Seasonal prescribed burning impacts to northern Minnesota lowland brush ecosystem plant communities

University of Minnesota M.S. thesis. July 2019. Major: Natural Resources Science and Management. Advisor: Rebecca Montgomery. 1 computer file (PDF); ix, 72 pages.Minnesota lowland brush ecosystems provide critical habitat for wide variety of wildlife including over 80 Species of Greatest Conservation Need. These ecosystems depend on fire disturbance to inhibit woody plant encroachment and maintain the herbaceous plant community. Without fire, woody plants become dominant in the overstory, reduce herbaceous cover, and reduce the quality of habitat for wildlife that rely on spatial and structural diversity. Natural resource managers use prescribed burning to decrease woody plant density and enhance the herbaceous plant community in these ecosystems. Currently, the prescribed fire regime in lowland brush ecosystems is largely limited to the spring season, and research in other ecosystems has found that burn season can result in a wide range of impacts to burn severity and both woody and herbaceous plant communities. Understanding the impacts of burn season is critical for natural resource managers to effectively conduct prescribed burns to meet their management objectives. However, little research currently exists on the impacts of fire in lowland brush ecosystems, let alone burn season. The objective of our study was to determine whether season of prescribed burning led to significant differences in burn severity, changes in total woody plant density, changes in density of common woody species, and changes in herbaceous cover. In 2016, we established permanent sample plots at 4 study sites throughout northern Minnesota in order to monitor burn severity and response of vegetation. Each site was broken into 4 burn units including a spring, summer, fall, and a control where no burn was conducted. The results of this study focused on the impacts of burn season on burn severity and the plant community in the first growing season after the burns were conducted, and includes the results of four spring burns, two fall burns, and two summer burns. While we found that burn severity and plant community response differed among burn season treatments, our findings varied by spatial scale. Burns conducted in the spring burned more area those in fall or summer. Given that more area burned in spring compared to fall or summer, we examined the impacts of burn season at different scales to consider broad landscape scale impacts (burn unit scale) and direct fire impacts (plot scale). Burn unit scale included analysis of all permanent sample plots within each burn unit regardless of whether there was evidence of fire at the plot, and at the plot scale we included only on sample plots where evidence of fire was present. Additionally, we broke down the direct fire impacts at the plot scale to look at impacts on common woody plant species and species groups. At the burn unit scale, spring burns were the most severe, resulted in the highest amounts of topkilled woody stems, and the overall greatest reduction in woody plant density even though vigorous resprouting was likely occurring. At the plot scale, burn severity did not differ among burn seasons, but spring burns still resulted in an overall reduction in woody stems while fall and summer burns did not. Furthermore, woody species varied in their response to burn season with some species appearing to resprout prolifically and others not as much, while herbaceous cover did not change as a result of fire compared to the control units. Our results indicate that spring burns were the most successful at reducing woody stem density one year after burn. However, reduction in woody stem density may not be the only management objective. Our results also suggest that spring burns create a uniform understory of shrub regeneration, which may reduce heterogeneity on the landscape. Recent research suggests that high severity burns, which create a single cohort of regenerating woody shrubs, reduce habitat quality for the bird community (Zlonis et al., 2019). Thus, natural resource managers should view fire season as a tool for supporting a variety of outcomes in lowland brush ecosystems.Knosalla, Lori. (2019). Seasonal prescribed burning impacts to northern Minnesota lowland brush ecosystem plant communities. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/206700

Heart failure and sudden cardiac death in heritable thoracic aortic disease caused by pathogenic variants in the SMAD3 gene

