Methods

Our institution has maintained a database of angioscopic analyses since we first introduced this imaging method. Using this systematic database, we evaluated all 57 coronary artery disease (CAD) patients with DM who underwent angioscopic examination from April 2001 to December 2007. Patients provided informed consent to participate after receiving a full explanation of the study’s purpose, nature, and risks. Patients with coronary arteries who were not anatomically suitable for angioscopy (e.g., ostial stenotic, proximally tortuous, or severely calcified) were excluded.

Patients were diagnosed with stable CAD if they had a positive stress test for myocardial ischemia and no change in the frequency, duration, or intensity of clinical symptoms within 4 weeks, including various combinations of chest, upper extremity, jaw, or epigastric discomfort, or atypical symptoms (e.g., dyspnea or diaphoresis). ACS was defined as the occurrence of ischemic chest discomfort at rest with electrocardiographic changes specific to myocardial ischemia. Patients with an elevated cardiac troponin T level (>0.01 ng/ml) on admission or at 6 to 8 hours after admission were diagnosed with acute myocardial infarction. If no cardiac troponin T elevation was noted, they were diagnosed with unstable angina.

DM was defined as a fasting plasma glucose concentration of ≥126 mg/dl, self-reported clinician-diagnosed diabetes, or a glycated hemoglobin (HbA1c) level of ≥6.5% (National Glycohemoglobin Standardization Program). The value of HbA1c (Japan Diabetes Society +0.4%) was estimated as a National Glycohemoglobin Standardization Program equivalent value calculated using the appropriate formula. DR was diagnosed by a specialist in ophthalmology, using direct ophthalmoscopy through dilated pupils or fundus uorescein angiography, as needed. Retinal findings were classified into 3 categories according to the status of the worse eye: no retinopathic changes, background retinopathy (microaneurysms, microinfarcts, hard exudates, or hemorrhages), and proliferative retinopathy (neovascularization or previous laser coagulation therapy).

Hyperlipidemia was defined as medication-dependent or previously known hyperlipidemia, fasting serum low-density lipoprotein cholesterol ≥140 mg/dl, or fasting serum total cholesterol ≥220 mg/dl.

The coronary angiograms were analyzed with a computer-assisted, automated, edge-detection algorithm (CMS; MEDIS, Nuenen, the Netherlands) using standard quantitative coronary angiography measurements by an expert angiographer who was blinded to the clinical and angioscopic findings The number of stenosed vessels with >50% luminal narrowing in the main coronary arteries was recorded (1- to 3-vessel disease). Abnormal findings were defined as haziness, wall irregularity, or filling defects.

The coronary angioscopic procedure has been reported previously. Before observation, the white balance was adjusted for color correction. The light power was adjusted to avoid reflection and to obtain images with adequate brightness for determination of the plaque color. During angioscopic observations, an assistant adjusted the light power to maintain a constant brightness level on the target plaque. Angioscopic images and fluoroscopy during the angioscopic observations were recorded simultaneously on videotape for later analysis. The yellow grade was classified semiquantitatively according to the surface color: 0, white; 1, light yellow; 2, yellow; or 3, intense yellow. The number of yellow plaques (NYP) was determined for each vessel observed and averaged per vessel. The maximum yellow grade (MYG) was defined as the deepest yellow grade in all the coronary arteries observed in an individual patient. A ruptured plaque was considered to be a wall irregularity, including a tear, flap, or ulceration on the plaque surface. A thrombus was defined as a coalescent red superficial or protruding mass adhering to the vessel surface but clearly a separate structure that remained after flushing with Ringer’s lactate. The angioscopic images were evaluated by an investigator who was blinded to the patients’ clinical characteristics. In a previous study performed in our institution, the intraobserver agreements for thrombus, yellow plaque, and complex plaque were 95%, 100%, and 95%, respectively, and the interobserver agreements were 95%, 98%, and 93%, respectively. The κ values for the intraobserver and interobserver agreements of those items were 0.93, 1.00, and 0.88, respectively, and 0.93, 0.95, and 0.84, respectively. A representative case is shown in Figure 1 .

