DESIGN AND DEVELOPMENT OF MEDICAL ELECTRONIC ...

THE FIRST PACEMAKERS 377V SenseA SenseV SenseA V RA ToutA PaceAV ToutV PaceR ToutFigure 8.7 Dual-chamber pacemakers synchronize the activation of the ventricles to atrial activity. This simplified DDD pacemaker statemachine can pace both atria ([A Pace]) and ventricles ([V Pace]). It has the following possible states: [A], atrial and ventricular alert, duringwhich the pacemaker may sense signals from either or both chambers; [V], ventricular alert, during which sensing of intrinsic events isenabled only for the ventricle; and [R], refractory state. Possible events that cause transition between states are: [A Sense], sensing of anintrinsic atrial event; [V Sense], sensing of an intrinsic ventricular event; [A Time Out], maximum time that the state machine waits for anatrial sense event after exiting from the refractory period; [AV Time Out], maximum time that the state machine waits for a ventricular senseevent after an atrial event; and [R Time Out], refractory period.Possible events that cause transition between states are:• [A Sense]• [V Sense]• [A Time Out]• [AV Time Out]• [R Time Out]Sensing of an intrinsic atrial eventSensing of an intrinsic ventricular eventMaximum time that the state machine waits for an atrial sense eventafter exiting from the refractory periodMaximum time that the state machine waits for a ventricular senseevent after an atrial eventRefractory periodPossible actions taken by the state machine are:• [A Pace]• [V Pace]Pacing pulse delivered to the atriumPacing pulse delivered to the ventricleThe states of this pacemaker state machine are:• [A]• [V]• [R]Atrial and ventricular alert, during which the pacemaker may sense signalsfrom either or both chambersVentricular alert, during which sensing of intrinsic events is enabled only forthe ventricleRefractory stateIf intrinsic events are not detected from the heart, the state machine’s period is given bythe following sequence:1. Pacing pulse delivered to the atrium2. AV delay ([AV Time Out])3. Pacing pulse delivered to ventricle