Optimization of the Patient and Equipment

Introduction

Optimal performance of the comprehensive two-dimensional (2D) transthoracic echocardiography (TTE) examination depends on the interaction between the operator (sonographer and/or physician), instrument (ultrasound system), and patient ( Fig. 11.1 ). This chapter will focus on techniques for optimizing acquisition that relate to the patient and ultrasound system, including optimizing the patient and transducer positions as well as using maneuvers and machine settings to optimize the 2D imaging, spectral, and color Doppler display.

Optimizing Patient and Transducer Positions

The TTE examination is built on the framework of standard views (e.g., parasternal long axis, apical four chamber), as discussed in Chapter 9 . Optimal acquisition of TTE images/Doppler for these views is dependent on appropriate patient and transducer positioning ( Fig. 11.2 ). While some patients have easily accessible echocardiographic windows, others are far more challenging, resulting in studies that are often described as “technically difficult.” The sonographer has a variety of tools available to assist in obtaining the best possible echocardiographic images/Doppler signals for each patient. They include positioning the patient, manipulating the transducer, and the effective utilization of ultrasound machine settings. The standard echocardiographic windows therefore are primarily a guide, as nonstandard windows and maneuvers may be necessary, based on individual patient characteristics ( Table 11.1 ). Additionally, nonstandard views may be required to delineate pathology and answer the clinical question posed. The goal therefore is to use whatever patient and transducer positions, maneuvers, and machine settings are needed to deliver the optimal image and/or Doppler display. The use of contrast is discussed in detail in Chapter 3, Chapter 12 , but it should be noted here that appropriate use of echocardiographic contrast agents is a critical component of image optimization.

The ultrasound transducer is separated from its target organ, the heart, by the bony chest wall and the air-filled lungs. These can greatly impede ultrasound beam transmission and have a negative impact on image quality. The rationale for the various TTE transducer positions or “windows,” including patient maneuvers during the examination, is the desire to minimize obstacles to beam transmission, thereby optimizing image quality.

The comprehensive TTE examination generally begins at the left parasternal window, with the patient in the left lateral decubitus position, his/her left arm up and away from the chest, and the transducer positioned at the left sternal border at or near the third intercostal space (see Fig. 11.2 ). Sometimes the patient’s medical condition, prior surgery, or congenital abnormalities may necessitate a more exploratory approach, but this is generally the best starting point. The left lateral decubitus position pulls the heart closer to the chest wall, displacing the air-filled lungs, thereby expanding the window. Breath holding at end-expiration or acquiring images during shallow breathing often helps. Parasternal long and short axis views can be acquired here. It is essential that parasternal views be recorded on axis—that is, with the long axis of the heart pointed due left or horizontally in parasternal long axis views. Frequently, the image recorded is one in which the long axis of the ventricle points up toward the upper left corner of the image, typically reflecting a lower than ideal window. With such off-axis views, it will be impossible to obtain accurate measurements of the left ventricular (LV) cavity and walls, and the short axis views obtained from the same window will be ovoid rather than circular, making it difficult to assess septal contour and regional wall motion. Off-axis views can be avoided by trying higher windows and repositioning the patient, often further over in the left lateral decubitus position ( Figs. 11.3 and 11.4 , and Video 11.1, Video 11.2 ). That said, while basal and mid-ventricular short axis views can and should be obtained from the optimized parasternal view, it will typically be necessary to move the transducer down and away from the sternum to capture a short axis image of the true apex. With the transducer rotated 90 degrees from this new window, typically midway between the parasternal long axis and apical four-chamber views, a long axis of the apex can be achieved that can minimize the risk of missing true apical wall motion abnormalities and thrombi. Note that the standard parasternal views do not show the true apex. In the case of the ascending aorta, moving up an intercostal space and tilting slightly downward can often yield an effective window, as can right parasternal views (discussed later).

The apical views are best obtained with the patient in the steep left lateral decubitus position that brings the LV apex closer to the chest wall, with the transducer positioned at or near the palpable apex beat (see Fig. 11.2 ). Positioning the patient near the edge of the examination bed or using a cutout window facilitates transducer maneuvers at the apex. For apical views, care should be taken to move sufficiently lateral and down far enough to see the true apex of the heart, avoiding foreshortened images. Images acquired at end expiration or with the patient holding a small breath can assist with many apical images, particularly the apical two-chamber and apical three-chamber views. Especially in patients with known regional wall motion abnormalities, it may be helpful to also move the transducer down an interspace from what appears to the optimal apical view and then have the patient take a breath in. This may reveal segments apical to those seen on the earlier view and unmask aneurysms ± thrombi.

The subcostal (subxiphoid) views are optimally acquired with the patient lying supine with knees flexed, which relaxes the abdominal muscles (see Fig. 11.2 ). Elevating the head of the bed often helps, as gravity pulls the heart closer to the transducer. Acquiring images at end-inspiration facilitates this further. Respiratory variation in the size of the inferior vena cava (IVC), which is used to estimate the right atrial pressure, can be assessed with M-mode or 2D imaging while the patient takes a vigorous sniff. However, care must be taken to ensure that the appearance of a diminution in the size of the IVC is not artifactually created by simply losing the correct imaging plane with the sniff. Biplane 2D imaging derived from 3D images can be helpful in this regard.

For the suprasternal notch (SSN) views, the patient remains in the supine position, but with the neck extended or hyperextended and the head rotated to facilitate transducer positioning. Placing a pillow under the shoulders promotes neck hyperextension. Right parasternal views that are essential for assessing patients with aortic stenosis are best acquired just to the right of the sternum, with the transducer oriented as it was in the parasternal long axis. The patient should be lying on her or his right side, with the right arm up and away from the torso. The smaller imprint of the nonimaging Pedoff transducer facilitates suprasternal and right parasternal Doppler interrogation ( Table 11.2 ).