conclusion, multidetector 64-slice CTA is a valuable tool for direct visualization of coronary bypass grafts and assessment of their patency. Dysfunctional bypass grafts can be detected with high diagnostic accuracy.

Use of a constitutively active hypoxia-inducible factor-1alpha transgene as a therapeutic strategy in no-option critical limb ischemia patients: phase I dose-escalation experience

BACKGROUND

Critical limb ischemia, a manifestation of severe peripheral atherosclerosis and compromised lower-extremity blood flow, results in a high rate of limb loss. We hypothesized that adenoviral delivery of a constitutively active form of the transcription factor hypoxia-inducible factor-1alpha (ie, Ad2/HIF-1alpha/VP16 or HIF-1alpha) into the lower extremity of patients with critical limb ischemia would be safe and might result in a durable clinical response.

METHODS AND RESULTS

This phase I dose-escalation program included 2 studies: a randomized, double-blind, placebo-controlled study and an open-label extension study. In total, 34 no-option patients with critical limb ischemia received HIF-1alpha at doses of 1x10(8) to 2x10(11) viral particles. No serious adverse events were attributable to study treatment. Five deaths occurred: 3 in HIF-1alpha and 2 in placebo patients. In the first (randomized) study, 7 of 21 HIF-1alpha patients met treatment failure criteria and had major amputations. Three of the 7 placebo patients rolled over to receive HIF-1alpha in the extension study. No amputations occurred in the 2 highest-dose groups of Ad2/HIF-1alpha/VP16 (1x10(11) and 2x10(11) viral particles). The most common adverse events included peripheral edema, disease progression, and peripheral ischemia. At 1 year, limb status observations in HIF-1alpha patients included complete rest pain resolution in 14 of 32 patients and complete ulcer healing in 5 of 18 patients.

CONCLUSIONS

HIF-1alpha therapy in patients with critical limb ischemia was well tolerated, supporting further, larger, randomized efficacy trials.

Toxic vessel reaction to an absorbable polymer-based paclitaxel-eluting stent in pig coronary arteries

OBJECTIVES

The goal of this study was to evaluate a new drug-eluting stent (DES) comprising a bioabsorbable polymer eluting a moderate dose of paclitaxel in a clinically relevant animal model.

BACKGROUND

Although DES limit restenosis, adverse vascular pathologies and toxicities continue to be of major concern. Optimization of DES components, especially completely absorbable polymers, may reduce these toxicities.

METHODS

Bare-metal (BM), absorbable polymer coating only (POLY), and polymer-based paclitaxel-eluting (PACL) stents were implanted in porcine coronary arteries using intravascular ultrasound (IVUS) to optimize stent apposition. The dose density of paclitaxel was 0.30-0.35 mcg/mm2, with in vitro elution studies demonstrating a gradual elution over 6-8 weeks. The animals were terminated at 1 week, 1 month and 3 months. Histopathologic and histomorphometric analyses were perform.

RESULTS

The arteries with PACL showed extensive smooth muscle cell necrosis at 1 week and poor apposition of stent struts at 1 month (malapposition measured as gap width between strut and internal elastic lamina), with greater gap width compared to the BM and POLY groups (0.22 mm +/- 0.02 vs. 0.03 mm +/- 0.02 and 0.02 mm +/- 0.01, respectively; p < 0.001). At 3 months, the PACL group showed rebound neointimal thickness and histological percent stenosis compared to the BM group (0.48 mm +/- 0.14 vs. 0.07 mm +/- 0.02, respectively; p < 0.001 and 59% +/- 11 vs. 17% +/- 2, respectively; p < 0.001).

CONCLUSIONS

Despite in vitro data showing slow, sustained release of paclitaxel from a bioabsorbable polymer, the porcine coronary artery model demonstrated a sequence of medial necrosis, stent malapposition and late neointimal thickening. Since the therapeutic window for paclitaxel may be narrower than currently inferred, thorough preclinical testing coupled with the polymer development process for stents eluting paclitaxel is needed.

Safety of intramyocardial injection of autologous bone marrow cells to treat myocardial ischemia in pigs

OBJECTIVE

The purpose of this study is to determine the potential adverse consequences of intracardiac injections of bone marrow mononuclear cells (BMCs) to facilitate the revascularization of ischemic myocardium.

BACKGROUND

Bone marrow mononuclear cells are used to treat heart failure, though there are few studies that evaluated the safety of BMC transplantation for chronic myocardial ischemia.

