pacemaker rate

[zzyzx]

I had a patient yesterday who's pacemaker was pacing at just over 100 BPM. I confirmed that each beat was paced using the 12-lead. His rate later when down to 70, still paced. I had another patient recently who's pacemaker was also pacing at above 100 BPM. I always thought that a pacemaker wouldn't pace above a whatever the setpoint is, which I think would be somewhere near 70 BPM. What gives?

[AZCEP]

There are many different types of pacemakers, to begin with. The two most common are fixed rate and demand pacemakers. The fixed will only pace at a set rate. These are not as common due to the lack of adaptability to a patient's needs. A demand pacemaker will change it's rate due to the needs of the patient. A demand pacemaker will usually monitor the atrial activity, and adjust the ventricular rate accordingly.

[crazycanuck]

Intervention set point is going to be different according to the patient but you are correct that most times this minimum rate is usually set around 50-80bpm.

There are a few possibilities that come to mind here.

1) It is possible this is a pacemaker-mediated tachycardia (PMT). This can easily be tested by placing a magnet over the pacemaker which will set it into an asynchronous pacing mode (each device has a set rate, somewhere usually around 85bpm). This mode will cease the re-entry circuit that is needed for pacemaker mediated tachycardia to occur. (**I would not suggest placing a magnet over an implanted defibrillator without appropriate defibrillation backup as usually this will place the ICD into a non-sensing mode and will not deliver cardioversion. The magnet is often used in the case of "electrical storms" or multiple possibly inappropriate shocks from a device)

http://www.emedicine.com/med/topic2918.htm

2) The intervention rate is sometimes set to 100bpm or a hysteresis rate to prevent rapid rate drops. This newer algorithm called rate drop response (RDR) is often used in patients with severe debilitating vasovagal syncope or cardioinhibitory syncope. Though this may not be the reason for your patient being paced at this rate, it is out there. This intervention pacing is set to detect a specified drop of x bpm then set to intervene and pace at x bpm for x minutes. For eg. If there is a drop of 25bpm in 30 sec, then the pacemaker is set to pace at 100bpm for 2 minutes. One current model of pacemaker with this is the Medtronic EnPulse RDR.

http://europace.oxfordjournals.org/cgi/con...bstract/2/3/245

3) It is possible the rate responsiveness on the device has gone out of whack. Devices will vary but often on most newer ones a rate responsive feature can be programmed and activated. The purpose of this is to allow the patient to attain a rate appropriate to their activity level. Older pacemakers were set rates and the patient could be stuck at 60bpm regardless of if they were sleeping or running. With developments many attempts at designing sensors based on minute ventilation or peizo-electric crystals were designed to sense either body movement or activity level and then a program would tell the pacemaker to pace higher because the person is exercising or being active. The problem here sometimes is that this can be triggered by vibrations or electromagnetic interference (now uncommon with shielding of devices).

www.ipej.org/0403/greco.pdf

4) Another possibility though unlikely is a pacemaker lead malfunction. This is fairly uncommon and I think would be more likely to result in under-sensing or failure to capture than an inappropriate intervention rate. This problem can be more troublesome in ICDs as it can lead to inappropriate therapy.

www.ipej.org/0304/toquero.pdf

Pacemakers and cardiac implants have come a very long way. There is a lot that can be customized in programming and though I can't answer why this patient had what appeared to be an inappropriate intervention rate, it is very likely that a device rep would be called to come and interrogate the pacemaker. Th read out would include all of the specific details and likely reprogramming would solve it if it is a problem.

A couple of questions: was this patient paced only in the atrium? Could you just see pacer spikes in the p-wave area? Or did this look like a slow wide rhythm? Patients who are A-V paced sequentially can appear to have a very wide complex and it can even be mistaken for a slow VT, especially if it is one of those higher intervention rates or with the case of PMT.

You said his paced rate was >100bpm then later went down to 70bpm. When he was at 100bpm was anything going on? Had he just been moving around or was there anything to suggest that vibrations could have activated the rate responsive setting?

If the patient has one of those RDR algorithms, this usually only lasts for a minute or two but can happen repeatedly if they satisfy the criteria for pacing intervention.

From the information and in retrospect I don't know the answer but those are some of the possibilities.

Do you have any follow-up? Was this related to the patient complaint or an incidental finding on exam?

Oh and one more thing....you mentioned you thought it would not pace above a set point. Most newer devices have a much higher tracking and pacing rate available than the older fixed ones. Now a patient who wants rate responsiveness can be set at a very high or sensitive activity level and is able to be paced quite fast when needed some up to 150-160bpm. Many will have tracking rates up to 180bpm.

[BushyFromOz]

crazy, its always a pleasure reading your responses! :wink:

[akroeze]

Just a question. Do you need a 12 lead to really confirm paced beats? Can you not tell on a strip?

[crazycanuck]

Another tidbit for your perusal:

www.kardio.ch/pdf/2006/2006-06/2006-06-001.PDF

[AZCEP]

Just a question. Do you need a 12 lead to really confirm paced beats? Can you not tell on a strip?

Just like any other electrical event in the heart, a given lead may not show the best picture of what is happening. A 12 lead isn't needed to confirm, but you may not be able to see the pacer spike in a single lead.