What connectors and interconnects are used in pacemakers and ICDs?

Pacemakers and implantable cardioverter defibrillators (ICDs) are small, battery-powered devices implanted under the skin to manage abnormal heart rhythms. Pacemakers deliver low-energy electrical impulses to treat bradycardia, while ICDs monitor life-threatening arrhythmias and deliver controlled, high-energy shocks. Despite their functional differences, both devices rely on specialized connectors and interconnects to ensure safe, long-term performance.

This article explores pacemaker and ICD system architecture, with a focus on connector types and interconnect technologies. It covers legacy and emerging standards — such as IS-1, DF-1, DF-4, IS-4, and nanominiature connectors — and outlines typical lead and header configurations. The article also discusses reliability and system integration, detailing key design factors such as fixation, sealing, and conductor and insulator materials.

Pacemaker architecture and function

As shown in Figure 1, surgeons implant compact, battery-powered pacemakers under the skin near the collarbone.

Figure 1. Anatomical placement of a pacemaker and leads, showing the pulse generator near the collarbone and lead pathways into the right atrium and right ventricle. (Image: MedlinePlus)

They regulate slow or irregular heart rhythms by delivering electrical impulses to the heart muscle. By supplementing or replacing the heart’s natural electrical signals, pacemakers help maintain cardiac output in patients with bradycardia, heart block, or other types of heart failure.

Most pacemakers comprise two main components: a pulse generator, which contains the battery and circuitry that control pulse timing and amplitude, and leads, which function as interconnects between the pulse generator and the heart, delivering electrical impulses and sensing cardiac activity.

Pacemaker leads typically incorporate MP35N alloy for the main conductor, selected for its mechanical durability and corrosion resistance. Manufacturers commonly use platinum-iridium for electrode tips, which provides excellent conductivity and biocompatibility. Insulation materials such as silicone rubber or polyurethane offer flexibility and long-term biocompatibility.

During implantation, surgeons thread leads through veins into the heart under local anesthesia or sedation. Leadless pacemakers, used in patients requiring single-chamber pacing, are implanted directly into a heart chamber, reducing the risk of lead-related complications. Some pacemakers, such as biventricular devices, stimulate multiple chambers to improve synchronization in heart failure patients. Devices can also be programmed to adjust pacing based on patient activity level.

Pacemaker connectors and interconnects

A reliable electrical and mechanical connection between the pulse generator and pacing leads is critical to ensure safe, long-term device performance. These connections must withstand continuous mechanical stress, fluid exposure, and electrical cycling over many years. To meet these requirements, pacemakers use standardized, medical-grade connectors engineered for compatibility, secure fixation, and biocompatibility.

As shown in Figure 2, the IS-1 connector is the global standard for bradycardia pacemaker leads:

Figure 2. The IS-1 connector interface between a pacemaker header port and pacing lead, highlighting the port end, setscrew mechanism, sealing components, and bipolar electrode configuration. (Image: HowToPace)

It supports bipolar pacing with a 3.2 mm pin diameter and is typically secured in the device header using a set screw. The IS-1 specification enables interchangeability across manufacturers, simplifies replacements, and reduces the risk of lead-to-device incompatibility.

Hermetic sealing protects internal components by preventing moisture intrusion and pressure-related failures. Engineers choose connector materials such as titanium and silicone rubber for their durability, corrosion resistance, and long-term biocompatibility within the body.

Other cardiac-related connector types include:

Nanominiature connectors are used in some compact or leadless pacemakers. They feature contact spacing as small as 0.635 mm and typically incorporate twist-pin contacts and vacuum-sealed housings to resist corrosion, fluid ingress, and pressure fluctuations.
DF-1 and DF-4 are used primarily in ICDs and cardiac resynchronization therapy defibrillators (CRT-Ds) for high-voltage defibrillation, not in standalone pacemakers.
IS-4 supports leads with multiple electrodes, such as those used in cardiac resynchronization therapy. They are rarely incorporated into standard pacing systems.
SQ-1 is specific to subcutaneous ICDs (S-ICDs) and is not used in pacemakers.

ICD architecture and function

As shown in Figure 3, surgeons implant ICDs under the skin in the chest.

