Effects of Coronary Stenting on Restenosis and Occlusion After Angioplasty of the Culprit Vessel in Patients With Recent Myocardial Infarction
Background PTCA of an infarct-related lesion is associated with a high rate of restenosis and/or vessel occlusion. Recent studies have shown that coronary stenting in patients with stable or unstable angina is associated with a significant reduction in the restenosis rate compared with conventional balloon angioplasty. However, no information is available concerning the long-term effect of coronary stenting at infarct-related lesions compared with balloon angioplasty alone.
Methods and Results One hundred consecutive patients undergoing stent implantation at an infarct-related lesion and systematic 6-month angiographic follow-up were matched for major pre-PTCA clinical and angiographic variables with a group of patients undergoing conventional angioplasty. Preprocedural, postprocedural, and 6-month follow-up angiograms were analyzed with quantitative angiography. Coronary stenting was performed as a bailout procedure after failed balloon angioplasty in 20%, for a suboptimal result after balloon angioplasty in 71%, and electively in 9%. Stent implantation was associated with a higher acute gain than balloon angioplasty. At follow-up, the minimal lumen diameter was significantly (P<.0001) larger in the stent group (1.72±0.69 versus 1.23±0.72 mm). Restenosis (>50% DS at follow-up) occurred in 27% of the stent group versus 52% of the balloon group (P<.005). At follow-up, total occlusion at the dilated site occurred in 1% of the stent group versus 14% of the balloon group (P<.005).
Conclusions Coronary stenting of infarct-related lesions is associated with a highly beneficial effect on 6-month angiographic outcome compared with balloon angioplasty alone. Further studies are needed to establish whether the beneficial effect of coronary stenting on long-term vessel patency is associated with an improvement in left ventricular function or in clinical outcome.
Recent studies have emphasized the importance of a patent infarct-related vessel after acute MI. Experimental and clinical studies suggest that a patent infarct-related vessel has beneficial effects on ventricular remodeling and on the subsequent occurrence of arrhythmias and may favorably affect survival.1 2 3 4 5
Thrombolytic therapy remains the most frequently used therapeutic option in patients with acute MI. However, angiographic studies have shown that thrombolytic therapy results in sustained patency of the infarct-related vessel in fewer than two thirds of cases.6 Angiography with a view to subsequent revascularization is frequently performed in the weeks after infarction. Although PTCA of an infarct-related lesion can be performed with a high rate of immediate success, the long-term benefit of the procedure is hampered by the frequent occurrence of restenosis and of reocclusion. Previous reports have shown that up to 50% of the patients with initial angiographic success develop restenosis at 6-month follow-up7 ; furthermore, 10% to 15% of patients have complete occlusion at the PTCA site,7 8 a rate much greater than that reported after angioplasty of non–infarct-related vessels, in which occlusion at the dilated site is extremely rare.9 In this particular setting, vessel occlusion (even if it occurs late after the acute phase) is associated with a significant deterioration in left ventricular function and with a higher incidence of clinical events (recurrent MI, need for repeat revascularization, or death).7 8 10
Two large randomized studies have shown that coronary stenting in patients with stable or unstable angina is associated with a significant reduction in the restenosis rate compared with conventional balloon angioplasty.11 12 Recent studies have shown that coronary stenting can be performed at infarct-related lesions with excellent short-term outcome13 14 ; however, no information is available concerning the long-term effect of coronary stenting at infarct-related lesions compared with conventional balloon angioplasty.
We thus designed a study to analyze restenosis and occlusion rates in a group of consecutive patients undergoing coronary stent implantation at an infarct-related lesion. These patients were matched for major pre-PTCA clinical and angiographic variables with a group of patients undergoing conventional balloon angioplasty of an infarct-related lesion. The occurrence of occlusion and/or restenosis at 6-month follow-up was compared between the two groups by quantitative angiography.
From the records of our catheterization laboratory, we identified 118 consecutive patients who, between October 1993 and February 1996, underwent successful stent implantation at an infarct-related lesion 24 hours to 30 days after an acute MI. The infarct-related artery was determined from the entry ECG, ventriculographic contraction abnormalities, and coronary angiographic findings. During the time period of this study, the strategy management in patients undergoing coronary angiography after a recent MI in our institution was to perform immediate angioplasty of the infarct-related vessel, provided that the DS was >50% and that the overall anatomy of the coronary vessels did not preclude angioplasty, eg, left main coronary artery disease and lesions judged unsuitable for angioplasty by the investigator.
Coronary stenting was performed by standard techniques as previously described.15 The reasons for stent placement were classified into three categories: (1) bailout implantation (for acute or threatened acute occlusion during or after the procedure), (2) implantation for a suboptimal result (presence of a visually estimated residual stenosis >40% after dilatation), or (3) elective implantation (when it had been decided before the procedure). Stent implantation was considered successful when the residual luminal narrowing immediately after stent implantation was <30% according to a visual estimate and when no major complication (ECG or enzymatic evidence of MI, the need for bypass surgery during hospitalization, or in-hospital death) occurred. At the time of stenting, all the patients were asked to return for a 6-month follow-up angiogram, regardless of symptomatic status; angiography was performed earlier if there was a clinical indication. Angiographic follow-up was actually performed in 100 patients (85%), who form the stent group. Clinical follow-up was obtained for the 18 patients who did not return for the scheduled angiogram: 2 patients died during the follow-up period, and 16 were asymptomatic, had no event during the follow-up period, and refused the angiographic control.
To compare the results of coronary stenting and balloon angioplasty, 100 patients who underwent balloon angioplasty of an infarct-related lesion were individually matched with the 100 patients of the stent group for sex, diabetes, thrombolytic treatment for MI, stenosis location, reference diameter (within a range of ±0.4 mm), and MLD (within a range of ±0.4 mm). The 100 patients of the balloon group were selected from a consecutive series of 770 patients who were successfully dilated at an infarct-related lesion with balloon angioplasty between January 1989 and February 1996 and who underwent systematic 6-month angiographic follow-up. The matching was performed by a single investigator who was unaware of the 6-month angiographic outcome of the lesions.
Qualitative analyses were performed independently by two experienced interventional cardiologists. Disagreements were resolved by a further joint reading. Lesions were classified in accordance with the American Heart Association/American College of Cardiology classification as modified by Ellis et al.16 The anterograde blood flow was graded according to the classification of the Thrombolysis in Myocardial Infarction Study group.17
Quantitative computer-assisted angiographic measurements were performed on end-diastolic frames with the computer-assisted evaluation of stenosis and restenosis (CAESAR) system. A detailed description of this system has been reported previously.18 We routinely perform angiography in at least two projections after the intracoronary injection of isosorbide dinitrate (2 mg). These projections were recorded in our database, and the follow-up angiogram was performed, after injection of isosorbide dinitrate, in the same projections. The following definitions were used: the acute gain associated with the procedure was defined as the difference between the MLD immediately after the procedure and the MLD before the procedure; the late loss during the follow-up period was defined as the difference between the MLD immediately after the procedure and the MLD at follow-up; the net gain was defined as the difference between the acute gain and the late loss; and finally, restenosis was defined as a >50% DS at follow-up.
Data are presented as mean±SD. Comparisons between groups for continuous data were performed with Student’s t tests. Differences between proportions were assessed by χ2 analysis. A value of P<.05 was considered to indicate statistical significance. A multivariate logistic regression model was used to examine the effect of stent implantation on restenosis adjusted for age, sex, diabetes, hypertension, smoking, family history of coronary artery disease, hypercholesterolemia, unstable angina, time interval from MI to angioplasty, stenosis location, reference diameter, preprocedural DS, and postprocedural DS; adjusted odds ratio and 95% CIs were calculated. Statistical analysis was performed with SAS software (version 6.10; SAS Institute Inc).
