Reverse effects of exercise on the sinus and parasystolic cycle lengths

Ventricular arrhythmias in children with attention deficit disorder--a symptom of autonomic imbalance?

OBJECTIVES

Potential side effects of stimulants for attention deficit disorder are in the focus of scientific discussions, intensified by the higher number of prescriptions. Children with known arrhythmias or other severe cardiac problems should not receive stimulants because of their sympathomimetic effects.

METHODS

This is a retrospective analysis of 24-hour Holter electrocardiograms from 100 consecutive children with attention deficit disorder from January, 2006 to April, 2012.

RESULTS

In all, nine children had significant ventricular arrhythmia (mean age 11.4 ± 3.1 years, 77% male, 77% received methylphenidate). All these children had ventricular parasystole - four of them with an accelerated idioventricular rhythm. A significant circadian rhythm of premature ventricular contractions in seven children and the effect of standing and exercise clearly indicate the influence of the autonomic nervous system. In these children, hourly analysis of circadian rhythm within a 24-hour period showed a highly significant correlation between premature ventricular contractions and the vagal tone indicated by the heart rate variability parameter RMSSD (r = -0.83; p < 0.001). Ventricular arrhythmia was unaffected in seven children who received methylphenidate before diagnosis and decreased during metoprolol treatment in two children.

CONCLUSION

By Holter electrocardiogram analysis, we observed a remarkably high incidence of ventricular parasystole and accelerated idioventricular rhythm in nine of 100 children with attention deficit disorder, which depends on autonomic imbalance and not on stimulant treatment.

Apparent disappearance of ventricular parasystole due to a marked difference between the long form and the short form of the ectopic cycles

Electrocardiograms were taken from a 44-year-old man with irregular ventricular parasystole in whom pure parasystolic cycles without any intervening nonectopic QRS complexes were found. When a sinus impulse fell late in the parasystolic cycle, it hastened occurrence of the next parasystolic discharge. This suggested that type I second degree entrance block occurred in the re-entrant pathway containing the parasystolic focus. When a sinus impulse fell early in the parasystolic cycle, it delayed occurrence of the next parasystolic discharge. This suggested that electrotonic modulation occurred in the parasystolic focus. As a result, the difference in length between the short form and the long form of the parasystolic cycle became markedly great. When the length of two adjacent sinus cycles ranged between the short and the long parasystolic cycle, manifest parasystolic QRS complexes disappeared for a long time. In true ventricular parasystole with pure ectopic cycles, such long disappearance has never been reported before.

Ventricular parasystolic couplets originating in the pathway between the ventricle and the parasystolic pacemaker: mechanism of "irregular" parasystole

This article explains the mechanism of "irregular" parasystole. Two theories have been suggested: "electrotonic modulation" and "type I second degree entrance block." This study attempts to clarify the mechanism of irregular parasystole in cases of true ventricular parasystole associated with ventricular parasystolic couplets. Cases associated with ventricular parasystolic couplets were selected from 37 clinical cases of true ventricular parasystole in which one or more pure parasystolic cycles with no intervening nonectopic QRS complexes were found. Of the 37 cases of true ventricular parasystole, ventricular parasystolic couplets were found in 4 cases. In none of the other 33 cases, ventricular parasystolic couplets were found. In all the cases coexisting with ventricular parasystolic couplets, the latter ectopic QRS complex of the couplet failed to reset the parasystolic rhythm. The above findings suggest that the latter ectopic QRS complex of the parasystolic couplet originated not in the parasystolic pacemaker but in the pathway between the ventricle and the parasystolic pacemaker. It seems that when a sinus impulse fell late in the parasystolic cycle, it passed through the site of second degree entrance block and that the parasystolic couplets originated from the reentrant pathway between the ventricle and the pacemaker. This strengthens our previous suggestion that the mechanism of irregular parasystole is governed by "type I second degree entrance block" and not by "electrotonic modulation."

Effects of exercise and standing on atrial parasystole: prolongation and shortening of the parasystolic cycle length

In recently reported cases of ventricular parasystole, it was shown that after exercise the parasystolic cycle length is prolonged, in contrast to a shortening of the sinus cycle length, whereas during standing the parasystolic cycle length and the sinus cycle length both shortened. In this report, to explore whether the same features as occur in ventricular parasystole are seen in atrial parasystole, effects of exercise and standing on the parasystolic cycle length were investigated in two men with atrial parasystole. The atrial parasystolic cycle length was prolonged after exercise, whereas it shortened during standing, similar to what occurs in ventricular parasystole. This is the first report to show such changes of cycle length in atrial parasystole. These findings suggest that in atrial parasystole, as in ventricular parasystole, influences on the parasystolic cycle length do not always act in the same direction as those on sinus cycle length.

Effect of standing on ventricular parasystole: shortening of the parasystolic cycle length

OBJECTIVE

To investigate the effect of standing on the parasystolic cycle length in cases of "true" ventricular parasystole.

METHODS

Parasystolic cycle length and sinus cycle length were measured during lying and standing in eight men with true ventricular parasystole. These cycle lengths were also measured after exercise in the lying position.

RESULTS

In all cases, parasystolic cycle length and sinus cycle length both shortened on standing, by a mean of 6.4% and 17.8%, respectively, compared to lying. In all cases, the rate of shortening of the parasystolic cycle length was less than that of the sinus cycle length. Parasystolic cycle length was prolonged after exercise, in contrast to a shortening of the sinus cycle length.

CONCLUSIONS

Influences on the parasystolic cycle length are not always in the same direction as on the sinus cycle length. This suggests that the effect of autonomic changes on parasystolic rhythm is not always parallel to that on sinus rhythm.