Laboratory diagnostics in heart failure
For quite some time reliable parameters are available for specific clarification of heart failure in the laboratory. In the past laboratory diagnostics of primary or secondary cardiac diseases relied on the evaluations of CBC count, electrolyte- and enzyme concentrations, like the CK (creatinkinase), the LDH (lactate dehydrogenase) and their iso-enzyme the α-HBDH (alpha-hydroxybutyrat-dehydrogenase). Thus the activity of the CK already exceeds the reference range after damages or ischemia of the heart muscle after 4-8 hours, drops back however already after 2-3 days again into the reference range. The CK is for a short period a sensitive parameter, which exhibits however no high specificity for heart muscle damage. Values increase there among other things also with skeleton muscle diseases, physical effort, diabetes mellitus, intramuscular injections and haemolysis. Similar diagnostic uncertainties result in the case of increased LDH values. Already a small haemolysis of the sample can supply false high results. As reference to heart muscle damage, the disproportionate increase of α- HBDH in comparison to LDH (ratio: LDH: α-HBDH, normally 2:1) is of diagnostic value.
In contrast the parameters pro-ANP and Troponine I exhibit a high specificity for cardiac changes with malfunctions and/or during cell damage in the myocardium and permit for the individual case also statements about therapy success and prognosis. Recently the investigation on Nt-pro-BNP, in human medicine an established cardiac parameter, is now available in dogs.
| ANP (Atrial Natriuretic Peptid)|
ANP is a peptidhormone in dogs consisting of 28 amino acids. It is synthesized, stored and released by myocytes of the atrium walls and in small concentrations also in the ventricles and in the brain. ANP is present in form of the pro-ANP in membrane-bound vesicles of the myoendocrine cells, which move on specific
stimuli to the cell surface. They are split into a-ANP and N-terminal peptide and are released in aequimolar quantities into the coronary-venous blood. ANP leads due to the decrease of renin release, the aldosterone synthesis and the arginin-vasopressin distribution to an abnormal retention of sodium and water and by an increase in the blood volume to a reduction of the blood pressure following to the cardiac relief.
Proven stimuli for the ANP secretion are e.g. an increased atrial stretch due to hyperhydration, hypertension or cardiac insufficiency and an increase of heart beat frequency. Besides the cardiac secretion also an ANP secretion from the central nervous system, primarily within the range of the basal medial hypothalamus, the brain stem and the circumventricular structures could have been detected.
ANP is a parameter whose blood concentration permits a statement over physiologically and pathologically changed pressure ratios in the atria. High and increased ANP concentrations in the plasma are seen with congestive heart failure (CHF), mitral valve insufficiency, renal failure and heartworm disease.
The plasma concentrations correlate directly with the severity of the heart failure. In dogs with congestive heart failure up to 6-times increased values are detected. In patients with renal failure up to twice the concentration of the upper reference level. ANP is therefore a sensitive parameter for impaired cardiac pressure and a marker for the early recognition of cardiac insufficiencies. It is supportive in addition to other diagnostic procedures. Similar to investigations in human patients it is now known for dogs that the level of the ANP in the plasma permits a positive correlation with mortality. Animals with constant high ANP values have a bad prognosis.
ANP plasma concentrations within the reference range do not give a reference to an
increased pressure in the atrium. Investigations showed that just like in healthy dogs also in patients with asymptomatic CHF and in dogs with additional primary respiratory signs they do not have an increased ANP level. The results of dog plasma samples examined lately in our lab (n=390) show the following distribution: no increased ANP level in166 animals, with 36 samples in the „grey area “ (1350-1700 fmol/ml). 188 dogs supply an ANP level more than 1700fmol/ml with findings for an increased atrial pressure at the time of the sampling.
So for more than 90% of the cases a therapy regime can be developed.
On one hand in dogs with plasma ANP levels within the reference range a broader clinical evaluation should be performed since a CHF can be e.g. excluded as a cause for existing dyspnoea. On the other hand the clinical picture is objective by dogs with ANP concentrations over the threshold value. Repeated ANP plasma detection of a treated patient can be useful and it is easier to give a prognosis.
Figure 1.: relative distribution of pro-ANP results in dog plasma.
The biologically inactive pro-ANP made of EDTA plasma, which was spun down immediately after the sampling, separated from its cellular portions and send cooled to the laboratory is examined by ELISA technique.
| BNP (Brain Natriuretic Peptid)|
BNP is another peptide, which was isolated for the first time from the brain of pigs. The following in-vitro studies showed that the main source of the BNP synthesis and secretion is of cardiac origin: in humans from ventricles and in dogs from the atrium. Some myoendocrine cells of the atrium synthesize both ANP and BNP. Contrary to the ANP, BNP is not stored but is released directly after its synthesis. The releasing physiological stimulus for the synthesis and the following secretion within two minutes is the increased wall tension. BNP plays an important role with the sodium- and blood pressure homeostasis. The biological effect of the BNP resembles from ANP. Despite the homologies of the BNP to the ANP a different genexpression and the different metabolisms refer to a separate role of the BNP.
