Sébastien Buczinski, Dr. Vét., DACVIM
The cardiovascular diseases of cattle remained challenging for the clinician before classical signs of heart failure appeared.1 In more advanced stage of heart disease (HD) the differential diagnosis need further ancillary tests than simple physical and clinical examination.1 Some of these tests can be done under field conditions (blood tests, echocardiography, pericardiocentesis), others are available only in an hospital setting with high valuable animals (thoracic radiographs in adults, cardiac catheterism, angiography, magnetic resonance imaging). These ancillary tests have an interesting value in the diagnosis of the disease and therefore can have an impact on the therapeutic approach and the prognosis. The aim of this presentation is to make an up-to date review of the different ancillary tests that can be used in the diagnosis of cardiac and vascular diseases of cattle as well as their prognostic importance.
Ancillary Tests and Cardiac Diseases
The four most common HD in cattle are pericarditis, bacterial endocarditis (BE), cardiac manifestation of enzootic lymphoma, and congenital HD (in which ventricular septal defect (VSD) is the most common category). Other diseases such as dilated cardiomyopathy, cor pulmonale secondary to high altitude disease are also but less frequently encountered depending on the area of practice. Various ancillary tests can be used for the diagnosis of those HD.
Blood Sampling and Cardiac Diseases
Those tests can add valuable information concerning the etiology and the repercussion of the disease. Classic inflammatory changes (increased fibrinogenemia) are seen with BE, traumatic pericarditis and VSD which are classically accompanied with pneumonia.2 Chronic inflammatory process with hyperglobulinemia is classically associated with BE,1,3 although its specificity has never been reported. Several biochemical anomalies can be noted in case of HD. Depending on the degree of myocardial damage, an increase of creatine kinase (CK) values can be noted. However, this increase, although sensitive, is not specific of HD. With the progression of HD to the clinical syndrome of heart failure, the classic indicators of poor renal and liver perfusion increase. The electrolytes levels can also be affected especially if the animal is treated with diuretic drugs.4 Finally, a serologic diagnosis of infection by the bovine leucosis virus can be helpful although not diagnostic in suspected cases of cardiac lymphoma.5
The echocardiography is effective to see the pericardium, cardiac chambers, valvulae and myocardium in cattle.6,7,8 The diagnosis of the main cardiac disorders can be reasonably done with this ancillary tool.1-3,9-13 When compared with the gold standard of necropsy its sensitivity varied from 83%1 to 95%3 for BE, it was 78% for pericarditis1, 73% for congenital HD1,11 and 94% in a retrospective study on VSD.2 Those results agree with studies in other species in which echocardiography is one of the gold standard in a lived patient. The limitation of echocardiography are the narrow intercostal space, the patient size and the operator ability especially for complex congenital diseases.11 However, with a small amount of experience, the most common cardiac disorders can be detected easily with echocardiography except for tumoral disease which must be confirmed with neoplastic cells detection.
The pericardiocentesis is a useful tool to assess pericardial effusion when clinically suspected (muffled heart sounds, splashing heart sounds) or when diagnosed by echocardiography. The procedure is done blindly on the 5th intercostal space or can be performed after choosing the best side with echocardiography. The sample must be collected for cytological and microbiological examination. Classical cytological findings are compatible with suppurative inflammatory effusion in traumatic pericarditis, mixt inflammation with blood in case of idiopathic pericarditis,13 hemopericardium, neoplastic effusion in case of heart tumor or pure to modifiate transudate in case of hydropericardium.14
Aseptic sampling of venous blood is a valuable tool to diagnose infectious endocarditis and to adapt the therapy depending on the causative agent. However, its sensitivity is variable. On nine cases with a definitive diagnosis of BE that had a blood culture in the workup diagnosis, only one cow yielded positive result.3 Six positive samples on 8 cases (sensitivity of 66%) have been mentioned in another study.15 This was confirmed in a larger number study with 58 confirmed bovine cases of BE. In this study, on 138 cases with blood culture, the sensitivity of a single blood culture was 70.7% and the specificity 93.8%.16 In human medicine, 3 samples obtained from different sites on a 24h period need to be obtained, to increase the sensitivity of this test.17
Cardiac biomarkers have not been extensively studied in cattle although they can add valuable help in the management of HD in other species. Classical biomarkers of cardiac injury include isoenzyme of creatine kinase (CK-MB) and lactic dehydrogenase 1 (LDH1). However, those biomarkers lacked of sensitivity and specificity.18 The cardiac troponins (cTn), especially cTnI, are highly specific of myocardial damage and are normally absent in blood when there is no myocardial damage.19 Preliminary results in case reports13 and case series19 have shown that cTnI was increased in cases of bovine pericarditis when compared with controls. Further studies are still needed to confirm the exact place of this ancillary test in the diagnosis and prognosis of HD in cattle.
