Page 350 - Clinical Small Animal Internal Medicine

318 Section 4 Respiratory Disease

artery (PA). To date, RV hypokinesis (apical sparing) has
VetBooks.ir not been confirmed in dogs or cats with PTE.

Cardiac Biomarkers
In humans, echocardiographic RV dysfunction sec­
ondary to PTE is associated with elevated cardiac tro­
ponin (cTn) concentrations. A recent metaanalysis of
20 studies suggested that humans with PTE and an
increased cTn level are at high risk of short‐term death
and adverse events. Cardiac troponins are increased in
veterinary patients with primary, ischemic, congenital
and degenerative cardiac and pericardial diseases, but
also in gastric dilation‐volvulus (GDV) syndrome, sep­
sis, trauma, uremia, and hyperthyroidism. Serum cTn
Figure 32.4 Long‐axis four‐chamber echocardiographic view concentrations are related to the magnitude of myo­
showing a pendulous thrombus (arrowhead) adherent to the roof cardial injury in myocarditis, GDV syndrome, and
of the right atrium in this patient. LA, left atrium; LV, left ventricle; blunt chest trauma. In dogs with PTE secondary to
RA, right atrium; RV, right ventricle.
dirofilariasis, cTnI values were significantly higher
than in controls, and in dogs with experimental PTE,
Cardiac Function Testing
cTnI levels increase in proportion to the severity of
Echocardiography occlusion as indicated by PVR and mean pulmonary
In people, echocardiography is not a routine diagnostic artery pressure (MPAP). There is only one report on
test for PTE, although case registries report echocardiog­ cTnI in dogs with PTE. In that small study, patients
raphy is performed in 47–74% patients. Although many with CT‐confirmed PTE did not have significantly
echocardiography studies are normal in PTE, they may be increased cTnI values compared to dogs without PTE,
diagnostic if cardiac or RV outflow tract thrombi are pre­ but the sample size was limiting.
sent (Figure 32.4). Where PTE is present, echocardiogra­ It seems unlikely that cTn values will be sufficiently
phy can quantify the hemodynamic consequences of PTE specific to enhance the diagnosis of PTE and they may
and provides valuable prognostic information to guide prove most valuable in assessing PTE severity and pre­
patient management. Echocardiography can also identify dicting complications, rather than differentiating PTE
differential diagnoses such as cardiomyopathy, endocar­ from other disease processes. In contrast to D‐dimers,
ditis or pericardial tamponade noninvasively. which peak at 1–2 hours after PTE, cTnI levels peak at
Typical echocardiographic findings in humans with eight hours post embolism in people and are most diag­
PTE include right ventricular dilation and hypokinesis, nostically accurate at this time point. The availability of
septal flattening and paradoxical septal motion, diastolic POC tests for cTn in dogs makes accurate timing of this
left ventricular impairment, pulmonary arterial hyper­ assay a viable proposition.
tension, right ventricular hypertrophy, and patency of Atrial and B‐type natriuretic peptides are produced by
the foramen ovale. The degree of right ventricular dys­ cardiac muscle and released in response to volume over­
function is related to the cross‐sectional area of the pul­ load, hypertrophy, and hypoxia to elicit natriuresis and
monary vasculature affected; occlusion of >30% is vasodilation. Assays of BNP or the metabolic by‐product
frequently associated with RV hypokinesis. In people NT‐proBNP are used to diagnose cardiac disease, differ­
with severe PTE, the apex of the RV appears to be spared entiate respiratory from cardiac disease, assess severity,
the hypokinesis that affects the remainder of the right and guide management. In PTE, NT‐proBNP concentra­
ventricular free wall (RVFW). This apical sparing (the tions are closely related to the degree of RV dysfunction,
McConnell sign) is highly specific for the diagnosis of and this likely underpins their relationship with adverse
PTE in people. events and outcome in people with PTE. No studies on
There are currently few data regarding echocardiogra­ NT‐proBNP measurement in small animal PTE have
phy in canine PTE because in recent retrospective stud­ been reported to date. As with cTn, it is likely that con­
ies <20% of dogs underwent echocardiography. However, centrations of NT‐proBNP will be increased. The discri­
it is reasonable to suspect many small animals with PTE minant ability of this test in small animal PTE remains an
will have abnormal echocardiograms. Typically reported open question. Currently, the principal limitations of the
findings in small animals include right atrial and ventric­ NT‐proBNP test are the ex vivo stability of the analyte
ular enlargement, paradoxical septal motion, pulmonary which is time and temperature dependent, and the lack
hypertension, and thrombi in the heart or pulmonary of a POC test for dogs. Once a bedside test for dogs