BNP is a cardiac parameter which is increased in myocardial infarctions, supraventricular tachycardia, high blood pressure, ventricular overload and hypertrophic cardiomyopathy (HCM). In particular in cases of hypertrophic cardiomyopathy the BNP secretion seems to be more increased in the relation to the ANP secretion (BNP/ANP >2: 1) even when there is no increase in intraventricular pressure and no existing ventricular overload. Investigations in dogs show that the BNP plasma concentration correlates with the degree of the decomposition of heart failure and somehow weaker with the size of the left atrium. Also the mortality rate rises for the following 4 months with constantly increased BNP concentrations around 44%.
Increased BNP levels are also seen in hepatic cirrhosis. Positive correlations show up between BNP and liver function parameters (δ-GT, LDH, total-bilirubin).
Concerning the kidney function there is no connection between reduced function and increased BNP. In human medicine the determination of the BNP is established as a laboratory marker due to its high sensitivity for the differentiation of heart failure.
The fission product Nt-pro BNP is examined, since BNP exhibits a very short half-life in the plasma. The sample material which can be used is serum or plasma. The sample production corresponds described to the above for pro-ANP. Species specificity is clearly smaller with BNP than with ANP, so that an investigation of BNP will be possible with other animal species in the near future.
Troponins are Ca++ binding proteins, which are cell-specific in all striated muscles. Troponin C, I and T are elements of the Troponincomplex. The main parts of the Troponin are bound to the actin and myosin structures and only a very small portion is free in the cytoplasm. Between myocardial and skeletal Troponin I and T can be differentiated due to its structure.
Troponin mediates with its specific connection for Ca++ between cellular calcium-ion-obtained activation and the actin- as well as tropomyosinmolecules and makes therefore the contractile process possible. Physiologically there are only very small concentrations of cardial Troponin in the serum. An increase of Troponin concentrations in the serum arises due to a damage of cardiac myocytes. After cardial insults without following cell necrosis after 3 to 8 hours a single-phase rise is observed by the release of the cytosolic dissolved Troponin. With severe myocardium damage the following cell necrosis causes a further, clearly higher rise after 2 to 6 days by release of Troponin from the actin-myosin complexes. This second rise can continue over several days.
Troponin is a suitable heart parameter for an acute diagnosis. The serum half-life is approximately 2 hours. The disintegration takes place mainly in liver, pancreas and reticuloendothelial system. Previous insults are not (more) characterised by increased concentrations of Troponin in the serum.
Cardiac cell damage with ischemia and cell necrosis due to infarction, trauma, dilatative and/or hypertrophic cardiomyopathy, myocarditis, intoxication and pericardial diseases cause an increase of the Troponin-serum-level. The extent of the Troponin level
correlates here with the severity of the acute
Cats with hypertrophic cardiomyopathy show constantly increased concentrations, which refer again to a continuous damage.
Investigations from South Africa showed that in the context of an acute Babesiosis the accomplished serial Troponine level detection represents reliable control of the process of the disease and success of the therapy. Hypoxic conditions of the myocardium are detected, caused by inflammatory conditions, fibrin, micro thrombi and ischemia.
In the last half-year the following results (n=664) of Troponin I concentrations were determined and evaluated. Investigated were 564 (85%) samples of dogs and 57 (8.6%) of cats and 43 (6.4%) of horses.
Increased Troponinlevels were detected in about 28% of the dog sera (threshold value 0.6 ng/ml), 16% of the cat sera (threshold value 0,5ng/ml) and 12% of the horse sera (threshold value 0,35ng/ml). An evaluation of the results with consideration of the clinical picture was not possible due to the mostly missing preliminary reports (e.g.: acute happening or control investigation).
In three horses with increased Troponine I serum levels also the CK and LDH were determined. In all three the LDH concentration was not increased twice and the CK level was only slightly increased. In such cases the Troponin detection is clearly superior as CK and LDH increases are non-specific.
Figure 2.: Relative distribution of the results of the Troponin I from cat, dog and horse sera (n=664).
dog, cat, horse
spun down, cooled EDTA-plasma
spun down, cooled EDTA-plasma or serum
| reason of |
Different blood pressure due to:
• congestive heart failure
• mitral valve insufficiency
Different blood pressure due to:
• congestive heart failure
cellular myocardial damage due to:
• infarct (ischemia and
• dilatative and
• Pericardial diseases
|increase in: || (renal failure) || liver cirrhosis|| |
|indication of a single test||To rule out only respiratory dispnea||To rule out only respiratory dispnea||• trauma|
|Indikation of serial tests||• therapy control ||• therapy control ||• gastric torsion|