The recent investigative report by The New York Times on Boston Scientific’s pacemaker recalls has brought renewed attention to the critical issue of battery reliability in life-saving medical devices. According to The New York Times, Boston Scientific expanded its recall of Accolade pacemakers to include over 1.6 million devices, citing high battery electrical impedance as a key factor in their failure. This alarming revelation underscores the importance of addressing high impedance in battery technology, not just for medical devices but across industries.
But what is electrical impedance?
Electrical impedance is a measure of the opposition a component offers to the flow of electrical current. When impedance rises, a battery struggles to deliver the necessary power, especially during peak demand, leading to performance issues. The relationship between current, voltage, and resistance is described by Ohm’s Law, which is expressed as:
I = V / R
Where:
I is the current (measured in amperes, A),
V is the voltage (measured in volts, V),
R is the resistance (measured in ohms, Ω).
Additionally, the concept of power in electrical systems is closely tied to voltage and current. Power is defined as the product of voltage and current, expressed as:
P = V × I
Where:
P is the power (measured in watts, W),
V is the voltage (measured in volts, V),
I is the current (measured in amperes, A).
This formula highlights that the power delivered by a battery depends on both the voltage and the current. When impedance increases, the current decreases, which in turn reduces the power output. This reduction in power can severely impact the performance of devices relying on the battery, such as pacemakers. To better understand the concept of impedance, resistance, and power, consider the analogy of a water faucet:
Voltage (V) is like the water pressure in the pipes. It pushes water through the faucet.
Resistance (R) is like the size of the faucet opening. A smaller opening restricts the flow of water, just as higher resistance restricts the flow of electrical current.
Current (I) is like the amount of water flowing out of the faucet.
Power (P) is like the total amount of water delivered over time, which depends on both the pressure (voltage) and the flow rate (current).
When you open the faucet wider (reduce resistance), more water flows through, and the total water delivered increases. Similarly, reducing resistance in an electrical circuit allows more current to flow, increasing the power output. Conversely, if the faucet is barely open (high resistance), only a small trickle of water comes out, and the total water delivered is minimal—just as high impedance limits the flow of electrical current and reduces power.
In the case of Boston Scientific’s pacemakers, high internal impedance was identified as a key factor in battery failures. This condition prevented the batteries from delivering sufficient power, triggering the devices to enter Safety Mode—a backup setting designed to keep the heart beating until the pacemaker can be replaced. However, as The New York Times reported, Safety Mode itself can be dangerous for patients who rely on their pacemakers for continuous heart function, sometimes failing to engage or misinterpreting muscle activity as a heartbeat.
FDA statement on Accolade pacemaker replacements
In 2025, the FDA issued a statement regarding the manufacturing issue with the cathode of some Accolade pacemaker device batteries. According to the FDA:
The manufacturing defect may lead to underpowering the device system, causing pacemakers to permanently enter Safety Mode.
Pacemakers in Safety Mode require replacement because the limited functionality of Safety Mode has been associated with the inability to properly regulate the heart’s rhythm and rate in some patients.
Safety Mode can only be identified through office visits or remote monitoring using the Boston Scientific Latitude Communicator system.
Manufacturing processes for battery quality
Enhanced manufacturing processes are critical for addressing high impedance in batteries. Manufacturers are continually adopting stricter protocols to improve battery reliability and safety. These include:
Routine impedance testing: This involves measuring the internal impedance of batteries during production to identify and remove defective units. It ensures that only batteries with acceptable resistance levels are deployed in devices.
Chemical byproduct removal: Byproducts formed during manufacturing or operation can increase impedance. Manufacturers are improving electrolyte purity, using advanced cleaning techniques, and enhancing sealing to prevent contamination.
Improved cathode manufacturing: Cathode defects can also lead to high impedances. Manufacturers are refining cathode production by using advanced materials, ensuring uniform coating, and automating processes to reduce errors.
Addressing high electrical impedance in batteries is not just a technical challenge but a critical necessity, especially for medical devices like pacemakers. Enhanced manufacturing processes are vital steps toward improving battery quality and ensuring device reliability. By mitigating the risks associated with high impedance, manufacturers can prevent catastrophic failures, safeguard patient health, and restore confidence in life-saving technologies.
