[Dual-chamber cardiac pacemakers. Hemodynamic value].

Dual chamber pacemakers have been designed to restore normal atrio-ventricular synchronism and maintain it during exercise. Progressive acceleration of the electrically stimulated heart rate provides "physiological" adaptation of cardiac output. In subjects with a normal heart, the atrial systole plays a relatively minor role (about 20% of the cardiac output at rest), and it is only in rare cases (e.g. pacemaker syndrome) that implanting a dual-chamber pacemaker becomes necessary. However, the atrial systole plays a much greater role in acute or chronic heart diseases, notably in patients with cardiac failure, mitral or tricuspid valve regurgitation or reduced cardiac compliance. Dual chamber pacemakers are more frequently required in such cases to correct or prevent the detrimental effects of normal atrio-ventricular synchronism, among which atrioventricular conduction is the worst tolerated.