Quality In a Heartbeat: Designing Reliable Cardiac Implant Design & Componentry

At a Glance:

New trends in cardiac implant design such as miniaturization create new challenges to overcome.
Why regulations that guarantee patient safety and reduce post-surgery complications are reliant on in-country clinical data.
Understand the essentials of design, manufacturing, assembly and fluid process control needed to ensure the manual or automated solutions used to assemble pacemakers provide consistent operation.

The relevance of product accuracy and reliability can never be overstated when applied to the medical device industry. One such example is the cardiac implant and its ever-vital role in the lives of people with irregular heartbeats and other heart conditions. Since the 1950s, pacemakers and implantable cardioverter defibrillators (ICDs) have saved or improved the lives of millions of people. According to the American Heart Association, there are 3 million people worldwide with pacemakers and about 600,000 are implanted annually.

Introduced first as wearables and eventually evolving into implantable devices, the underlying design and electronics of these devices have advanced over the years. There are new trends afoot in this arena based on innovations in many manufacturing methodologies. To start, cardiac implants are much smaller in size to provide greater comfort to the patient and are far less invasive when surgically embedded. The re-engineering of these devices and components to micro and nano sizes has presented fresh challenges from production to micro-precision assembly for today’s medical device manufacturer.

Parts and Pieces

Cardiac implants consist of two parts: the implantable pulse generator or housing and the leads. Inside the generator, there are electronics to record the electrical activity of a heart so a cardiologist can later analyze this information. Inside the biocompatible titanium housing, there is a lithium battery to power the device, which lasts roughly 5-10 years. The leads are insulated conductors delivering electronic pulses or shocks when a patient’s natural pacemaker, the sinus node (SA node), is malfunctioning.

Traditional pacemaker illustration — Traditional pacemakers have one or more leads that are placed in the atrium (upper chamber) or ventricle (lower chamber), or in some cases both based on the patients’ medical condition.

Regulatory Rigor

The cardiac implant industry, much like other implantable device manufacturers, face heavy regulations to guarantee patient safety and reduce post-surgery complications. In the United States, the Food and Drug Administration (FDA) regulates medical devices and requires manufacturers to demonstrate their safety and effectiveness. This regulatory rigor includes trials on many patients and follow-up a year after surgery, taking adequate time to gather crucial information. Another important aspect of this process is to get in-country clinical data, meaning if the device is to be used in the U.S., it needs to be tested here.

These protocols help determine if the device is functioning properly in terms of lead function, battery life and programming. The two main goals are to help patients maintain a normal heart rate and for the mechanism to last roughly 10-20 years as the removal of these devices gets harder over time. Once the leads fuse to the walls of the heart, the removal process could lacerate the superior vena cava, the right atrium or right ventricle.

Getting It Right the First Time

Nearly one in 20 patients will get a bacterial infection within three years of undergoing surgery¹. The infection can be caused by the surgery or an issue with the pacemaker. The main approach to preventing this illness in patients is to ensure implant devices are properly built from start to finish.

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The roadmap to properly functioning devices is to meticulously create each component of the pacemaker, such as insulating the leads or molding of the pacemaker housing and precisely assembling those parts into the final product. The manual or automated solutions used to assemble pacemakers must provide consistent operation and repeatable results.

Fluid Control Essentials

Medical device manufacturers have been successful in developing miniscule components for cardiac implants. The final assembly of these parts calls for a high level of fluid process and control proficiency to ensure a quality implant product that will pass strict regulations. A variety of fluids including adhesives, lubricants and silicones are used to construct cardiac implants.

During the prototyping phase, manufacturers must develop procedures for operations such as insulating leads and electronic components with medical-grade adhesives such as Nusil silicone. Properly coated leads are vitally important as they acquire the electrical current from the pulse generator and stimulate the heart to beat at a normal rhythm. If the sealing gets damaged, the leads cannot send proper signals to the heart.

For this type of application, fluid process professionals like those at Nordson EFD (East Providence, R.I.) would provide consulting to identify the proper fluid dispensing technology. Nordson takes the additional step of testing the fluid+solution functionality in one of its global engineering labs.

