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

June 6, 2010

Pacemaker and reverse shoulder surgery

A 69 year old male presents for open reverse shoulder arthroplasty. His medical history is significant for atrial fibrillation for which he takes coumadin, htn, and a pacemaker. Upon asking the patient about his pacemaker he states that it was placed for atrial fibrillation. A review of his ECG appears that he is pacemaker dependent as all beats contained a pacer spike. He produced an pacemaker card that verified that he had a medtronic pacemaker. He stated that he has it interrogated regularly, most recently 3 months prior. He stated that a magnet is used for this process over the phone.

The surgeon was made aware of the pacemaker. The patient was taken to the OR where a single shot interscalene block was placed on the left (same side as the pacemaker generator) with 0.25% bupivacaine + Epi 1:400k with 40 mLs. The patient tolerated the block without problems. Current for the block was kept low (<0.7ma)>

GETA was induced and the patient was intubated. This he tolerated without problems. He was positioned and surgery commenced at which time it was noticed that the patient had an adequate block per blood pressure and heart rate remaining at baseline as well as respirtory rate remaining unchanged.

Unipolar electrocautery was used and indeed, as it was near the pacemaker leads caused very brief pauses in the paced rythym. After aproximately 30 minutes of carefully monitoring the situtaion, it was decided that it would be safer to proceed with a magnet in place. The magnet immediately resulted in a VOO mode at 85 bpm. Electrocautery no longer resulted in brief pauses and the case continued uneventfully.

A previous post on this blog has dealt with pacemakers and AICDs. Therefore, this post will provide an update and include information that was not included in the previous post.

Much of this post can be credited to information provided by Dr. Marc Rozner. According to the Dr. Rozner about 60% of pacemakers respond to a magnet by pacing at a high rate of between 80 to 100 bpm in an asynchronous mode. Another 25% switch to asynchronous pacing at a program rate and another 15% respond to a magnet with asynchronous pacing at 60 to 100 bpm for a brief time.

Therefore, because of the large number of pacemaker manufacturers there are a variety of responses to placement of a magnet. Knowing what this reponse is going to be may only be acheived by calling the sales representative which should always be possible by finding out who manufactured the device.

If the patient has an intrinsic heart rate of around 80 depending on the mode of the pacemaker you may inadvertently cause VF. If the pacemaker has a low battery and you place a magnet on a pacemaker it may pace at a rate of 50. VF or VT could result because of the R on T phenomenon, where the pacemaker competes with the intrinsic heart rate. If it fires during the vulnerable T wave of the ECG correlating to ventricular repolarization, the myocardium is susceptible to fibrillation. In summary, patients who have a native rate that is greater than the programmed rate, there is risk of competition between the device and the intrinisc native biologic cardiac pacemaking cells.
If a patient has a pacemaker, but does not know any other details and has failed to bring an identifier card with them, you shoot an xray. About 60% of the implanted devices have a code that can allow you to identify them. Unfortunately, that means that 40% will not.
Another area that should garner caution are devices that have minute ventilation sensors. Recently, Marc Rozner and Richar Nishman alerted the FDA Center for Devices and Radiologic Health about concerns in this regard. This led to an FDA alert.
There are a host of pacemakers made by a variety of manufactuers all of which may have slightly different functionality. This large variety makes for the potential of complications go way up. Therefore, it becomes essential for any anesthesiologist who is going to anesthetize a patient who has a pacemaker and will require monopolar EMI, to be knowledgeable about the reason the patient has the device, the most recent interrogation, the reaction to a magnet, and potential surgical insults that may require large cardiac output changes.

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