Effects of diltiazem on complications and restenosis after coronary angioplasty

Evaluation of the effect of oral verapamil on clinical outcome and angiographic restenosis after percutaneous coronary intervention

OBJECTIVES

We investigated the effect of oral verapamil on clinical outcome and angiographic restenosis after percutaneous coronary intervention (PCI).

BACKGROUND

Thus far, there is no established systemic pharmacologic approach for the prevention of restenosis after PCIs. Five small studies reported encouraging results for calcium channel blockers.

METHODS

Our randomized double-blind trial included 700 consecutive patients with successful PCI of a native coronary artery. Patients received the calcium channel blocker verapamil, 240 mg twice daily for six months, or placebo. Primary clinical end point was the composite rate of death, myocardial infarction, and target vessel revascularization (TVR) during one-year follow-up; the angiographic end point was late lumen loss at the six-month follow-up angiography.

RESULTS

We obtained complete clinical follow-up in 95% of the patients, and scheduled angiography was performed in 94%. The proportion of patients treated with stents was 83%. The primary clinical end point was reached in 67 (19.3%) patients on verapamil and in 103 (29.3%) patients on placebo (relative risk [RR] 0.66 [95% confidence interval (CI) 0.48 to 0.89]; p = 0.002). This difference between the groups was driven by TVR (17.5% with verapamil vs. 26.2% with placebo; RR 0.67 [95% CI 0.49 to 0.93]; p = 0.006). Late lumen loss was 0.74 +/- 0.70 mm with verapamil and 0.81 +/- 0.75 mm with placebo (p = 0.11). Compared with placebo, verapamil reduced the rate of restenosis > or =75% (7.8% vs. 13.7%; RR 0.57 [95% CI 0.35 to 0.92]; p = 0.014).

CONCLUSIONS

Verapamil compared with placebo improves long-term clinical outcome after PCI of native coronary arteries by reducing the need for TVR. This was caused by a reduction in the rate of high-grade restenosis.

Simultaneous intra/extravascular administration of antiproliferative agents as a new strategy to inhibit restenosis: the peak of reactive cell proliferation as a hallmark for the duration of the treatment

BACKGROUND

Strictly intravascular approaches for the treatment of postangioplasty restenosis are effective in the intima and the inner parts of the media but may be insufficient to control redundant pathways in the more outer parts of the media and the adventitia. An inverse situation may occur subsequently to a strictly extravascular approach, like the recently suggested pericardial approach in pigs. We hypothesized that simultaneous intra/extravascular administration of anti-restenotic agents inhibits restenosis by blocking all stimulatory pathways in the entire arterial wall.

METHODS

Fresh hearts of 25 domestic pigs were obtained from a local slaughterhouse. Left anterior descending coronary arteries (LAD) were harvested, cut into cylindric 5 mm segments, and cultured as ex vivo porcine organ cultures (POCs). After 9 bar ballooning simultaneous intra/extravascular administration of high dose diltiazem (50 microg/mL) was carried out for a period of 1, 2, 3, 4, 5, 6, and 7 days. At day 7 and 28 proliferative activity (BrdU), neointimal thickening, and staining against smooth muscle alpha-actin and vWF was analysed.

RESULTS

7 days after ballooning administration of diltiazem for 4, 5, 6, and 7 days inhibited reactive cell proliferation by more than 50% (n.s.) as compared to control, 28 days after ballooning administration for 6 and 7 days inhibited neointimal thickening by more than 75% (p < 0.05). Simultaneous intra/extravascular administration of high dose diltiazem did not affect the expression of vWF in endothelial cells or smooth muscle alpha-actin in smooth muscle cells.

CONCLUSIONS

Simultaneous intra/extravascular administration of high dose diltiazem (50 microg/mL) has to be maintained for at least 6 days to achieve a significant inhibition of neointimal thickening. The data demonstrate the importance of the maximal reactive cell proliferation (= day 7 in the POC-model) for the calculation of the duration of the treatment period.

Can angiotensin receptor antagonists prevent restenosis after stent placement?

Restenosis rates after coronary stent implantation in complex lesions are between 30 and 50%. Neointimal hyperplasia promoted by complex interaction between cellular and acellular elements, such as cytokines and growth factors, is thought to be the primary process responsible for restenosis. The risk of in-stent restenosis is increased in patients with a history of restenosis after percutaneous transluminal coronary angioplasty, in long lesions, in total occlusions, in patients with diabetes mellitus, in small vessels, in the proximal parts of the left anterior descending coronary artery and in cases of stent oversizing. In-stent restenosis represents a serious economic burden on society because treatment strategies include expensive approaches such as cutting-balloon angioplasty, rotational atherectomy and brachytherapy. A number of pharmacological agents, including ACE inhibitors, have been unsuccessful in preventing restenosis. Alternative procedures such as brachytherapy, radioactive stents and drug-eluting stents are under evaluation. Although sirolimus- or paclitaxel-eluting stents have been associated with very low restenosis rates over durations of 6 to 12 months, the long-term efficacy and tolerability of this approach is currently being investigated. Although ACE inhibitors have failed in reducing restenosis rates, the selective angiotensin II type 1 (AT(1)) receptor antagonist valsartan has shown encouraging results in the single-center Valsartan for Prevention of Restenosis after Stenting of Type B2/C lesions trial (ValPREST). The ValPREST trial is the first randomized, placebo-controlled study to have evaluated the effect of an angiotensin receptor antagonist on in-stent restenosis in a moderate number of patients. Compared with ACE inhibitors, angiotensin receptor blockers exert additional effects on the pathophysiological processes which lead to restenosis. Angiotensin receptor antagonists may affect several mechanisms involved in neointimal hyperplasia such as decreasing circulating cytokine and growth factor levels and reducing neutrophil activation, especially after stenting in acute coronary syndromes, but the results need to be confirmed in a large multicenter trial. The question whether long-term therapy, with an oral angiotensin receptor antagonist, is cost-effective and whether angiotensin receptor antagonists should be used as an add-on therapy to drug-eluting stents, requires clarification.

