The chick embryo heart as an experimental setup for the assessment of myocardial remodeling induced by pacing

The mechanisms regulating remodeling of the heart are not well understood a nd only rarely investigated for pacing. We therefore developed a model base d on the well-established chick embryo heart preparation. Hamburger Hamilto n 21 stage Leghorn chick embryos were used. Access to the heart was obtaine d after having dissected the shell membranes. The electrodes (platinum wire s) were placed in ave: the anode on the vitelline membrane and the cathode at at different sites of the heart (sinus venosus, base/apex of the ventric le). Sensing and stimulation thresholds were measured. Survival of the pace d chick was studied. Among 30 chick embryonic hearts, the stimulation thres holds were 1.4 mV +/- 0.5 SD for the atrium, 2.6 V +/- 1.4 SD at the base, and 3.2 V +/- 1.5 SD at the apex of the ventricle, while the sensing signal s were 1.3 mV +/- 0.5 SD at the atrium, 19.6 mV +/- 4.1 SD at the base, and 21.6 mV +/- 3.9 SD at the apex of the ventricle. Continuous pacing (pacing rate = intrinsic rate + 10%) could be maintained for 1.5 hours +/- 0.5 SD at the atrium, 8.9 hours +/- 0.7 SD at the base of the ventricle, and 7.9 h ours +/- 1 SD at the apex of the ventricle up to death of the embryos. By u sing intermittent electrical stimulation, the association of 5 minutes on/5 minutes off pattern during 18 hours and 5 minutes on/15 minutes off, durin g 30 hours resulted in an effective pacing period of 19 hours in 60% of the experiments, reflecting 15 cell turnover cycles. This experimental setup w ill allow the study of morphological, metabolic, and molecular bases of ven tricular remodeling induced by electrical stimulation.