Figure 3. Anatomical placement of an implantable ICD, showing the pulse generator near the chest wall and lead pathway to the ventricle for arrhythmia detection and therapy delivery. (Image: MedLinePlus)

It continuously monitors heart rhythm and delivers electrical therapy to correct life-threatening arrhythmias. Depending on the severity of the condition, it may respond to ventricular tachycardia or ventricular fibrillation with either low-energy pacing or high-energy shocks.

Like pacemakers, ICDs comprise a pulse generator, which houses the battery and electronic circuitry, and one or more leads, which function as interconnects between the generator and the myocardium, sensing cardiac activity and delivering electrical impulses.

These leads typically incorporate MP35N alloy for the main conductor, selected for its corrosion resistance, conductivity, and fatigue durability. Platinum-iridium is commonly used at the electrode tips to ensure stable electrical contact with cardiac tissue. Insulation materials such as silicone rubber or polyurethane provide flexibility and long-term biocompatibility.

Many ICDs also offer pacemaker functionality, delivering low-energy pulses to manage bradycardia in addition to their primary defibrillation role. While both devices are implantable and used to manage cardiac rhythm disorders, their core functions differ:

Pacemakers deliver low-energy electrical impulses to maintain a steady rhythm in patients with slow heartbeats.
ICDs detect and treat dangerously fast or irregular rhythms by delivering therapeutic shocks. These devices often include pacemaker capabilities as a secondary function.

ICD connectors and interconnects

The electrical interface between the ICD pulse generator and its leads is critical for therapy delivery, safety, and long-term reliability. These connections must endure repeated mechanical stress, electrical cycling, and exposure to internal body fluids over the device’s lifetime. To ensure optimal performance, cardiac-related connector designs have evolved to reduce procedural complexity, improve cross-device compatibility, and minimize implantation errors.

One example is the transition from the DF-1 connector, the legacy standard for high-voltage shock delivery in ICDs, to the more streamlined DF-4 connector. In a typical DF-1 configuration, the system includes one IS-1 connector for low-voltage pacing and sensing, along with one or two DF-1 connectors for high-voltage defibrillation.

In some legacy systems, the ICD pulse generator case — typically made of titanium — also functions as an active electrode for defibrillation. This configuration results in a bifurcated lead structure, which increases system bulk and interconnect complexity, complicating implantation and replacement.

As shown in Figure 4, the DF-4 connector addresses these limitations by integrating both low-voltage (pacing/sensing) and high-voltage (shock) functionality into a single, four-pole inline connector.

Figure 4. DF-4 ICD lead system with integrated pacing and defibrillation connections, combining four electrical contacts into a single inline connector to simplify implantation and reduce system bulk. (Image: Dr.S.Venkatesan)

It uses one plug and a single setscrew to simplify the interface. The design incorporates four contact points — two for pacing/sensing and two for defibrillation — and places sealing rings in the device header rather than on the lead. This reduces mechanical wear, improves reliability, eliminates the need for a yoke, and lowers the risk of lead misconnection. As a result, DF-4 is now the preferred standard in most new ICD implants.

Other connectors used in ICD systems include IS-1, which remains in use for low-voltage signals in some configurations, often paired with DF-1 leads in older systems. IS-4 supports quadripolar leads for cardiac resynchronization therapy (CRT) but isn’t typically used in ICD-only devices.

Regardless of type, all ICD connectors and interconnects must meet stringent performance and reliability requirements. Connectors require careful attention to fixation, sealing, and materials, while interconnects such as leads must provide long-term electrical integrity, mechanical flexibility, and biocompatibility.

ICD setscrews and spring contacts ensure stable mechanical and electrical coupling, while integrated sealing rings and hermetic housings protect against fluid ingress and maintain electrical isolation. Connector materials, such as medical-grade alloys and biocompatible polymers, offer corrosion resistance and long-term reliability within the body.

Summary

Pacemakers and ICDs rely on standardized connectors, hermetic seals, and biocompatible materials to ensure safe and reliable long-term performance. IS-1 remains the dominant standard for pacemakers, while ICD systems are shifting from the bulkier DF-1 to the integrated DF-4 connector, simplifying lead management and reducing complications. Additional connector types, such as nanominiature and IS-4, support specialized functions, including cardiac resynchronization and compact designs.