The decomposition of the roots (0-2 mm, 2-5 mm and 5-10 mm) of black alder (Alnus glutinosa (L.) Gaertn.) and hybrid poplar (Populus nigra L. X Populus trichocarpa Torr & Gray) was followed over a 462-day period in pure and mixed plantings in southern Quebec. Small roots of alder had the highest initial concentrations of nitrogen and lignin, and lost 9 and 10% less mass than medium and large roots, respectively. Large roots of poplar had the highest lignin-to-nitrogen ratio and showed the smallest loss of mass over the total incubation period. Slow root decomposition of black alder and hybrid poplar was characterized by a greater proportion of initial root nitrogen immobilized per unit of carbon respired. Lignin concentration in roots of alder and poplar increased rapidly at the beginning of the incubation. Our results suggest that high levels of nitrogen in roots of alder could contribute in slowing the rate of decomposition by allowing the formation of nitrogen-lignin derivatives and low levels of nitrogen in roots of poplar may limit the growth of microorganisms and the rate of root decomposition. A multiple regression was developed using initial nitrogen, lignin concentration and the ratio of lignin to nitrogen to produce an index of the rate of root decomposition. The correlation between the index values and the percentage of residual root mass was significant (r = 0.98, p < 0.01).

C ongenital absence of the pericardium is a rare condition (1). With contemporary imaging techniques, an increase of incidental pericardial defects has arisen. Significant concern comes from potential life-threatening complications. We report a case of congenital absence of the pericardium that was discovered in the throes of acute myocardial necrosis. Literature is reviewed, and investigative and therapeutic strategies are discussed. CASE PRESENTATIONA 49-year-old woman required medical attention for an episode of acute respiratory distress leading to syncope. She reported a history of uncontrolled asthma in the prior weeks, which led her to excessively self-medicate with inhaled beta-adrenergic agonists. She nevertheless had excellent exercise capacity. She never felt any chest, jaw or left arm discomfort, or had any palpitations. The patient was an active smoker, but did not have other coronary risk factors. Her past medical history included mild asthma, panic disorder and depression. She also described syncope of an unknown origin, which was investigated when she was 20 years of age. At that time, she was informed that she had a congenital cardiac anomaly, but she refused to undergo investigation and left the hospital against advice. Her physical examination was normal. The initial electrocardiogram (ECG) indicated sinus rhythm with diffuse T wave inversion and a prolonged QT interval (corrected QT 560 ms). Levels of creatine kinase (876 U/L; normal less than 165 U/L) and troponin T (0.17 μg/L; normal 0.0 μg/L to 0.02 μg/L) were elevated. A D-dimer test was normal. The patient was diagnosed with acute non-ST segment elevation myocardial infarction, treated with standard pharmacological therapies and transferred to the Quebec Heart Institute at Laval Hospital (Quebec, Quebec).Urgent selective coronary angiography revealed right dominance and angiographically smooth coronary arteries, with Thrombolysis In Myocardial Infarction (TIMI) grade 3 flow and normal blush. Ventriculography showed normal left ventricular ejection fraction (LVEF) and absence of mitral regurgitation, but a laterally displaced and vertically oriented heart. A follow-up ECG indicated the return of T waves to baseline, with slow R wave progression in the precordial leads; the QT interval also normalized. The chest x-ray ( Figure 1) was notable for leftward displacement of the heart and rectification of the left heart border, suggestive of pericardial absence. Echocardiography was technically challenging because of poor echogenicity, unusual heart orientation within the chest cavity and significant cardiac motion. The patient's regional LVEF was normal (55%).Cardiac magnetic resonance (CMR) imaging was performed to better define cardiac morphology and function. This confirmed the leftward position of the heart and found that the apex was orientated posteriorly (Figure 2). CMR imaging demonstrated the absence of pericardial recesses at the level of the great vessels. A lung was visible between the aorta and pulmonary artery, indicating the abs...

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