Domestic pigs, 25–35 kg in weight, were premedicated with 300 mg aspirin, 180 mg diltiazem, and 500 mg ticlopidine. Induction of general anesthesia was accomplished with intramuscular injections of ketamine (12 mg/kg) and xylazine (8 mg/kg). Local anesthesia of the mid-cervical region, using 2% lidocaine, was also applied prior to exposure and cut-down of the carotid artery using a midline cervical approach. The left carotid artery was cannulated with an 8 Fr. sheath. Under fluoroscopic guidance, with a C–arm (BV–25 Gold, Phillips, Best and Heerlen, Netherlands), catheters (7–8 Fr.) were advanced to the coronary ostia. Throughout the duration of the invasive procedures, the pigs were supplied with continuous oxygenation via face masks. Saline was infused through the auricular vein. The electrocardiography and blood pressure were monitored continuously. This study was approved by the Ethical Research Committee of the Chonnam National University Hospital.

Twelve pigs received a local delivery of radiopharmaceuticals with either ^99mTc–pertechnetate (n=5) or ^99mTc–HMPAO (n=7). Upon positioning of the catheter at the target region of the coronary artery, 1,110 MBq (555 MBq/mL) of the radiopharmaceutical were infused, at a rate of 1 mL/min, followed by infusion of physiologic saline for 5 minutes. The actual radiation dose delivered was determined using a dose calibrator on dissected coronary arteries. The residual radiation in the syringe and catheters were quantified and subtracted from the initial administered dose.

Experiments were performed on ten pigs. In the control group (n=3), balloons were attached to Palmaz–Schatz stents (Johnson & Johnson, Piscataway, NJ) and inflated in the coronary artery to 1.3 times the reference vessel diameter. In the experimental group (n=7), 1,110 MBq (555 MBq/mL) ^99mTc–HMPAO was delivered via a Dispatch Catheter (Boston Scientific, Boston, MA) prior to balloon dilation, as described for the control group. ^99mTc–HMPAO was infused using an infusion pump, such that a 1,110 MBq dose would occupy 2 mL of the syringe, at a rate of 1 ml/min followed by infusion of physiologic saline for 5 minutes. The diameter of the Dispatch catheter and balloon selection (3–4 mm) was determined by quantitative analysis of the coronary angiograms. Spiral balloons on the Dispatch Catheter were deployed with 4 atm of pressure. During local delivery of the ^99mTc–HMPAO, a radiocontrast dye was infused through the central channel to demonstrate the blood flow distal to the Dispatch catheter. Precautions were taken to avoid ischemia in the distal segment during the ^99mTc–HMPAO delivery. A Palmaz–Schatz stent was placed in the right coronary artery (RCA) and expanded with 8 atm of pressure for 20 sec using a non–compliant PTCA balloon catheter and standard indeflater. Neither heparin nor nitrates were administered after placement of the stent. Upon completion of the experiments, the carotid artery was repaired, and the incision site was sutured. Follow–up angiograms were obtained four weeks after the experiments. Quantitative analysis was performed with an image analyzer (Cardio 500, Kontron Inc., Eden Prairie, MN).

One pig was sacrificed after the local ^99mTc–HMPAO delivery. The hearts was extracted, rinsed, and the epicardial coronary arteries identified. A large section, including the entire coronary artery and surrounding myocardium, was obtained. Sections were placed in a container with dry ice vapor and packed in dry ice. Using a microtome, 20–40 mm sections were made, mounted on glass slides, and air-dried. In a darkroom, the glass slides were covered with X-ray film (NMB film) and stored at 70°C. The exposure times were 2, 8 and 18 hours. After developing the autoradiographs, the glass slides were stained with Hematoxylin and Eosin (H&E) ^{8, 9)}. Densitometry was performed using Image Pro Plus (Media Cybernetics, Silver Spring, MD).

The amount of radiation absorption in the vascular wall was determined according to the Monte Carlo Simulation Study using the EGS4 code. A cylindrical model was implemented in the description of the vessel. Assuming a 1 mm central lumen, the intima, media and adventitia were described as concentric cylinders, with wall thickness of 0.27, 0.82 and 0.12 mm, respectively. The distribution of ^99mTc–HMPAO was determined by setting the target volume to the smooth muscle layer. A computer analysis was repeated until the standard deviation (SD) was less than or equal to 5%.

