ABC | Volume 113, Nº4, October 2019

Review Article Magalhães et al. Principles of MPCT Arq Bras Cardiol. 2019; 113(4):758-767 Patients with blood pressure above 100 mmHg may receive sublingual nitrate (isosorbide dinitrate [5mg] or propatylnitrate [10mg]), with a minimum interval of 20 minutes for subsequent pharmacological stress, as validated in previous safety profile studies .24 Although there is a theoretical anti-ischemic effect of nitrates, its use according to steps described above was not relevant to mask perfusion defects under pharmacological stress by tomography, when using SPECT-MPI associated to cardiac catheterization as a reference. 24 – Use of beta-blockers as preparation for computed tomography coronary angiography Patients may receive intravenous or oral metoprolol prior to examination. Although there is no formal guideline for this purpose, the proposal is to use the following scheme used in a previous multicenter study: 24 If body mass index (BMI) is < 30 kg/m 2 and heart rate (HR) is > 60 bpm, 75 mg oral metoprolol should be administered. If BMI is ≥30 kg/m 2 and HR>60 bpm, oral 150mg metoprolol should be administered. If HR remains >60 bpm, intravenous metoprolol 5 mg every 5 minutes up to a total of 20 mg may be administered. – Use of stressors to evaluate myocardial perfusion by computed tomography Regardless of the mode of image acquisition or equipment available, fixed stressor administration protocols are used. In Brazil, stress protocols use mainly dipyridamole (0.56 to 0.84 mg/kg) in 4 minutes, with acquisition in the 6th minute of the beginning of injection or possibly adenosine (140 μg/kg/min for 4 minutes, with acquisition at the end of the last minute). Regadenoson can be used as a stressor at a single dose of 0.4 mg intravenous (IV) in a bolus, with stress imaging acquired within 1‑2 minutes after injection. 1 – 64-Row Multidetector Scanners The assessment of myocardial perfusion at rest and stress by tomography, as well as the coronary anatomical evaluation, should always be performed in a single protocol. Aiming at a low radiation dose, we always suggest performing resting perfusion study (CCTA study itself) with the usual low-dose protocols available on the device (preferably with dose modulation and/or prospective acquisition), and the protocol under pharmacological stress whenever possible, with a slightly lower radiation dose, but diagnostic quality, always prioritizing prospective acquisition. We encourage the option of the protocol to be used (stress/ rest or rest/stress) according to the experience of each center and particular characteristics of each patient or the CT scanner used. Figure 1 shows the rest/stress protocol, however stress imaging prior to rest is feasible. As an example, we can describe the following acquisition parameters for first-generation 64-channel scanners: 19,51,52 • Resting study – Retrospective Gating, 70-90 ml of contrast at 5 ml/s injection pump infusion after metoprolol (max. 20 mg), 64 x 0.5 mm or 32 x 0.6 mm collimation, mAs up to 850 depending on gender and weight and Kv of 100 (preferred). • Study under pharmacological stress – Retrospective Gating, 60ml contrast at 3ml/s injection pump infusion, Iodinated contrast 70 – 90 ml – 5 ml/s Preparatory images and calcium score Rest Perfusion Coronary anatomy Pharmacological Stress Perfusion Metoprolol IV if FC > 65 bpm maximum 20 mg Dypiridamole 0,56 mg/kg/4 min Iodinated contrast 60 ml – 3 ml/s 4 minutes 7 minutes 9 minutes Total time 20 minutes After 2 minutes This step may be cancelled depending on the clinical indication and the findings in the evaluation of the coronary anatomy Figure 1 – Acquisition protocol CCTA + myocardial CTP. CCTA: Coronary Computed Tomography Angiography; CTP: computed tomography perfusion. 761