S. Kinoshita et al., DIFFERENTIATION BETWEEN PARASYSTOLE AND EXTRASYSTOLES - INFLUENCE OF VAGAL-STIMULATION ON PARASYSTOLIC IMPULSE FORMATION, Journal of electrocardiology, 27(2), 1994, pp. 169-174
Recently, it has been shown that when a sinus impulse falls late in th
e parasystolic cycle, it usually hastens the next ectopic discharge. T
hus, in many cases, the classic criteria for the diagnosis of parasyst
ole (ie, varying coupling intervals and constant shortest interectopic
intervals) cannot be used. To differentiate between parasystole and e
xtrasystoles in such cases, the influence of vagal stimulation on para
systolic impulse formation was investigated in seven cases of ''true''
parasystole in which one or more ''pure'' ectopic cycles without any
intervening nonectopic QRS complexes were found spontaneously. In all
cases pure ectopic cycles were found during sinus arrest caused by vag
al stimulation; namely, none of the cases showed extreme prolongation
of the parasystolic cycle. These results strongly suggest that instead
of the classic criteria, vagal stimulation causing temporary sinus ar
rest is the optimal method for differentiation between parasystole and
extrasystoles in cases without spontaneous pure ectopic cycles.