Juan Manuel Bonelli
This chapter on Non-Invasive Cardiovascular Imaging of the Adult brings together most of the diagnostic methods used in the most frequent cardiovascular pathologies.
The recommendations are guides and suggestions that make references to specific pathologies and patients in general; its application will be at the discretion of the treating physician depending on the availability of the method, the experience of the operator center and the individual characteristics of each particular case.
Echocardiography is currently the most widely used imaging technique in clinical cardiology practice, as it provides a complete evaluation of cardiac, paracardiac and vascular structures and function.
The obtaining of images in real time, portability, absence of radiation exposure, accessibility and comparative low cost, in relation to the amount and quality of the information provided, makes it the Technique of choice for the diagnosis and follow-up of most of cardiovascular diseases, as well as its relationship with a wide range of pictures in general clinical practice.
The images derived from echocardiography allow, almost always, to arrive at an effective diagnosis for the management of patients; they assist in therapeutic decisions, in determining the response to therapies, and allow obtaining predictors of the evolution of patients.
Two-dimensional (2D) or three-dimensional (3D) images accurately define the size, volume, and function of the heart chambers, the thickness of the ventricular walls, the anatomy and function of the valves, and the size of the great vessels.
Pulse wave (PW), continuous wave (CW) and color Doppler provide measurements of flow velocities and allow evaluation of intracardiac hemodynamic and pressures, and thus detect and quantify the presence of stenosis, regurgitation, or other conditions abnormal flow rates.
Echocardiography also complements or has replaced many other technologies in clinical decision-making and in the evaluation of functional and structural changes after therapeutic interventions.
The limitations related to its dependence on adequate acoustic windows can be overcome most of the opportunities with the use of intraesophageal probes and improvements in the quality of imaging. In this sense, recent developments in echocardiography, such as harmonic imaging, broadband transducers, 3D echocardiography and the development of new techniques (tissue Doppler, strain, speckle tracking, etc.), have expanded the application of the technique, with greater growth in its clinical use.
INTRODUCTION TO IMAGING OF MYOCARDIAL PERFUSION BY RADIOISOTOPES
Nuclear Cardiology constitutes one of the most solid tools for the diagnosis, prognostic information and risk stratification of coronary disease.
Scientific societies recognize the usefulness of the method through Evidence-based Guidelines, provided by multiple clinical trials in four decades of experience and with tens of thousands of patients included, with myocardial perfusion being one of the most important tools in practice clinical cardiologist and interventional cardiologist.
Loong et al., In their meta-analysis published in 2014 with 79 studies, which included 8964 patients, conclude that the technique has a sensitivity of 86% and a specificity of 74%. Another meta-analysis, which included 29 studies with 20,963 patients who were followed for 28 months, showed that a normal SPECT has an annual event rate of 0.7% (1-3).
ECG-triggered SPECT has further improved the sensitivity and specificity of the method, which is in the order of approximately 90-97% and 75-83% respectively, with a negative predictive value close to 100% (4-6).
Image acquisition protocol in myocardial perfusion study
There are several modalities, equipment, and radiotracers. The most widely used technique in clinical practice is Spect myocardial perfusion (Single Photon Emission Computed Tomography) with gated-SPECT acquisition (triggered SPECT). It consists of the intravenous injection of a radiotracer in two stages: effort and rest.
The most widely used radiotracer today is technetium 99m sestamibi due to its availability and cost, although there are others on the market such as thallium-201.
The exercise phase consists of injecting the radioisotope at the maximum peak of the ergometric test during the greatest possible increase in HR. If the patient cannot exercise or does not reach the desired HR, the urge is carried out pharmacologically, with vasodilators such as adenosine or dipyridamole.
Triggered SPECT, in the 2 stages, uses the synchronization of the acquisition with the ECG or the R wave to obtain parameters of global and segmental motility, ejection fraction and ventricular volumes.
CARDIOVASCULAR NUCLEAR MAGNETIC RESONANCE
One of the greatest potential of Cardio-MRI is its ability to characterize myocardial tissue according to its relaxation properties, thus providing important diagnostic information. This tissue characterization is based on determining the presence of myocardial edema (T2 STIR), capillary hyperemia (T1 with ev contrast), fat (T1), iron deposition (T2 *), cell necrosis and / or focal fibrosis (late enhancement) and, in recent years, through new techniques such as T1 mapping, diffuse fibrosis.
The late enhancement sequence allows not only the detection of foci of irreversible damage, be it necrosis or fibrosis or both, with a very good spatial resolution and pathological correlation, but also differentiating with high specificity according to their pattern and intramyocardial extension the different heart diseases are ischemic necrotic or not (21, 22). Furthermore, it is an excellent method to characterize the different intra-extracardiac masses (tumors).
