Leak Testing Challenges of Cardiac Catheters

The term “catheter” is an insufficient description for a leak testing specialist. However, “cardiac catheter” immediately brings to mind a number of leak test challenges that must be considered and overcome, largely because of the need to operate over a wide range of pressures.

Safety and reliability of cardiac catheters is of vital importance. However, due to the number of tests that must be completed on them, this process can be lengthy and challenging. Let’s look at some of the challenges that can be encountered and ways to get around them.

The variety of catheters and their specialized function presents us with significant challenges. For example, one cardiac catheter enables the injection of contrast agents to study vasculature. Another is used to measure intracardiac and intravascular blood pressure. Add a stent and the fact that the device might be described as a cardiac catheter becomes somewhat secondary, in fact.

Uson has designed a great number of leak testing solutions for cardiac catheters, distilling the enormous variation in these devices into their commonalities is not difficult. Each leak test solution will be as unique as the cardiac catheter design, but what they all have in common is optimizing the test circuits for varying pressures. The range of pressure encountered can run from vacuum to 400psi or more.

The inclusion of stents further complicates the testing process. Some cardiac catheters must be tested under great pressures with the stent absent to ensure that the balloon does not leak. A common catheter might have two lumens that need to be leak tested separately in addition to an overall leak test. Another might include two or more lumens and/or subassemblies that must be leak-proof to a pre-set and negligible leak rate.

With hindsight, it is easy to report that, even the most efficient cardiac catheter leak test solutions have involved a certain degree of what might not be the best fit for- purpose. To understand why this is, one has to understand the different types of test sensors, accuracy, and how test cycle times are affected by sensors being in or out of tune with the precise sensitivity required for peak accuracy and speed.

A leak test pressure sensor has a particular range where it will work most efficiently and accurately. When a sensor is designed to work over a very wide range, it will not be as efficient at any smaller subset of that range compared to a sensor that is exactly designed for that specific narrow range. With that in mind, imagine a leak test sensor that somehow must test many lumens in a cardiac catheter, probably one with a stent, in ranges of 40 to 400 psi. There could be 10 times greater sensitivity of the test sensor for the 40-psi pressure test. That would mean that although the fill stage of a pressure decay test would be the same, the decay portion of the test cycle time would be 1/10th. That is a very significant efficiency gain that can and will impact production throughput.

Then, consider that many cardiac catheters need to be tested multiple times, both as sub-assemblies and as a final assembly. Consider a cardiac catheter that has multiple ports—one is a flush port, and one has a skive. It has multiple lumens—one is for illumination, and one is for the pressurized delivery of medicines where accurate flow rates must be checked. The distal end has a balloon that needs to be installed in the final assembly, while the proximal end (near the doctor) needs to be leak tested at a fraction of the pressure on the distal end. There are six subassemblies that combine to make the final part (i.e., complete cardiac catheter).

It’s easy to see that several leak testers can be combined with sensors at the various ranges required and set up in multiple test stations throughout the assembly process. That works, but it is not optimal. The reason why refers back to the consideration of the test sensor that could be precisely tuned to one pressure for a 10 times improvement in the pressure decay test portion of the overall test cycle time. When using typical multi-channel testers, there is also the challenge of getting each test instrument and/or each test channel to communicate with others in the testing solution. If they do “talk” to one another, there is likely to be a delay in that communication, which is yet another sub-optimal solution.