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Cardiac Catheter Leak Detection

Wed, 05/30/2012 - 12:58pm
Joe Pustka

With the variety of tasks a cardiac catheter must accomplish, testing them to ensure safety and reliability is of critical importance. However, due to the range of tests that must be completed on them, this process can be lengthy and challenging. This article highlights the difficulties that can be encountered and offers a solution in the form of a new testing system.

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The intuitive dashboard of Uson's eight-sensor enabled leak detector (Optima vT Leak and Flow Tester) allows operators to quickly drill down to the data feeds—test data details, pressure plots, trending, etc.—that are of interest.

The clinical applications for catheters have become so widespread that the term “catheter” does not convey enough to the testing specialist. To a leak testing specialist, however, “cardiac catheter” immediately opens up an encyclopedia of leak test challenges that must be considered and conquered, largely stemming from their commonality of needing to operate over a wide range of pressures.

As with all medical devices, the design of one product varies from another. From a cardiac specialist’s point of view, the need for a range of cardiac catheter designs would be intuitively obvious. One cardiac catheter enables the injection of contrast agents to study vasculature. Another cardiac catheter is used to measure intracardiac and intravascular blood pressure. Add a stent and the fact that the device could be described as a cardiac catheter becomes somewhat secondary, in fact.

However, having designed a great number of leak test 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 they will all have in common that the “lynch pin” is in optimizing the test circuits for varying pressures. These pressure ranges could vary as much as testing at vacuum to 400 psi.

This is especially the case when the cardiac catheter design includes a stent. In one cardiac catheter design, leak testing of a detachable stent must be engineered. Other cardiac catheters must be tested under great pressures with the stent absent to ensure that the balloon does not leak. One catheter might have two lumens that need to be leak tested separately in addition to an overall leak test. Another design might include two or more lumens and/or subassemblies that must be leak-proof to a pre-set and negligible leak rate.

With 20-20 hindsight, it is easy to report that, until now, 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 comprehend why this is, one has to have the same understanding 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 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. It would be similar to trying to use a mile long tape measure for purposes of measuring a foot. Every part of that tape measure beyond the foot will be a bit cumbersome and tend to get in the way.

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Anticipating medical device designs that are not even on the drawing board yet, USON's Optima vT Leak and Flow Tester features fully customizable pneumatic controls that can be configured with eight-sensor enabled concurrent testing with any combination of a dozen NDT tests.

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. Take a sample 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).

Many leak detectors 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.

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USON Optima vT Leak and Flow Tester features an intuitive operator control panel as shown here, where even lightly skilled operators will be able to quickly identify the highlighted red icons for rejected parts that do not meet leak rate specifications vs. the green highlighted icon that represent parts that pass the leak test parameters needed for that application.

This complexity that is inherent in cardiac catheter leak testing is precisely the challenge that led to the development of the world’s first leak and flow tester that has eight-sensors in two channels that can conduct eight concurrent tests of a dozen types (e.g. flow tests, burst test, pressure decay tests, etc.)—the USON Optima vT Leak and Flow Tester. Because cardiac catheters are versatile and every new cardiac catheter design has unique requirements, only a leak detection instrument that anticipates this versatility can meet the requirements of modern day cardiac catheter manufacture at optimal efficiency.

In fact, given the rate at which cardiac catheter innovations are being brought to the FDA and then to market, today’s leak test equipment needs to be similarly innovative and with built-in versatility that can anticipate optimal efficiency for producing designs not yet on the R&D to-do list. This means that if an engineer is sourcing any capital equipment for cardiac catheter manufacture—for leak testing or any requirement—flexibility and malleability to optimize equipment and instrumentation for multiple production scenarios should be a top-level concern.

Joe Pustka is the medical device leak testing technical support manager for USON, which first developed high accuracy leak testing methods for NASA, and for nearly half a century, has been at the forefront of leak detection, leak testing, and non-destructive testing for the medical device and medical packaging industries. He can be reached at 281-671-2212 or joe.pustka@uson.com.

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