Overview of therapies for prevention of restenosis after coronary interventions

Coronary artery disease is a leading cause of morbidity and mortality in the United States and across the world. The economic impact of coronary artery disease is staggering and on the rise. Percutaneous transluminal coronary angioplasty is widely used to treat severe, symptomatic coronary stenosis. The Achilles heel of angioplasty is restenosis of those treated arteries. As a result, numerous therapies, including mechanical and pharmacological approaches, to prevent restenosis have been studied. A greater understanding of the pathophysiology of restenosis has enhanced the success of these therapeutic approaches. To date, the most important and successful approach to limit restenosis has been the use of coronary stents. Stents have reduced the rate of restenosis from approximately 50% down to 20-30%. However, in-stent restenosis presents a new and an even more challenging dilemma. The success of adjunctive drug therapy has been promising, but, as of yet, very limited. Antithrombotic agents have reduced acute thrombosis and many of the acute complications of angioplasty. New approaches and therapies are very encouraging, and provide great hope in the treatment of restenosis. Brachytherapy has shown success in the treatment of in-stent restenosis, and recently has been approved by the United States Food and Drug Administration for this indication. Drug-eluting stents using antiproliferative drugs are the most exciting new advance in preventing restenosis, currently in Phase III trials. Gene therapy, targeted drug delivery, and newer antithrombotic agents are also under investigation. We will review the pathophysiology of restenosis, animal models, pharmacological therapies, and mechanical approaches for the treatment of restenosis.

Mechanisms of angioplasty and stent restenosis: implications for design of rational therapy

Restenosis after angioplasty or stenting remains the major limitation of both procedures. A vast array of drug therapies has been used to prevent restenosis, but they have proven to be predominantly unsuccessful. Recent trends in drug therapy have attempted to refine the molecular and biological targets of therapy, based on the assumption that a single biological process or molecule is critical to restenosis. In contrast, both stenting and brachytherapy, which are highly nonspecific, can successfully reduce restenosis after angioplasty or stenting, respectively. This review examines the biology of both angioplasty and stent stenosis, focussing on human studies. We also review the landmark human trials that have definitively proven successful therapies, such as stenting and brachytherapy. We suggest that the successful trials of stenting and brachytherapy and the failure of other treatments have highlighted the shortcomings of conventional animal models of arterial intervention, and gaps in our knowledge of human disease. In contrast to arguments advocating gene therapy, these studies suggest that the most likely successful drug therapy will have a wide therapeutic range, targeting as many of the components or biological processes contributing to restenosis as possible.

Effects of probucol on rat carotid artery responses to balloon catheter injury

Balloon catheter injury to the rat common carotid artery has been widely used for testing potential therapies for post-angioplasty restenosis. However, the model has become somewhat discredited because a number of drugs that inhibit intimal thickening, measured 14 days after balloon catheter injury, have been found to be ineffective in clinical trials. Probucol has recently been shown to reduce the incidence of post-angioplasty restenosis in a number of small clinical trials, making it possible to reassess the validity of the rat balloon injury model. The effects of probucol on the underlying causes of intimal thickening in balloon-injured rat carotid arteries were quantified. Probucol inhibited medial smooth muscle cell proliferation by 23% on day 4 after injury (P=0.009), and by 65% on day 10 after injury (P=0.026). Smooth muscle cell migration was reduced by 64% (P=0.008) in probucol-treated animals. In marked contrast, intimal smooth muscle cell proliferation was significantly increased by 41% (P=0.024) by probucol. There was no significant effect on intimal thickening or smooth muscle cell death. These data suggest that drugs that inhibit both medial smooth muscle cell proliferation and migration in the rat balloon injury model may prove useful in the treatment of post-angioplasty restenosis.

Usefulness of Nisoldipine for prevention of restenosis after percutaneous transluminal coronary angioplasty (results of the NICOLE study). NIsoldipine in COronary artery disease in LEuven

The NIsoldipine in COronary artery disease in LEuven (NICOLE) study investigates (1) whether nisoldipine, a dihydropyridine calcium antagonist, reduces the progression of minor coronary arterial lesions in the long term, and (2) whether it reduces the restenosis rate after successful percutaneous transluminal coronary angioplasty (PTCA). The NICOLE study is a single-center, randomized, double-blind trial in 826 patients, who underwent a successful PTCA. Nisoldipine 40 mg coat-core or placebo was started the morning after the procedure and continued for 3 years. All coronary arterial segments were measured on preprocedural angiogram and on the second follow-up angiogram at 3 years. On the first follow-up angiogram at 6 months only the dilated segments were measured. Although the study is still ongoing until the primary end point is reached, we report in this study the angiographic restenosis data as well as the clinical events observed at 6-month follow-up. The per-protocol population consisted of 646 patients. Restenosis, defined as a > or =50% loss of the initial gain (National Heart, Lung, and Blood Institute criterion IV) occurred in 49% and 55% of the 308 nisoldipine-treated and the 338 placebo-treated patients, respectively (p = NS). At follow-up, the rates of death and myocardial infarction were low and similar in both groups, but in the nisoldipine group, less patients required early coronary angiography (18% vs 26%, p = 0.006) and subsequent revascularization procedures (32% vs 41%, p = 0.057). Thus, nisoldipine did not significantly reduce the angiographic restenosis rate after PTCA, but reduced the number of repeat revascularization procedures, which may be due to its antianginal action.

