Point-of-Care Ultrasound Techniques for the Small Animal Practitioner. Группа авторов
Читать онлайн книгу.
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.
Use for Cardiac Tamponade
The noncardiologist sonographer will grapple with this clinical question that often causes marked degrees of anxiety – does my patient have cardiac tamponade? And, taking it a step further – does my patient need emergent pericardiocentesis?
The diagnosis of cardiac tamponade is discussed in more detail in Chapters 18 and 21. Most importantly for the AFAST chapter, there exists a nonecho option, the characterization of the patient's CVC (see Figure 7.12)! Think about why and when an emergent pericardiocentesis would be indicated, and the answer – the presence of obstructive shock from PCE. By definition, obstructive shock from PCE results in a “FAT,” distended, with little respirophasic diametric CVC change. Thus, if the CVC is not “FAT” or distended and has a diametric respirophasic “bounce” to it, then your patient does not have cardiac tamponade. Moroever, if your patient is weak and collapsed, you need to investigate for other causes (using Global FAST). If your patient does have CVC characteristics suggestive of cardiac tamponade, look at your patient! If they are alert and in no distress, take a few breaths and relax, you have time on your side, the procedure may be delayed, complete echocardiography may be scheduled, and the procedure, if indicated, performed electively. However, if your patient is weak and unstable, an emergent life‐saving pericardiocentesis is indicated.
Figure 7.13. The racetrack sign of PCE with integration of the CVC characterization. (A,B) Inverted lateral thoracic radiographs to illustrate the anatomy in the ultrasound images in (C) and (D) with PCE evidenced by the rounding of anechoic fluid, referred to as the “racetrack sign” (Lisciandro 2014a,b, 2016a). Characterization of the CVC is helpful for evidence that obstructive shock and tamponade may be present. In (A) the CVC is unremarkable and in (B) the CVC is “FAT” and has associated hepatic venous distension supporting obstruction of blood flow to the right atrium. In (C) there is a small‐volume ascites (circled) and if a modified transudate, supports a more chronic case of PCE and a better prognosis. In (B) gallbladder wall edema, the “cardiac gallbladder,” is shown which is only expected with hepatic venous congestion and more chronicity to the PCE.
Source: Reproduced with permission of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.
Interestingly, the use of IVC distension (a “FAT” IVC) in people is only about 40% specific for the presence of cardiac tamponade. Conversely, a nondistended IVC at the subxiphoid view that has its expected normal variation in diameter in spontaneously breathing people effectively rules out cardiac tamponade with a sensitivity of 97% (Candotti and Arntfield 2015; Tchernodrinski and Arntfield 2015). The CVC in small animals likely proves similarly helpful with indirect nonechocardiographic (fallback view) information regarding the presence of obstructive shock from cardiac tamponade. We like the saying “Don't risk your patient's life trying for an echo view” – use the Global FAST fallback views (see Figure 36.7).
Figure 7.14. Relative positioning of gallbladder to diaphragm to caudal vena cava. (A,B) Line drawing overlays of the gallbladder (GB) and caudal vena cava (CVC). In (A) the heart is faintly visible on the still image analogous to the overlay in (B). In real time the beating heart is readily apparent. (B) Orientation of the heart as it lies against the diaphragm in both dogs and cats. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle. The orientation and proportionality in the longitudinal plane are nearly identical independent of standing/sternal versus right lateral recumbency.
Source: Reproduced with permission of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.
Pearl: Always look cranial to the diaphragm because most cases of clinically relevant pericardial effusion are detected via the DH view, which is part of AFAST, TFAST, and Vet BLUE.
Pearl: Ascites (modified transudate) in cases of PCE cases carries a better prognosis because the PCE has been a more chronic process in that patient (Johnson et al. 2004). Always stage with Global FAST and encourage pericardiocentesis when indicated in these cases.
Pearl: The nonecho option for the presence or absence of cardiac tamponade is characterization of the CVC. A “bounce” to the CVC rules out tamponade versus a “FAT” distended CVC which supports the presence of obstructive shock and cardiac tamponade and the need for emergent pericardiocentesis in weak, collapsed patients, although it's best to look at the patient to make that final decision (stable, can wait; unstable, needs emergent pericardiocentesis).
Prevalence of Pericardial Effusion
Pericardial effusion brings up a fascinating change in teaching paradigms because a more effective first‐line screening test is being used since the FAST movement began in 2004 (Boysen et al. 2004; Lisciandro 2014a,b, 2016a). We were screening with less sensitive imaging, using thoracic radiography, an unreliable test (Guglielmini et al. 2012; Côté et al. 2013; Lisciandro 2016a). Before FAST, the patient was only diagnosed if they were scheduled for echocardiography or CT. As a case in point, the author's practice documented three cases of PCE in 2005 before AFAST‐TFAST and 28 cases in 2012 (Lisciandro 2014a,b, 2016a). Why the difference? Simply, we were using the wrong test (Guglielmini et al. 2012; Côté et al. 2013). Ultrasound is arguably the gold standard test for PCE.
Causes of Pericardial Effusion
So now fast forward through 15 years of AFAST and TFAST. Using ultrasound as a first‐ line screening test, veterinarians (and physicians) are now capturing PCE cases that would have otherwise been missed (Lisciandro 2014a,b, 2016a). However, what we are finding with the paradigm change is that there are two subsets of PCE, acute and chronic, and they are remarkably different (Table 7.8).
In the past, a feline or canine patient may have had acute PCE and cardiac tamponade but with radiography dominating as first‐line imaging, the unremarkable