Patients with sick sinus syndrome and a double-chamber cardiac pacemaker are studied.~To investigate the role of non-pharmacological heart rate change on central hemodynamics in the first part of the study, the investigators acutely change pacing rate from atrial paced-atrial sensed (AAI)-mode 60 to 40 to 90 bpm and obtain hemodynamic parameters noninvasively after a short stabilisation period after each pacemaker rate change.~Subsequently, to investigate the acute effects of beta-blockers or ivabradine on central hemodynamics in the second part of the study, the investigators obtain central hemodynamic parameters noninvasively after acute administration of atenolol, nebivolol or ivabradine at the same pacing rate levels used in the first part of the study (AAI-mode 60, 40 and 90 bpm).
This study is divided into two parts:~The first part evaluates the acute effect of non-pharmacological heart rate change on central hemodynamic parameters noninvasively in sick sinus syndrome patients with a permanent cardiac pacemaker~The second part evaluates the acute effects of atenolol, nebivolol and ivabradine on central hemodynamic parameters noninvasively in sick sinus syndrome patients with a permanent cardiac pacemaker at different pacing rate levels