ABC | Volume 110, Nº5, May 2018

Original Article Gabriel et al Diagnosis of coronary artery disease Arq Bras Cardiol. 2018; 110(5):420-427 Therefore, the main aim of this study is to evaluate the frequency of coronary atherosclerotic plaque, its degree of obstruction and associated factors in patients with zero CS and clinical indication for CCTA. Methods Subjects This was a cross-sectional, analytical, prospective study carried out from April 2011 to November 2016. Subjects were consecutively and not randomly selected, and subjected to CCTA by referral from their assistant physicians in four diagnostic imaging centers, two public centers: Instituto Dante Pazzanese de Cardiologia de São Paulo-SP e Hospital Universitário do Campus da Saúde Dr. João Cardoso Nascimento da Universidade Federal de Sergipe and two private centers: Hospital Primavera e Clínica de Medicina Nuclear e Diabetes-CLIMEDI. Data on cardiovascular risk factors were collected from each participant. Chest pain was classified according to the Diamond and Forrester method, and most patients were classified as at intermediate risk for CAD. Patients with no calcium in the coronary arteries (zero CS) were included. Patients who had undergone percutaneous or surgical myocardial revascularization, patients with history of acute coronary syndrome or cardiomyopathy of ischemic cause, and those who declined to participate were excluded. The tests performed at private institutions were free of charge for both patients and investigators. The study was approved by the research ethics committee (CAAE identification number 0289.0.107.000-11). CS and CCTA of coronary arteries CCTA of coronary arteries were performed using a 64-slice (or greater) scanner of the following models and manufacturers: Aquilion64 ™ - Toshiba™ Medical Systems Corporation, Otawara, Japan and Discovery STE VCT - General Electric Company, Connecticut, USA. Non-contrast computed tomography for CS analysis was carried out using a longitudinal scan coverage from the level of the tracheal bifurcation to the superior border of cardiac silhouette, including the whole diaphragm for evaluation of the whole cardiac area. For CS examination, a field of view (FOV) of 200 mm was used, slice thickness 2.5-3 mm and interval 1.25-1.5 mm, 2 x 32 x 0,6 mm collimaton, rotation time 350 msec, tube current up to 600 mAs. The study was conducted in two phases: in the first phase, CS was determined by the Agatston score; 6 calcification was defined as the presence of a lesion with an area greater than 1 mm 2 , and peak intensity equal to or greater than 130 Hounsfield Units (HU), which was automatically identified and marked with color by the software. The presence of coronary plaques and extension of stenosis was evaluated in patients with zero CS. In the second phase, CCTA was performed using the CS parameters for FOV construction, voltage 120 kv, and 400 miliamperes. Up to 1.5mL/kg iopamidol was administered intravenously to patients still positioned on the table. Iopamidol is a nonionic, iodinated contrast, administered at concentrations of 350-370 mg/mL and rate of 4.5-5.5 mL/s (Ultravist® 370, Bayer HealthCare and Pharmaceuticals, Berlin, Germany; HenetiX® 350, Guerbet, Paris, France). An oral betablocker was administered within 24 hours before the test, or intravenously on the day of the test in patients with sinus rhythm and heart rate (HR) > 70 bpm. The system uses HR values monitored during the exam to establish the parameters for imaging acquisition, such as the helical pitch (relationship between table distance traveled in one 360° X-ray tube rotation, slice thickness and the number of detector rows), speed of gantry rotation, and exposure time, to achieve the best possible temporal resolution. Images were sent to the workstation for analysis of coronary arteries by three experienced observers. The presence of atherosclerotic plaque was examined in vessels with a luminal diameter larger than 2 mm, divided into 15 segments. 7 Extension of stenosis was estimated by calculating the area of the narrowest part of the lumen in relation to the area of the lumen immediately distal to the same segment. Plaques detected by the CCTA were classified into nonobstructive and obstructive lesions, with a reduction ≥ 50% of the lumen in the latter. Data analysis Quantitative variables were described as mean and standard deviation. Kolmogorov-Smirnov test was used to test normality of the sample. The Student’s t-test was used for independent groups, according to data normality. Absolute and relative frequencies were used for categorical variables. For between‑group comparisons of these variables, the chi-square test of the Fisher’s exact test was used as appropriate. Differences were considered statistically significant when probabilities were lower than 5% (p≤ 0.05) and power of 0.80. For analysis of independent predictors for the presence of plaque, a manual backwards selection (Backward:Wald method) for logistic regression was used. A p ≤ 0.25 was considered for an initial selection and the variable was maintained in the model when p < 0.05. The outcome variable presence of plaque was adjusted for age, sex, smoking, diabetes mellitus, systemic arterial hypertension, dyslipidemia, family history, obesity and alcohol consumption. Statistical analyses of results were performed using the SPSS software for Windows version 20.0 (IBM ® Corporation, Somers, USA). Results Clinical characteristics of the sample In the study period, 1,639 patients were subjected to CCTA at the four participating centers; 619 of them had zero CS. However, 252 were excluded due to lack of clinical data or refusal to participate in the study. Patients were referred to CCTA for atypical chest pain (40.4%), typical chest pain (24.9%), risk factors for CAD, family history of early CAD (51.4%) and positive or inconclusive tests for ischemia (44.4%). 421