[Contribution of the exercise test to the diagnosis of sinus dysfunction. Correlation with endocavitary explorations].

Standardised exercise electrocardiography was performed in 50 patients undergoing endocavitary electrophysiological investigation of sinus node function. There was no previous history of cardiac failure or coronary insufficiency, and the patients, who were not trained athletes, were investigated after interruption of any medication which could affect sinus node function. The endocavitary investigations comprised overdrive suppression with rapid atrial pacing (Mandel) premature extrastimulus method (Strauss) and stimulation at a relative constant prematurity of 50% (Normal values: A2 A3 - 2d - return cycle - sinoatrial conduction time - = 0,77 A1 A1 - spontaneous cycle - +345). A significant difference in the maximal heart rate on stress testing between normal subjects and patients with sinus node dysfunction was observed only when values obtained with the relative constant prematurity method was taken into consideration (24 cases) the relative constant prematurity method became more significant (p less than 0,001). This held true to a lesser degree for Mandel's method (p less than 0,02), but no significant difference was obtained with Strauss' method. The ratio of maximal heart rate to theoretical maximal heart rate for age gave similar results. The correlation between stress testing and the relative constant prematurity method is probably related to intra sinusal shift of the dominant pacemaker. Both investigations would seem to test the functional properties and the reserve of the sinus node, taking extrinsic factors such as vago sympathetic stimulation into account. Patients with functional sinus node dysfunction increase their heart rates normally on exercise (average maximum of 170 bpm); a maximal heart rate of less than 120 bpm is very suggestive of organic sinus node dysfunction.