Anatomy of the axolotl heart.

<p>(A) Anatomical drawing [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0183446#pone.0183446.ref016" target="_blank">16</a>], the sinus (<i>S</i>.) sends collected bodily blood to the left atrium (<i>L</i>.<i>A</i>.) while the right atrium (<i>R</i>.<i>A</i>.) receives oxygenated blood from the lungs and gills. Both atria simultaneously pump the blood into the ventricle (<i>V</i>.), where a dense network of muscle fibres will contract to squeeze out the blood into the bulbus cordis (<i>B</i>.) and then truncus arteriosus (<i>T</i>.<i>A</i>.). (B) Euthanized axolotl in ventral view. The heart is located close to the throat, more cranially than the heart of most mammals. (C) Coronal section of an axolotl scanned with a T2 weighted MRI sequence. The three images aid in understanding the anatomy of the axolotl heart. A = atria, V = ventricle, S = sinus, B = bulbus cordis, TA = truncus arteriosus, L = liver, Sp = spleen. Panel (A) was reproduced and reprinted with permission from The Royal Society of London from reference [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0183446#pone.0183446.ref016" target="_blank">16</a>].</p

The cardiac function parameters of the three axolotls, as measured by MRI and US.

<p>For US, the heart rate was calculated before and after the MRI scans.</p

Average HR (A), EF (B), SV (C), and CO (D) calculated by LA, SA or US techniques.

<p>Wilcoxon signed-rank tests showed significant differences between LA and SA methods for both EF and SV (p 0.015 and 0.008) but not between LA, SA, and US methods for HR (p = 0.374, 0.779, and 0.066 for LA vs SA, LA vs US, and SA vs US).</p

A step-by-step procedure to obtain all axes of the axolotl heart.

<p>(A) A pilot scan (T₁-weighted) was used to locate the heart. (B) An axial FLASH scan is positioned around the middle or lower end of the ventricle—green line in (A); a scan perpendicular to (B) is positioned to cross the ventricular wall in the ventral side and the dorsal intersection of the ventricle and sinus. This yields the apparent long axis (C). The next scan is made perpendicular to this, intersects the apex of the heart and then crosses through the three-way intersection of the ventricle, atria and bulbus to yield the vertical long axis (D). A scan perpendicular to this that crosses the AV valve and the apex of the ventricle is considered the horizontal long axis (E). The short axis was then be obtained by planning a series of scans covering the whole heart that are at a 90° degree angle from the horizontal long axis (panel F, the 7^th slice in a short axis series, displays the ventricle). Green lines represent the slice orientation for the next scan. In panel D, the green line shows the orientation for the horizontal long axis of panel E and the blue line shows the first slice of the short axis scan series of panel F. A = atria, V = ventricle, S = sinus, B = bulbus cordis.</p