Chapter 1 Conventional echocardiography—basic principles Andreas Hagendorff Contents Introduction 3 Principles of transthoracic echocardiography—practical aspects 3 Standardized data acquisition in transthoracic echocardiography 7 Principles of transoesophageal echocardiography—practical aspects 20 Standardized data acquisition in transoesophageal echocardiography 23 Standard values in transthoracic and transoesophageal echocardiography 30 M-mode measurements 30 Two-dimensional measurements 31 Pulsed spectral Doppler measurements 31 Continuous wave Doppler measurements 31 Pulsed spectral tissue Doppler measurements 31 Acknowledgements 33 References 33 Introduction Echocardiography is an imaging technique that enables accurate assessment of cardiac structures and cardiac function. Conventional echocardiography involves different modalities—especially the M-mode, the 2D and colour Doppler, as well as the pulsed wave and continuous wave Doppler. The M-mode illustrates the reflections of a single sound beam plotted against time. 2D echocardiography enables the documentation of views, which represent characteristic sectional planes of the moving heart during one heart cycle. Colour Doppler echocardiography adds the information of blood flow to the 2D cineloop. Pulsed wave Doppler is the acquisition of a local blood flow spectrum of a defined region represented by the dimension of the sample volume, whereas continuous wave Doppler displays the blood flow spectrum of all measured blood flow velocities along a straight line sound beam from its beginning to the end. The handling of the transducer has to be target-oriented, stable with respect to the imaging targets, and coordinated with respect to angle differences between the defined views to use all these modalities correctly to get optimal image quality of the cineloops and spectra. Thus, the focus of this chapter will be a mainly practically oriented description of scanning technique in transthoracic and transoesophageal echocardiography. The echocardiographic documentation requires ultrasound machines, which fulfil the international laboratory standards in echocardiography. Thus, the equipment has to be minimally capable to enable broadband 2D imaging, M-mode imaging, pulsed and continuous wave Doppler, as well as colour-coded imaging, pulsed tissue Doppler imaging, and complete digital storage capability. In addition, the ultrasound system has to have all technical possibilities for transoesophageal, contrast, and stress echocardiography. An ECG recording should generally be performed in order to be able to capture complete heart cycles according to the ECG trigger. This chapter is written in accordance with the current international guidelines and recommendations [1–8]. Principles of transthoracic echocardiography— practical aspects The main principle of echocardiographic scanning is an exact or best possible manual control of the region of interest during the technical procedure. This principle includes the ability to move a certain cardiac structure within the scan sector from the left to the right and vice versa without losing the cardiac structures of the selected sectional plane.
4 chapter 1 conventional echocardiography—basic principles In addition, this aspect is documented by the ability to rotate the transducer exactly about 60 or 90° without losing the defined cardiac structure in the centre of the primary scan sector before rotating. In other words, the visualization of cardiac structures in the centre of the scan sector has to be combined with the technical skill of the investigator to change only one plane within the spatial coordinates to achieve accurate characterization and documentation of the target cardiac structure. Thus, the easy message of transthoracic echocardiography is scanning by tilting without flipping and rotating, by flipping without tilting and rotating, as well as by rotating without tilting and flipping. This sounds easy, but it requires a stable transducer position next to the skin of the patient, an absolutely stable guiding of the transducer, and a stereotactic manual control of the transducer. Regarding these aspects it is surprising that the finger position of holding a transducer has almost never been described in lectures and books about echocardiography, whereas in every book about musical instruments instructions of hand and finger positions, and illustrations of fingering charts are given. In transthoracic echocardiography there is a complex interaction between the eyes, the brain and the hand muscles to coordinate looking to a monitor to detect incongruities between the actual view and defined views and to correct them by manual manoeuvres to get the standardized views. Thus, it is like ‘seeing’ the heart with your hands. A basic position of the transducer in the hand is necessary to get the orientation for the scan procedure for an easy, but controlled change of a sectional plane. This implies that a defined holding of the transducer is always linked to a defined hand position which has to be linked with a defined view. In echocardiography in adult patients, the echocardiographic investigation normally starts with the left parasternal approach. It is obvious that the basic holding of the transducer should be linked to the long-axis view of the left ventricle. In consequence, all possible long-axis views that can be acquired between the position of the left parasternal and the apical approach should be linked to this defined hand-holding of the transducer. If you change your basic position of holding the transducer during the scanning procedure of the same sectional plane, the imagination and association of the individual coordinates of the heart within the thorax will be lost by the investigator, which means that he will become disoriented or blind during scanning. It has to be mentioned and emphasized, that scanning is possible with the right as well as with the left hand. The argument for a correct scanning technique is always the acquisition of standardized images with high image quality. Thus, echocardiographic scanning can be performed as the investigator is, or has been, taught how to do it. The author of this chapter, however, scans with the right hand. Thus, the images of how to hold the transducer and adjust the finger positions are shown for right-hand scanners. To get a stable position for the transducer holding, all fingers are generally lifted and not extended. The pulps of the fourth and fifth fingers conveniently lie on the small edge of the transducer without any muscle tension ( Fig. 1.1a). The pulp of the thumb is conveniently placed on the notch of the transducer without any muscle tension ( Fig. 1.1b). This convenient relaxed transducer holding has to be conceptionally combined with the basic Fig. 1.1 Correct relaxed holding of the transducer using the right hand. The transducer lies on the fourth and fifth finger without any muscle tension (a), the pulp of the thumb only has contact to the notch of the transducer (b). The pulps of the fourth and fifth finger have contact to the skin (c) and the feeling of this transducer holding is combined with the parasternal log axis view (d).