Restenosis and clinical outcome in patients treated with amlodipine after angioplasty: results from the Coronary AngioPlasty Amlodipine REStenosis Study (CAPARES)

OBJECTIVES

Our intent was to investigate the effect of the dihydropyridine calcium channel blocker amlodipine on restenosis and clinical outcome in patients undergoing percutaneous transluminal coronary angioplasty (PTCA).

BACKGROUND

Amlodipine has sustained vasodilatory effects and relieves coronary spasm, which may reduce luminal loss and clinical complications after PTCA.

METHODS

In a prospective, double-blind design, 635 patients were randomized to 10 mg of amlodipine or placebo. Pretreatment with the study drug started two weeks before PTCA and continued until four months after PTCA. The primary angiographic end point was loss in minimal lumen diameter (MLD) from post-PTCA to follow-up, as assessed by quantitative coronary angiography (QCA). Clinical end points were death, myocardial infarction, coronary artery bypass graft surgery and repeat PTCA (major adverse clinical events).

RESULTS

Angioplasty was performed in 585 patients (92.1%); 91 patients (15.6%) had coronary stents implanted. Follow-up angiography suitable for QCA analysis was done in 236 patients in the amlodipine group and 215 patients in the placebo group (per-protocol group). The mean loss in MLD was 0.30 +/- 0.45 mm in the amlodipine group versus 0.29 +/- 0.49 mm in the placebo group (p = 0.84). The need for repeat PTCA was significantly lower in the amlodipine versus the placebo group (10 [3.1%] vs. 23 patients [7.3%], p = 0.02, relative risk ratio [RR]: 0.45, 95% confidence interval [CI]: 0.22 to 0.91), and the composite incidence of clinical events (30 [9.4%] vs. 46 patients (14.5%), p = 0.049, RR: 0.65, CI: 0.43 to 0.99) within the four months follow-up period (intention-to-treat analysis).

CONCLUSIONS

Amlodipine therapy starting two weeks before PTCA did not reduce luminal loss, but the incidence of repeat PTCA and the composite major adverse clinical events were significantly reduced during the four-month follow-up period after PTCA with amlodipine as compared with placebo.

Pharmacologic effects of calcium channel blockers on restenosis

The understanding and control of the healing process after percutaneous transluminal coronary angioplasty (PTCA) and of the pathogenesis of restenosis are incomplete. To date, only stent implantation has been shown to successfully reduce the rate of restenosis. Calcium channel blockers have positive effects on a number of processes that may be associated with restenosis, including reduction of platelet aggregation, minimization of vasospasm, and inhibition of mitogens. Clinical trials have therefore been performed to assess the effect of calcium channel blockers on restenosis and ischemia. A meta-analysis of five restenosis trials investigating calcium channel blockers demonstrated a 30% reduction in the risk for restenosis. The Coronary Angioplasty Amlodipine Restenosis Study (CAPARES) is therefore assessing the effect of amlodipine, a long-acting, third-generation calcium channel blocker in angioplasty patients. Therapy (amlodipine 5 mg with a forced titration to 10 mg once daily, or placebo), is begun 2 weeks before angioplasty and is continued for 4 months after the procedure. The rationale of CAPARES is that amlodipine may offer anti-ischemic protection before, during, and after angioplasty, may have more beneficial effects on restenosis and various clinical end points than calcium channel blockers used in previous trials, and may improve the long-term outcome of PTCA therapy.

Influence of calcium antagonists on long-term survival of patients treated with coronary angioplasty

A meta-analysis reported that nifedipine increased mortality dose-dependently in patients with coronary artery disease. However, there have been few studies (specifically in Asians) on the long-term prognosis of patients treated with calcium antagonists after successful coronary angioplasty (PTCA). The subjects consisted of 583 consecutive patients (461 males, aged 59 +/- 10), who underwent successful elective PTCA between 1985 and 1990. First, they were divided into two groups; the calcium antagonist (+) group (n = 560) and the calcium antagonist (-) group (n = 23), and were evaluated in terms of total survival and cardiac events. Second, the calcium antagonist (+) group was further divided into 4 groups according to calcium antagonist type, i.e., short-acting nifedipine group (n = 156), long-acting nifedipine group (n = 203), diltiazem group (n = 184) and the other group (n = 17), and these groups were evaluated in the same way. The primary end-point was set as death from any cause. Secondary end-points were any cardiac events, including non-fatal acute myocardial infarction, coronary artery bypass surgery and repeat PTCA. The mean follow-up period was 4.5 +/- 1.8 years. A multivariate analysis was performed with the Cox proportional-hazard model. The Kaplan-Meier analysis showed that the calcium antagonist (-) group had significantly worse prognoses than the calcium antagonist (+) group (p < 0.05), and that there was no significant difference among the prognoses of the four calcium antagonists groups. The multivariate analysis revealed that the use of a calcium antagonist was one of the independent factors positively contributing to the prognosis. The use of any type of calcium antagonist did not increase mortality in patients who underwent successful elective PTCA, rather, it contributed to a favorable outcome.

Effect of high dose verapamil on restenosis after peripheral angioplasty

OBJECTIVES

We sought to determine whether treatment with high dose verapamil prevents restenosis in patients at high risk for reoccurrence after successful percutaneous transluminal coronary angioplasty (PTCA).

BACKGROUND

Restenosis is the major limitation of PTCA. Calcium antagonists have demonstrated some potential as inhibitors of this process.

METHODS

A total of 98 patients with peripheral occlusive arterial disease (POAD), stable angina pectoris, mild hypertension and at least one additional risk factor increasing the likelihood of restenosis after angioplasty were selected for this placebo-controlled, double-blind, randomized trial. Verapamil (240 mg twice daily) or placebo was taken for 6 months. Efficacy variables assessed before and after angioplasty and at 6 weeks and 6 months after PTCA included thickness of the intima/media complex degree of stenosis, interventricular septal thickness, crurobrachial pressure ratios of dorsalis pedis and posterior tibial arteries, distance to claudication and total vessel diameter.

