Temporary pacemakers are frequently of perioperative value. Unexpected interruption of the pacing can have dire consequences.1We recently encountered the contrary malfunction. One of our pacemakers developed a fault that caused the device to unexpectedly become turned on.

In preparation for anesthesia for a patient requiring coronary revascularization, a fresh 9-volt battery was placed in a dual chamber temporary pacemaker (5388; Medtronic, Minneapolis, MN). The pacemaker appeared to be undamaged and indicated a successful self-test upon installation of the battery. The pacemaker was turned off and set aside but was soon found to be turned on to deliver 10-mA atrioventricular pulses at a rate of 80/min in the demand mode. Those settings are programmed to occur if the “on” button is firmly depressed. We assumed that the button had been inadvertently hit. The “off' button was pushed twice (as required), and, accordingly, the display panel indicated that the device was turned off. A few minutes later, the device was found to be turned on again. No corporeal perpetrator was apparent and a restless soul was feared to be at work.2Thankfully, a mechanical defect accounted for the vexation.

An internal part of the device had come loose so that accelerated motion of the pacemaker tended to turn the pacer on. The most economical motion occurred when the facedown pacer was grasped in the pronated right hand and the hand was then supinated. Until this feature was appreciated, the malfunction appeared to have a random component. After the persistent pacer had been set aside for a weekend, the deteriorating device turned itself on after any gentle motion.

The Medtronic 5388 pacemaker has two ”on“ buttons. One initiates demand pacing, and the other, labeled “emergency,” initiates asynchronous pacing. Our malfunction involved the demand-pacing button. A similar malfunction involving the emergency button, leading to asynchronous pacing, could have proven clinically disastrous.

The Medtronic 5388 pacemaker has been previously cited for its ability to lock itself off during awkward attempts to turn it on quickly.3That is, if another button is pushed too soon after the “on” button is depressed, the machine self-test fails. Unknown to some operators, the battery must then be reinserted to permit reactivation of the frozen pacer. Our problematic pacer emphasizes another caveat. Although turned off, a cardiac pacemaker attached to a patient requires vigilant attention.

* Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts. talston@partners.org

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