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Angiographic and Clinical Characteristics of Patients with Acetylcholine-Induced Coronary Vasospasm on Follow-up Coronary Angiography Following Drug-Eluting Stent Implantation
Recent studies have shown that drug-eluting stents (DES) induce vascular endothelial dysfunction in both sirolimus-eluting Cypher (Cordis Corporation, Miami Lakes, Florida) and paclitaxel-eluting Taxus stents (Boston Scientific Corporation, Natick, Massachusetts).1–11 These studies evaluated coronary vasomotion in the peri-stent coronary segment for only 1 lesion with 1 DES. However, most of these studies did not mention coronary vasospasm, which can be the strongest manifestation of coronary endothelial dysfunction, of the entire coronary bed. On the other hand, coronary vasospastic angina has ethnic characteristics and has higher frequencies in Asian countries than in Caucasian countries.12,13 In fact, in 2 reports from Asian countries, the coronary endothelial dysfunction observed after DES implantation may have been more severe than that in other studies from European countries and the United States.2,4 Thus, in the present study, we attempted to identify the angiographic and clinical characteristics of real-world Japanese patients with coronary vasospasm after DES implantation.
Methods
Study patients. All patients at our hospital who underwent coronary angiography at follow-up after DES deployment between July 2007 and March 2009 were included. We performed an acetylcholine (ACh) provocation test for diagnosing coronary vasospasm in all subjects, with the exception of those with significant stenosis or in-stent restenosis (ISR) (defined as > 75% diameter stenosis by visual estimation) or contraindications to ACh administration. In 2 patients, the ACh provocation test was performed before DES implantation to rule out coronary vasospasm as the cause of angina pectoris. Although patients with multivessel stenting using 1 DES (Cypher or Taxus) for each coronary artery were included in this study, vessels in which both Cypher and Taxus were implanted in the same vessel were excluded. The ACh provocation test was performed in all patients irrespective of whether they were symptomatic or asymptomatic because silent coronary spasm is clinically important. Written informed consent for the ACh provocation test was obtained from all study patients.
Protocol of coronary spasm provocation test. All anti-anginal drugs were stopped 24 hours before the follow-up coronary angiography. If an angina attack occurred, sublingual nitroglycerine was administered. This test was performed using the routine clinically-driven protocol in effect at our hospital to diagnose coronary spastic angina in patients with chest pain. Control coronary angiograms were taken in the 30 degree right anterior oblique view for the left coronary artery and in the 50 degree left anterior oblique view for the right coronary artery. These angles and skews were kept identical after ACh provocation and isosorbide dinitrate (ISDN) administration. If there was no significant stenosis or ISR, the patient underwent the ACh provocation test. At first, the pacemaker lead was inserted from the brachial vein. ACh (20 µg followed by 50 µg) was injected into the right coronary artery via a diagnostic catheter by manual injection for 30 seconds. An angiogram was obtained after each dose was administered or until an ischemic sign emerged. After the spasm was resolved, ACh (50 µg followed by 100 µg) was administered into the left coronary artery. Final coronary angiograms were obtained after intracoronary injection of ISDN (2–5 mg). During an ACh provocation test, a 12-lead electrocardiogram (ECG) was continuously monitored. If spasm induced unstable hemodynamics or unbearable chest pain, ISDN was injected without provocation of the other vessels. Non-stented vessels were also evaluated as controls in order to assess the vasoconstriction after ACh administration in stented vessels. A positive result was defined as coronary stenosis > 90% using the final angiogram as a reference by visual estimation along with symptoms and any ischemic ECG changes.14,15
Quantitative coronary angiography (QCA). QCA was analyzed by an edge-detection algorithm using the CAAS II system (Pie Medical Imaging, Maastricht, The Netherlands). QCA was performed after baseline angiography, and after intracoronary infusion of ACh or ISDN. The change in vessel diameter was calculated at 3 points in each stented vessel. The 3 different points consisted of proximal, distal, and far distal segments. Proximal and distal segments were defined as those areas 5–10 mm proximal and distal to the stent edge; far distal segments were defined as those 10–20 mm distal to the stent edge. As a control, the change in vessel diameter in non-stented vessels was calculated at the corresponding level to the distal segment. QCA was performed at the most vasoactive points in each of the 4 segments. Coronary artery vasoconstriction was calculated using the following formula: (1 - luminal diameter after ACh infusion/luminal diameter after ISDN infusion) × 100%. QCA and evaluation of the ACh provocation test were performed blindly to both the stent information and clinical features by an independent reviewer.