RESULTS

No significant intergroup differences emerged before or immediately after PTCA. Six weeks after angioplasty, a significant thickening of the intima/media complex in the treated vascular segment of 14.3% occurred in the placebo group versus 0% among verapamil patients (p < 0.01). At 6 months, the intima/media thickness was 35.7% greater in the placebo group but had decreased by 14.3% in the verapamil group (p < 0.001). At 6 months, a marked reduction in septal thickness was observed in the verapamil group versus that in the placebo group (p < 0.001). The rate of restenosis was also significantly lower in the verapamil group (p < 0.001). Few minor side effects were reported.

CONCLUSIONS

In patients with POAD at increased risk for restenosis, the administration of high dose verapamil prevented recurrent stenosis for 6 months after successful peripheral angioplasty and was well tolerated.

Coronary artery vasomotion after percutaneous transluminal coronary angioplasty

Substantial evidence of postangioplasty vasoconstriction is available, both at the dilated site and distal to balloon injury, demonstrating its frequent occurrence. It is likely that even mild or moderate vasoconstriction at the site of balloon injury may create flow turbulence, promoting platelet aggregation and contributing to thrombotic vessel closure. The regulation of arterial smooth muscle tone is a complex process and should be distinguished from elastic recoil, which occurs at the site of balloon injury due to passive elastic properties of the artery, generally immediately after balloon deflation. The contribution of a variety of messengers generated by humoral, neurogenic, myogenic, and endothelium-derived factors in this regulatory process has been implicated. The possible mechanisms of post-percutaneous transluminal coronary angioplasty vasoconstriction at the dilated site (local) and in segments of coronary artery beyond the dilated site (distal) are reviewed in this article.

Short-term exposure to thapsigargin inhibits neointima formation in human saphenous vein

Vascular smooth muscle cell (VSMC) migration and proliferation are involved in the intimal thickening responsible for late vein graft failure. In addition to growth and chemotactic factors, VSMCs require expression of matrix-degrading enzymes, e.g., metalloproteinases (MMP), to relieve the antiproliferative and antimigratory constraints of the extra-cellular matrix. Thapsigargin irreversibly inhibits Ca(2+)-ATPase, eliciting an increase in intracellular Ca2- and depletion of the intracellular calcium pools that are thought to be involved in the control of VSMC migration, VSMC proliferation, and MMP activity. We therefore studied the effect of thapsigargin on VSMC migration, VSMC proliferation, and MMP expression in human saphenous vein organ cultures. Vein segments were cultured for 14 days, and VSMC proliferation and migration were determined by autoradiography. Cell death was assessed using in situ end-labeling and lactate dehydrogenase release. Using Western blotting, we examined MMP-2 and MMP-9 and tissue inhibitor of metalloproteinases (TIMP)-1 and TIMP-2 expression. Exposure to thapsigargin at 10 nmol/L for 60 minutes before culture significantly inhibited neointimal thickening (60%, P < .05), intimal and medial VSMC proliferation (32%, P < .05 and 37%, P < .05, respectively), and VSMC migration (36%, P < .05). Thapsigargin at 10 nmol/L did not significantly increase cell death or MMP-2, MMP-9, TIMP-1, and TIMP-2 expression. These results suggest that blockade of Ca(2+)-ATPase by thapsigargin inhibits VSMC migration and proliferation involved in neointimal formation without affecting MMP-2 and MMP-9 expression. Because short-term exposure to thapsigargin was sufficient to inhibit neointima formation, this drug may prove useful in the treatment of intimal thickening after arterial bypass graft surgery.

Effect of the direct nitric oxide donors linsidomine and molsidomine on angiographic restenosis after coronary balloon angioplasty. The ACCORD Study. Angioplastic Coronaire Corvasal Diltiazem

BACKGROUND

Nitric oxide (NO) donors, in addition to their vasodilator effect, decrease platelet aggregation and inhibit vascular smooth muscle cell proliferation. These actions could have beneficial effects on restenosis after coronary balloon angioplasty.

METHODS AND RESULTS

In a prospective multicenter, randomized trial, 700 stable coronary patients scheduled for angioplasty received direct NO donors (infusion of linsidomine followed by oral molsidomine) or oral diltiazem. Treatment was started before angioplasty and continued until 12 to 24 hours before follow-up angiography at 6 months. The primary study end point was minimal lumen diameter, assessed by quantitative coronary angiography, 6 months after balloon angioplasty. Clinical variables were well matched in both groups. However, despite intracoronary administration of isosorbide dinitrate, the reference diameter in the NO donor group was significantly greater than in the diltiazem group on the preangioplasty, postangioplasty, and follow-up angiograms. Pretreatment with an NO donor was associated with a modest improvement in the immediate angiographic result compared with pretreatment with diltiazem (minimum luminal diameter, 1.94 versus 1.81 mm; P = .001); this improvement was maintained at the 6-month angiographic follow-up (minimal lumen diameter, 1.54 versus 1.38 mm; P = .007). The extent of late luminal narrowing did not differ significantly between groups (loss index in the NO donor and diltiazam groups, 0.35 +/- 0.78 and 0.46 +/- 0.74, respectively; P = .103). Restenosis, defined as a binary variable (> or = 50% stenosis), occurred less often in the NO donor group (38.0% versus 46.5%; P = .026). Combined major clinical events (death, nonfatal myocardial infarction, and coronary revascularization) were similar in the two groups (32.2% versus 32.4%).