Background: Predominant cardiovascular manifestations in the spectrum of Heritable Thoracic Aortic Disease include by default aortic root aneurysms- and dissections, which may be associated with aortic valve disease. Mitral- and tricuspid valve prolapse are other commonly recognized features. Myocardial disease, characterized by heart failure and/or malignant arrhythmias has been reported in humans and in animal models harboring pathogenic variants in the Fibrillin1 gene. Methods: Description of clinical history of three cases from one family in Ghent (Belgium) and one family in St. Louis (US). Results: We report on three cases from two families presenting end-stage heart failure (in two) and lethal arrhythmias associated with moderate left ventricular dilatation (in one). All three cases harbor a pathogenic variant in the SMAD3 gene, known to cause aneurysm osteoarthritis syndrome, Loeys-Dietz syndrome type 3 or isolated Heritable Thoracic Aortic Disease. Conclusions: These unusual presentations warrant awareness for myocardial disease in patients harboring pathogenic variants in genes causing Heritable Thoracic Aortic Disease and indicate the need for prospective studies in larger cohorts

Strain and Strain Rate Imaging by Echocardiography – Basic Concepts and Clinical Applicability

Echocardiographic strain and strain-rate imaging (deformation imaging) is a new non-invasive method for assessment of myocardial function. Due to its ability to differentiate between active and passive movement of myocardial segments, to quantify intraventricular dyssynchrony and to evaluate components of myocardial function, such as longitudinal myocardial shortening, that are not visually assessable, it allows comprehensive assessment of myocardial function and the spectrum of potential clinical applications is very wide. The high sensitivity of both tissue Doppler imaging (TDI) derived and two dimensional (2D) speckle tracking derived myocardial deformation (strain and strain rate) data for the early detection of myocardial dysfunction recommend these new non-invasive diagnostic methods for extensive clinical use. In addition to early detection and quantification of myocardial dysfunction of different etiologies, assessment of myocardial viability, detection of acute allograft rejection and early detection of allograft vasculopathy after heart transplantation, strain and strain rate data are helpful for therapeutic decisions and also useful for follow-up evaluations of therapeutic results in cardiology and cardiac surgery. Strain and strain rate data also provide valuable prognostic information, especially prediction of future reverse remodelling after left ventricular restoration surgery or after cardiac resynchronization therapy and prediction of short and median-term outcome without transplantation or ventricular assist device implantation of patients referred for heart transplantation

Surrogates for myocardial power and power efficiency in patients with aortic valve disease

We aimed to assess surrogate markers for left ventricular (LV) myocardial power and efficiency in patients with isolated aortic stenosis (AS) and combined stenosis/regurgitation (AS/AR). In AS (n = 59), AS/AR (n = 21) and controls (n = 14), surrogates for LV myocardial power and circulatory/external myocardial efficiency were obtained from cardiac MRI. Median surrogate LV myocardial power was increased in AS, 7.7 W/m2 (interquartile range 6.0-10.2; p = 0.010) and AS/AR, 10.8 W/m2 (8.9-13.4; p < 0.001) when compared to controls, 5.4 W/m2 (4.2-6.5), and was lower in AS than AS/AR (p < 0.001). Surrogate circulatory efficiency was decreased in AS, 8.6% (6.8-11.1; p < 0.001) and AS/AR, 5.4% (4.1-6.2; p < 0.001) when compared to controls, 11.8% (9.8-16.9). Surrogate external myocardial efficiency was higher in AS, 15.2% (11.9-18.6) than in AS/AR, 12.2% (10.1-14.2; p = 0.031) and was significantly lower compared to controls, 12.2% (10.7-18.1) in patients with reduced ejection fraction (EF), 9.8% (8.1-11.7; p = 0.025). In 16% of all cases, left ventricular mass/volume indices and EF were within normal ranges, wheras surrogate LV myocardial power was elevated and patients were symptomatic. Although influenced by pressure/volume load, the myocardium is additionally affected by remodelling processes. Surrogates for circulatory efficiency and LV myocardial power gradually reflect alterations in patients with AS and AS/AR, even when surrogate external myocardial efficiency, EF, mass and volume indices still remain compensated

Myocardial Work Assessment for the Prediction of Prognosis in Advanced Heart Failure