The HPx high-pressure dispensing tool makes it easy to apply medical-grade adhesives for medical device assemblies.

Coating Leads and the Pulse Generator

For the coated leads use case, an HPx high-pressure dispense tool was chosen as it consistently applies viscous fluid through dispense tips as small as 0.004 in. Device manufacturers use handheld fluid dispensing devices for fine motor control, especially when applying very viscous fluids.

These can be paired with a benchtop fluid dispenser such as a Nordson Ultimus 1 for control of the dispensed amount via a foot pedal and dispensing settings, with time adjustment as fine as 0.0001 sec. This system, including micro dot dispense tips ranging from 27-33 gauge, delivers repeatable micro-dispensing.

Constructing the pacemaker housing assembly, or pulse generator, is another critical step in production. The electronic circuitry and battery are located in the housing, and a special silicone formulation such as pyrroline is used to coat the outside of the pacemaker. The pulse generator not only monitors heartbeat but also captures data that can be remotely collected by a patient’s doctor.

It is crucial for this part to function properly as it constantly monitors and analyzes the patient’s heart rate depending on physical or physiological changes. This information is then sent through the leads to stimulate the heart.

Lubricating Titanium

Aside from coating applications, fluid usage is prolific in cardiac implant assembly. Manufacturers utilize lubricants to coat flat pieces of titanium before they press and form them into the housings of the pacemaker and ICD generator. Getting a proper seal reduces the likelihood of the pieces cracking as they get pressed into the molds. Most cardiac implants are roughly two inches long and about two quarters stacked in width. Working with such small parts, the Nordson 781Mini allows manufacturers to reliably dispense uniform spray patterns as small as 1 mm (0.04 in.) wide. The small form factor also allows the valve to get close to the part and dispense exactly where it is needed.

The form factor of the 781Mini spray valve is significantly smaller than conventional spray valves, which allows manufacturers to mount more valves for high volume assembly operations.

Bonding Septum to Cavity is a High Octane Dispense

During the pacemaker assemblage, a septum needs to be inserted into each circular header cavity on a transparent device header using medical adhesive. Septums are small, circular, flexible barriers that are placed over the openings of a pacemaker header. These holes provide access points for surgeons to puncture with a needle to manipulate the leads during surgery or any follow-up procedures. Septums essentially prevent bodily fluids from entering the device, which could cause contamination.

For this process, a high-end PICO XP jetting system is used for extremely precise fluid placement that maintains accuracy even as temperatures rise and fall. Jetting technology is beneficial because it consistently deposits fluid onto uneven workpieces that are being assembled. The dispense action is much faster than contact valves because it does not involve a Z-axis movement.

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If paired with an automated dispensing system and advanced robot, operators can use a high-definition CCD smart camera to easily visualize each accurately dispense point even on transparent surfaces. The robot is equipped with laser height sensing, which is useful when working with delicate and small substrates.

Automating the Insulation of Electrical Parts

Another assembly function is the attachment of the head of a pacemaker to the pulse generator with a medical grade silicone. This fluid is well tolerated by the human body and it acts as an insulator for electrical parts. An Ultimus high precision dispenser works well with silicones, and the assembly task can also be automated with a PROX dispensing system. This particular solution has a larger working area of 500 mm × 500 mm to fit even more pacemaker housing parts to keep up with production demands. The system robot uses a contactless linear motor, which lowers motor wear and tear for improved longevity.

Protecting PCBs with UV Masking

In the final step to protect the PCB from bodily fluids, manufacturers will use UV masking to shield component areas from a conformal coating. This fluid control application requires precise, drip-free dispensing of UV coatings using a high flow diaphragm valve. The corrosion-resistant valve integrates a positive shutoff for a clean dispense, ensuring that the fluid is dispensed exactly where it is needed. This valve is also easily mounted to almost any automated dispensing solution.

Glimpse of the Future

As the world’s aging population continues to grow each year, the number of heart conditions has also increased. Cardiac implant manufacturers are facing greater demand for pacemakers as technology improves, and more information about the heart is being discovered. Engineers schooled in design, manufacturing, assembly and fluid process control are in a strategic position to take on the complexities of building high-quality cardiac implant devices.