CONCLUSIONS

Treatment with linsidomine and molsidomine was associated with a modest improvement in the long-term angiographic result after angioplasty but had no effect on clinical outcome. The improved angiographic result related predominantly to a better immediate procedural result, because late luminal loss did not differ significantly between groups.

Restenosis: is there a pharmacologic fix in the pipeline?

One of the most frustrating aspects of restenosis is that it is the result of advances in medical care (there was no restenosis before the days of balloon angioplasty), yet it seems to be resistant to all that science has to offer. Still we believe there is reason to be optimistic. We are at last beginning to see some promise from clinical trials, and data being generated confirm some of the hypotheses previously generated from animal experiments. Thus the effects seen with the GP IIb/IIIa antibody 7E3 suggest that thrombosis may be as important in its long-term sequelae as it is for acute reocclusion. The jury is still out on whether antiproliferative approaches will be a therapeutic option, but local delivery paradigms using novel formulations delivered by catheter or impregnated in stents may allow the concept to be tested without the risk of systemic toxicity. Plans are also underway for gene therapy trials, although we may have to wait for better vector technology before taking these into the coronary bed. Perhaps we should move away from the "single pill" approach and accept that, like many infections, malignancies, or even heart failure, a multifaceted approach with combination therapy will provide the first glimmer of that brighter tomorrow.

Use of calcium channel antagonists in myocardial revascularization procedures

Calcium channel antagonists possess a number of properties that may be beneficial after revascularization procedures. Therefore, we present an overview of the use of these drugs after percutaneous intervention in the Coronary Angioplasty Versus Excisional Atherectomy Trial (CAVEAT), and compare the results in CAVEAT with those in published randomized trials. Also reviewed are the use of calcium channel antagonists to control perioperative hypertension, reduce myocardial necrosis, and prevent arrhythmias during cardiopulmonary bypass.

Identification of a potential role for the adventitia in vascular lesion formation after balloon overstretch injury of porcine coronary arteries

BACKGROUND

In the present series of experiments, we examined the onset of cell proliferation and growth factor expression after balloon overstretch injury to porcine coronary arteries.

METHODS AND RESULTS

Domestic juvenile swine underwent balloon overstretch injury to the left anterior descending and circumflex coronary arteries with standard percutaneous transluminal coronary angioplasty balloon catheters. To identify proliferating cells, 5-bromo-2-deoxyuridine (BrDU) was administered over a period of 24 hours before the animals were killed at either 1, 3, 7, or 14 days after injury. Immunohistochemistry was performed with monoclonal antibodies to BrDU and smooth muscle cell markers. Three days after injury, a large number of proliferating cells were located in the adventitia, with significantly fewer positive cells found in the media and lumen. Seven days after injury, proliferating cells were found primarily in the neointima, extending along the luminal surface. In situ hybridization for PDGF A-chain and beta-receptor mRNAs revealed that the expression of these two genes was closely correlated with the sites of proliferation at each time point. Studies in which BrDU was injected between days 2 and 3 and the animals were killed on day 14 suggested that the proliferating adventitial cells may migrate into the neointima.

CONCLUSIONS

These data suggest that adventitial myofibroblasts contribute to the process of vascular lesion formation by proliferating, synthesizing growth factors, and possibly migrating into the neointima. Increased synthesis of alpha-smooth muscle actin observed in the adventitial cells after arterial injury may constrict the injured vessel and contribute to the process of arterial remodeling and late lumen loss after angioplasty.

Restenosis--an open file

The main procedural drawback to percutaneous coronary angioplasty is restenosis of the treated site within 6 months. Despite advances in equipment, technique, and adjunctive therapies, restenosis has occurred in approximately one-third to one-half of all patients. The biology of restenosis can be divided into plaque persistence and recoil, thrombus formation and transformation, and cellular proliferation and vascular remodeling. Animal models of restenosis have helped to elucidate these mechanisms of restenosis and provide a means to test pharmacologic and mechanical strategies to reduce stenosis recurrence. While numerous agents have been tested in animal models, until recently none has translated into benefit in large-scale clinical trials. Two therapeutic "hopefuls" which have recently emerged in clinical practice are the potent platelet inhibitors, glycoprotein IIb/IIIa receptor antagonists, and intracoronary metallic stents. The IIb/IIIa receptor antagonists target thrombus formation at the angioplasty site, thereby minimizing abrupt vessel closure acutely and neointimal growth chronically, while intracoronary stents safely produce a large coronary arterial lumen acutely and prevent vessel recoil. Separately, these therapeutic strategies have been shown to reduce clinical restenosis 20-30% at 6-month follow-up. With these encouraging results, the future will certainly provide more pharmacologic and mechanical therapies targeting restenosis. With increased understanding of the restenotic process and continued refinement of effective treatments, it may be possible one day to prevent stenosis recurrence.

Role of calcium channel blockers in reducing acute ischaemia and preventing restenosis in PTCA

Calcium channel blockers (calcium antagonists) are widely used before, during and after percutaneous transluminal coronary angioplasty (PTCA). When administered during PTCA, calcium channel blockers may be beneficial in decreasing regional ischaemia in patients with proven or suspected variant angina, as a result of their cardioprotective effects, their ability to enhance collateral flow, and their antispastic effects at the epicardial level. More recently, the agents have also proven to be effective in patients who have developed "no-reflow' phenomenon during PTCA. Preliminary findings suggest that calcium channel blockers may also have potential benefits when administered after angioplasty. The combined results of 5 studies, evaluating a total of 919 patients, showed a trend towards angiographic reduction in restenosis. These observations are of interest but may be due to reporting bias. In conclusion, calcium channel blockers are effective in reducing ischaemia induced by PTCA. These agents may, thus, be appropriate in high risk patients. Further large studies examining the effects of calcium channel blockers on restenosis are required to confirm the observations available to date.