Although routinely performed in small animals and human patients, electrocardiography (ECG) has some limitations in large animal since the diffuse organization of Pürkinje fiber limits the intensity of the vector of depolarization.18 The ECG is indicated in case of arrhythmia in order to precise the type of dysrhythmia. The most frequently encountered dysrhythmia in cattle is tachyarrhythmia which is most commonly associated with atrial fibrillation. The manifestation of AF is absence of the P wave with fibrillation of the baseline. Other type of dysrhythmia can also be detected with ECG.14 The ECG can be an objective assessment tool for the detection for observing the patient's improvement under hospital conditions.
The thoracic radiographs can be used in the detection of cardiac enlargement in calves, especially in cases of suspected congenital HD.2,20 However, there are no available references concerning the objective determination of heart size in cattle. A recent study has shown that cattle with various heart diseases had an increased caudal vena cava (CVC)/aorta and CVC/thoracic vertebra ratios when compared with healthy cattle.21
Catheterisation and Angiography
The catheterisation of the pulmonary trunk via the jugular vein and assessment of the pulmonary arterial pressure is an important tool to diagnose brisket disease22,23 and to detect susceptible animals.22 The cardiac catheterisation with injection of water soluble ionic iodine contrast media has been used for the diagnosis of various congenital HD.14,24 The thermodilution curves technique has also been mentioned as an interesting diagnostic test of VSD in calves.25 However, with the advance of knowledge in echocardiography, the catheterisation has decreased in importance except for an accurate measurement of blood pressure and rare complex malformations.
Other Diagnostic Imaging Devices...
The other diagnostic tools that can be used for the management of suspected HD consisted in magnetic resonance imaging and computed tomography. Their use has been limited for research purposes in calves26 since these imaging techniques are expensive; require general anaesthesia and small sized patients. Their potential interest for complex cardiac malformations27 could be useful when a precise diagnostic is required in valuable calves.
Ancillary Tests and Vascular Diseases
The more important vascular diseases in cattle consist in phlebitis, thrombophlebitis, thrombosis of the CVC, arteritis and vascular injury. The precise diagnosis of those affections is supported by clinical and imaging findings.
Ultrasonographic and Doppler study
The vascular ultrasonography is among the most important ancillary tests concerning the detection of vascular diseases in cattle. It has been described for the detection of jugular phlebitis and periphlebitis28 and thrombosis of the jugular vein,28 the tarsal vein,29 the CVC,30,31 the ovarian and vaginal veins32 umbilical vein phlebitis and thrombosis33 as well as in cases of aortic thrombosis in calves.34 The classical findings of thrombosis are compatible with echogenic material in the lumen with distension of the affected vessel proximal to the thrombus.35 The long term assessment of the affected vessel has not been studied except in the case of tarsal vein thrombosis in a cow.29 The ultrasonography can allow the assessment of thrombus progression or regression as well as determination of collateral vascularisation. The color flow Doppler is useful to assess the blood flow in the affected vessel as well as blood turbulences that occur with partial obstruction.34 Recently, this function has been useful in the diagnosis of portacaval shunt in a calf confirming the hepatofugal blood flow from the shunt to the CVC.36 The pulsed wave Doppler function has not been extensively studied except in the assessment of the carotid artery and the jugular vein, 37 the uterine blood flow and ovarian perfusion.38 The pulsed-wave Doppler could be useful in detecting abnormal blood flow pattern that occur with various arterial anomalies.
The angiography indicated in the assessment of major blood vessels emerging from the heart as well as assessment of liver39 and limbs vessels.29,40 By contrast to ultrasonography, this is an invasive technique that also requires radiographs. The angiography has also been used to assess vascular injury in cases of suspected vascular trauma or tear secondary to injury or frostbite. One of the limitation of angiography is that vascular catheterisation which is required to inject contrast medium can increase the risk of thrombosis in a suspected compromised vessel.
Other Ancillary Tests
Various other imaging techniques can be used in cases of suspected vascular anomaly. Of those, nuclear scintigraphy, magnetic resonance imagings have giving promising results in other species despite their high cost.
With the advent of numerous ancillary procedures, the precise diagnosis of cardiovascular disease is easier than before in food animals. However, by contrast to other species, prognostic importance of the various available ancillary tools is still lacking. Further studies are needed to know if prognostic parameters used in other species can be used in cattle. However, the relatively low prevalence of these diseases combined with the costs of ancillary and therapeutic tools can be a bias in the assessment of the real prognosis of these diseases.
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