This dissertation focuses on the effect of breeding on the myocardium of stallions using cardiac troponin I (cTnI) as the preferred blood biomarker for detection of myocardial cell injury. Haematological, echocardiographic and heart rate (HR) parameters are also reported. Fourteen clinically healthy phantom-trained stallions were assessed. Cardiac troponin I concentration was determined pre-semen collection and at 4, 6, 12 and 24 hours following semen collection. Predictors that were measured included mean HR during each stage of semen collection, maximum HR, area under the curve for HR and fractional shortening (FS). Pre-semen collection cTnI concentrations were within reported reference ranges for all stallions. Following semen collection, cTnI concentration was significantly increased at 4 and 6 hours post-semen collection. Results also suggest that the HR of stallions peak during mounting of the phantom. Five stallions failed to show an expected increase in FS immediately post-semen collection. No association was identified between the measured predictors and increased cTnI concentration. This study concluded that cTnI concentration may increase in stallions following semen collection although the clinical significance of this observed increase in healthy stallions is unclear without histopathological evaluation of the myocardium. No conclusion regarding FS immediately post-semen collection could be drawn from results in this study. The research reported in this dissertation can serve as a reference for future studies investigating cTnI concentrations in stallions. / Dissertation (MSc)--University of Pretoria, 2010. / Companion Animal Clinical Studies / unrestricted

Background: Once aortic stenosis (AS) is severe, patients develop symptoms at different stages. Indeed, symptom status may correlate poorly with the grade of valve narrowing. Multiple pathophysiological mechanisms, other than valvular load, may explain the link between AS and symptom severity. We aimed to describe the relationship between the severity of symptoms and the characteristics of a cohort of patients with severe AS already referred for aortic valve replacement (AVR). Methods: We analyzed 118 consecutive patients (70 ± 9 years, 55% men) with severe AS referred for AVR. We identified 84 patients with New York Heart Association (NYHA) I–II, and 34 with NYHA III–IV symptoms. Clinical and echocardiographic parameters were compared between these two groups. Left ventricular ejection fraction (LVEF), global longitudinal peak systolic strain (GLPS), NT-pro-B-type natriuretic peptide (BNP), and high-sensitive troponin T (hs-TNT) were determined at the time of admission. Results: AS severity was similar between groups. Compared with the NYHA I–II group, patients in NYHA III–IV group were older and more likely to have comorbidities, worse intracardiac hemodynamics and more LV damage. Variables independently associated with NYHA III–IV symptomatology were the absence of sinus rhythm, higher E/e0 ratio, and increased hs-TNT. GLPS showed a good correlation not only with hs-TNT as a marker of myocardial damage, but also with markers of increased afterload imposed on LV, being not directly related with advanced symptoms. Conclusions: Advanced symptoms in patients with severe AS referred for AVR are associated with worse intracardiac hemodynamics, absence of sinus rhythm, and more myocardial damage. It supports the concept of transition from adaptive LV remodeling to myocyte death as an important determinant of symptoms of heart failure. :Einführung................................................................................................3 Publikationsmanuskript...........................................................................12 Zusammenfassung..................................................................................19 Literaturverzeichnis..................................................................................24 Erklärung über die eigenständige Abfassung der Arbeit.........................28 Darstellung des eigenen Beitrags............................................................29 Curriculum vitae.......................................................................................30 Danksagung.............................................................................................36

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(1) Background: Highly sensitive cardiac troponin T (hs-cTnT) plays an essential role in the diagnosis of myocardial injury. The upper reference limit of the respective assay is generally applied, irrespective of age, renal function, or sex. We aimed to identify age-adjusted and sex-adjusted upper reference limits in relation to renal function in a large population-based cohort without cardiac diseases. (2) Methods: We included 5428 subjects of the population-based LIFE-Adult cohort, free of diagnosed cardiac diseases. Sex-adjusted and age-adjusted 99th percentiles for hs-cTnT in subjects with preserved renal function were obtained. (3) Results: The hs-cTnT values were higher in men of all age groups. In both sexes, an increasing age positively correlated with higher hs-cTnT values. Hs-cTnT weakly correlated with serum creatinine. The three-dimensional analysis of age, creatinine, and hs-cTnT showed no relevant additional effect of creatinine on hs-cTnT. In men aged above 60 and women above 70, the calculated 99th percentiles clearly exceeded the commonly applied thresholds. (4) Conclusion: Age and sex have a major impact on the serum concentration of hs-cTnT, while renal function does not. We propose to consider age-adjusted and sex-adjusted reference values.