Restenosis following coronary angioplasty: clinical presentations and therapeutic options

Restenosis following angioplasty is an iatrogenic disease of increasing frequency. Restenosis may be defined in terms of either angiographic or clinical criteria. Definitions of angiographic restenosis have varied in different studies, accounting in part for the differences in reported restenosis rates. Most studies now define angiographic restenosis as either a > 50% loss of initial gain or an absolute lesion stenosis of > or = 50% at follow-up angiogram. Common clinical end points used in defining restenosis include recurrent angina, need for repeat revascularization, or myocardial infarction. Despite technical advances and multiple pharmacologic interventions, most studies have found that the incidence of angiographic restenosis remains in the range of 40%; in none of these studies, however, was complete angiographic follow-up obtained, and thus actual restenosis rates may be somewhat higher. In several studies, clinical restenosis has been found to occur in approximately 36-40% of patients. Thus, a minority of patients with angiographic restenosis have no clinical manifestations. Most patients who develop symptoms of restenosis develop these symptoms within the first 3 months after angioplasty. The presenting symptom in the majority of these patients is progressive exertional angina. Patients occasionally will present with unstable angina and only rarely with acute myocardial infarction. In patients who present with recurrent chest pain, several features have been found to be helpful in predicting whether they will have angiographic restenosis at follow-up angiography. Patients who present 1-6 months after angioplasty with typical anginal symptoms have a high likelihood of having angiographic restenosis. By contrast, patients who present more than 6 months after percutaneous transluminal coronary angioplasty with recurrent chest pain are more likely to have new, significant coronary lesions to account for their symptoms. Noninvasive testing in patients with clinical presentations suggestive of restenosis can, in general, add only modest information in predicting whether restenosis is indeed present. A negative exercise thallium test appears to have a high specificity in ruling out restenosis and may be helpful in patients who present with more atypical symptoms. Repeat angioplasty is the therapy most frequently utilized to treat restenosis, although coronary artery bypass surgery or medical therapy may be reasonable alternative therapies. Clinical success rates with repeat angioplasty are > 90%, and major complications are rare; however, restenosis will recur in a significant percentage of these patients. Some patients who develop such recurrent restenoses will ultimately benefit from a strategy of repeat angioplasties, although many will require surgical revascularization.

Effect of nonanticoagulant heparin (Astenose) on restenosis after balloon angioplasty in the atherosclerotic rabbit

PURPOSE

To determine whether intravenous administration of Astenose, a high-molecular-weight nonanticoagulant heparin, can reduce restenosis following balloon angioplasty in a rabbit model.

MATERIALS AND METHODS

Focal atherosclerosis was induced in 54 rabbits (89 vessel), and angioplasty was performed after animals were randomized into five groups. Group 1 vessels (control) were treated with lactated Ringer solution for 28 days (n = 19); group 2, Astenose at 0.10 mg/kg per hour for 28 days (n = 16); group 3, Astenose at 0.33 mg/kg per hour for 28 days (n = 16); group 4, Astenose at 0.60 mg/kg per hour for 28 days (n = 17); and group 5, Astenose at 0.33 mg/kg per hour for 14 days (n = 21). Arteriograms were obtained to measure minimal luminal diameters before, immediately after, and 28 days after angioplasty, and the rabbits were killed for histologic analysis.

RESULTS

Angiographically demonstrated restenosis was significantly reduced in groups 3 (18.9% +/- 3.7, P = .04) and 4 (20.2% +/- 3.1, P = .04) compared with the control group (32.4% +/- 4.8). Group 5 showed a nonsignificant trend toward reduced restenosis (23.1% +/- 2.9, P = .09), and group 2 showed restenosis similar to that in group 1 (31.0% +/- 2.5, P = .80). However, quantitative histopathologic analysis detected no differences among the groups in absolute plaque area. Medial area was significantly smaller in groups 2 and 5 (P < or = .002) than in group 1, and there was a nonsignificant trend toward reduced medial area in groups 3 and 4 (P = .12).

CONCLUSION

Long-term intravenous Astenose therapy resulted in a modest but statistically significant reduction in angiographically demonstrated restenosis after angioplasty in this atherosclerotic rabbit model.

A meta-analysis of randomized trials of calcium antagonists to reduce restenosis after coronary angioplasty

The usefulness of calcium antagonists to reduce restenosis after coronary angioplasty remains uncertain despite 5 randomized trials involving 919 patients. Review and meta-analysis of these trials are performed to provide insight into whether calcium antagonists reduce angiographic restenosis. In aggregate, these trials suggest that patients treated with calcium antagonists had approximately a 30% reduction in the odds of angiographic restenosis (odds ratio = 0.68; 95% confidence interval of 0.49 to 0.94, p = 0.03) compared with control patients. Given the relatively low toxicity and cost of these agents, this reduction in angiographic restenosis may translate into a meaningful clinical benefit. A large, randomized clinical trial should be performed to confirm these findings before widespread adoption of this treatment strategy.

Verapamil treatment after coronary angioplasty in patients at high risk of recurrent stenosis

OBJECTIVE

To evaluate the efficacy of high-dose verapamil treatment (240 mg twice daily) in the prevention of angiographic restenosis after primary successful coronary angioplasty in patients at high risk of recurrent obstruction.

DESIGN

A placebo controlled, double blind trial in which patients with stable angina pectoris and patients with unstable angina or non-Q wave infarction treated with 330 mg aspirin and 75 mg dipyridamole twice daily were randomised to a verapamil group or a control group. Follow up angiography was performed 6 months after angioplasty or sooner if signs of recurrent ischaemia developed.

SETTING

University department of cardiology.

