An analytical triad for the diagnosis of pulmonary embolism

24-Hour Kinetics of Cardiac Troponin-T Using a "High-Sensitivity" Assay in Thoroughbred Chuckwagon Racing Geldings after Race and Associated Clinical Sampling Guidelines

Background

A “high‐sensitivity” cardiac troponin‐T (hscTnT) assay recently has been validated for use in horses and is a specific biomarker of myocardial damage. Postexercise release kinetics of cTnT utilizing the hscTnT assay have yet to be established in horses.

Objectives

To determine: (1) cTnT release kinetics in racing Thoroughbreds after a high‐intensity 5/8th mile Chuckwagon race; (2) the effects of age on pre‐ and postrace cTnT concentrations; and (3) sampling guidelines for clinicians evaluating horses presenting after exercise.

Animals

Samples were obtained from 38 Thoroughbred geldings aged 5–16 years before racing and immediately, 2, 3, 4, 6, 12, and 24 hour postrace.

Methods

Prospective, observational study with convenience sampling. A fifth‐generation hscTnT assay was used for plasma sample analysis, and concentrations were compared at all time‐points. Correlations were determined between cTnT concentrations and age. Biochemistry analysis was performed to assess rhabdomyolysis, renal failure, and exercise‐induced dehydration.

Results

All horses with measureable cTnT concentrations had significant postexercise increases in cTnT with a median peak (8.0 ng/L) at 3‐hour postrace. All horses had peak postexercise cTnT concentrations 2‐ to 6‐hour postrace ≤ the 99th percentile upper reference limit of 23.2 ng/L, after which all cTnT concentrations decreased until returning to baseline by 12–24 hours. There was no correlation over time between cTnT concentrations and age.

Conclusions and Clinical Importance

In racing Thoroughbreds completing short‐duration, high‐intensity Chuckwagon races, cTnT concentrations are expected to be increased 2‐ to 6‐hour postrace and to decrease by 12–24 hours while remaining ≤23.2 ng/L throughout. This study contributes to establishing guidelines for clinical use of the hscTnT assay in exercising horses.

Troponin I, but not BNP, is associated with phosphorus, calcium and vitamin D in stable coronary artery disease

BACKGROUND

Elevated plasma cardiac troponin, elevated plasma phosphorus and decreased plasma vitamin D have been shown to be associated with negative outcomes.

METHODS AND RESULTS

Troponin I, calcium, phosphorus and 25-OH vitamin D were studied in a cohort of 60 patients with stable coronary heart disease and preserved left ventricular function. Using a cut-off value of 0.012 ng/mL for plasma troponin I, patients with higher values (18 patients), when compared to the other patients (n=42), had higher mean values for plasma phosphorus (3.42+0.45 mg/dL vs 3.17+0.45 mg/dL, p= 0.041) and calcium (5.08+0.23 mEq/L vs 4.92+0.18 mEq/L, p= 0.016) and lower values for 25-OH vitamin D (14.2+5.6 ng/mL vs 19.4+8.8 ng/mL, p= 0.032). Binary logistic regression analysis showed that troponin I > 0.012 ng/ml is associated with increased phosphorus, increased calcium and decreased 25-OH vitamin D concentrations. A similar analysis using BNP >100 pg/mL failed to show signifcant associations with phosphorus, calcium and 25-OH vitamin D concentrations.

CONCLUSIONS

In patients with stable coronary artery disease and preserved left ventricular function, those having cardiac troponin I > 0.012 ng/ml, but not those having BNP >100 pg/mL, had higher plasma phosphorus, higher plasma calcium and lower plasma 25-OH vitamin D concentrations than those having cardiac troponin I ≤ 0.012 ng/ml (or BNP ≤ 100 pg/mL).

Do induced tachycardias within the scope of electrophysiological studies lead to elevated plasma troponin I levels?

AIMS

Troponin I (TNI) is an established marker for the diagnosis of acute coronary syndrome (ACS). The study evaluated if (induced) tachycardiac arrhyhthmias within the scope of the electrophysiological studies (EPS) led to elevation of TNI serum levels.

METHOD

TNI was measured in the serum of 28 patients before and after the EPS. The left ventricular ejection fraction (LV-EF) was investigated by two-dimensional echocardiography. Left ventricle hypertrophy (LVH) was measured according to the recommendations of the American Society of Echocardiography. All patients underwent coronary angiography prior to the EPS, and significant coronary heart disease was defined as stenosis > 50%. The EPS revealed supraventricular and ventricular tachycardias using the 18-step protocol with one, two, and three extrastimuli.

RESULTS

Indications for the EPS were syncope (n = 15), atrioventricular tachycardia (n = 4), non-sustained VT (n = 6), and sustained VT (n = 3). Coronary heart disease (CHD) was detected in 8 patients (1-vessel: n = 3; 2-vessel: n = 4; 3-vessel: n = 1), and 2 patients underwent percutaneous coronary intervention before EPS. Echocardiography revealed normal LV-EF in 18 patients and a reduction in the others (low n = 3, middle n = 5, high n = 2). Thirteen patients suffered from LVH. In 2 patients, external cardioversion was required during the EPS. TNI was elevated over 0.1 ng/ml (risk stratification cut-off for ACS) in 4 patients before and in 12 patients after EPS. There was no relationship between LV-EF, CHD, and the elevation of TNI after the EPS.

