Pacemaker Learning Package
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D D Chamber P aced Chamber S ensed Action or R esponse to a Sensed Event Figure 17 & 18: PSR. Pacing ppt. P.Nekic 2011 1 st Letter 2 nd Letter 3 rd Letter Chambers P aced Chambers S ensed R esponse to Sensing A= Atrium A= Atrium T=Triggered V=Ventricle V= Ventricle I= Inhibit (Demand Mode) D= Dual (both Atrium and Ventricle) D= Dual D=Dual O= none O= none (Asynchrony) Remembering the letters PSR helps to remember the function of each letter. Liverpool Hospital Intensive Care: Learning Packages Intensive Care Unit Pacemaker Learning Package LH_ICU2016_Learning_Package_Pacemaker_Learning_Package 26 | P a g e Therefore when you collate the information in the tables above you end up with different codes and or modes of pacing. The most common modes are outlined in the table below. MODES OF PACING CODE Chamber P aced (1st Letter) Chamber S ensed (2 nd Letter) R esponse to sensing Trigger or Inhibited (3 rd Letter) MEANING AOO Atrial pacing None None Asynchronous atrial pacing occurs at a set rate, regardless of intrinsic atrial activity. VOO Ventricular Pacing None None Asynchronous ventricular pacing occurs at a set rate, regardless of intrinsic Ventricular activity. DOO Ventricular & atrial pacing None None Asynchronous atrial & ventricular pacing at a set rate regardless of intrinsic atrial & ventricular activity AAI Atrial pacing Atrial sensing Inhibits pacing A sensed P wave will cause the pacemaker to withhold atrial pacing. Absence of intrinsic p wave will lead to atrial pacing VVI Ventricular pacing Ventricular sensing Inhibits pacing A sensed R wave will cause the pacemaker to withhold ventricular pacing. Absence of intrinsic R wave will lead to ventricular pacing DDD Atrial & ventricular pacing Atrial & ventricular sensing Inhibition of pacing & trigger of pacing impulses Intrinsic P & R waves cause pacemaker to withhold pacing. Pacing impulses will be triggered when programmed intervals are exceeded Liverpool Hospital Intensive Care: Learning Packages Intensive Care Unit Pacemaker Learning Package LH_ICU2016_Learning_Package_Pacemaker_Learning_Package 27 | P a g e What does it all mean? : DDD DDD MODE: The first letter is D , so both the Atrium and the Ventricles are being paced . The second letter is also D which means that the pacemaker is looking for sensed intrinsic beats in both the Atrium and the Ventricle The third letter D means that the pacemaker can both Trigger a Ventricular pace in response to a sensed Atrial event, and inhibit the Atrial and/or Ventricular pace if it senses an intrinsic event in that chamber before its internal timing tells it to pace.
Inhibits the next scheduled atrial pace Re-starts the lower rate timer Triggers an AV interval (called a Sensed AV Interval or SAV) An atrial pace: Re-starts the lower rate timer Triggers an AV delay timer (the Paced AV or PAV) A ventricular sense: Inhibits the next scheduled ventricular pace Examples of DDD mode and how it works DDD mode can have four possible outcomes for pacing depending on the patient’s condition or underlying rhythm Atrial and ventricular pacing • Atrial pace re-starts the lower rate timer (Long arrow) and triggers an AV delay timer (PAV)( shorter arrow) • The PAV expires without being inhibited by a ventricular sense, resulting in a ventricular pace Both the atrium and the ventricles are being paced, first the atrium and then the ventricle. The pacemaker begins by pacing in the atrium. 2 timers are started: Liverpool Hospital Intensive Care: Learning Packages Intensive Care Unit Pacemaker Learning Package LH_ICU2016_Learning_Package_Pacemaker_Learning_Package 28 | P a g e The lower rate timer The AV Interval timer (we call this timer the PAV or Paced AV interval) The AV Interval timer expires WITHOUT BEING INHIBITED by a ventricular sense – so the pacemaker paces in the ventricle. The lower rate timer continues. If it expires without being inhibited by an atrial event (as shown above), the pacemaker paces in the atrium, and the cycle begins again. Why does the pacemaker’s AV interval timer expire without being inhibited? Perhaps the patient has a heart block Perhaps the patient has delayed AV conduction — the patient’s P-R interval is longer than the PAV programmed into the pacemaker Why does the pacemaker’s atrial escape interval expire? The patient’s sinus rate is less than the pacemaker’s programmed rate e.g. sinus bradycardia Atrial pacing and ventricular sensing Atrial pace re-starts the lower rate timer and triggers an AV delay timer (PAV) The PAV expires without being inhibited by a ventricular sense, resulting in a ventricular pace Lower rate timer 1000ms In this example we see atrial pacing with an intrinsic ventricular response (VS). The pacemaker begins by pacing in the atrium. The 2 timers are started: • The lower rate timer (longer arrow) • The AV Interval timer (this is the PAV or Paced AV interval)(shorter arrow) The AV Interval timer IS INHIBITED by a ventricular sense – so the AV timer is reset, but the lower rate timer continues. It expires without being inhibited by an atrial event, so the pacemaker paces in the atrium, and the cycle begins again. Atrial pacing and ventricular sensing can occur if: Liverpool Hospital Intensive Care: Learning Packages Intensive Care Unit Pacemaker Learning Package LH_ICU2016_Learning_Package_Pacemaker_Learning_Package 29 | P a g e Patient’s intrinsic AV conduction occurs faster than the PAV interval, but the patient’s sinus rate (his A-to-A interval) is still longer than the lower rate interval programmed into the pacemaker. Atrial sensing, ventricular pacing The intrinsic atrial event (P-wave) inhibits the lower rate timer and triggers an AV delay timer (SAV) The SAV expires without being inhibited by an intrinsic ventricular event, resulting in a ventricular pace In this example we see P-waves followed by ventricular pacing. This is also called “tracking,” and is pretty common in pacemakers programmed to the DDD mode. An intrinsic P-wave inhibits the scheduled atrial output. The lower rate timer is reset to zero and begins again. The AV interval timer (this time called a Sensed AV or SAV – because it follows a sensed atrial event) begins. This timer expires before a ventricular sense occurs, so a ventricular pace occurs, and the lower rate timer continues, and before it can expire, another intrinsic atrial event is sensed and the cycle begins again. Another way to describe this is that the patient’s A-A interval is shorter than the Lower Rate Interval, but his intrinsic P-R interval is longer than the SAV. tải về 1.43 Mb. Chia sẻ với bạn bè của bạn:
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