METHODS

The pigs received coronary ameroid constrictors to induce chronic myocardial ischemia and left ventricular dysfunction. At 4 weeks, autologous BMCs were injected intramyocardially by Boston Scientific Stiletto catheter with low-dose (10(7) cells) or high-dose BMC (10(8)). Control animals received saline. Blood samples were collected for hematological and chemical indices, including cardiac enzyme levels at regular time intervals postinfarction. At 7 weeks, animals underwent electrophysiological study to evaluate the arrhythmic potential of transplanted BMC, followed by necropsy and histopathology.

RESULTS

No mortalities were associated with intramyocardial delivery of BMC or saline. At Day 0, the total creatine phosphokinase (CPK) was in the normal range in all groups. All groups had significant elevations in CPK after ameroid placement, with no significant differences between groups. At 7 weeks, CPK in all groups had returned to pretreatment levels. Electrophysiological assessment revealed that one control animal had an inducible arrhythmia. No arrhythmias were induced in low- or high-dose BMC-treated pigs. There were no histopathological changes associated with BMC injection.

CONCLUSION

This study showed, in a clinically relevant large-animal model, that catheter-based intramyocardial injection of autologous BMC into ischemic myocardium is safe.

Naked plasmid DNA encoding fibroblast growth factor type 1 for the treatment of end-stage unreconstructible lower extremity ischemia: preliminary results of a phase I trial

OBJECTIVE

The objective of this study was to evaluate the safety and tolerance of increasing single and repeated (n = 2) doses of intramuscular naked plasmid DNA encoding for fibroblast growth factor (FGF) type 1 (NV1FGF) administered to patients with unreconstructible end-stage peripheral arterial occlusive disease (PAD). The secondary objectives were to determine the biologic activity of NV1FGF on hemodynamic and clinical parameters associated with improved perfusion.

METHODS

Fifty-one patients with unreconstructible peripheral arterial occlusive disease with rest pain or tissue necrosis underwent treatment with intramuscular NV1FGF. Increasing single (500, 1000, 2000, 4000, 8000, and 16,000 microg) and repeated (2 x 500, 2 x 1000, 2 x 2000, 2 x 4000, and 2 x 8000 microg) doses of NV1FGF were injected into the ischemic thigh and calf. Arteriography was performed before treatment and was repeated 12 weeks after treatment. Side effects and serious adverse events were monitored. Measurements of plasma and urine levels were performed to evaluate NV1FGF plasmid distribution. Serum FGF-1 was measured as an analysis of gene expression at the protein level. Transcutaneous oxygen pressure, ankle brachial index, toe brachial index, pain assessment with visual analog scale, and ulcer healing also were assessed. The safety results are presented for 51 patients, and the clinical outcomes are presented for the first 15 patients (500 to 4000 microg) who completed the 6-month follow-up study.

RESULTS

NV1FGF was well tolerated. Sixty-six serious adverse events were reported; however, none were considered to be related to NV1FGF. Four patients had adverse events that were possibly or probably related to the study treatment: injection site pain, pain, peripheral edema, myasthenia, and paresthesia. No laboratory adverse events were related to the study treatment. Two deaths remote from the treatment were considered not related. Biodistribution of plasmid was limited and transient in plasma and absent in urine. No increase in the FGF-1 serum level was detected. A significant reduction in pain (P <.001) and aggregate ulcer size (P <.01) was associated with an increased transcutaneous oxygen pressure (P <.01) as compared with baseline pretreatment values. A significant increase in ankle brachial index (P <.01) was seen.

CONCLUSION

NV1FGF is well tolerated and potentially could be effective for the treatment of patients with end-stage limb ischemia. Biologic parameters indicate improved perfusion after NV1FGF administration. Dose response is not yet evident. The safety of NV1FGF and the magnitude of improvement observed in this study encourage further investigation with a placebo-controlled, double-blind clinical trial.

The use of electron beam computed tomography in the primary care setting

EBT has become a clinical tool that has allows physicians to gain another piece of data to help predict which patients may be at risk for coronary artery disease. Valuable information that predicts a patient's risk at a relatively young age (fourth or fifth decade) may allow attenuation of such risk by aggressive risk factor modification over the ensuing decades. Coronary calcium can be quantified and subsequently followed to see if risk factor modification is effective. The task for the primary care physician is to properly use these new imaging tests to improve the care they provide for their patients.