Relationship between coronary atherosclerosis and ACh-induced coronary spasm. Coronary atherosclerosis was classified according to the American Heart Association classification committee report16 in the DES-implanted vessels as well as in the non-DES implanted vessels. The incidence of atherosclerosis was compared between ACh positive and negative vessels.
Clinical and procedural variables. We compared the clinical features and procedural factors between the groups with the positive and negative results in the ACh provocation test. Commercially-declared values were used for stent size and length. In the multiple stent cases, total stent length was obtained by simple addition, regardless of overlapping, and stent size was averaged. Symptoms manifested after DES implantation were divided into typical symptoms, i.e., angina pectoris (chest pain, oppression) at rest or on effort, atypical symptoms, and asymptomatic.
Clinical follow up. Clinical follow up was performed for all study patients as outpatients or by telephone interview. Symptoms, stent thrombosis, and major adverse cardiac events (target vessel revascularization, myocardial infarction, all-cause death) were evaluated at mid-term follow-up.
Statistical analysis. Data are expressed as mean ± standard deviations or percentages. The frequencies were compared between the groups using the Chi-square or Fisher’s exact test. The two mean values were compared using the non-paired Student’s t-test. The data for total stent length were normally distributed, although there was a slight shift to higher values. Thus, a logarithm of total stent length was also analyzed. A one-way analysis of variance was performed, followed by the Bonferroni test for post-hoc comparison of group means. A confidence level of p
Results
Study population. During the study period, a total of 46 patients with 60 DES-implanted vessels underwent an ACh provocation test. Four patients with 5 vessels 
were excluded from the study because of hybrid use of Cypher and Taxus stents for a single vessel. Thus, the following data were obtained from 42 patients with 55 vessels. Five patients had multivessel stents (4 patients with 2 stented vessels, 1 with 3 stented vessels). Preprocedural ACh provocation test was negative in both patients. The baseline characteristics of the study population are shown in Table 1. There were no significant differences between the two groups with positive and negative ACh provocation test results, with the exception of hypertension. All patients received aspirin and a thienopyridine (ticlopidine or clopidogrel). Other drugs were used at the discretion of the operators. There were no significant differences with regard to the medical therapy.
Positive rate of ACh provocation test (Table 2). Overall, the ACh provocation test was positive in 36 out of 55 vessels (65.4%). There was no significant difference in the positive rate between vessels with a Cypher stent and those with a Taxus stent (18/25 [72.0%] versus 18/30 [60.0%], respectively; p = 0.539).
Comparison of clinical and procedural variables between vessels with positive and 
negative results in ACh provocation test (Table 1). There was no difference in the symptoms between patients with and without a positive rate. A total of 13/20 asypmtomatic patients (65.0%) also showed positive results. Vessels with positive results had a longer stent length compared with those with negative results (31.6 ± 13.6 mm versus 24.2 ± 11.2 mm, respectively; p = 0.049) (Figure 1). 
The total stent length was significantly shorter in the left circumflex artery (LCX) (Table 3). The total number of stents also tended to be larger in the ACh provocation test positive group than in the ACh provocation test negative group (1.51 ± 0.51 versus 1.26 ± 0.45, respectively; p = 0.094).
Location of spasm in stented vessels (Figure 2). Out of 36 vessels, spasm was provoked in the segments distal to the stent alone in 27 vessels. Segments both proximal and
distal to the stent were provoked in 6 vessels. In 3 vessels, a proximal segment could not be evaluated because of ostial stenosis. Spasm was diffuse in all vessels. Spasm started at the just proximal or distal stent edge in 28 vessels, except in 8 vessels where spasm was provoked only in the distal coronary bed apart from the stent edge.
Arterial response to ACh provocation in non-stented vessels (Figure 3). Among the 30 patients with positive results in the stented vessels, twelve (48.0%) also showed 
positive results in non-stented vessels. In 5 patients (9 vessels), the non-stented coronary arteries could not be evaluated because ISDN was administered to resolve severe spasm provoked in the DES-implanted vessels. On the other hand, in the 12 patients with negative results in the DES-implanted vessels, only 2 patients showed positive results in the non-stented vessels. Thus, the frequency of spasm provocation in the non-DES implanted vessels tended to be higher in the ACh test positive group (12/25 versus 2/10, respectively; p = 0.084).
QCA analysis. The coronary vasoconstrictive response to ACh was significantly 
greater at distal, far distal, and non-stent vessel segments in the ACh test positive group than in the ACh test negative group (Figure 4). The vasoconstriction to ACh in distal segments of stented vessels was greater than in non-stented vessel segments at the corresponding level in the total patient population and in the ACh test positive patients (0.46 ± 0.27 versus 0.31 ± 0.20; p = 0.008) (Figure 5). However, there was no difference in vasoconstriction between distal segments in the stented 
vessels and segments of non-stented vessels in ACh test negative patients.
