SummaryThe effect of phosphotungstic acid (PTA) and iodine solution (IKI) staining was investigated as a method of enhancing contrast in the X-ray computed tomography of porcine anterior cruciate ligaments (ACL) and patellar tendons (PT). We show that PTA enhanced surface contrast, but was ineffective at penetrating samples, whereas IKI penetrated more effectively and enhanced contrast after 70 hours of staining. Contrast enhancement was compared when using laboratory and synchrotron based X-ray sources. Using the laboratory source, PT fascicles were tracked and their alignment was measured. Individual ACL fascicles could not be identified, but identifiable features were evident that were tracked. Higher resolution scans of fascicle bundles from the PT and ACL were obtained using synchrotron imaging techniques. These scans exhibited greater contrast between the fascicles and matrix in the PT sample, facilitating the identification of the fascicle edges; however, it was still not possible to detect individual fascicles in the ACL.

P ulmonary hypertension (PHT) is a disease characterized by raised pulmonary vascular resistance. It has a poor prognosis typically resulting in progressive right ventricular failure and death. The incidence of arrhythmias in patients with PHT is high.1-3 All forms of supraventricular tachycardia are more common in PHT with studies suggesting an incidence of ≈3% per year and a prevalence of supraventricular arrhythmia of ≈12%.3 Atrial flutter, atrial fibrillation, and atrioventricular (AV) nodal reentrant tachycardia are common. 3,4 There is evidence of AV node dysfunction in PHT with a 14% incidence of first-degree heart block, a mean PR interval of 180±50 ms (mean±SD), and 2% of patients requiring a pacemaker for high-degree heart block on initial screening of PHT patients. 1This can be compared with an incidence of first-degree heart block of 2.1% and mean PR interval of 160±22 ms (mean±SD) for men and 153±22 ms (mean±SD) for women in the general population.5 Sleep apnea causes PHT 6 and is associated with heart block (heart block during sleep has been described in ≤10% of patients with obstructive sleep apnea).7 Despite the evidence of a high burden of arrhythmias in patients with PHT, including dysfunction of the AV node, there are limited experimental data looking at the mechanisms of arrhythmia © 2016 American Heart Association, Inc. Original ArticleBackground-Heart block is associated with pulmonary hypertension, and the aim of the study was to test the hypothesis that the heart block is the result of a change in the ion channel transcriptome of the atrioventricular (AV) node. Methods and Results-The most commonly used animal model of pulmonary hypertension, the monocrotaline-injected rat, was used. The functional consequences of monocrotaline injection were determined by echocardiography, ECG recording, and electrophysiological experiments on the Langendorff-perfused heart and isolated AV node. The ion channel transcriptome was measured by quantitative PCR, and biophysically detailed computer modeling was used to explore the changes observed. After monocrotaline injection, echocardiography revealed the pattern of pulmonary artery blood flow characteristic of pulmonary hypertension and right-sided hypertrophy and failure; the Langendorff-perfused heart and isolated AV node revealed dysfunction of the AV node (eg, 50% incidence of heart block in isolated AV node); and quantitative PCR revealed a widespread downregulation of ion channel and related genes in the AV node (eg, >50% downregulation of Ca v 1.2/3 and HCN1/2/4 channels). Computer modeling predicted that the changes in the transcriptome if translated into protein and function would result in heart block. Conclusions-Pulmonary hypertension results in a derangement of the ion channel transcriptome in the AV node, and this is the likely cause of AV node dysfunction in this disease. (Circ Arrhythm Electrophysiol. 2016;9:e003432.

X-ray computed tomography (XCT) has been shown to be an effective imaging technique for a variety of materials. Due to the relatively low differential attenuation of X-rays in biological tissue, a high density contrast agent is often required to obtain optimal contrast. The contrast agent, iodine potassium iodide (), has been used in several biological studies to augment the use of XCT scanning. Recently was used in XCT scans of animal hearts to study cardiac structure and to generate 3D anatomical computer models. However, to date there has been no thorough study into the optimal use of as a contrast agent in cardiac muscle with respect to the staining times required, which has been shown to impact significantly upon the quality of results. In this study we address this issue by systematically scanning samples at various stages of the staining process. To achieve this, mouse hearts were stained for up to 58 hours and scanned at regular intervals of 6–7 hours throughout this process. Optimal staining was found to depend upon the thickness of the tissue; a simple empirical exponential relationship was derived to allow calculation of the required staining time for cardiac samples of an arbitrary size.