Intrinsic and extrinsic sinus node dysfunction: diagnostic problems.

Based on clinical and experimental experience, pacemaker dysfunction in sick sinus syndrome can be differentiated into intrinsic and extrinsic. Sinus node activity is characterized electrophysiologically by automaticity, recovery and sinoatrial conduction. The automaticity of the sinus pacemaker cell groups and sinus recovery can be differentiated properly under experimental conditions. Studies of the electrophysiological characteristics have shown the basic functional parameters to be normal in extrinsic-autonomic sinus dysfunction. Diagnosis is either based on clinical observation or on the data of Holter monitoring, the electrophysiological methods being inadequate for diagnosing this neurovegetative form of sick sinus syndrome. On the other hand, intrinsic sinus dysfunction can be diagnosed by electrophysiological tests. If completed by complex pharmacological studies, in this organic form of sick sinus syndrome, even the severity of the intrinsic injuries can be assessed quantitatively. The above division provides a basis for selection and evaluation of the differential diagnostic procedures, while information on the aetiopathology of sinus dysfunction and on the degree of the functional injuries of the electrophysiological structure of the heart provides an adequate basis for therapy.