PATIENTS

196 consecutive patients undergoing coronary angioplasty from the beginning of April 1987 to the end of March 1989 and meeting the selection criteria that included the presence of at least one of six predefined risk factors for restenosis. At the time of coronary angioplasty 113 patients had unstable angina or non-Q wave infarction and 83 had stable angina pectoris.

RESULTS

In 89 (91%) patients in the verapamil group and in 83 (85%) control patients follow up angiograms were available. The restenosis rate was lower in the verapamil group (48.3%) than in the placebo group (62.7%) (odds ratio 0.56, 95% confidence interval (CI) 0.303 to 1.025 p = 0.059). Of the 172 patients in whom follow up angiograms were available, 24 (13 taking verapamil and 11 taking placebo) did not comply with the trial for more than 40 (34) days (mean (1 SD)). For the remaining 148 patients the restenosis rate was 47.4% in the verapamil group and 63.9% in the placebo group (odds ratio 0.52, 95% CI 0.271 to 0.993, p = 0.046). In the 97 patients with unstable angina or non-Q wave infarction the restenosis rate was not significantly influenced by verapamil (55.8% with verapamil v 62.2% with placebo, odds ratio 0.77, 95% CI 0.339 to 1.728, p = 0.520). In the 75 patients with stable angina pectoris the restenosis rate dropped from 63.2% with placebo to 37.8% with verapamil (odds ratio 0.36, 95% CI 0.137 to 0.917, p = 0.038).

CONCLUSION

The observed beneficial effect of high-dose verapamil treatment on the angiographic restenosis rate in patients with stable angina pectoris and at increased risk of recurrent obstruction requires confirmation in further prospective studies.

Gamma irradiation inhibits neointimal hyperplasia in rats after arterial injury

BACKGROUND AND PURPOSE

Restenosis complicates a significant proportion of endovascular and open vascular procedures such as carotid endarterectomy. In contrast to the primary atheroma, restenosis is characterized by intimal hyperplasia of vascular smooth muscle cells. We hypothesized that gamma radiation would reduce restenosis by limiting intimal hyperplasia after arterial injury.

METHODS

To demonstrate the effect of gamma radiation on smooth muscle hyperplasia in vivo, a standardized bilateral carotid balloon catheter arterial injury was produced in 37 rats. A single dose of 750, 1500, or 2250 cGy (1cGy = 1 rad) gamma radiation was delivered to the right carotid artery at either 1 or 2 days after injury; the shielded contralateral carotid artery served as matched control. At 21 days after injury, vessels were perfusion-fixed in situ, and cross-sectional area of neointima was determined from axial sections using image analysis.

RESULTS

Marked reductions in neointimal cross-sectional area were demonstrated in vessels subjected to 1500- and 2250-cGy radiation at both 1 and 2 days after injury. A less prominent effect was noted for 750 cGy, reaching statistical significance only at 2 days after injury. By two-way ANOVA, radiation dose (P = .0002), timing of radiation delivery (P = .003), and an interaction between timing and dose (P = .0278) were significantly associated with reduction in neointimal cross-sectional area. At 1500 cGy, delivery of radiation 1 day after injury inhibited neointimal hyperplasia more prominently than the same dose 2 days after injury; a dose-response relation was evident at 1 day.

CONCLUSIONS

Radiation may be an important adjunctive therapy for reducing the incidence of restenosis after angioplasty or endarterectomy.

Southwestern internal medicine conference: restenosis: the Achilles heel of coronary angioplasty

Percutaneous transluminal coronary angioplasty has become the treatment of choice for many patients with symptomatic coronary artery disease. Increased experience with the procedure and improvements in equipment have resulted in high initial success rates; however, a significant number of patients develop restenosis. Insights into the pathophysiologic mechanisms of restenosis have led to the use of various pharmacologic agents and devices to prevent its occurrence. Although many have been successful in decreasing the incidence of restenosis in animal studies, none has yet proven successful in decreasing the incidence of restenosis in humans. Newer approaches and novel therapies are needed to prevent restenosis after percutaneous transluminal coronary angioplasty.

Restenosis after coronary angioplasty

Coronary angioplasty is used to treat coronary disease in many patients. Indications for angioplasty have expanded since it was first performed, mainly as a result of improvement in equipment and techniques. One problem with coronary angioplasty is the phenomenon of renarrowing of the treated coronary lesion, a process called restenosis. The events that constitute restenosis appear to be a universal response to the arterial wall injury of angioplasty. They are currently characterized as follows: platelet adhesion and aggregation on the damaged endothelium and within deep splits into the tunica media; release of platelet-derived growth factors; inflammation of the mechanically injured medial zone; transformation of smooth muscle cells of the tunica media after their activation by several of the growth-promoting substances; migration and proliferation of transformed smooth muscle cells, with secretion of copious amounts of extracellular matrix material; and, finally, termination of the growth process with regrowth of endothelium over the injured area. A decade of research work has helped identify clinical correlates of restenosis after coronary angioplasty procedures. This work is hindered by lack of a uniform angiographic definition of restenosis. In addition, much of the information has come from small studies, with incomplete follow-up and retrospective orientation. Nevertheless, some data are available. Patient-related correlates include male gender, unstable angina, diabetes, and continued smoking after angioplasty. Lesion-related correlates include multilesional and multivessel procedures, higher postangioplasty residual stenosis, proximal vessel location, location in the left anterior descending artery, location in a vein graft, long lesions, and total occlusions. The only consistent procedure-related correlate has been incorrect sizing of the angioplasty balloon to the treated artery. For the purposes of individual patient care, clinical correlates are not helpful. No group of variables has been found to be associated with complete freedom from restenosis, and no group is completely predictive of restenosis. All patients undergoing angioplasty procedures require some follow-up through subsequent months and years. Symptom status and the results of noninvasive studies have been investigated for purposes of follow-up. Symptoms are virtually useless by themselves for predicting restenosis or its absence. When symptom status is combined with exercise thallium 201 scintigraphy performed 4 to 6 months after an angioplasty procedure, the two factors are less than ideal but have a negative predictive value of more than 90%. This means that more than 90% of patients who have neither symptoms nor evidence of ischemia by thallium 201 scintigraphy will not have angiographic restenosis.(ABSTRACT TRUNCATED AT 400 WORDS)