Representative angioscopy image of patient with DR. No angiographic stenosis was observed in the right coronary artery (Panel A) , whereas an intramural red thrombus was observed at the middle site (Panel C) and 3 yellow plaques were identified on angioscopy (Panels B to D) . The yellow intensity of these plaques was defined as grades 2, 3, and 2, respectively. Significant stenosis was not observed in the left circumflex artery (Panel E) , whereas 2 yellow plaques were defined as grades 2 and 1, respectively (Panels F and G) . A 90% stenosis was identified on angiography in the proximal part of the left ascending artery (Panel H) . On angioscopy, 2 yellow plaques were identified on angioscopy in the proximal and middle parts of the left ascending artery (Panels I and J) . The yellow intensity of these plaques was defined as grades 2 and 3, respectively. In this case, the average NYP was 2.33 (7 yellow plaques in 3 vessels), the MYG was 3.

We followed all patients for de novo ACS events until January 2013. Follow-up data were obtained from medical records and telephone contact. The medical ethics committee at Nippon Medical School, Chiba-Hokusoh Hospital, approved this study protocol (no. 482), and written informed consent was obtained from all patients before the catheterization procedures.

Continuous quantitative data were presented as mean value ± SD. All variables were evaluated using the Student t test. Categorical variables were presented as frequencies and were compared using the Pearson’s chi-square test. Kaplan–Meier survival curves for subjects with DR or non-DR were plotted for incidences of ACS. Differences between the curves were tested by the log-rank test. Cox proportional hazards regression models were used to estimate hazard ratios (HRs) and 95% CIs for incidences of ACS. HRs were adjusted for age. All differences were evaluated at the 95% level of significance (p <0.05). All statistical analyses were performed using IBM SPSS version 21 (IBM Japan, Tokyo, Japan).

Results

The clinical characteristics of the 57 patients are summarized in Table 1 . There were 42 patients (74%) without DR (non-DR group) and 15 patients (26%) with DR (DR group). Eight patients (14%) were receiving insulin, 36 (63%) oral hypoglycemic agents, and the other 18 patients (32%) diet therapy alone. In the DR group, 10 patients (67%) had background retinopathy and 5 (33%) had proliferative retinopathy.

Baseline characteristics did not differ between the groups, except for insulin therapy, which was more prevalent in the DR than in the non-DR group (p <0.001). The mean duration of DM did not significantly differ between the 2 groups (p = 0.102). Mean levels of fasting plasma glucose and HbA1c were also similar between the 2 groups (p = 0.247, p = 0.219, respectively). Statins were prescribed almost equally, in 64% of patients in the non-DR and 60% in the DR group (p = 0.766). Levels of low-density lipoprotein cholesterol were also similar between the 2 groups (p = 0.791).

The angioscopic findings are listed in Table 2 . The distributions of observed coronary arteries were similar between the 2 groups. Total NYP and yellow intensity were higher in DR than in non-DR patients (p <0.001 and p = 0.004, respectively). No significant differences were observed in the frequency of plaque rupture or thrombus (p = 0.188, p = 0.066, respectively). The average NYP per vessel and the MYG are shown in Figure 2 . These values were higher in DR than in non-DR patients (2.08 ± 1.01 vs 1.26 ± 0.77, p = 0.002; and 2.40 ± 0.74 vs 1.90 ± 0.82, p = 0.044, respectively).

Table 2

Angiographic and angioscopic findings

Variable	Retinopathy		p Value
	Absent (n = 42)	Present (n = 15)
Angiographic findings
Severity findings
1-vessel disease	13 (31%)	2 (13%)	0.409
2-vessel disease	14 (33%)	6 (40%)
3-vessel disease	15 (36%)	7 (47%)
Abnormal findings	5 (12%)	4 (27%)	0.223
Angioscopic findings
Observed coronary artey
Left anterior descending	30 (71%)	13 (87%)	0.312
Left circumflex	20 (48%)	5 (33%)	0.381
Right	18 (43%)	5 (33%)	0.558
Total No. of yellow plaques	90	52
Coronary distribution of yellow plaques
Left anterior descending	38 (42%)	28 (54%)	0.395
Left circumflex	20 (22%)	10 (19%)
Right	32 (36%)	14 (27%)
Yellow grade
Grade 1 (light yellow)	35 (39%)	11 (21%)	0.004
Grade 2 (yellow)	44 (49%)	24 (46%)
Grade 3 (intense yellow)	11 (12%)	17 (33%)
Rupture	4 (10%)	4 (27%)	0.188
Thrombus	13 (31%)	9 (60%)	0.066

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