Therapeutic angiogenesis with recombinant fibroblast growth factor-2 improves stress and rest myocardial perfusion abnormalities in patients with severe symptomatic chronic coronary artery disease

BACKGROUND

We report the effects of the administration of recombinant fibroblast growth factor-2 (rFGF-2) protein on myocardial perfusion using single photon emission computed tomography imaging in humans with advanced coronary disease.

METHODS AND RESULTS

A total of 59 patients with coronary disease that was not amenable to mechanical revascularization underwent intracoronary (n=45) or intravenous (n=14) administration of rFGF-2 in ascending doses. Changes in perfusion were evaluated at baseline and again at 29, 57, and 180 days after rFGF-2 administration. In this uncontrolled study, perfusion scans were analyzed by 2 observers who were blinded to patient identity and test sequence; scans were displayed in random order, with scans from nonstudy patients randomly interspersed to enhance blinding. Combining all dose groups, a reduction occurred in the per-segment reversibility score (reflecting the magnitude of inducible ischemia) from 1.7+/-0.4 at baseline to 1.1+/-0.6 at day 29 (P:<0.001), 1.2+/-0.7 at day 57 (P:<0.001), and 1.1+/-0.7 at day 180 (P:<0.001). The 37 patients with evidence of resting hypoperfusion had evidence of improved resting perfusion: their per-segment rest perfusion score of 1.5+/-0. 5 at baseline decreased to 1.0+/-0.8 at day 29 (P:<0.001), 1.0+/-0.8 at day 57 (P:=0.003), and 1.1+/-0.9 at day 180 (P:=0.11).

CONCLUSIONS

These preliminary data suggest that the administration of rFGF-2 to patients with advanced coronary disease resulted in an attenuation of stress-induced ischemia and an improvement in resting myocardial perfusion; these findings are consistent with a favorable effect of therapeutic angiogenesis.

Irradiation and postangioplasty restenosis: a recent overview

One of the most intriguing developments in recent years towards prevention of restenosis after angioplasty is the use of ionizing radiation. The background for the use of radiation treatment for this application is sound, since radiation is used not only to treat malignant cancerous growths but also is used for treatment of benign hyperplastic disorders such as post-surgical keloid formation and recurrence of pterygium after surgical removal. Restenosis can be considered a form of overexuberant wound healing triggered by angioplasty. Ionizing radiation inhibits serum-stimulated proliferation of many cell types including fibroblasts and smooth muscle cells in vitro and also suppresses the synthesis of collagen by cultured fibroblasts. Liermann who showed inhibition of post-stent restenosis first used ionizing radiation for restenosis prevention clinically in iliac and iliofemoral arteries. Subsequently, extensive animal studies in various restenosis models have shown a profound inhibitory effect of catheter-based radiation (endovascular brachytherapy) on neointima formation and overall vessel shrinkage (negative remodeling). Based on these results clinical trials have been initiated with several types of devices and isotopes. Among these are 192Ir, 32P, 90Y, 90Sr/Y and 188Re. Additionally, radioactive stents have been developed; devices for clinical use are made radioactive at the microCi level by surface implantation of 32P ions. Results from early clinical trials are encouraging and brachytherapy appears safe for clinical use and at an appropriate dose, may be highly effective for restenosis prevention.

GPIIbIIIa inhibitors as adjunctive therapy in acute myocardial infarction

Thrombolytic therapy has proved useful in the treatment of acute myocardial infarction but is frequently associated with limited vessel reperfusion and early reocclusion. Local platelet aggregation and activation play a role in these pathological processes, explaining the benefit of aspirin, a weak antiplatelet agent. Recent interest has turned to GPIIbIIIa antagonists, a class of potent inhibitors of platelet aggregation. Their concomitant use with fibrinolytics, in rescue and primary angioplasty for acute myocardial infarction treatment is explored. Efficacy and safety issues are addressed and the potential pivotal role of these agents in the treatment of acute myocardial infarction is discussed.

Increased platelet responsiveness following coronary stenting. Heparin as a possible aetiological factor in stent thrombosis

AIMS

Platelet activation may be a determinant of thrombotic and restenotic complications following intracoronary stenting. In order to measure the effect of stenting on platelet activation antigen expression we used whole blood flow cytometry in 18 patients undergoing Palmaz-Schatz stenting (treated with full anticoagulation) and compared these with a group of 18 patients undergoing elective angioplasty. The effects of low molecular weight heparin and unfractionated heparin on platelet behaviour were also studied, both in vitro and in vivo to determine the contribution of prolonged heparin therapy to platelet activation following stenting.

