Repolarizing currents in ventricular myocytes from young patients with tetralogy of Fallot

Objective: It was the aim of our study to describe repolarizing currents in ventricular myocytes isolated from children with tetralogy of Fallot. This is the first report on outward currents in ventricular myocytes from child ren. Methods: Ventricular myocytes were isolated from tissue samples of the outflow tract of the right ventricle which were obtained during corrective surgery of tetralogy of Fallot. Action potentials and whole-cell currents were recorded with the patch clamp technique at a temperature of 36-37 degr ees C. Results: The mean resting potential was -71.7+/-1.92 mV, action pote ntial amplitude was 110+/-2.96 mV and action potential duration at 90% repo larization was 794+/-99.5 ms (n = 12). In four out of 12 myocytes early aft erdepolarizations (EADs) were observed. Upon hyperpolarization Ba2+-sensiti ve inward currents similar to the inward rectifier current (I-K1) could be observed. The current density at -120 mV was -22.8+/-2.47 pA/pF (n = 14). A transient outward current (I-to 1) could be recorded in all myocytes studi ed, the current density varied from 0.3 to 8.6 pA/pF with a mean of 3.77+/- 0.47 pA/pF at +40 mV (n=38). Recovery of I-to 1 from inactivation was fast (70% recovery within 100 ms), rate-dependent reduction amounted to 38.2% at 4 Hz. A delayed rectifier current was seen in only two out of 38 myocytes (rapid component I-Kr). Conclusions: The electrophysiological characteristi cs of right ventricular myocytes isolated from children with tetralogy of F allot resemble in most cases subendocardial myocytes from adults. The most prominent difference is a fast recovery from inactivation as well as a smal l rate dependent reduction of I-to 1. The observed EADs may have clinical i mplications. (C) 1999 Elsevier Science B.V. All rights reserved.