Coronary atherosclerosis and ACh-induced coronary spasm. There were 29 plaques (25% in 20, 50% in 6, 75% in 3 plaques) in 55 DES-implanted vessels. The three 75% stenoses were located in the diagonal artery. Multiple plaques were detected in 6 vessels (2 in 5 vessels and 3 in 1 vessel). Only 9 plaques were involved in the spasm-induced segments. In the lesions with the remaining 20 plaques, spasm was not induced because they were located proximal to the stents, even in the spasm-induced vessels. There were 25 plaques (25% in 14, 50% in 5, and 75% in 6 plaques) in 71 non-DES implanted vessels. Two plaques were detected in 1 vessel. Only 4 plaques were present in the spasm-induced segments; the remaining 21 plaques did not exhibit spasm, even in the ACh-induced vessels. The incidence of vessels with plaque(s) was not statistically different between vessels with positive and negative results in the ACh provocation test for DES-implanted vessels or non-DES implanted vessels (12/36 versus 7/19, respectively; p = 0.795 in DES-implanted vessels and 10/20 versus 13/42, respectively; p = 0.147 in non-DES implanted vessels). The ACh provocation test could not be performed in 9 non-DES-implanted vessels.
Clinical events during mid-term follow up after ACh provocation test. Mean follow-up period was 23.9 ± 4.5 months. Four patients who complained of angina were treated medically. One patient died of unknown causes 7 months after the ACh provocation test. This patient underwent PCI for advanced (90%) stenosis in the right coronary artery 1 month after the test. One patient suffered a cerebral infarction after discontinuation of antiplatelet therapy and another patient experienced cerebral bleeding after falling down. All 7 patients described above had positive results in ACh provocation tests. The frequency of angina was not different between patients with positive and negative results in the ACh provocation test (4/30 versus 0/12, respectively; p = 0.308).
Representative cases (Figures 6 and 7). Figure 6 presents a representative case 
of coronary vasospasm after DES implantation. Coronary vasoconstriction increased gradually in the distal and far distal segments, and ultimately diffuse severe vasospasm occurred in the distal coronary bed. We could perform the ACh test both before and after Taxus stent implantation in the 61-year-old patient shown in Figures 7A and 7B. Coronary artery spasm was induced in the entire distal 
segment starting just adjacent to the distal stent edge.
Discussion
The results of the present study demonstrate that spasm was detected predominantly distal to the stents rather than proximal to the stents. Implanted stent length was longer in ACh test positive vessels than in ACh negative vessels. Although we could not determine the incidence of new-onset spasm after DES implantation (only 2 patients were identified) in this study, vasoconstriction to ACh was exaggerated in DES-implanted vessels compared with non-DES implanted vessels in patients with a positive ACh provocation test result.Prevalence of coronary vasospasm by ACh provocation test in DES implanted vessels. According to a nation-wide study conducted by questionnaire in Japan, ACh and ergonovine tests were performed in a total of 5,267 patients, and the number of positives was 2,316 (44.0%) in 47 hospitals, although there was variation between hospitals.17 Similarly, a recent survey on the prevalence of coronary spasm at multiple institutions in Japan showed that coronary spasm was documented in 921 of the 2,251 consecutive patients (40.9%) with angina pectoris who underwent coronary angiography.18 Another study showed that the prevalence of coronary spasm due to ACh provocation ranged from 33.8% on effort angina pectoris to 49% on rest and on rest and effort angina pectoris.14 Compared to these historical reports, patients in the present study with DES implantation showed higher positive rates. However, the possibility that our study population was more susceptible to coronary spasm before DES implantation cannot be denied.
Coronary vasoconstriction in the peristent area and coronary vasospasm in the far distal coronary bed. Our results are consistent with those of previous studies that reported endothelial dysfunction after DES implantation.1,3,4–8 However, they only examined vasoconstriction in the peristent segments after DES implantation. In a few reports from Asian countries, the arterial response to ACh appeared to be strong, indicating the possibility of coronary vasospasm.2,4,6 Thus, we examined the frequency of provoked spasm in the entire coronary bed as well as peristent vasoconstriction by QCA. The peristent vasoconstriction was stronger in the distal segment than proximal segment. No case had spasm localized in the peristent segment. In almost all cases, strong peristent vasoconstriction was associated with spasm in the far distal bed. Kaku et al19 reported on the incidence of stent-edge spasm after bare-metal stent implantation. Spasm was provoked in 19.2% of the patients with vasospastic angina 6.4 ± 2.0 months after stent implantation. If moderate stent-edge spasm was included, stent-edge spasm occurred in 38.4% of these patients. Even in patients without vasospastic angina, the rate was 30.4%. In our study, the pattern of spasm after DES implantation was different to that in bare-metal stents. This might be due to the pathogenesis of ACh-induced spasm after DES implantation.
