Atrioventricular Conduction Defects in Patients with Sinus Bradycardia

A-V conduction was analyzed in 75 patients (mean age, 73 years) with sinus bradycardia (SB) by His bundle (BH) recordings. Forty-five of these patients had normal QRS complexes (≦0.10 sec) and 30 had abnormal QRS complexes (≧0.12 sec). The conduction times through the atrium (P-A), A-V node (A-H), and His-Purkinje system (H-V) were measured during normal sinus rhythm and transient right atrial pacing up to rates of 150/min. The normal range of conduction times through various regions is: P-A = 25 to 45 msec; A-H = 50 to 120 msec, and H-V = 35 to 45 msec. Overall A-V conduction was completely normal only in 25 (33%) patients. Of these 25 patients, 20 had a narrow QRS complex and five had an abnormal QRS complex. The remaining 50 patients showed abnormal A-V conduction in one or more regions (P-A in 10, A-H in five, BH in six, H-V in 10, and mixed in 19). In some patients despite normal ECGs, the H-V time was abnormal and 1:1 A-V conduction was present during atrial pacing up to 150/min. An abnormal H-V time in association with a normal QRS complex is suggestive of delay in the His bundle. Fourteen patients were restudied at intervals of 6 months to 2 years. Three of these 14 patients showed prolongation of conduction times over 1½ to 2 years. Our data demonstrate that SB is often (67%) associated with A-V conduction abnormalities. A-V conduction was abnormal in 56% of patients with normal and 83% with abnormal QRS complexes. The ECG and atrial pacing are of limited value in assessing A-V conduction. The BH recordings in symptomatic patients with sinus bradycardia may be of clinical significance in the selection of site for pacemaker implantation, that is, atrial or ventricular.