a rate - responsive cardiac pacemaker implements a novel pacing mode , identified as adir / vvir , which is especially effective for patients with sick sinus syndrome and only intermittent atrioventricular block . within the same pacemaker circuitry , an aair pacemaker and a vvi pacemaker are provided with atrial blanking following both atrial and ventricular events . ventricular blanking after atrial pacing is minimized for better detection of r - waves following an atrial paced event .