Factors related to ACh-induced coronary vasospasm in DES-implanted vessels. This study is the first description of the clinical features of patients with ACh-induced coronary vasospasm following DES implantation. The Cypher and Taxus stents showed similar results to those already reported.6 The total stent length was longer in ACh test positive vessels than in ACh negative vessels. Although the frequency of spasm tended to be lower in the LCX, it seemed to be related to total stent length, as shown in Table 3. Infarct-related arteries have been reported to be associated with endothelial dysfunction showing a high spasm provocation rate.20,21 Indeed, all 6 infarct-related coronary arteries showed positive results in the ACh test, although the frequency was not statistically significant. In both Japan and Caucasian countries, the frequency of a positive rate in the spasm provocation test decreases as time passes.12,22 In Japan, the frequency was 22–37% after 1 month, while in other countries it was 6.2% after 6 weeks.12 Thus, the influence of infarction on spasm is thought to be low because the mean duration after DES implantation is over 1 year in this study. The extent of atherosclerosis was not related to the results of ACh provocation tests in either the DES-implanted or non-DES implanted vessels.
Potential clinical relevance of asymptomatic coronary vasospasm in DES-implanted vessels. It is well known that coronary spasm plays an important role in acute myocardial infarction (AMI) patients.20,23 A previous study has identified aggravated coronary spasm as a risk factor for AMI and cardiac death. It has been reported that coronary spasm is a trigger for coronary thrombus and subsequent AMI.24 It was also reported that provoked coronary spasms are closely associated with the prognosis of AMI patients.25 On the other hand, DES have the challenging problem of late or very late stent thrombosis. Several reasons have been proposed for this thrombosis, including stent malapposition26 and chronic inflammation.27 Even death has been reported among patients with severe coronary vasospasm after DES implantation.28 Spasm may have been a potential risk factor for stent thrombosis in both symptomatic and asymptomatic patients who showed ACh-induced spasm in this study. Thus, we propose the potential benefit of calcium-channel blocker administration as a clinical implication of this study for prevention of stent thrombosis, particularly in patients with long DES, but also in asymptomatic patients. Although the study size was small, the incidence of cardiac events was relatively low and not different between patients with positive and negative results in ACh provocation tests. The symptoms of angina observed in 4 patients might have been related to the coronary spasm that occurred after DES implantation. The cause of 1 sudden death was unknown. A larger study is warranted to clarify the clinical significance of this clinical entity.
Study limitations. There are several limitations associated with this study. First, we did not evaluate baseline endothelial dysfunction before DES implantation in all patients. Thus, we cannot exclude the possibility that in some patients, factors relevant to intrinsic spasm already existed prior to DES implantation. We were able to evaluate baseline endothelial dysfunction in 2 cases with negative results. Second, ACh infusion was performed manually from the diagnostic catheter via the coronary artery ostium. However, the infusion speed was kept constant as much as possible and the injection time was accurately measured. With this method, we could administer ACh into the left anterior descending coronary artery and LCX at the same time. Third, the results of the ACh test were evaluated by visual estimation, but not QCA. Typical focal or diffuse vasospasm by ACh shows very severe narrowing even though they are not subtotal or total occlusions. The minimal lumen diameter seems to be too small for QCA evaluation. For diameters smaller than 0.75 mm, edge detection tends to overestimate the minimal lumen diameter.29,30 Fourth, smoking is a well-known risk factor for coronary spasm. We included the current smokers and did not prohibit smoking before the study. Thus, a smoking habit might have partly influenced the results of the coronary spasm provocation test. Fifth, variant angina has been reported to have inherent fluctuations in the strength and location of provoked spasm in some patients during long-term follow up. We should also consider this phenomenon when evaluating the location and degree of induced coronary artery spasm.31,32 Sixth, we could not compare the features of coronary vasoconstrictions after bare-metal stent, first-generation DES, and second-generation DES implantation. Finally, this study could not elucidate the differences in clinical long-term outcomes between patients with positive and negative results in the ACh provocation test. A larger study is warranted to elucidate this important aspect of DES in not only first-generation DES but also in bare-metal stents and second-generation DES.
Conclusion
Coronary vasoconstriction was exaggerated at distal segments in DES-deployed vessels compared to non-stented vessel segments and stent length was longer in the ACh provocation test positive group.
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