To the Editor:—
We recently encountered a failure of ventricular capture that occurred during right-sided, elective shoulder arthroscopy in an 89-yr-old man with a dual-chamber pacemaker. The patient was treated 4 yr previously for a bradycardia–tachycardia syndrome by β-blockers and heart pacing with an atrioventricular sequential pacemaker (ELA Medical Chorum 7234; Montrouge, France). The generator, located below the right clavicle and connected to screwed endocardial pacing leads, was functioning normally on the DDD mode before surgery. Electrocardiography showed 100% atrial pacing at 70 beats/min, triggering atrioventricular-conducted ventricular events. Chest radiography showed that the pacemaker and pacing leads were correctly positioned (fig. 1A).
After administration of oral propranolol and hydroxyzine, a brachial plexus block was performed with 0.5% bupivacaine (20 ml) and 2% lidocaine (20 ml) using a peripheral nerve stimulator. General anesthesia was then induced with propofol and maintained with propofol infusion and 50% nitrous oxide in oxygen (laryngeal mask). No electrocautery was used during the procedure. After 45 min of surgery, bradycardia at 35 beats/min occurred. Electrocardiography showed regular atrial pacing at 70 beats/min and one half loss of ventricular capture. Intravenous isoproterenol was used to keep the ventricular rate at more than 70 beats/min. Surgery was rapidly discontinued, and a major edema of the shoulder was noted, caused by an unexpected massive subcutaneous diffusion of the saline used for joint irrigation. Chest radiography showed that the generator was displaced toward the shoulder and that there was traction on both the atrial and the ventricular leads (fig. 1B). The wire did not seem to be pulled from the pacer, and the most probable cause of the loss of ventricular capture was displacement of the tip of the electrode from the heart. Late lead displacement of a screwed pacing lead is rare. 1,2The phenomenon observed in our case can be compared with the lead retraction from the heart seen in Twiddler syndrome, which occurs when the patient repeatedly rotates the pacer under the skin. 3This hypothesis was supported by the resumption of ventricular pacing 2 h later, when the shoulder edema decreased and the pulse generator returned to its initial position. Pacemaker program and lead impedance were found to be unchanged 3 h after surgery. Other causes of pacing failure, including electromagnetic interference or increase in pacing threshold secondary to toxic plasma concentration of bupivacaine after brachial plexus block, are unlikely. 4
It is important to monitor pacemaker function closely in the perioperative period because uncommon phenomenon may induce pacemaker failure.