METHODS AND RESULTS

Fibrinogen binding to activated GPIIb-IIIa, and surface expression of P-selectin, GPIb and GPIIb-IIIa antigens were measured in unstimulated peripheral blood samples (rest) and on stimulation with adenosine diphosphate (0.1-10 micromol x 1(-1)) and thrombin (0.02-0.16 U x ml(-1)). No changes were seen in resting samples following angioplasty or stenting. Agonist responsiveness was unaltered after angioplasty, but in stented patients antigen expression in response to thrombin was significantly reduced (P< or =0.04), whilst the adenosine diphosphate response was significantly increased (P=0.01). Similar effects were observed in patients with unstable angina treated with either low molecular weight heparin or unfractionated heparin in vivo. In vitro, both unfractionated and low molecular weight heparin inhibited thrombin-induced platelet activation, but stimulation of adenosine diphosphate responses was more marked with unfractionated than low molecular weight heparin.

CONCLUSIONS

There was a significant increase in platelet responsiveness to adenosine diphosphate following intracoronary stenting in patients treated with conventional anticoagulants. This was probably a consequence of treatment with heparin. Activation of platelets by heparin may explain the increased rate of stent thrombosis in patients treated with anticoagulant therapy. Low molecular weight heparins stimulate platelets less than unfractionated heparin.

Use of abciximab in interventional cardiology

The advent of platelet membrane glycoprotein (GP) IIb/IIIa inhibitors has changed the landscape of interventional cardiology. Given the commercial availability of abciximab and expected regulatory approvals for other receptor blockers, defining appropriate use of these agents in the interventional setting is mandated. One key issue is selection of patients who may benefit from GP IIb/IIIa receptor blockade. Focusing specifically on abciximab, data from three large-scale, randomized trials demonstrate that abciximab is appropriate for all patients undergoing percutaneous transluminal coronary angioplasty, regardless of risk stratum. Other important issues to consider when prescribing this therapy include benefits in conjunction with stents and new devices, dosing and timing of administration, and the role of prophylactic versus "bailout" administration. This article reflects a distillation of the views and consensus regarding the use of GP IIb/IIIa inhibitors in patients undergoing coronary intervention expressed by a group of international experts convened in Davos, Switzerland, February 16, 1997. This report attempts to review clinical progress to date, formulate recommendations, and map out potentially fruitful lines of inquiry for future investigation.

Use of abciximab in interventional cardiology

The advent of platelet membrane glycoprotein (GP) IIb/IIIa inhibitors has changed the landscape of interventional cardiology. Given the commercial availability of abciximab and expected regulatory approvals for other receptor blockers, defining appropriate use of these agents in the interventional setting is mandated. One key issue is selection of patients who may benefit from GP IIb/IIIa receptor blockade. Focusing specifically on abciximab, data from three large-scale, randomized trials demonstrate that abciximab is appropriate for all patients undergoing percutaneous transluminal coronary angioplasty, regardless of risk stratum. Other important issues to consider when prescribing this therapy include benefits in conjunction with stents and new devices, dosing and timing of administration, and the role of prophylactic versus "bailout" administration. This article reflects a distillation of the views and consensus regarding the use of GP IIb/IIIa inhibitors in patients undergoing coronary intervention expressed by a group of international experts convened in Davos, Switzerland, February 16, 1997. This report attempts to review clinical progress to date, formulate recommendations, and map out potentially fruitful lines of inquiry for future investigation.

[Endovascular radiation and restinosis]

Restenosis following coronary angioplasty is still the most vexing problem facing percutaneous coronary interventions, despite advances in stent designs and new antiplatelet therapies. Endovascular radiation has shown to limit the formation of neointimal tissue in the vascular wall in recent studies and it appears as a promising method to control the restenotic process. This article reviews the experimental and clinical data with the use of this form of radiation and analyses its potential role in Interventional Cardiology.

