Failure of communication and capture: The perils of temporary unipolar pacing system

Abstract

We present a case of a patient with pacemaker dependence secondary to complete heart block who developed loss of capture of her temporary pacemaker. Patient developed torsades de pointes then ventricular fibrillation, requiring CPR and external cardioversion. After patient was stabilized, it was noticed that loss of capture of pacemaker corresponded with nursing care, when the pulse generator was lifted off patient׳s chest wall, and that patient׳s temporary pacing system had been programmed to unipolar mode without knowledge of attending cardiologist. This case highlights the importance of communication ensuring all caregivers are aware of mode of the temporary pacing system.

1. Introduction

A pacing circuit consists of a pulse generator and one or more leads that allow communication between the pulse generator and the heart. Some of the common reasons for noncapture include lead dislodgement or break in circuit, lead failure, and inflammation and fibrosis at the electrode-myocardium interface leading to a higher threshold for stimulation [1]. The usual treatment of a pocket infection involves removing the entire infected pacing system (pulse generator and leads); this reduces the risk of reinfection by 75% [2].

2. Case report

The patient is a 64 year old female with dilated cardiomyopathy and complete heart block with pacemaker dependence. She was admitted for treatment of a pocket infection of her AICD (Automatic Implantable Cardioverter Defibrillator) system after an upgrade to a biventricular ICD. At her local hospital the pacemaker pocket was explored, and the pulse generator was removed, but the cardiologist was not able to remove the right ventricular lead. She was sent to a university center for extraction of the lead. A bipolar right ventricular active fixation lead coupled to a pulse generator taped to the patient׳s chest wall was used as her temporary pacing system. She was transferred back to her local hospital for antibiotics, and eventual implantation of a permanent pacing system. Several times, the patient developed symptomatic loss of capture of her temporary system. During one episode, she developed asystole, polymorphous ventricular tachycardia, and ventricular fibrillation requiring CPR and external cardioversion (Figs. 1 and 2). It was ultimately noted that the episodes of apparent malfunction of the temporary pacing system corresponded with nursing care in which the patient was receiving a bath or wound care. The pulse generator was being lifted off the patient׳s chest wall, resulting in episodes of loss of capture and asystole. It was also noted that the patient׳s pacemaker had been programmed to unipolar mode without the knowledge of the attending cardiologist. The system was reprogrammed to bipolar mode, and no subsequent episodes of loss of capture occurred.

Fig. 1.

Noncapture unipolar mode.

Fig. 2.

Shocked with external cardioverter (arrow) and brought back to normal pacing (in bipolar mode).

The explanted pacing system was from Medtronic. The pulse generator was an InSync Sentry Model 7299. The right atrial lead was a Model 5076, the right ventricular lead a Model 6947, and the coronary sinus lead a Model 4194. St. Jude Model 5142 was the temporary pulse generator connected to the temporary transvenous lead, a Medtronic Model 5076.

3. Discussion

When the pulse generator, i.e. anode of the circuit, is not in contact with the skin, the circuit is interrupted and becomes ineffective. When nurses were changing dressings and bathing the patient, the pulse generator was removed from contact with the skin. Hence, the device failed to capture, leading to complete heart block, torsades, and ventricular fibrillation.

The IPG׳s being out of contact with the skin is not an issue in a bipolar system. The reason is that the two electrodes on a bipolar lead make the circuit, and the IPG does not serve as the anode as the leads function to receive the impulse. In a bipolar pacing system, the lead tip is located at the distal portion of the interventricular septum, near the right ventricular apex. The impulse travels a short distance to the heart. In contrast, in a unipolar system, sensing of skeletal myopotentials, i.e. movement of the IPG against muscle, can generate electrical activity that may be missensed and cause potential pacemaker inhibition or failure to pace. In a bipolar system, in which the electrode leads are in very close proximity, sensing of noncardiac signals such as myopotentials or electromagnetic interference is less likely [1]. Hence, AICDs are used with bipolar leads so that it is less likely that a shock will be delivered after sensing an extracardiac signal.

4. Conclusion

Pacemaker infections are frequently treated by extraction of the infected system and temporary transvenous pacing with an external pulse generator. When patients require an externally placed pulse generator, the system must not be programmed in the unipolar mode to eliminate the possibility of disruption of the circuit. If unipolar mode must be used, proper communication between the electrophysiologist and the attending cardiologist and nursing personnel is essential so that all caregivers are aware of the mode of the temporary system.

Conflict of interest

Authors have no conflicts of interest. No financial support was received.