The Effect of Cardiac Filling on Heart Rate Variability in Rabbit Isolated Heart

Abstract

Presence of heart rate variability (HRV) IntroductionPresence of heart rate variability (HRV) in isolated hearts is widely recognized; however, its mechanisms are still subject of debate. One of the possible explanations is that mechanoreceptors in cardiac tissue affect HRV. This hypothesis is supported by the fact that mechanical stimulus can induce changes of heart rhythm [1, 2]. In order to evaluate effect of mechanical stimulation of isolated heart during atrium and ventricle filling, HRV parameters were compared between Langendorff and working heart modes. MethodTen New Zealand rabbit isolated hearts (both sex) were studied. All experiments followed the guidelines for animal treatment approved by local authorities and conformed to the EU law. Isolated heartsIn deep anaesthesia with xylasin and ketamine, the hearts were excised and perfused in Langendorff mode (constant pressure of 85 mmHg) and consecutively in working heart mode (8 cmH2O preload, 60 cmH2O afterload) with Krebs-Henseleit solution (in mM: NaCl 118, NaHCO3 24, KCl 4.2, KH2PO4 1.2, MgCl2 1.2, glucose 5.5, Taurine 10, and CaCl2 1.2). The KrebsHenseleit solution was continuously oxygenated with 95% O2 and 5% CO2 and solution temperature was stabilized at 37°C in order to avoid temperature effect on RR intervals. The isolated heart itself was submerged in Krebs-Henseleit solution in bath tempered (37°C) with water jacketed system. The details of perfusion system have been published previously [3]. Stabilization of temperature was secured by closed-loop of temperature sensor and feedback controlled thermostat, resulting in precision under 0.1°C. Data acquisitionElectrograms of 5 minutes duration were recorded in Langendorff and working heart modes. The 30 minutes long stabilization period preceded recording in Langendorff mode to avoid effect of heart excision and cannulation.Electrograms were recorded by touch-less method [4] with sampling frequency of 10 kHz and with 12-bit resolution (PCI-6111E, National Instruments) by custom software (LabView 2010). Electrograms degraded by noise were excluded from further processing.R-peaks were automatically detected by own R-wave detector (Matlab R2013a, MathWorks) and carefully reviewed by human. Tachograms were then obtained from RR series.