Apparent pacemaker failure caused by activation of ventricular threshold test by a magnetic instrument mat during...

A patient with a permanent pacemaker underwent radical neck dissection. After induction of anaesthesia, a magnetic surgical instrument mat was placed over the patient's chest. This caused the pacemaker to go into a threshold test which included a 2.5-s period of asystole. Surgery had to be abandoned temporarily. We suggest that magnetic instrument mats should not be used with pacemaker patients; not all pacemakers are converted to a fixed magnetic rate by application of a magnet. The anaesthetist should check to see if the patient has a pacemaker with a threshold test and, if possible, this should be rendered inactive.