CONCLUSION

TNI can be elevated by (induced) tachycardias within the scope of electrophysiological studies without a relationship to LV-EF, LVH, and CHD.

Pseudo myocardial infarction - a condition in need to be redefined?

Since the introduction of cardiac plasma troponin measurements, a significant number of patients were seen with chest pain, elevated troponin levels but no significant coronary artery disease. Pulmonary embolism, aortic valve disease, myocarditis, sepsis, trauma, arrythmias, stress cardiomyopathy and dilated cardiomyopathy stand among possible causes for this syndrome. In some cases, myocardial strain could be the mechanism underlying this phenomenon, since it is known that the stimulation of stretch-responsive integrins may lead to the release of cardiac troponin I. In the present text, a case is made in favour of classifying this syndrome, of chest pain with increased values for plasma cardiac troponin, with or without ECG changes, in the absence of definite myocardial infarction or coronary artery disease, as pseudo myocardial infarction (PMI). This constitutes a new definition for a concept with decades, formerly centered on clinical and electrocardiographic changes mimicking infarct. The case is based on the search of scientific truth, on avoidance of unnecessary cardiac examinations, on avoidance of unnecessary drug therapy and on avoidance of unnecessary legal liability. PMI should be seen as a working diagnosis, since a more definitive diagnosis can be reached at all time. It should also be seen as a heterogeneous group of patients - several different diseases and conditions can lead to this phenomenon. But it must certainly not be seen as a benign condition, since published studies point in a totally different direction.

Release of cardiac troponin I from viable cardiomyocytes is mediated by integrin stimulation

Elevated cardiac troponin-I (cTnI) levels have been demonstrated in serum of patients without acute coronary syndromes, potentially via a stretch-related process. We hypothesize that this cTnI release from viable cardiomyocytes is mediated by stimulation of stretch-responsive integrins. Cultured cardiomyocytes were treated with (1) Gly-Arg-Gly-Asp-Ser (GRGDS, n = 22) to stimulate integrins, (2) Ser-Asp-Gly-Arg-Gly (SDGRG, n = 8) that does not stimulate integrins, or (3) phosphate-buffered saline (control, n = 38). Cells and media were analyzed for intact cTnI, cTnI degradation products, and matrix metalloproteinase (MMP)-2. Cell viability was examined by assay of lactate dehydrogenase (LDH) activity and by nuclear staining with propidium iodide. GRGDS-induced integrin stimulation caused increased release of intact cTnI (9.6 +/- 3.0%) as compared to SDGRG-treated cardiomyocytes (4.5 +/- 0.8%, p < 0.001) and control (3.0 +/- 3.4%, p < 0.001). LDH release from GRGDS-treated cardiomyocytes (15.9 +/- 3.8%) equalled that from controls (15.2 +/- 2.3%, p = n.s.), indicating that the GRGDS-induced release of cTnI is not due to cell necrosis. This result was confirmed by nuclear staining with propidium iodide. Integrin stimulation increased the intracellular and extracellular MMP2 activity as compared to controls (both p < 0.05). However, despite the ability of active MMP2 to degrade cTnI in vitro, integrin stimulation in cardiomyocytes was not associated with cTnI degradation. The present study demonstrates that intact cTnI can be released from viable cardiomyocytes by stimulation of stretch-responsive integrins.

Cardiac troponin I in aortic valve disease

BACKGROUND

Plasma cardiac troponin I levels may be higher than normal in conditions other than ischemic heart disease. We aimed at measuring troponin I levels in aortic valve patients, in which increased values for left ventricular dimensions and pressure are frequently found.

METHODS

Plasma levels of troponin I, creatine kinase (CK) and the MB fraction of the same enzyme were measured in a group of 25 clinically stable aortic valve patients. Echocardiographic study was performed in all patients; hemodynamic and coronary angiographic study was performed in 19 patients. Troponin I was also measured in a control population (n=305).

RESULTS

The mean value for troponin I was found to be higher in aortic valve patients (0.07+/-0.02 ng/ml), when compared to controls (0.01+/-0.02 ng/ml; P<0.05). Significant correlations were found between troponin I and both creatine kinase and its MB fraction. When the 25 patients were divided into two groups, with lower (up to 0.04 ng/ml; 12 patients) and higher (0.05 ng/ml or greater; 13 patients) values for troponin I, patients with higher values were found to have greater mean left ventricular wall thickness (9.9+/-0.3 mm, n=11, vs. 12.1+/-0.3 mm, n=13) and pulmonary artery systolic pressures (36.6+/-2.5 mmHg, n=7, vs. 53.7+/-3.4 mmHg, n=9).

CONCLUSIONS

We conclude that slightly raised plasma levels of cardiac troponin I are relatively common in aortic valve patients with no evidence of ischemia. Higher left ventricular wall thickness and pulmonary artery systolic pressure may be related to slightly raised troponin I plasma levels.