ATRIAL TRACKING IN AN INTRACARDIAC VENTRICULAR PACEMAKER
FIG2B is a conceptual diagram of another example of the intracardiac ventricular pacemaker shown in FIG1  FIG2A is a conceptual diagram of the intracardiac ventricular pacemaker shown in FIG1
FIG2B is a conceptual diagram of another example of RV pacemaker 14. In FIG2B, RV pacemaker 14 includes a proximal sensing extension 165 extending away from housing 150 and carrying a pair of sensing electrodes 167 and 168. The proximal sensing extension 165 may be coupled to the housing 150 for positioning a return sensing electrode 168 or 167 which may be paired with distal electrode 164 at an increased inter-electrode distance compared to the inter-electrode spacing of housing-based electrodes 162 and 164. The increased inter-electrode distance may facilitate sensing of far-field atrial signals such as P-waves attendant to atrial depolarization.  FIG2A is a conceptual diagram of the intracardiac RV pacemaker 14 shown in FIG1. RV pacemaker 14 includes electrodes 162 and 164 spaced apart along the housing 150 of pacemaker 14 for sensing cardiac electrical signals and delivering pacing pulses. Electrode 164 is shown as a tip electrode extending from a distal end 102 of pacemaker 14, and electrode 162 is shown as a ring electrode along a mid-portion of housing 150, for example adjacent proximal end 104. Distal end 102 is referred to as "distal" in that it is expected to be the leading end as pacemaker 14 is advanced through a delivery tool, such as a catheter, and placed against a targeted pacing site. Housing 150 is formed from a biocompatible material, such as a stainless steel or titanium alloy. In some examples, the housing 150 may include an insulating coating. Examples of insulating coatings include parylene, urethane, PEEK, or polyimide among others. The entirety of the housing 150 may be insulated, but only electrodes 162 and 164 uninsulated. Electrode 1 64 may serve as a cathode electrode and be coupled to internal circuitry, e.g., a pacing pulse generator and cardiac electrical signal sensing circuitry, enclosed by housing 150 via an electrical feedthrough crossing housing 150. Electrode 162 may be formed as a conductive portion of housing 150 as a ring electrode that is electrically isolated from the other portions of the housing 150 as generally shown in FIG2A. In other examples, the entire periphery of the housing 150 may function as an electrode that is electrically isolated from tip electrode 164, instead of providing a localized ring electrode such as anode electrode 162. Electrode 162 formed along an electrically conductive portion of housing 150 serves as a return anode during pacing and sensing.
conceptual diagram
166
fixation tines
160
battery subassembly
158
delivery tool interface
168
electrodes electrode
104
proximal end
6
U.S. Pat. No.
162
electrodes electrode
102
distal end
10
system
150
housing
['1. An intracardiac ventricular pacemaker, comprising: a pulse generator (202) configured to generate and deliver pacing pulses to a ventricle of a heart via electrodes coupled to the pacemaker; a motion sensor (212) configured to produce a motion signal comprising an atrial systolic event and at least one ventricular diastolic event; and a control circuit (206) coupled to the motion sensor and the pulse generator and configured to: set an atrial refractory period; determine a ventricular diastolic event metric from the motion signal; compare the ventricular diastolic event metric to change criteria to detect a change in the ventricular diastolic event metric compared to at least one previously determined ventricular diastolic event metric; adjust the atrial refractory period in response to detecting the change; detect the atrial systolic event from the motion signal; set an atrioventricular pacing interval in response to detecting the atrial systolic event after an expiration of the atrial refractory period; and control the pulse generator to deliver a pacing pulse to a ventricle of the heart in response to the atrioventricular pacing interval expiring.', '14. The pacemaker of any of claims 1-13, further comprising a housing (150) enclosing the pulse generator, the motion sensor, and the control circuit, wherein the electrodes are housing-based electrodes.']