Autonomic influences and cardiac conduction in patients with sinus node disease.

18 patients with sinus bradycardia (8 SB) and tachycardia-bradycardia syndrome (10 TBS) were investigated using various vagan reflex manoeuvres, atrial pacing (AP), pharmacological tests and His bundle (HB) recordings, to assess autonomic influences, sinus node function and atrioventricular (AV) conduction. Three types of responses (R) were defined as normal (N), supernormal (SN), poor autonomic (PA). Poor reflex responses to vagal manoeuvres, performed in 12 patients, have no statistical significance. MxCSRT at AP suppression was measured in 13 patients: it was normal (less than or equal to 500 msec) in 8 and increased (from 680 to 4,200 msec) in 5 patients with appearance of junctional escapes. Moreover, AP suppression revealed a sinoatrial block (SAB) in 1 patient with normal MxCSRT. Isoprenaline, administered intravenously (3-6 mug) in 9 patients, showed 4 NR, 3 PAR und 2 SNR (unusual sinus tachycardia, 1; atrial fibrillation, 1). Atropine (0.5-1 mg), used in 15 patients, revealed 5 PAR and 1 SNR. Prostigmine (0.5 mg), used in 11 patients, induced 6 NR and 5 PAR. Lanatosid C (0.08 mg), administered in 16 patients, showed 10 NR, 5 PAR and 1 SNR. Finally, ajmaline (100 mg), given in 13 patients, revealed 5 junctional rhythms and one 2:1 SAB. HB recorded in 17 patients showed an increase of AH interval (greater than 140 msec) in 5 patients and a slight increase (60 msec) of HV interval in 2 patients. Three patients developed 2nd-degree AV block at paced rates greater than or equal to 110/min. Abnormal responses at AP suppression and reduced drug responses were noted in 5 patients suffering from Adam-Stokes attacks; a permanent pacemaker was inserted in 4 of these 5 patients. In conclusion, provocative tests, in 18 patients with SB or TBS, suggest a diffuse process disease involving the autonomic function of both sinus node and AV junction (11 patients) and the AV system (6 patients). These immediate results must be correlated with histological findings in the conduction system, as shown in one of our cases previously reported.