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Effects of Chronic Hypoxemia on the Electrophysiological Properties of Right Atria Tissue in Children

The purpose of this study was to determine the electrophysiological properties of normal right atrial tissue in children and to evaluate the role of chronic hypoxemia in the genesis of atrial arrhythmias. Using standard mocroelectrode techniques we studied the electrophysiological properties of preparations of right atrial tissue obtained during open heart surgery in two groups of patients. Group A consisted of 6 patients with uncomplicated ventricular septal defects. Group B comprised 6 patients with tetralogy of Fallot with arterial O2 saturations of 80-84%. All patients underwent cardiovascular diagnostic studies and had normal right atrial pressures and no evidence of atrial shunting. In Group A mean resting potential (RP) was −86±5.7 mV, action potential duration was 210±8 msec at a cycle length of 1,000 msec and conduction velocity was 0.45±0.05 M/sec. The relationship between the rate of rise of phase 0 of the action potential (AP) and the membrane potential at which the AP was elicited (membrane responsiveness) was ‘S’ shaped. Cells were unresponsive at a mean RP of −56±1.6 mV and maximum rate of rise occured at a mean RP of −86±5.7 mV. An increase in extracellular [K+] above control caused a decrease in the RP which was linearly related to log [K+]. When [K+] was reduced below control levels, RP decreased slightly. There were no significant differences (p = >0.05) between Group A and Group B for all properties measured. Results from Group A can be used for ‘normal’ reference values. Chronic hypoxemia does not seem to alter the electrophysiological properties of right atrial tissue. This is consistent with the clinical observation of the lack of atrial arrhythmias in cyanotic congenital heart disease when there is no pressure or volume overloading of the right atrium.