Electric Stimulation of Isolated Hearts: Age Dependence of the Threshold Electric Field

Mammalian hearts undergo substantial growth and differentiation after birth with major changes in cell geometry and dimensions, as well as in intracellular constitution. It was not clear, however, whether these factors actually affect the response of the whole hearts to electric stimulation. In this work we showed that the threshold electric field (ET) needed to stimulate isolated hearts of rats depends strongly on the age of the animal (adults 0.22±0,02 V/cm; 60 day rats 0,23±0,01 V/cm; 30 day rats 0,27±0,01 V/cm and 15 day rats 0,37±0,03 V/cm). We also showed that there is a negative correlation between ET and the average diameter (D) of the hearts and that the value of ET*D seems to be constant (approximately 0.3V), in the different age groups. We believe that our data can be useful in eletrophysiological studies on the fundamentals of electric stimulation of whole hearts as well as in practical problems as pediatric stimulation and pacing.