Читать книгу Point-of-Care Ultrasound Techniques for the Small Animal Practitioner - Группа авторов - Страница 239

The premise is simple – always, always, always look cranial to the diaphragm at the FAST DH view (Figure 7.13; see also Figures 6.8 and 6.9) (Lisciandro 2016a, 2019). The use of the DH view for pericardial effusion (PCE) avoids air interference (ultrasound cannot transit through air) from lung at transthoracic views, especially since dogs and cats (and people) often have respiratory distress as their chief complaint. In fact, the subcostal FAST view in human medicine is the number 1 view for PCE that may be used a single view because the heart is so well imaged through the acoustic window provided by the liver and gallbladder into the thorax. In dogs and cats, the observation of the “racetrack sign” is essentially pathognomonic for PCE (Lisciandro 2014a, 2016a) (see Figure 7.13).

The best way to comprehend the relevant anatomy at the DH view is to look at an inverted canine (and feline) lateral thoracic radiograph (TXR). The TXR helps in learning the relative locations of the major structures, including the location of the muscular apex of the heart, called the “cardiac bump,” the expected positioning of heart chambers relative to the diaphragm, location of the CVC, and the expected location of the canine and feline gallbladder (Figure 7.14; see also Figures 6.11 and 6.12). The “cardiac bump” is the descriptor used for the observation of the beating heart and its muscular apex immediately against and, in dogs, often indenting the surface of the diaphragm where the heart and diaphragm come into contact (see Figures 7.14, 6.11, and 39.5). From our retrospective case series in which the methodology did not establish whether transthoracic TFAST views or the DH view was first performed, ~85% of PCE cases were imaged via the DH view (Lisciandro 2016a). In a prospective case series with subsequent improvements in training since our study, likely the DH view would prove to be nearly 100% sensitive and 100% specific for PCE in standing/sternal positioning in both dogs and cats. In other words, the DH view is a very good screening test.

Interestingly, the cardiac and diaphragmatic interface differs between people and dogs and cats. The human heart has its right ventricle and right atrium closest to the diaphragm whereas it is the left ventricle and left atrium in dogs and cats (see Figure 7.14). This is important when imaging the CVC because in people, the analogous IVC may be imaged as it enters the right atrium whereas in dogs and cats, the closest the CVC may be imaged to the right atrium is where the CVC passes through the diaphragm. Learning the DH view's cardiac orientation is a good add‐on skill. The DH cardiac view is helpful in PCE cases that have a left atrial tear/rupture from chronic mitral valve disease because the severely enlarged left atrium is commonly obvious here (conversely finding a small left atrium), and the DH view is generally less stressful and a better acoustic window for respiratory distressed patients.