Cardiac arrhythmia is caused by various factors. In this study, the correlation between coupling interval and pre-R-R interval in premature ventricular contraction (PVC) was analyzed and one of possible mechanisms was discussed in relation to the changes in intracellular Ca²⁺ concentration. Data from 95 young athletes group (average age: 19 y. o.) and 7 healthy men and women (non-athletes group) (average age: 20 y. o.) with PVC during ambulatory electrocardiographic monitoring. No apparent organic heart diseases in their medical checks were recognized. These subjects wee classified into two types based on the frequency of PVC and the mean heart rate. Both groups showed PVC with two types; in one type, frequency of PVC increased when heart rate was increased (increasing type) and in the other type, frequency of PVC decreased with increased heart rate (decreasing type). Significant correlation was observed between pre-R-R interval and coupling interval in the group of the increasing type in the athletes and non-athletes (r=0.71, 0.73 respectively). In addition, statistical difference was observed in vulnerability index in increasing type of non-athletes group (p<0.05).
　During exercise, heart rate and plasma catecholamine level increase and both are known to raise intracellular Ca²⁺ concentration. Underlying mechanism of PVC was studied by measuring intracellular Ca²⁺ concentration with aequorin when stimulation frequency was increased in the presence of 0.5μM adrenaline. In the presence of adrenaline, high stimulation frequency (1/0.5s) caused oscillations of Ca²⁺ signal in the diastolic phase. These results suggested that higher heart rate in the presence of high concentrations of catecholamine might an spontaneous increase of intracellular Ca²⁺ concentration during diastole which might cause abnormal excitation.

DESCENTE SPORTS SCIENCE Vol.9/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE