Medtronic Manual - Projected Life

Hello,

Am PM dependent since 1995. Had replacement done in 2007 and 2011. The last one caused site infection. This led me to a long ordeal of explantation, lead extraction through sternotomy and finally new PM implantation at the other shoulder site. Procedure concluded last week. Now, am taking more than passing interests in the settings and the workings of the device so that I am more informed.

My current device is Medtronic Advisa MRI. While I was going through the manuals, I saw the section on projected life. It has something like this :

2.5 V 3.5 V
DDD100% 8.7 yrs 6.7 yrs

Does anyone have any idea what this voltage value (2.5V, 3.5V) stands for ?

The nominal voltage for Advisa PM is 3.2V as per spec. In the Battery Measurement reports, it shows Battery Voltage as 3.04V.

I am confused by various voltage values here.

Thanks,
DP.

10 Comments

Threshold & impedance

by golden_snitch - 2012-09-29 01:09:49

Hi again!

1. Maybe your report just doesn't tell, but during check-ups the threshold test is usually the one where they tell you before that your heart might slow down for a few seconds. This is because they test how much energy is needed to stimulate the heart effectively, and so they lower the voltage bit by bit until your heart does not respond to it any longer - the last voltage before it stopped responding is the threshold. So, there is no way your doctor programmed an amplitude without checking the threshold, it probably just isn't included in the report.

2. You're right, the lead impedance is also important for longevity. However, I thought the higher the impedance, the more ohm, the shorter the longevity. I had a fractured lead a while ago, and we realized that because the pacer had recorded impedance peaks (I think up to a few thousand ohms). To get the impulse through the broken part of the lead required more energy as the resistance (impedance) was high. Lead impedance is something that cannot be programmed. It's given.

3. I don't know what this nominal voltage means, sorry.

Best wishes
Inga

Clarification

by dpandit1037 - 2012-09-29 07:09:10

The website gobbled up all the whitespaces. I will make the table more clear :


************** 2.5 V ****** 3.5 V ***
=========================
DDD ******** 8.7yrs ******* 6.7 yrs ***
----------------------------------------------------

Amplitude

by golden_snitch - 2012-09-29 08:09:12

Hi!
It's the amplitude, the energy needed to stimulate your heart effectively (make it beat). They give two examples: When the amplitude is 2.5V you'll get 8.7 years, when it's 3.5V you'll have 6.7 years. The higher the amplitude, the sooner the battery will run low, because the pacer needs to stimulate with more energy. The amplitude depends on the threshold. You usually take the threshold and program the amplitude so that it doubles/triples the threshold. Thereby, you're on the safe side in case the threshold changes (for example due to scar tissue). To give you an example: My atrial threshold is 1.0V, and the atrial amplitude is 2.5V; ventricular threshold is 0.75V, and amplitude is 1.5V.
Hope this helps.
Best wishes
Inga
Inga

Thanks and some more queris

by dpandit1037 - 2012-09-29 12:09:32

Hi Inga,

Thanks a lot. And here I go with some more of my doubts ... :)

1. Looked up my last reports. Artrial Amp is at 2.75V and RV Amp at 3.5V. How does EP or Med Tech take a call on these values. I could not get threshold values anywhere.


2. Apart from Amp, the longevity is also dependent on the impedance. 500 ohm is 1 yr less than 900ohm. Are these impedance referring to lead impedence. If yes, how to increase 500 ohm to 900 ohm. Or is it not in our hands.

3. My device spec says the nominal voltage is 3.2V. And the time to change voltage is 2.83V. I got the implantation done 1 week back and the Battery Voltage currently is 3.04V. Why is this not 3.2V. Where is my 0.16V ?


Thanks
DP.

Lead Impedance

by dpandit1037 - 2012-09-30 12:09:32

Hi Inga,

Thanks again !!

I have an appointment scheduled for this week. I would pick brains of EP and MedTech and share any more information that I gather for fellow members.

As I have understand, lead impedance are a curious case. If the impedance is in thousands, it shows there is a lead breakage somewhere. This would result in battery depletion as the device would need to operate overtime to provide same V amp. If the impedance is less than 300 ohm, it shows leakage some in the lead insulation. This would result in higher current being drawn due to leakage and again, battery depletion would occur.

Normal lead impedance would be 500 to 900. I think, among the good working leads (no breakage, no leakage), the one giving higher impedance would provide higher battery life.

Thanks,
DP

Voltage readings

by ElectricFrank - 2012-10-01 02:10:09

Lets start with the nominal battery voltage. The 3.2 volts is the open circuit voltage of the battery when new. As soon as a load is applied to the battery the voltage immediately drops. This is a characteristic of all batteries. It is a function of the batteries internal impedance, the load current being drawn, and the number of milliamp hours used from the battery. The estimated life is calculated from these numbers at each checkup. As the pacemaker adjustments are changed the estimated life can increase or decrease.

The lead situation is even more complex. The amount of battery energy drawn by a lead depends on lead impedance, voltage, pulse width, and average heart rate. The final measurement is in Joules, but is not usually shown on the report.

High lead impedance can happen from an actual lead problem, but can also be caused my scar tissue or inflammation in the heart wall at the point of insertion. My pacers upper impedance warning level is 2000 ohms. Actually the important thing about the lead impedance is to track the changes over time.

frank

asfasfas

by boxxed - 2012-10-01 02:10:27

Based off that manual, sounds like the nominal voltage is the BATTERY voltage. It starts @ 3.2V. It'll deplete to 2.62V or whatever that is the voltage amount that'll trigger ERI and it's time for replacement.

As for question 1, they check threshold values and typically program 2x the value for a good safety margin. So if your threshold is 1V @ 0.4ms, they'll program 2V @ 0.4ms or greater.

As for impedance, that is the currently measured electrical level of resistance between the lead and the heart tissue. As previously mentioned. High impedance indicates fracture. Low impedance indicates insulation breach. I wouldn't worry about fluctuations between 300-1200, as those are generally accepted "normal" values. It's not a programmable setting. It's just a current reading.

In industry (device company) terms, nominal typically means out of the box. So nominal amplitude settings for Medtronic devices will have outputs of 3.5V @ 0.4ms. Devices nominally have rate response on (I think). And the device will nominally have a set BOL (beginning of life) battery voltage value.

Thanks folks

by dpandit1037 - 2012-10-01 02:10:28

Thanks boxxed and Frank for your inputs. Helped a lot.

DP.

Nominal

by ElectricFrank - 2012-10-02 01:10:17

That's what they said to the Challenger shuttle just before it blew up.
"All's nominal for throttle up" BOOM

So watch that Rate Response.

frank

Boxxed

by ElectricFrank - 2012-10-02 01:10:48

I didn't aim to give repeat info to yours. I was composing the comment when a phone call interrupted me. When I returned yours hadn't refreshed on the screen so I didn't see it.

cheers,

frank

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