Objectives: The aim of this study was to investigate whether echocardiographic assessment of myocardial work is a predictor of outcome in advanced heart failure. Background: Global work index (GWI) and global constructive work (GCW) are calculated bymeans of speckle tracking, blood pressuremeasurement, and a normalized reference curve. Their prognostic value in advanced heart failure is unknown. Methods: Cardiopulmonary exercise testing and echocardiography with assessment of GWI and GCW was performed in patients with advanced heart failure caused by ischemic heart disease or dilated cardiomyopathy (n = 105). They were then followed up repeatedly. The combined endpoint was all-cause death, implantation of a left ventricular assist device, or heart transplantation. Results: The median patient age was 54 years (interquartile range [IQR]: 48–59.9). The mean left ventricular ejection fraction was 27.8 ± 8.2%, the median NT-proBNP was 1,210 pg/ml (IQR: 435–3,696). The mean GWI was 603 ± 329 mmHg% and the mean GCW was 742 ± 363 mmHg%. The correlation between peak oxygen uptake and GWI as well as GCW was strongest in patients with ischemic cardiomyopathy (r = 0.56, p = 0.001 and r = 0.53, p = 0.001, respectively). The median follow-up was 16 months (IQR: 12–18.5). Thirty one patients met the combined endpoint: Four patients died, eight underwent transplantation, and 19 underwent implantation of a left ventricular assist device. In themultivariate Cox regression analysis, only NYHA class, NT-proBNP and GWI (hazard ratio [HR] for every 50 mmHg%: 0.85; 95% CI: 0.77–0.94; p = 0.002) as well as GCW (HR for every 50 mmHg%: 0.86; 95% CI: 0.79–0.94; p = 0.001) were identified as independent predictors of the endpoint. The cut-off value for predicting the outcome was 455 mmHg% for GWI (AUC: 0.80; p < 0.0001; sensitivity 77.4%; specificity 71.6%) and 530 mmHg% for GCW (AUC: 0.80; p < 0.0001; sensitivity 74.2%; specificity 78.4%). Conclusions: GWI and GCW are powerful predictors of outcome in patients with advanced heart failure

Circulatory efficiency in patients with severe aortic valve stenosis before and after aortic valve replacement

Background: Circulatory efficiency reflects the ratio between total left ventricular work and the work required for maintaining cardiovascular circulation. The effect of severe aortic valve stenosis (AS) and aortic valve replacement (AVR) on left ventricular/circulatory mechanical power and efficiency is not yet fully understood. We aimed to quantify left ventricular (LV) efficiency in patients with severe AS before and after surgical AVR. Methods: Circulatory efficiency was computed from cardiovascular magnetic resonance (CMR) imaging derived volumetric data, echocardiographic and clinical data in patients with severe AS (n = 41) before and 4 months after AVR and in age and sex-matched healthy subjects (n = 10). Results: In patients with AS circulatory efficiency was significantly decreased compared to healthy subjects (9 +/- 3% vs 12 +/- 2%; p = 0.004). There were significant negative correlations between circulatory efficiency and LV myocardial mass (r = - 0.591, p < 0.001), myocardial fibrosis volume (r = - 0.427, p = 0.015), end systolic volume (r = - 0.609, p < 0.001) and NT-proBNP (r = - 0.444, p = 0.009) and significant positive correlation between circulatory efficiency and LV ejection fraction (r = 0.704, p < 0.001). After AVR, circulatory efficiency increased significantly in the total cohort (9 +/- 3 vs 13 +/- 5%; p < 0.001). However, in 10/41 (24%) patients, circulatory efficiency remained below 10% after AVR and, thus, did not restore to normal values. These patients also showed less reduction in myocardial fibrosis volume compared to patients with restored circulatory efficiency after AVR. Conclusion: In our cohort, circulatory efficiency is reduced in patients with severe AS. In 76% of cases, AVR leads to normalization of circulatory efficiency. However, in 24% of patients, circulatory efficiency remained below normal values even after successful AVR. In these patients also less regression of myocardial fibrosis volume was seen. Trial Registration clinicaltrials.gov NCT03172338, June 1, 2017, retrospectively registered