On the change of cardiac action potential with age: a study in dogs

The action potential duration (APD) was measured using an Ag-AgCl electrode, in open chest anaesthetised dogs (n = 8) and puppies, 4 to 6 months old (n=8), with complete atrio-ventricular dissociation and β-adrenergic blockade. They were paced in the control period at a frequency of 120 beats·min−1. Both adults and puppies showed maximum action potential duration at a test pulse interval of over 700 ms. Below this the adult dogs showed a progressive shortening of the action potential duration (mean APD 81.5% at 200 ms). In contrast, the puppies showed much less shortening (91% at 200 ms; p