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<p>Worldwide, more than 2 million patients die within 30 days after noncardiac surgery anually. Postoperative ischemic myocardial injury is frequent, however, no consensus exists about its definition.</p> <p><strong>Objective: </strong>to develop a term Myocardial Injury after Noncardiac Surgery (MINS) caused by myocardial ischemia, requiring at least, troponin T (TnT) elevation, and with prognostic relevance at 30 days after surgery.</p> <p><strong>Methods: </strong>we performed a prospective study including 15,167 patients ³45 years-old undergoing noncardiac surgery, who had fourth-generation TnT measurements during the first 3 postoperative days. We undertook Cox regression analyses with 30-day mortality after surgery as the dependent variable, using different TnT thresholds, clinical features and several perioperative variables. Non-ischemic etiologies were excluded. Furthermore, we developed a scoring system to predict risk in MINS patients.</p> <p><strong>Results:</strong> MINS was defined as TnT ≥0.03 ng/mL with or without clinical features, and it was an independent predictor of 30-day mortality (adjusted HR 3.82, CI 95% 2.84-5.10). We determined that MINS incidence was 8%, its population attributable risk 33.7%, and 30-days mortality rate 9.6%. Patients did not experience ischemic symptoms in 84% of MINS cases. Additionally, we developed a scoring system in patients suffering MINS with 3 independent predictors of death (age ≥75 years, new ST elevation or left bundle branch block, and anterior location of ECG changes),</p> <p><strong>Conclusion: </strong>Among patients undergoing noncardiac surgery, we defined MINS based on a TnT threshold ≥0.03 ng/mL. Mostly, MINS patients were asymptomatic. Therefore, this strongly suggests the importance of a troponin monitoring during the first few days after surgery.</p> / Master of Health Sciences (MSc)

<p>Reduced kidney function around the time of surgery is an important risk factor for postoperative mortality. Despite this there is limited information on how reduced kidney function prior to surgery alters prognosis, what causes sudden decrements in kidney function after surgery (known as acute kidney injury), or how they might be avoided. The studies in this thesis inform these knowledge gaps. Chapter 2 describes the results of a post hoc analysis of the interaction between preoperative estimated glomerular filtration rate, a marker of kidney function, and postoperative cardiac troponin T, a marker of heart damage, for predicting 30-day mortality in a prospective cohort study of patients undergoing noncardiac surgery. Chapter 3 uses administrative and clinical data from a single centre to inform the risk of acute kidney injury after noncardiac surgery by concentrations of preoperative hemoglobin and change in postoperative hemoglobin. Chapter 4 uses the same data to determine a definition of intraoperative hypotension that is prognostic of acute kidney injury, myocardial injury and death. Chapter 5 describes a randomized controlled trial that compares a novel therapeutic procedure called remote ischemic preconditioning to a sham procedure in patients undergoing cardiac surgery.</p> / Doctor of Philosophy (PhD)

A novel luminescence resonance energy transfer (LRET) nanocircuit assay involving a donor and two acceptors in tandem was developed to study the dynamic interaction of skeletal muscle contraction proteins. The donor transmits energy relayed to the acceptors distinguishing myosin subfragment-1 (S1) lever arm orientations. The last acceptor allows the detection of S1's bound near or in between troponin complexes on the thin filament. Additionally, calcium related changes between troponin T and myosin were detected. Based on this data, the troponin complex situated every 7 actin monomers, hinders adjacently bound myosins to complete their power stroke; whereas myosins bound in between troponin complexes undergo complete power strokes.

Mechanistic details on the regulation of striated muscle contraction still need to be determined, particularly the specific structural locations of the elements comprising the thick and thin filaments. Of special interest is the location of the regulatory component, troponin, on the actin filament and how its presence influences the behavior of myosin binding to the thin filament. In the present study: (1) Luminescence resonance energy transfer was used to monitor potential conformational changes in the reconstituted thin filament between the C-terminal region of troponin T and myosin subfragment 1; (2) Location of troponin in previously derived atomic models of the acto-myosin complex was mapped to visualize specific contacts; and (3) Shortened tropomyosin was engineered and protein binding and ATPase assays were performed to study the effect of myosin binding close to the troponin complex. Analysis of the results suggest the following: (1) Irrespective of calcium levels, the C-terminal region of troponin T is located close to myosin loop 3 and a few actin helices that may perturb strong acto-myosin interactions responsible for force production. (2) Atomic models indicate myosin subfragment 1 cannot attain the post- powerstroke state due to the full motion of the lever arm being sterically hindered by troponin. (3) A shortened tropomyosin with five actin binding modules (instead of the native seven in muscle cells) binds actin contiguously in a head-to-tail manner and serves to increase the periodicity of troponin complexes on the actin filament. Such behavior eliminates the structure of the actin filament being responsible for the binding location of tropomyosin. (4) Differential behavior of myosin subfragment 1 i.e. (a) binding adjacent to troponin and (b) binding further away from troponin, is apparent as tropomyosin and troponin appear to govern the regions or "target zones" where myosin can bind productively along the actin filament. Physiologically, myosins able to bind close to troponin, but not participate in force production may function as mechanical sensors to attenuate or dampen the force generated from the so-called "target zones". Therefore, this could be a pseudo-regulatory mechanism that functions to protect the contractile apparatus from damage.