In vitro comparison of the effects of contrast media on coagulation and platelet activation

The aim of this study was to compare the in vitro effects of different classes of contrast media on both the blood coagulation system and on platelet function. Global tests (APTT, TT) and FpA and F1 + 2 generation measurements showed that ioxaglate (ionic dimer) presents the highest anticoagulant potential. The anticoagulant effects of nonionic agents were less marked, iodixanol (nonionic dimer) being significantly less anticoagulant than iohexol (nonionic monomer). Major platelet activation was observed with release of PF4, serotonin and PDGF-AB when iohexol was incubated for 1 min in whole blood. Iodixanol showed no effect over the same period, while moderate platelet activation was observed after 30 min. Under the same experimental conditions, ioxaglate had no effect on platelets even after incubation for 30 min, whereas activation was observed with 9 g/l saline control at this time. Prevention of thrombin formation and platelet activation is only achieved with ioxaglate, the ionic dimer. These findings may be clinically important in the thrombotic environment of radiological procedures and may explain the increased thrombotic risks observed with nonionic agents in interventional procedures.

Electro-encapsulating drugs within blood platelets: local delivery to injured arteries during angioplasty

Prostacyclins (PGl2) inhibit platelet-platelet interactions at concentrations that do not affect platelet adhesion to collagen and other arterial subendothelial structures exposed during injury. Such compounds can be encapsulated within platelets by reversible electroporation and, using the platelet's natural haemostatic propensity, they can be targeted to injured vessels in vivo. In rat (aorta), rabbit (ileofemoral) and pig (carotid) angioplasty models, autologous platelets, electro-loaded with the stable prostacyclin iloprost and given intravenously after balloon overstretch injury, substantially reduced platelet deposition at the lesion site as compared with control platelets. In the pig model, when the drug-loaded platelets were delivered directly to the injury site during angioplasty via a double balloon delivery catheter, platelet deposition was restricted to monolayer coverage (> 80% reduction compared with controls). Candidate antiproliferative drugs (for co-encapsulating with iloprost) are being investigated in order to develop a combined antithrombotic/antirestenosis strategy for use during angioplasty and thrombolysis procedures. Autologous platelets as drug-targeting vehicles should obviate many of the immunological, toxicological and biodegradability concerns inherent in the use of other drug transport vectors such as antibodies, viruses, liposomes and synthetic polymer microcapsules.

Evaluation of whole blood flow cytometric detection of platelet bound fibrinogen on normal subjects and patients with activated platelets

Activated platelets can be detected by measuring platelet-bound fibrinogen in a whole blood, flow cytometric assay, using a fluorescently-conjugated polyclonal antibody. Fibrinogen binding to unstimulated platelets from normal subjects was low in this assay, as was expression of the CD63 antigen. Single cell counting of samples prepared for flow cytometric analysis showed platelet aggregates do not form during the assay procedure. Immune complexes were not seen, and fibrinogen binding to the platelets was unaffected by the CD32 MAb, IV.3. Artefactual activation of the unfixed samples could be minimised by control of phlebotomy, time and temperature of incubation. Variations in platelet count in the range 140-430 x 10(9) 1(-1) and in plasma fibrinogen in the range 2-6 g 1(-1) did not affect the assay results. Comparison of fibrinogen binding with expression of CD63 antigen on normal platelets, stimulated with agonists in vitro, demonstrated that fibrinogen binding detects an earlier stage of platelet activation. Platelet bound fibrinogen was shown to be sensitive in detecting small numbers of activated platelets in clinical samples in twelve patients on intensive care, four undergoing haemofiltration. The patients had a significantly higher median percentage of circulating platelets with bound fibrinogen (p < 0.005), but fibrinogen binding was significantly lower (p < 0.02) in response to 10(-5) M ADP, compared to twelve age-matched normal controls.

Implantation of half Palmaz-Schatz stents in short aorto-ostial lesions of saphenous vein grafts

Two cases are presented in which a half Palmaz-Schatz stent was implanted in a short lesion located in the ostium of a saphenous vein graft. Aorto-ostial stenoses are a technical challenge for balloon angioplasty and stenting. Short stents may offer several advantages as regards deployment, positioning, thrombogenicity, and restenosis.

Thyrotoxicosis presenting as a life threatening hypokalaemic paralysis: investigation of the Na/K pump in isolated leucocytes

A 37-year-old Chinese man presented with the rapid onset of profound muscle weakness, and a serum potassium of 1.7 mmol/l. The intravenous infusion of undiluted potassium chloride (2 mmol/ml) through a central venous catheter resulted in rapid recovery. Further investigation revealed thyrotoxicosis. He was treated with carbimazole and subsequently remained well. We assessed Na/K pump activity in isolated leucocytes taken from the patient and found an exaggerated response to adrenaline which ceased after he became euthyroid.