Table 5.

Developmental changes in cardiomyocyte electrophysiology

Age range	Cardiomyocyte type	Key points	Citation
<2 years	Right ventricular	Age-dependent difference in IK1 IK1 density ~50% less than previously reported for adult cells	Schaffer et al. (1999)
<1–68 years	Right atrial	No age-dependent difference in IK1 IK1 density is comparable in paediatric and adult cells (room temperature)	Crumb et al. (1995)
<2 years	Right ventricular	No age-dependent differences in If	Schaffer et al. (1999);
<1–53 years	Right and left ventricular	If detected in ~90% of cardiomyocytes; If density only slightly higher in paediatric cells versus values previously reported for adult cells	Zorn-Pauly et al. (2003)
<3.4–42.5 years 2–63.5 years	Right atrial Ventricular	Age-dependent difference in INa INa density is lower, with slower activation/inactivation; negative shift in voltage-dependent inactivation in paediatric versus adult cells	Cai et al. (2011); Sakakibara et al. (1993)
<1–74 years	Right atrial	Age-dependent difference in INa Faster depolarization in paediatric versus adult cells, suggests enhanced INa current	Wang et al. (2003)
<1–54 years	Right atrial	Age-dependent difference in transient outward current (Ito) Paediatric action potential has a smaller notch and more positive action potential plateau phase; suggests age-dependent increase in Ito	Escande et al. (1985)
<1–57 years	Right atrial	Ito is absent in children Ito is absent in cardiomyocytes from children aged 2–5 years. Samples were all dilated, which could also reduce Ito	Mansourati and Le Grand (1993)
<1–68 years	Right atrial	Age-dependent difference in Ito Ito is detected in 67% of paediatric cells and 100% of adult cells. Reduced Ito density, slower recovery time and frequency-dependent inhibition in paediatric cells versus adult cells	Crumb et al. (1995)
<1–74 years	Right atrial	Ito is present in neonatal cells, but properties are age dependent Greater Ito density, faster inactivation, slower recovery from inactivation, and frequency-dependent inhibition in neonatal versus adult cells; neonatal action potential has a less prominent notch, a more positive plateau phase and longer action potential duration at 30% compared with adult cells	Wang et al. (2003)
<1–13 years	Right atrial	Similar Ito properties across different age groups No difference in Ito density or recovery, but slightly slower inactivation in younger cells	Gross et al. (1994)
<2 years	Right ventricular	Frequency-dependent inhibition of Ito amplitude in young cells No observed age difference in Ito density, but measurements were variable even within same patient	Schaffer et al. (1999)
<1–75 years	Right atrial and ventricular	Age-dependent difference in action potential morphology Paediatric atrial myocytes have a prominent overshoot and longer action potential duration at 30–50% compared with adult cells. Paediatric ventricular myocytes have a less prominent notch, more positive plateau phase and longer action potential duration compared with adult cells	Cohen and Lederer (1993)
<1–75 years	Right atrial and ventricular	Age-dependent difference in ICa Reduced ICa density in paediatric versus adult ventricular myocytes (not atrial). Paediatric atrial and ventricular myocytes have a positive shift in steady-state activation and inactivation, resulting in a prominent calcium window current	Cohen and Lederer (1993)
1–8 years	Right ventricular	Prominent calcium window current in paediatric cells Window current might contribute to longer action potentials and after-depolarizations in paediatric cells. Results might also be linked to the disease state of paediatric cells	Pelzmann et al. (1998)