CHAPTER TWO

The Two-Dimensional Echocardiographic Exam

Introduction

Ultrasound’s popularity leaped with the advent of real-time imaging and the easy to understand twodimensional images of the heart. Normal two-dimensional cardiac anatomy and some quantitative two-dimensional information in the dog (1–6), the cat (6,7), the horse (8–14), and the cow (15) were described in this early phase of veterinary echocardiography. Today there are reference ranges and descriptive articles pertaining to two-dimensional echocardiography in many species, and most of these are listed in the appendices. Assessment of these images and application of information is presented in the chapter on hemodynamics and assessment. Standards for two-dimensional imaging planes and terminology have been recommended for the dog, cat, and horse (2,4,7,16–20).

Examination technique is less frequently described, and even then, often lacks the detail necessary for the novice ultrasonographer to obtain appropriate cardiac images. This chapter describes normal two-dimensional imaging planes and the scanning techniques necessary to correctly obtain those images. The importance of correct technique, measurement, and assessment cannot be overemphasized. A methodical approach to scanning and interpretation should be used in order to increase technical proficiency and diagnostic accuracy. Try to perform the ultrasound exam the same way each time. Consistency in patient placement, transducer orientation, table height, and equipment location with respect to the patient, allows the examination technique to become almost automatic.

Patient Preparation

Most animals require shaving on both the right and left sides of the thorax in order to minimize the effects of air on sound transmission. Shave the right 4th to 6th intercostal spaces in dogs, and the 3rd to 5th intercostal spaces in horses, cows, and cats (Figure 2.1). The left side should be shaved from about the 4th intercostal space to just past the last rib in all small animals. The clipped area should extend from the costochondral junction to the sternum in small animals and from several inches above the olecranon to several inches below it in the large animal (Figure 2.2). Some animals with thin hair coats may be examined by simply moving aside the hair and applying generous amounts of ultrasonic transmission gel. Applying alcohol before the transmission gel helps eliminate air and improve skin contact when the animal is not shaved.

Figure 2.1 Shave between the right 4th to 6th intercostal spaces, from the costochondral junction to the sternum, in small animals.

Figure 2.2 Large animals should be shaved if coats are thick. Clip from several inches above the olecranon to several inches below it in the right 3rd to 5th intercostal spaces.

Patient Positioning

Small Animal Positioning

Most echocardiographers use a scanning table similar to that seen in Figure 2.3. The animal is placed in right lateral recumbency with the right 3rd to 6th intercostal spaces positioned over a cut-out section in the table. Gently restrain the animals by standing behind their back and placing your arms over the animal’s hips and neck while holding the legs (Figure 2.4).

Figure 2.3 A scanning table with a cutout, to allow imaging from below the small animal, improves

image quality.

Figure 2.4 Hold the animal in a recumbent position with the shaved area over the cutout in the exam table. Place your arms over the neck and hips while holding the legs extended.

Images are obtained by scanning from beneath the table since this method of examining the heart routinely produces better images. The heart drops down toward the thoracic wall creating less of a problem with lung interference on echocardiographic images. It also allows a higher frequency transducer to be used during many exams, since less depth penetration is necessary. Although good images can be obtained from the right side with the animal placed in left lateral recumbency or standing, it takes more experience to become proficient at obtaining these images consistently, and air interference from the lung is common.

Construction of an exam table has been described (21). Important design considerations are length

of the table, placement of the cutout, and table height. Enough length should be provided so the animal’s head does not extend past the edge of the table when the thorax is positioned properly over the cutout. The cutout should also extend toward the edge of the table near the examiner so that very deep chested or large dogs do not feel as though they are falling off the back of the table. Cats and smaller animals can be held so the sternum extends just beyond the edge of the cutout and so they will feel secure. Tables do not necessarily need to have an incline. Inclined tables have you constantly fighting gravity to keep the animal from sliding toward you. They can have removable cutouts that can be inserted or removed in order to reduce or increase the size of the opening for a variety of animal sizes. An oval cut-out section, oriented as in Figure 2.3, is necessary when using longer transducers in order to tilt the transducer into the more horizontal positions required for some images. The table should also be high enough to hold the transducer vertically without restricted movement.

Occasionally an animal will not tolerate a recumbent position because of discomfort or dyspnea. These animals are easier to exam while standing on a table or on the floor. To prevent them from lying down, position yourself on the animal’s left side and place your arm under the animal in order to scan from the right side (Figure 2.5). Transducer positions and manipulations are similar to those used while in lateral recumbency. Scanning with the animal in sternal recumbency is possible, but it is difficult to obtain some images. Necessity sometimes dictates holding a small animal in your lap.

Figure 2.5 When an animal can not tolerate a recumbent position, exams can be performed with the patient standing. Stand on the left side and place your arm under the animal in order to keep him up. The transducer is placed on the animal’s right side for standard images.

Large Animal Positioning

Horses and food animals are examined while standing in a stall, chute, or stanchion. Imaging still takes place from the right side of the animal for all standard longand short-axis views. The examination is then completed on the left side if the entire heart cannot be imaged from the right side. Many Doppler studies require examination from the left side of the thorax.

Most standard images require that the right front leg is pulled forward and slightly abducted. Imaging becomes difficult when the animal does not cooperate with leg placement since the transducer will have to be pushed forward into the leg (Figure 2.6). Imaging from the left side is also easier when the left forelimb is positioned forward.

Figure 2.6 When a horse will not keep the front leg forward and abducted, the transducer has to be

pushed forward into the leg. Keep the transducer perpendicular to the chest wall when sliding the transducer forward.

Cows are usually placed in a head stanchion, but at times a squeeze chute is required. The front leg on the side to be examined from must be pulled forward and abducted. This usually requires tethering the leg in place. When this cannot be accomplished, the examination is almost impossible. A food animal surgery table has been used successfully by strapping the animal left side down, tilting the table slightly upward, and pulling the right front leg forward so that the ultrasonic window (transducer location) is exposed.

Llamas are typically placed in a chute that holds their head up and prevents them from lying down (Figure 2.7). Imaging their hearts also requires forward placement and abduction of their legs.

Figure 2.7 Llamas are typically placed in a chute, which keeps their head up and prevents them from lying down.