[Electrophysiological characteristics of the heart with special reference to the sinoatrial node function in patients with disorders of the atrioventricular and intraventricular conduction].

UNLABELLED: Sinus node function and other electrophysiologic properties of the heart in patients with atrioventricular or intraventricular blocks are not well documented. I therefore performed electrophysiological studies in 35 patients with chronic high degree atrioventricular block (AVB--group I), 20 patients with bifascicular block (BFB--group II) and in 24 control subjects (group III). Multilevel conduction disturbances were found in 51.5% of patients with AVB and in only 10% of patients with BFB. Sinus node dysfunction was disclosed in 3 patients (8.6%) with AVB (in 1 it was functional) and in 3 patients (15%) with BFB. A new modified method for recording sinus node electrogram (SNE) was described. By applying this method, SNE was recorded successfully in 80% of cases. The results are comparable to those of other methods. Retrograde conduction was observed in 34% of patients with AVB, 75% of patients with BFB and in 38% of control subjects. It plays an important role in the pathogenesis of the "pacemaker syndrome" in patients with VVI pacemakers. Atrial hyperexcitability was observed in 5.7% of patients in gr. I, 10% in gr. II and 4.2% in control group only. Rare occurrence of atrial arrhythmias provoked by electrical stimulation provides the possibility to use DDD or VDD pacing systems in patients with AVB or BFB. Inadequate rate of response to exercise (chronotropic incompetence) was observed in most patients with sinus node dysfunction, but it occurred also in patients with normal sinus function.

CONCLUSIONS: 1) Sinus node dysfunction is uncommon in patients with atrioventricular or intraventricular blocks. 2) Persistence of abnormal sinus node function and atrioventricular or intraventricular conduction disturbances after autonomic inhibition is an argument for organic disseminated injury of the conduction system (binodal disease). 3) Electrophysiological evaluation of sinus node function, retrograde conduction, artial hyperexcitability and chronotropic response to exercise permit suitable choice of physiological pacing mode (VDD, DDD, DDR, VVIR) in patients with AVB or BFB.