Blog with interesting cases and/or problems related to anesthesia with discussion based on best evidence in the literature.

August 29, 2011

Boston Scientific AICD

A few days ago a patient came to the OR for a hip pinning. The patient had a biventricular pacer and AICD. Presumably this was for his significant heart failure (likely class III). Since the patient was unable to give a history, we referred to the chart for information. A cardiologist had seen the patient and recommended that the patient have a magnet placed over the pacer to turn off the tachyarrythmia function. It was noted that the patient had a Boston Scientific. In an earlier post on this issue I detailed how some pacers/defibrillators may respond in different ways to placement of a magnet. My colleague was doing the anesthetic so I suggested that he not place a magnet since EMI was not anticipated and bipolar was possible at a site (the hip) distant from the pacer leads.
Please see previous posts on this topic: pacemakers and magnet, AICD.

Boston Scientific has merged with Guidant, however, they still have pacemakers and AICDs floating around. In the end, it is really important to contact the sales rep for the device to understand how best to proceed if there is any thought that EMI will occur.

In the case of a Boston Scientific AICDs, the company has provided some guidance.

1. First determine if the unit can be turned off using a magnet. Place a magnet over the device and ausculate using a stethoscope. If you hear tones then you have two types: a long constant tone or a beeping tone. If you hear a long constant tone then the tachy Mode is programmed OFF. This means that the patient came to you with no automatic defibrillation capability. You may need to contact a rep to program on if the patient needs the availability of this function.
2. If you hear beeping tones then continue to listen for 30 sec. If the beeps CHANGE to a long constant tone then you can remove the magnet; you have successfully inhibited anti-tachy therapy. At the end of the case to turn the therapy back on, replace the magnet and listen until tones change to beeping; remove and therapy will be on.
3. If after placing the magnet you hear beeping tones but after 30 s there is no change, you must LEAVE the magnet in place to maintain inhibition (which you have acheived by placing the magnet). After the case, you can remove the magnet and therapy will be programmed ON.

Unfortunately, the article from Boston Scientific (dated March, 2009) has some slight contradictions. For example, it explains in the detailed desription that a change in tone from long to beeps or from beeps to long is equivalent and means that the device is programmed off. By replacing the magnet for 30 sec another change in tones (i.e. from long constant tone to beeps or from beeps to long constant) the device has been reprogrammed to on. For this reason, it is likely that it will be prudent to call a technician to better understand how to proceed.

There are two take home points from this post:
1) You CAN'T just place a magnet over any type of AICD and be 100% confident that you have disarmed the anti-tachy therapy.
2) Even if you know what model and brand you have, you probably should consult the sales rep by phone, and NOT assume the cardiologist knows what he/she is talking about. In our case placing a magnet over the pulse generator as recommended by the cardiologist may have: 1) done nothing at all as some Boston Scientific pulse generators do not reprogram with magnet placement or if the magnet was not left in place for at least 30 sec, 2) turned off therapy, but not have turned it back on at the end of the case when the magnet was removed, 3) turned off therapy and turned it back on at the end of the case when it was removed.
Finally, it should be noted that if you do turn off the anti-tachy therapy, please remember that you really should place defibrillator pads in position and be ready to shock the patient if the need should arise suddenly during the procedure.

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