A device to select the optimal time to replace the pacemaker activated by a lithium-iodine battery: results of 8 years of experience.

Abstract

The discharge curve of lithium-iodine batteries does not have features which make the clinical decision to replace the pacemaker easy. The output voltage fall corresponding to the end of their life is evidenced by variations of the output variables (frequency and/or length of pulse) and the time of elective replacement time (ER) is arbitrarily established by the manufacturer, ER may be too early or too late in relation to the threshold value of myocardial stimulation. Furthermore, the variables indicating end of life may be changed by troubles in the circuit components, irrespective of the state of battery. A device to detect the optimal time for replacement (OR) of pacemaker was studied in 1692 subjects with implanted LEM VVl electro-stimulators. This device consists of a resistance of 110 Ω connected in series with the catheter through a magnetic switch, which is activated by placing a magnet over the skin. The transient connection of the resistor reduces the output voltage by an amount depending on the resistive load between the electrodes. In a follow-up of 35 000 months the OR device revealed a very good reliability. Pacemaker replacement, established when stimulation becomes ineffective during the application of the magnet or when the spike amplitude in the standard oscilloscope rapidly declined, was necessary in 77 patients (six of them were excluded due to a circuit blackout). The OR device was useful in 53 patients (74.6%) with a chronic myocardial threshold of more than 2.5 V, useless in 18 patients with a myocardial threshold lower than 2.5 V; to obviate this limitation a new OR device is described feigning a temporary increment of battery impedance. The employment of the OR device rather than using ER enabled the patients to gain 1333 months of stimulation. The gain of pacing varied from a few months to 3 years, with an average of 18.7 months.