The clinical role of closed loop stimulation pacemakers in the treatment of patients with sinus node dysfunction: a review.

Sinus bradycardia, sinoatrial block, sinus arrest, and bradycardia-tachycardia syndrome are manifestations of intermittent or persistent sinus node dysfunctions (SNDs). SND is classified as intrinsic, when related to an anatomic disease of sinoatrial cells, or extrinsic, when bradycardia is caused by inappropriate vagal outflow. Chronotropic incompetence is often associated with SND, especially in elderly patients. When symptoms are related to SND, pacemaker implantation is the recommended therapy, and rate-adaptive pacing modes are often preferred in cases of chronotropic incompetence. Closed-Loop Stimulation (CLS) is a rate-adaptive system based on continuous evaluation of contractility and contraction speed through the analysis of right-ventricular unipolar impedance trends during the systole of each cardiac cycle. An increase in contractility or contraction speed modifies the impedance trends, to which the CLS algorithm responds by adapting the pacing rate, and thereby heart rate and cardiac output. Therefore, CLS is integrated into the autonomic mechanisms of cardiac output regulation. This feature has drawn interest in the use of CLS in several forms of SND, from the treatment of intrinsic bradycardias to the prevention of vasovagal syncope and device-detected atrial fibrillation. We will examine the working principle of CLS and review the results of recent clinical investigations.