Novel axolotl cardiac function analysis method using magnetic resonance imaging

Abstract

The salamander axolotl is capable of complete regeneration of amputated heart tissue. However, non-invasive imaging tools for assessing its cardiac function were so far not employed. In this study, cardiac magnetic resonance imaging is introduced as a non-invasive technique to image heart function of axolotls. Three axolotls were imaged with magnetic resonance imaging using a retrospectively gated Fast Low Angle Shot cine sequence. Within one scanning session the axolotl heart was imaged three times in all planes, consecutively. Heart rate, ejection fraction, stroke volume and cardiac output were calculated using three techniques: (1) combined long-axis, (2) short-axis series, and (3) ultrasound (control for heart rate only). All values are presented as mean ± standard deviation. Heart rate (beats per minute) among different animals was 32.2±6.0 (long axis), 30.4±5.5 (short axis) and 32.7±4.9 (ultrasound) and statistically similar regardless of the imaging method (p > 0.05). Ejection fraction (%) was 59.6±10.8 (long axis) and 48.1±11.3 (short axis) and it differed significantly (p = 0.019). Stroke volume (μl/beat) was 133.7±33.7 (long axis) and 93.2±31.2 (short axis), also differed significantly (p = 0.015). Calculations were consistent among the animals and over three repeated measurements. The heart rate varied depending on depth of anaesthesia. We described a new method for defining and imaging the anatomical planes of the axolotl heart and propose one of our techniques (long axis analysis) may prove useful in defining cardiac function in regenerating axolotl hearts.

Magnetic Resonance Imaging (MRI) reveals high cardiac ejection fractions in red-footed tortoises (Chelonoidis carbonarius)

“…2). Previous reports revealed some disparity between biplane and volumetric measurements in axolotls and humans using echocardiography or MRI, with a tendency to obtain smaller EFs with volumetric measurements in comparison with biplane measurements (Chuang et al, 2000;Gomes et al, 2018). This was also the case in our study, where volumetric measurements led to slightly, but statistically significantly lower EFs (81±12% and 87±8% after atropine).…”

Gross and Ultrasonographic Anatomy of the Coelomic Organs of Healthy Axolotls (Ambystoma Mexicanum)

“…Cardiac findings supplement previous findings about cardiac function and hemodynamics in sedated versus conscious axolotls, especially concerning ventricular wall thickness and heart rate in conscious and unrestrained animals. 13,35 The outlines and the position of atria, truncus arteriosus, and sinus venosus were unclear, probably because of the thinness or small size of these structures. 13,35 The esophageal diameter was difficult to assess, probably because of its small size and deep, dorsal location.…”

“…13,35 The outlines and the position of atria, truncus arteriosus, and sinus venosus were unclear, probably because of the thinness or small size of these structures. 13,35 The esophageal diameter was difficult to assess, probably because of its small size and deep, dorsal location. Colonic layering could not be observed in all subjects, possibly because of the presence of air or digesta, or superimposition of fat bodies in males, and proximal salpinx and ovaries in females.…”