Thierens et al.¹⁰⁾ reported that intracellular radiation in lymphocytes, by Auger electrons from ^99mTc–HMPAO, was equivalent to 20 to 30 times the external x-ray irradiation. Thus, the theoretical dosimetry was calculated as the number of cells in the coronary arterial wall exposed to intracellular irradiation from ^99mTc–HMPAO.

After follow-up coronary angiography, the pigs were sacrificed by an intravenous injection of barbiturates or KCI. The extracted porcine heart was fixed in 10% formalin solution for 24 hr. The stents in the isolated coronary arteries were easily identified under fluoroscopic guidance and were also readily palpable. Each coronary artery was dissected to remove the stented portion, including a 1 cm vessel segment both proximal and distal to the stent. Sections of the stented portion were taken at 2–3 mm intervals with a stereomicroscope to avoid distortion of or damage to the artery. Each section of the stented portion of the coronary artery was H&E stained. In order to assess neointimal proliferation, immunohistochemistry was performed using a murine monoclonal antibody (clone PC 10, Dako, Carpinteria, CA) to the proliferating cell nuclear antigen (PCNA). All morphometric analyses were performed using image analysis systems, according to previously established methods^{11, 12)}. The lumen diameters were determined using calibrated digital microscopic planimetry. Subtraction of the cross–sectional areas of the lumen (luminal area), internal elastic lamina (IEL) and external elastic lamina (EEL) from that of the vessel wall yielded the cross–sectional area of the neointima and media. Reference values for the vessel wall thickness were obtained from the averages of those found 1 cm proximal and distal to the stented region. The neointimal cross–sectional area was determined by subtracting the luminal area from that demarcated by the IEL. The degree of restenosis was calculated as the percent area of restenosis (%) = 100 (1–luminal area/IEL area).

All data are shown as the average ± standard error, and the comparison between the two groups was performed using unpaired Student’s t– and Chi–squared tests. A p value less than 0.05 was considered as significant.

Of the patients attending the heart center the Chonnam National University Hospital between June and Oct. 2001, 11 (10 males, mean age 62.4±5.7 years) that had had a coronary artery stent restenosis lesion and simultaneous local delivery of ^99mTc–HMPAO the same way as in the animal experiment following PCI, were entered onto this study

The subject patients were administered 1.100MBq (30 mCi)/2 mL, with the Dispatch Catheter™ following a successful PCI, in the same way as in the animal experiments. Both pre– and post–PCI, electrocardiogram, CBC, and chemistry tests were performed.

From quantitative coronary angiography, some patients were chosen whose vessel diameter and lesion length were 2.5–4.0 and under 20 mm, respectively. The informed consent of these patients were obtained. Patents with acute myocardial infarctionwithin 72 hours, a thrombus–containing target lesion, graft vessel PCI and chronic total occlusion were excluded, and those with more than 30% remaining stenosis post–PCI and no complications, such as coronary artery dissection, acute vessel closure or myocardial infarction, were included.

Coronary angiography was performed before and 6 months after PCI. Significant coronary artery stenosis was defined as over 50% stenosis of the major coronary artery or of the diameter of the major branch. The morphological classification of the stenotic areawas in accordance with the guidelines of the American College of Cardiology/American Heart Association (ACC/AHA). The reference vessel and minimal luminal diameters were measured using the Philips H5000 or Allular DCI program pre and post–PCI. Every patients took aspirin (100–200 mg) and either ticlopidine (500 mg) or clopidogrel (75 mg) one or twice a day pre–PCI, and aspirin constantly and ticlopidine or clopidogrel for 6 months post–PCI. PCI was undertaken on the coronary artery lesion using the currently preferred techniques. The femoral artery sheath was removed 6 hours post–PCI, and heparin was only administered if there was complication. Compression of the vascular access site was performed for 20 minutes by a well–trained doctor, and then pressed employing a Femostop device. Following PCI, those cases where the remaining restenosis was under 30%, myocardial infarction was not observed on EKG, cardiac enzyme assay, and major complications, such as emergent coronary artery bypass graft (CABG), and coronary revascularization, or death did not doccur, were considered successful. In–stent restenosis was classified by the criteria of Mehran et al¹³⁾, which was deemed to have occurred when the restenosis was over 40% that of the normal diameter.

As the follow-up the major adverse cardiac events (MACE) and survival were analyzed once a month at the out patients department, In–hospital MACE were defined as cardiac death, myocardial infarction, CABG, any stroke, and target lesion revascularization. The primary end point was the result of quantitative coronary angiography from the follow–up coronary angiography by 6 months; the second end point was cardiac death, myocardial infarction, target vessel revascularization or a stroke.