Page 36 - Medicine and Surgery
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         BLUK007-02  BLUK007-Kendall  May 25, 2005  17:25  Char Count= 0







                   32 Chapter 2: Cardiovascular system


                   imaged. It requires technical expertise to obtain images  Two dimensional is useful for evaluating the anatomical
                   and clinical expertise to interpret the results appropri-  features. Standard views are obtained.
                   ately. The following features are typically assessed:     Left parasternal: With the transducer rotated appro-
                     Anatomical features such as cardiac chamber size, my-  priately through a window in the third or fourth inter-

                     ocardial wall thickness and valve structure or lesions.  costalspace,longandshortaxisviewscanbeobtained.
                     Ventricular aneurysms or defects such as atrial or ven-     Apical: This is a view upwards from the position of
                     tricular septal defects can be seen.         the apex beat and gives a long axis view of the heart,
                     Functional features including wall motion (any lo-  where all four chambers can be seen simultaneously.

                     calised wall motion abnormality as well as a general  M-mode is a way by which the motion of individual
                     assessment of the overall contractility of the ventri-  structures along a narrow path can be carefully studied.
                     cles, often measured as fractional shortening or ejec-  It is a one-dimensional view (depth) with time as the
                     tion fraction) and valve motion. Doppler ultrasound  second dimension on the image produced. Structures
                     is used to measure the velocity of jets of blood, e.g. to  that do not move appear as a horizontal line, whereas
                     assess severity in valve stenosis.         structures that move, e.g. valves, are seen as zigzag lines,
                     The aortic root may be examined for dilatation or  which move in time with the cardiac cycle. The distances

                     dissection.                                between structures, or the thickness of structures, can
                     Pericardialfluidappearsasanecho-freespacebetween  therefore be carefully measured at different times of the

                     the myocardium and the parietal pericardium.  cardiac cycle.
                     Mass lesions such as thrombus or tumour may be seen  Doppler allows the analysis of the direction and velocity

                     within the heart.                          of blood flow, and therefore is particularly useful in the
                   The principles of echocardiography are the same as  evaluation of valve lesions. It is used to calculate pressure
                   those of ultrasound. A transducer is used to generate  gradients, e.g. in aortic stenosis. It can also be used to
                   ultrasound waves that are directed at the heart. When  generate 2-D images with simultaneous imaging of flow
                   awaveencounters an interface of differing echogenic-  direction and velocity.
                   ity, some of it is reflected and some absorbed. Any  Common indications for echocardiography:
                   reflected waves (echoes) that reach the transducer are     Suspected valvular heart disease, including infective
                   sensed and processed into an image. The time taken  endocarditis.
                   for the wave to bounce back measures the distance of     Heart failure, to assess left ventricular function and
                   the interface. Tissues or interfaces that reflect the waves  look for any valve lesions or regurgitation, and any
                   strongly such as bone/tissue or air/tissue will appear  evidence of a cardiomyopathy.
                   very white (echogenic) and also prevent any tissues un-     Postmyocardial infarction for suspected complica-
                   derneath from being imaged well. Fluid is anechoic, so  tions, such as ventricular septal rupture or papillary
                   appearsblack.Theribsandlungslimittheabilitytovisu-  muscle rupture. It will also identify areas of ischaemic
                   alise the heart because they cast acoustic shadows. Tran-  myocardium or previous myocardial infarction as ar-
                   soesophagealechocardiography(TOE)isamoreinvasive  eas of hypokinetic or akinetic myocardium, as well as
                   method used when poor views are obtained on transtho-  an overall assessment of left ventricular function.
                   racic echocardiography, or when more detailed views are
                   required particularly of structures near the oesophagus
                   such as the atria and great vessels, the mitral valve or  Ischaemic heart disease
                   prosthetic valves. A transducer probe is mounted on the
                   tip of a flexible tube that is passed into the oesophagus.
                   The patient needs to be nil by mouth prior to the proce-  Ischaemic heart disease
                   dure, local anaesthetic spray is used on the pharynx, and
                   intravenous sedation may be required for the procedure  Definition
                   to be tolerated.                             In the normal heart there is a balance between the oxy-
                     There are three types of echocardiography: two di-  gen supply and demand of the myocardium. A supply of
                   mensional, M-mode and Doppler.               oxygen insufficient for the myocardial demand results
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