Cardio-MRI is considered the preferred method (gold standard) for the evaluation of ventricular volumes, mass and function. The different techniques used, especially cine sequences (steady state free precession), allow an excellent delineation of the myocardial-blood interface in addition to obtaining different planes for the measurement of cardiac volumes with high accuracy and reproducibility without an assumption geometric (10). It is important to note that the volumes must be indexed according to age, sex and body surface area (for which there are normalization tables) (11).
On the other hand, in addition to the quantification of volumes, the precise measurement of wall thickness is feasible, accurately determining the hypertrophic segments and, therefore, the identification of the different phenotypes of hypertrophic cardiomyopathy as a cause of HF (12), the areas of parietal thinning in the case of ischemic-necrotic heart disease and the assessment of trabeculae and, therefore, the non-compact / compact relationship in order to differentiate non-compact cardiomyopathy from different types of cardiomyopathies with hypertrabeculation (13).
In addition, cardiac magnetic resonance imaging (Cardio-MRI) is a non-invasive imaging technique that, through a targeted protocol, can assess the morphological and functional characteristics of the RV (81, 82). It is considered the gold standard for evaluating both RV volumes and regional motility (83), in suspected RV-LV arrhythmogenic cardiomyopathy.
Limitations of Cardio-MRI in the study of patients with HF
Given the electromagnetic properties of the resonator, patients with HF with pacemakers or implantable cardioverter-defibrillators should not undergo a Cardio-MRI study, although this could change in the future with development. of new devices compatible with a resonator.
Considering the prevalence of AF in patients with HF, the accuracy of functional studies is limited in the presence of this type of arrhythmia.
The use of gadolinium should be avoided in patients with renal failure with a GFR <30 ml / m / m3, or renal failure caused by hepatorenal syndrome, regardless of the degree of this. This is because it is associated with a rare condition known as nephrogenic systemic fibrosis (47).
CARDIAC COMPUTED TOMOGRAPHY
Cardiac computed tomography is an imaging modality that allows, through computed tomography coronary angiography (CTCA), to detect or exclude non-invasively the presence of coronary artery disease, to quantify the degree of stenosis and characterize the type and morphology of the coronary plaques. On the other hand, it also provides the analysis of cardiac cavities, valves, myocardium and cardiac volumes (1-10).
From the technological point of view, multislice tomographs (multislice) of 64 or more number of slices are currently considered as appropriate (state-of-the-art) for conducting a CTCA study; There is a further spectrum of equipment that varies in number of cuts (128; 256), number of rows (128; 320), and number of X-ray tubes (single or double tube).
A rational and justified use of CCTA is important, taking into account the scope and limitations of the technique, the clinical setting and the characteristics of the patient. In the target population of CCTA we found (3-10):
- suspicion of coronary anomalies.
- low or intermediate risk of coronary heart disease, including patients with chest pain and normal laboratory and ECG results, which are unclear or inconclusive.
- non-acute chest pain.
- new or worsening symptoms, when the results of a previous stress test were normal.
- stress test results that are inconclusive or inconsistent.
- new episode of heart failure with reduced left ventricular function and low or medium risk of coronary heart disease.
- average risk of coronary heart disease before non-coronary heart surgery.
- coronary bypass grafts.
Like any diagnostic method that uses radiation, its use must be responsible. The effective radiation dose expresses the potential biological effect of radiation on an exposed tissue and is expressed in millisieverts (mSv).
The significant advances that have emerged in computed tomography have made it possible to optimize cardiac studies. These are currently carried out with high temporal, spatial and contrast resolution, in a few seconds and with low radiation doses.
Future cardiac CT machines will surely improve image quality with more robust systems and further reduce radiation doses, resulting in new applications in the cardiology field.
UTILITY OF MULTIDETECTOR COMPUTED ANGIOTOMOGRAPHY IN CHRONIC AORTIC PATHOLOGY Multidetector
Computed Tomography Angiography (MDCT-angiography) is a highly effective method for evaluating the anatomy of the arterial tree.
The acquisition of isovolumic images allows the entire arterial tree to be studied with enormous precision, both in the axial plane and also in the coronal and sagittal planes, and to obtain multiple oblique planes that will allow a correct measurement of the aorta throughout its entire trajectory, avoiding false appreciations in the cases of very tortuous routes.
Three-dimensional (3D) reconstructions provide information that is relevant for the planning of eventual surgical or endovascular interventions.
It also allows to recognize pathologies of the structures and organs adjacent to it that may be associated with aortic pathology.
Computed tomography angiography (CT-angiography) is a highly relevant complementary method that allows the differential diagnosis of the different acute aortic syndromes (dissection, wall hematoma and penetrating ulcer) to be established with great precision.
TRIPLE RULE OUT
The evaluation of acute chest pain and its differential diagnosis in the emergency service is a complex problem for the emergentologist, and at the same time a public health problem of great consequence. The most clinically relevant causes of acute chest pain that must be differentiated in the emergency department are mainly acute pulmonary embolism, acute aortic syndrome and coronary disease, which presents as acute coronary syndrome.