Friday, November 16, 2012

ICD parameters and interrogation data sheet

As I approach the 5th anniversary of my implant (11/19), I wanted to share a spreadsheet I keep with a few numbers pulled from my interrogation reports.

But what can I tell from the above data sheet?
  • Remaining battery life is on target to last me a few more years. At least 3 more, I hope. The Recommended Replacement Time (RRT) for my model of ICD is 2.62 Volts (see an estimated battery depletion curve here);
  • The capacitor charge times remain excellent (around 9 seconds) and the capacitor reforming continues to be done automatically at every 6 months. Defibrillators use electrolytic capacitors to accumulate the charge before shock delivery and these types of capacitors require periodic recharging to reduce large leakage currents over time;
  • The impedance of my leads (as measured in ohms, Ω) has been within range. A sudden increase in lead impedance ( > 2000 Ω) may indicate a conductor fracture, while a sudden drop in lead impedance ( < 200 Ω) may indicate an insulation breach.
What do you know about your device?


Mitchell said...

Hugo - As one who has worked with data all his life, I find your recording and monitoring of the data very impressive and interesting. Good for you. However, I am not sure I see the immediate value in it, given that the majority of things you are looking for are not trends over time, but one off events that would be checked with each individual device read. For example, a lead fracture does not gradually happen over time - it's a one time event that will probably show a significantly elevated impedance level at one specific reading, which will likely cause follow-up testing and then possibly the need to repair it. But there would have been no trend over time to show this would happen. On the battery life side, you are right that this is something trend data could reveal; however, most modern device reads today already provide you with a fairly accurate estimate as to the time remaining before battery replacement is required.

So, is there anything I may be overlooking in terms of something that could be tracked with a trend or where a trend may give you an early indication that something is not right?


Hugo Campos said...


Thank you for your thoughts. I'm neither a statistician nor an expert in trend analysis, so my ability to make sense of these numbers is somewhat limited. Still, I keep looking for patterns in order to understand everything I can about device therapy. I believe it's important to have another pair of eyes confirming all is OK. And patients should be allowed to take on this role if we so desire. Ultimately, for me, this is about transparency and control over my life.

Doctors and the manufacturer have 24/7 access to patient data, including direct mobile access to reports and alert notifications about potential problems. Patients, on the other hand, are limited to hard copies of their interrogation reports (a "right to access", under HIPAA). Such disparity in access is ironic considering that patients are the ones living with heart disease, not doctors or the manufacturer.

I know of a few cases in which access to data would have saved a patient a lot of trouble. In one instance, VT/VF therapy had been disabled during a minor procedure and it was NOT turned back on. This serious oversight resulted in the patient being sent home without the protection of the ICD. In this instance, the patient himself caught the error by looking at an interrogation report months after the fact. He had been unprotected, and at risk of dying of a sudden cardiac arrest, for all that time.

I hope that in the future, device patients will be in control of their data and able to share it with researchers, non-profit and for-profit organizations, and with other patients as they see fit. Perhaps then we'll be able to pool our device data and crowd source the expertise of people like yourself in order to learn more about our data and ourselves.

Hugo Campos said...

Also, since you mentioned battery, I should also mention the following:

It gives me peace of mind to be able to say that I am satisfied with the performance of my device battery. At 3.04 volts after 60 months, it has behaved quite well so far. (The battery was measured at 3.14 volts at the time of implant, on 11/19/2007.)

It also feels good to know in detail what the battery had to support in the course of the last 5 years:
• 21 in-office interrogations
• 1 CareLink (remote) transmission
• 3 bursts of (appropriate) ATP
• 9 capacitor reformations
• Considering the above in the context of 99.9% A-sense/V-sense.

Knowing the above (and more) puts me at ease and reassures me of the quality of the device and my doctor's ability to set it up to suit my needs.