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Thursday, December 24, 2020

Normal pacemaker function near battery depletion can pose clinical problems

 Can normal pacemaker behavior near battery depletion cause alarming symptoms and clinical diagnostic difficultly?

To put the topic in context we need to describe normal PM functioning as the battery nears depletion.

My PM is a Consulta CRT-P model and according to the Medtronic manual, here is the sequence, which we can use as an example of PM behavior at near battery depletion. 

When the battery reading reaches a value equal to or less than 2.77 volts a replacement indicator named RRT or Recommended Replacement time is displayed on the interrogation.  More precisely, there has to be a reading of 2.77 V or less for three consecutive daily readings A "clock" is  then set to run for  3 months and when it is timed out ,another replacement indicator named ERI or Elective Replacement Indicator is displayed. 

At this point the PM is switched to a VVI Mode at 65bpm. If a magnet is paced on the PM ,the rate will read 65 indicating that the unit is in the RRI mode.If battery life is adequate this power saving mode will continue for three months and then the unit reaches EOS or end of service.

VVI mode works in the following way.The right  ventricles is  paced unless a spontaneous ventricular activation occurs first and then the lower limit for ventricular activation is reset.If a spontaneous ventricular activation does not occur first then the ventricle is paced.Atrial activity and ventricular activity are independent.

According to reference 1 and 2 (see below ) only Medtronic PMs exhibit this near end of service behavior.

A PM in the VVI  mode is in an asynchronous mode meaning that there is loss of synchrony between the atrium and ventricle possibly resulting in a clinical scenario called pacemaker syndrome .Symptoms can include chest pain,shortness of breath, fatigue.palpitations  and neck pulsation among others.The heart was not designed to have the atria contract against closed AV valves nor to have the ventricles contract with the AV valves open.

A 2020  case report (which seems to be very similar to a case referenced in 2010 (ref 2)) of a 70 year old man with a Medtronic  Adapta PM presented to ER with palpitations and dyspnea. Physicians were unable to do a PM interrogation ( another feature of the ERI mode in some . ( but not all) Medtronic models is  that the interrogation feature is disabled ) . The clinical problem was solved and a replacement PM was implanted with resolution all symptoms .

It should be noted the the device was not malfunctioning. At manufacture it was programmed to shift into an asynchronous mode when it reached ERI status. To the manufactures of the PM this was a feature not a bug. However, as a pacemaker patient, I consider this a bug-one in which "normal" behavior of the unit can cause serious symptoms and to add insult to injury have the interrogation function disabled making the diagnosis of the problems difficult even to cardiologists. 

The authors of both referenced  articles were critical of ERI management  in Medtronic PMs. Dr. John Mandrola (ref 2) stated in 2010  he has personally seen 4 cases in which this type of syndrome occurred in a patient with a PM whose unit shifted into a VVI mode with resultant pacemaker syndrome, a situation  in which the diagnosis may not be apparent potentially  leading to further  further diagnostic tests with missed diagnosis even by cardiologists.Mandrola mentions two patients who were subjected  to unnecessary  coronary angiograms before the diagnosis was finally made.Here failure to warn by the patient's EP doc and/or by the PM manufacturer lead to possible harm.Coronary angio is not a zero risk procedure. Siroky made his criticism obvious in the title to the case report ,"bad device behavior or malfunction".

 An obvious comment is -should not EP cardiologists and PM manufacturers inform patients of the untoward events that may  occur  as their battery approaches depletion. In my limited experience patient education before and after the PM implantation has much room for improvement .


1)Siroky,GP et al Shortness of breath and palpitation in an elderly man:Bad device behavior or malfunction .Journal of Arrhythmia,2010:36,1109 -1111

2) Madrola, J. https://www.drjohn.org/2010/09/answer-to-this-weeks-clinical-vignette/

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