[Methods of studying sinus function. Critical study].

Holter electrocardiographic monitoring and endocavitary electrophysiological investigations are often necessary in order to confirm the diagnosis of sinus dysfunction which may be suggested by the patient's symptoms and/or standard E.C.G. signs. A critical evaluation of these methods can be made on the basis of the experience gained in the course of recent studies. Provided sufficiently rigorous criteria are selected, the Holter monitor has an excellent specificity, about 90%, and a sensitivity of more than 70%. The value of the sinus refractory period reflects both sinus automatism and sino-atrial conduction; it is a sensitive criterion of sinus dysfunction. In contrast, the period of sino-atrial conduction has a much more limited sensitivity. However, analysis of the various parameters which reflect the response of the sino-atrial node to premature atrial stimulation provides important information. The authors also stress the value of the pharmacological tests used to sensitize the manoeuvres of atrial stimulation or to test the effects of the autonomic nervous system on sinus function. Autonomic blocking with a combination of atropine and propranolol can reveal certain disorders which can be masked by sympathetic activity and it can also determine the intrinsic or extrinsic nature of the sinus dysfunction. Thus electrophysiological investigations appear to be often essential in order to confirm a suspected diagnosis and in order to determine the severity and the nature of the sinus dysfunction.