Restenosis after coronary angioplasty

Coronary angioplasty is used to treat coronary atherosclerotic disease in many patients. One problem with coronary angioplasty is the phenomenon of restenosis. Restenosis appears to be a universal response to arterial wall injury. The biological events that underlie restenosis are characterized by: platelet adhesion and aggregation at sites of damaged endothelium, and within dissections into the medial layers, release of platelet derived growth-promoting substances, inflammation of the injured medial zone, transformation, migration, and proliferation of smooth muscle cells of the media following their activation by growth-promoting substances, secretion of copious amounts of extracellular matrix material, and finally, termination of the growth process following regrowth of endothelium over the damaged area. More than a decade of research work has helped identify clinical correlates of restenosis after coronary angioplasty. Patient-related correlates include male gender, unstable angina, diabetes, and continued smoking after angioplasty. Lesion-related correlates include multilesion and multivessel procedures, higher post-angioplasty residual stenosis, proximal vessel location, location in the left anterior descending coronary artery, location in a vein graft, long lesions, and total occlusions. However, for the purposes of individual patient care, clinical correlates are not particularly helpful. No group of variables has predicted complete freedom from restenosis, and conversely no group of variables has reliably indicated its presence. All patients undergoing angioplasty will require some form of follow-up evaluation. Symptom status by itself has not been found to be useful for predicting restenosis. However, when symptom status is combined with exercise thallium-201 scintigraphy, performed 4-6 months after angioplasty, it is less than ideal, but has a negative predictive value of over 90%. This means that over 90% of patients who are asymptomatic and have no evidence of ischemia by thallium-201 scintigraphy, will not have angiographic restenosis. Numerous clinical trials have been performed in order to reduce or prevent restenosis. Almost all have been disappointing, while a few have been encouraging. Studies of antiplatelet agents such as aspirin, dipyridamole (Boehringer Ingelheim Pharmaceuticals Inc., Ridgefield, CT, USA), and Ticlopidine (Syntex, Humgcao, Puerto Rico) have not shown efficacy, yet studies of an inhibitor of platelet-derived growth factor have been provocatively encouraging. No reduction in restenosis rates was found with the anticoagulants Coumadin (Du Pont Pharmaceuticals, Wilmington, DE, USA) and Heparin (Wyeth-Ayerst, Philadelphia, PA, USA). Fish oils (omega fatty acids) have been found in several clinical trials to provide modest, but encouraging, reductions in restenosis, but await further confirmation.(ABSTRACT TRUNCATED AT 400 WORDS)

Generalized model of restenosis after conventional balloon angioplasty, stenting and directional atherectomy

OBJECTIVES

This study was designed to extend the results of a quantitative model originally developed for restenosis after stenting or atherectomy to include restenosis after conventional balloon angioplasty.

BACKGROUND

We have previously described a continuous regression model that explains late (6-month) lumen narrowing as the difference between the immediate gain and the subsequent normally distributed late loss in lumen diameter after Palmaz-Schatz stenting or directional atherectomy.

METHODS

Lumen diameter was measured immediately before and after coronary intervention on 524 consecutive lesions including those treated by Palmaz-Schatz stenting (102), directional atherectomy (134) and conventional balloon angioplasty (288). Of these lesions, 475 (91%) underwent follow-up angiography 3 to 6 months after treatment. The immediate increase in lumen diameter produced by the intervention (immediate gain) and the subsequent reduction in lumen diameter between the time of intervention to follow-up angiography (late loss) were examined. Association between demographic or angiographic variables and continuous measures of restenosis (late lumen diameter or late percent stenosis) was tested with linear regression techniques; a traditional binary measure of restenosis (late diameter stenosis > or = 50%) was evaluated with logistic regression analysis.

RESULTS

Regression models relating late lumen diameter to the immediate lumen result were successfully fitted to all segments studied. According to these models, three indexes of restenosis (late lumen diameter, late percent stenosis and binary restenosis) were found to depend solely on the immediate lumen diameter after the procedure and the immediate residual percent stenosis, but not on the specific intervention used. Moreover, the late loss in lumen diameter was found to vary directly with the immediate gain provided by an intervention, and the "loss index" (a measure that corrects for differences in immediate gain) was uniform among all three interventions.

CONCLUSIONS

The quantitative model originally developed for restenosis after stenting or atherectomy may thus be generalized to include conventional balloon angioplasty. It shows that the apparent differences in restenosis among the three interventions studied are due solely to differences in the immediate result provided and not to differences in the behavior of subsequent late loss. Moreover, although the late loss in lumen diameter was found to correlate with differences in the immediate gain provided by an intervention, the "loss index" (a measure that corrects for differences in acute gain) was uniform across all three interventions. It is thus the immediate result (and not the procedure used to obtain that result) that determines late outcome after coronary intervention.

Biology of restenosis and therapeutic approach

Numerous attempts have been made to prevent restenosis after successful transluminal dilation of an atherosclerotic vessel using a variety of pharmacologic and mechanical approaches. This article reviews the pathobiology of the restenosis process, offers a hypothesis as to its cause, reviews attempts to modify the process, and outlines therapeutic approaches to future treatment.