Dr Shreetal Rajan Nair Senior resident, Department of Cardiology MCH, Calicut.

DDD pacemaker- 4 rhythm scenarios

Dual Chamber Timing Cycle Lower rate interval (LRI) Upper rate interval (URI) – Maximum tracking rate (MTR) – Maximum sensor rate AV and VA interval Refractory period Blanking period

Dual-chamber Timing Intervals AV Interval TARP VA Interval LRI A-Blanking PVARP V-Blanking URI/MTR VRP ApVp ApVp ApVp

Upper rate behavior refers to how a dual-chamber pacemaker will behave when the atrial rate exceeds the programmed maximum tracking rate There are three types of upper rate behavior 1:1 Tracking Pacemaker Wenckebach 2:1 Block The key to upper rate behavior is in the atrium Observed only when the device is tracking intrinsic P waves (A sense/V pace) Upper rate behavior

Normal 1:1 tracking

Pacemaker Wenckebach (PSEUDOWENCKEBACH) W AsVpAsVp MAXIMUM TRACKING RATE TARP PVARP AV TARP PVARP AV

Upper Rate Pacing Characteristics Wenckebach (4:3 Block) AsVpAsVpAsVp(As)AsVpAsVpAsVp TARP AV Delay VA Interval MTR

Upper Rate Pacing Characteristics As Vp(As)As Vp (As) TARP AV Delay VA Interval MTR LRI 2:1 Block

AV PVARP TARP MAXIMUM TRACKING RATE AV PVARP TARP AsVp(As)AsVp 2:1 Rate = 60,000 / TARP Upper Rate Pacing Characteristics

1:1 Wenckebach 2:1 Block TARP MTR LRI Sinus Rate Upper Rate Behavior is determined by TARP and MTR

Solution In young patients, the upper rate of the pacemaker to be programmed to faster rates corrected for the patient's age to prevent Wenckebach behavior of the pacemaker during exercise. Programming dynamic AV interval and dynamic PVARP allows the TARP to be shorter at higher pacing rates and avoid sudden slowing of ventricular pacing rates. Sensor driven pacing : a separately programmable sensor rate allows the pacemaker to continue to pace at the sensor-driven rate during exercise

Dynamic AVI and PVARP  Programmed AV Delay shortens with increasing rate  Allows programming a higher MTR for higher 1:1 P-synchronous tracking

Dynamic AVI and PVARP AV Delay+PVARP=TARP 65 ms300 ms365 ms (164 ppm) 130 ms300 ms430 ms (139 ppm) 200 ms300 ms500 ms (120 ppm) Effects of Shorter AV Delay

Dynamic AVI and PVARP Rate= 65 ppmAV Delay~ 180 msRate  to 135 ppm AV Delay  ~ 80 ms

Rate-responsive Pacing Sensor driven (DDDR) pacing promotes a more regular rhythm if the sinus rate exceeds the MTR. It is not dependent on the PVARP DDD - Wenckebach DDDR