Observation on the effect of digitalis on sinus node function by recording of twenty-four hour continuous electrocardiogram.

Twenty-four hour recording of electrocardiogram was performed in 5 cases, aged from 42 to 75 years, with paroxysmal tachyarrhythmias (paroxysmal supraventricular tachycardia (PSVT) 2 cases and paroxysmal atrial fibrillation (PAf) 3 cases) for the purpose of assessing the effects of digitalis on sinus node function from the chronobiological point of view. All of the pauses following the termination of PSVT or PAf observed during a day were measured in 4 cases as the sinus node recovery time (SNRT). Corrected sinus node recovery time (CSNRT) was determined by subtracting the penultimate P-P cycle length from the SNRT. Both SNRT and CSNRT were prolonged in all cases after digitalis administration. In 1 case observation on the diurnal variation of SNRT and CSNRT showed the most marked prolongation of these values at 6:00 a.m. after digitalis administration. The second degree of SA block was observed in 2 cases in the early morning after digitalis treatment. In the other 2 cases sinoatrial conduction time (SACT) was calculated by the use of premature atrial contraction and corrected by dividing by the basic cycle length before and after digitalis administration. Neither SACT and CSACT showed significant differences between the values before and after the treatment in 2 cases, nor the diurnal variation of SACT and CSACT showed significant differences. Above results suggest that digitalis should be used with caution in patients with paroxysmal tachyarrhythmia because even small amounts of digitalis might provoke sinus node dysfunction. Twenty-four hour recording of electrocardiogram is useful in the earlier recognition of sinus node dysfunction induced by digitalis.