There was a high proportion of men (89%), with a mean age for all patients of 57±11 years. The baseline characteristics for the two groups of patients are shown in Table 1⇓. The adequacy of the matching process was confirmed by the lack of differences between groups with respect to sex, diabetes, thrombolytic treatment for MI, and stenosis location. There were no statistically significant differences in any other baseline characteristics between the two groups except for the antiplatelet treatment administered after the procedure: the majority (97%) of the patients in the stent group received a combination of ticlopidine and aspirin, whereas the majority (89%) of the patients in the balloon group received aspirin alone.
In the stent group (Table 2⇓), stenting was performed as a bailout procedure after failed balloon angioplasty in 20%, for a suboptimal result after balloon angioplasty in 71%, and electively in 9%. Palmaz-Schatz stents were used in the majority of cases (67%). In 81%, a single stent was used. High-pressure inflation (>12 atm) was used to deploy the stent in most cases (mean inflation pressure, 14±4 atm).
The luminal dimensions at baseline, immediately after the procedure, and at follow-up are shown in Table 3⇓ and the Figure⇓. At baseline, there were no differences in reference diameter or in stenosis severity between groups. Immediately after the procedure, as a result of the larger acute gain in the stent group (P<.0001), the MLD (2.58±0.44 mm) was significantly greater in the stent group than in the balloon group (1.97±0.43 mm, P<.0001). At follow-up angiography, despite a trend for a higher late loss, patients in the stent group had a larger net gain (1.02±0.79 versus 0.56±0.68 mm, P<.0001), resulting in a larger MLD at follow-up (1.72±0.69 versus 1.23±0.72 mm, P<.0001). When analyzed by the categorical approach with the >50% DS criterion, 27% of the stent group and 52% of the balloon group had restenosis (P<.005). At 6-month follow-up, the rate of target vessel revascularization was 13% in the stent group versus 35% in the balloon group (P<.0005).
Total occlusion of the dilated site at follow-up occurred in only 1% of the stent group but in 14% of the balloon group (P<.005). When patients with total occlusion at follow-up were excluded from the analysis (Table 4⇓), the net gain and the MLD at follow-up were still significantly higher in the stent group than in the balloon group (net gain, 0.96±0.76 versus 0.72±0.59 mm, P<.05; MLD at follow-up, 1.72±0.68 versus 1.45±0.56 mm, P<.005).
To confirm the beneficial independent effect of stent implantation on restenosis, we performed a multivariate logistic regression including the following variables: age, sex, diabetes, hypertension, smoking, family history of coronary artery disease, hypercholesterolemia, unstable angina, time interval from MI to angioplasty, stenosis location, reference diameter, preprocedural DS, and postprocedural DS. The adjusted odds ratio of the effect of stent on restenosis was 0.37; 95% CI, 0.15 to 0.95; P<.04. Other variables associated with restenosis were a high preprocedural DS, left anterior descending artery location, and hypertension. In the stent group, the sole procedural characteristic associated with restenosis was the implantation of more than one stent (P<.05).
This study demonstrates that coronary stenting for an unsatisfactory result after angioplasty of infarct-related lesions is associated with a highly beneficial effect on 6-month angiographic outcome compared with balloon angioplasty alone.
Coronary stenting is emerging as an effective treatment for patients with coronary artery disease. Recent studies have shown that implantation of permanent metal prosthetic stents significantly reduces clinical and angiographic recurrence rates compared with conventional balloon angioplasty11 12 ; these two studies, however, excluded patients with recent MI. Furthermore, the greater thrombotic potential of such lesions was until recently considered to be a relative contraindication to stenting in this setting. More recently, probably as a result of new poststent management regimens and optimal deployment of the prosthesis, stent implantation has been performed at infarct-related lesions with an excellent short-term outcome.13 14 However, it is not known whether stenting improves clinical and angiographic outcome in the longer term in this setting. The assessment of long-term outcome by angiography in this group of patients is of critical importance, because restenosis and especially reocclusion may be clinically silent.7
Balloon angioplasty of infarct-related lesions is associated with a high rate of angiographic restenosis.7 8 This high rate of recurrence may be related to the unstable nature of the underlying atherosclerotic plaque and/or to superimposed residual thrombus. Indeed, we have recently shown, using coronary angioscopy, that the presence of an intraluminal thrombus at the PTCA site before the procedure, a very common finding in the weeks after an MI,19 was a strong predictor of restenosis at 6-month follow-up.20 Two different mechanisms appear to be involved in lesion recurrence after balloon angioplasty in this setting: progressive luminal renarrowing, as documented after angioplasty of stable lesions, and total occlusion (ie, reocclusion) of the infarct-related vessel, which occurs in 10% to 15% of the patients.7 8 This high rate of occlusion, which is much greater than that seen in patients undergoing elective angioplasty at non–infarct-related lesions,9 accounts for the excess rate of restenosis after PTCA at infarct-related lesions. In the present study, the 52% overall restenosis rate and the 14% occlusion rate observed in the balloon group are concordant with previously published data7 ; the angiographic outcome of the patients selected by the matching process thus appears to be representative of the angiographic outcome after balloon angioplasty of infarct-related lesions.
In the present study, coronary stenting for an unsatisfactory result after balloon angioplasty of infarct-related lesions was associated with a major reduction in the restenosis rate. This effect is mainly due to the dramatic reduction (from 14% to 1%) in the rate of occlusion at stented lesions compared with that observed at lesions treated by balloon angioplasty alone. The exact mechanism(s) responsible for the effect of stents in preventing vessel occlusion is not known but may be related to a consolidation of the ruptured atherosclerotic plaque, to an improved acute result with a better postprocedural flow that would decrease the risk of thrombosis, or to an antithrombotic effect of ticlopidine. Recent studies have shown that the combination of aspirin and ticlopidine, a potent antiplatelet agent,21 is very effective in preventing subacute stent thrombosis.15 22 In the present study, 99% of the patients received ticlopidine after stent implantation compared with 1% in the balloon group; therefore, we cannot exclude the possibility that the use of ticlopidine may have contributed to the lower rate of occlusion in the stented group. However, the beneficial effect of coronary stenting at infarct-related lesions does not appear to be related solely to an “antithrombotic” effect. When patients with total occlusion of the dilated site at follow-up were excluded from the analysis, the 6-month angiographic outcome was still significantly better in the stent group. This result is concordant with previously published studies in which coronary stenting in an elective setting has reduced restenosis rates.11 12
Although the end points of this study were solely angiographic, our results may have important clinical implications. Previous studies (reviewed in Reference 1010 ) have shown that reocclusion of an infarct-related vessel, even if it occurs late after the acute phase, precludes left ventricular contractile recovery and may be associated with recurrent angina, reinfarction, or death. We have recently shown that occlusion of the culprit vessel after successful PTCA in patients with a recent MI was associated with a deterioration in left ventricular function at follow-up.7 Further studies will be needed to demonstrate whether the beneficial effect of coronary stenting on long-term vessel patency is associated with an improvement in left ventricular function or in clinical outcome.
Potential limitations of this study need to be addressed. First, most of the patients in the stent group were not treated electively but because there was a suboptimal result after balloon angioplasty or as a bailout procedure. However, because bailout coronary stenting has been associated with high restenosis rates,23 one would expect an even better 6-month angiographic outcome if the procedure had been performed electively. Second, our study included only patients who underwent delayed (>24 hours) coronary stenting of an infarct-related lesion; further studies are needed to determine whether immediate coronary stenting of an infarct-related lesion is also associated with an improved long-term angiographic outcome. Finally, it must be acknowledged that this retrospective study based on matching does not have the value of a prospective randomized study. However, in the past, similar studies based on matching performed to analyze angiographic outcome after directional coronary atherectomy24 or coronary stenting25 have accurately predicted the results of prospective randomized trials.11 12 26
Selected Abbreviations and Acronyms
|MLD||=||minimal lumen diameter|
|PTCA||=||percutaneous transluminal coronary angioplasty|
- Received March 24, 1997.
- Revision received June 13, 1997.
- Accepted June 14, 1997.
- Copyright © 1997 by American Heart Association
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