LAUSR

To the Editor, In the era of rate‐responsive, multi‐chamber pacemakers, we are continuing to monitor a patient who was implanted with an isotopic single‐lead cardiac pacemaker 40 years ago. Ms. L. was implanted via anterolateral thoracotomy with an isotopic pacemaker at the age of 2 following a complete atrioventricular block complicating ventricular septal defect surgery (Figure 1). The device was set in VVI mode at 72 beats per minute. No energy output nor heart rate program is possible with this model (Medtronic‐Alcatel 9090). The device has functioned properly for 40 years with a quasi‐unlimited nuclear energy source. The magnetic rate of the device is measured annually to follow battery decay (a rapid decrease of 8 ± 3 impulsions indicates that the device needs to be replaced). Cardiac ultrasound showed the absence of left intraventricular desynchronization with a normal left ventricular ejection fraction. In 1965, when pacemakers were equipped with mercury batteries that lasted 2 to 4 years, Alcatel and Dr. Paul Laurens of Broussais Hospital developed an isotopic pacemaker. The first implantation was performed in April 1970 at the same hospital. The generator operates on plutonium 238. The heat produced by this unfissionable isotope is used to produce the electricity that stimulates the heart. At first, this type of pacemaker only existed in VOO mode and then evolved with the appearance of a VVI model that is programmable in frequency and energy stimulation. The advantage of this pacemaker lies in its service life. It is still operating in our patient after 40 years, and the plutonium used in this stimulator has a half‐life of 87.7 years. These devices were essentially considered for young subjects and implanted via epicardial route. However, a certain number have been explanted owing to repeated electrode failures or for hemodynamic reasons in complete atrioventricular block. Follow‐up studies of patients implanted for more than 10 years have reported no stimulator dysfunction nor wearing out of the battery. In the United States, 50 to 100 people are still using these nuclear stimulators.2‐6 In 1975, the isotopic battery was supplanted by lithium batteries, whose service life can exceed 10 years (or even 20 years for certain models). The safety of the isotopic battery is ensured by a triple‐layer armored capsule that protects the patient from radioactive radiation, and two other titanium capsules cover the battery and stimulator. The hard titanium of the device is designed to resist any event. In practice, there is no possibility of a radiation leak resulting from accidental damage. The radiation emitted is minimal, with exposure to the entire body evaluated at 0.1 rem/year for the patient and approximately 7.5 mrem/y for the patient's spouse. When this type of stimulator was first developed, the Atomic Energy Commission confirmed that there was nothing to fear regarding exposure to these minimal doses of radioactivity. However, it is a toxic material whose absorption is very dangerous for humans. Annual magnet rate measurements have been sufficient for electronic follow‐up. There is nothing to fear regarding exposure to the minimal doses of radioactivity generated by nuclear stimulators.