It is easy for the non-technical reader to pass over judgments relating to patents. These often involve highly technical issues.  However there is one aspect of the judgment in Thoratec Europe Limited -v- AIS GMBH Aachen Innovative Solutions [2016] EWHC 2637 (Pat) that may have a familiar ring.  It illustrates:

  1. The importance of case management orders setting out the discipline of the experts to be called.

  2. The need for expert witnesses to be independent.

  3. The way in which an expert can be tied up in knots in cross-examination, to the extent that the judge was unable to expert the expert’s opinions.


The claimant was seeking a declaration of non-infringement in relation to two patents. Both parties  were given permission to call two expert witnesses.  However the judge was surprised about the defendant’s choice, particular of their second expert.


  1. At the time of the case management conference in this case, I gave the parties permission to call two experts each. I did so because it appeared possible that the parties would need to adduce evidence from a biomedical engineer and from a clinician. Unfortunately, the order as drawn up did not specify that the two experts were to be in those fields. As should have been clear, I did not intend to give either party permission to call two experts in the same discipline. It is well established that the Patents Court does not permit duplicative expert evidence to be adduced (or give it any greater weight if it is adduced). In the event neither party saw the need to adduce evidence from a clinician, and accordingly Thoratec only served evidence from one technical expert. AIS served evidence from a second technical expert in addition to Dr Gaddum, namely Dr Sieß. This was purportedly to “supplement” Dr Gaddum’s report, even though Dr Gaddum’s report ran to 148 pages (not including an annex tabulating prior VADs and two annexes dealing with infringement issues) and dealt with every issue in the case.
  2. Inevitably, there was overlap between Dr Sieß’s evidence and Dr Gaddum’s evidence. This became particularly blatant in their respective second reports, when both dealt with the topic of synergy. Counsel for AIS elected to rely on Dr Sieß’s evidence on that topic rather than Dr Gaddum’s, which avoided the problem of duplication in that respect. It did not, however, address the other problems with Dr Sieß’s evidence.
  3. First, as Dr Sieß accepted, he was not independent, but on the contrary was both a senior manager of AIS and a person with a financial interest in the outcome of the litigation.
  4. Secondly, Dr Sieß was not only the inventor of the Impella, but also had spent most of his working life developing, promoting and marketing that device. Inevitably, he was heavily committed to that approach to the design of VADs.
  5. Thirdly, on the face of it, the main purposes of Dr Sieß’s first report were (i) to describe the Hemopump in considerable detail and the RCP, Impella and A-Med devices in less detail and (ii) to outline the functional requirements for a catheter-based VAD. It appears that the reason why AIS wanted to adduce this evidence was that Dr Gaddum had had little knowledge of catheter-based devices at the time and even now was not an expert in that sub-field of VADs. Yet both Dr Sieß and Dr Gaddum stated that parts of Dr Sieß’s evidence concerning the Hemopump were not common general knowledge. Moreover, it was Dr Gaddum who gave all the primary evidence on the issues in the case. Thus Dr Sieß’s evidence was not properly integrated into AIS’s case.
  6. The fourth and most serious problem with Dr Sieß’s evidence only emerged in cross-examination. At the end of his first report, Dr Sieß stated: “Although I have not considered the Prior Use, in my opinion, it was not obvious to develop any of the documentary prior art into any of the arrangements featured in the claims in the Patents in Suit.” When Dr Sieß was asked the simple question why he had not considered the prior use, he was unable or unwilling to give a straightforward answer. On the contrary, in a painful passage of evidence that extends for 12 pages of the transcript, he stated that he had not written this sentence, it had been written by AIS’s lawyers; professed not to understand it despite speaking good English; contradicted himself more than once as to whether or not he had in fact considered the prior use; and was unconvincing when he denied that the reason why he had not considered the prior use in his report was that he appreciated that it anticipated or rendered obvious the main claims of the Patents.
  7. In these circumstances I do not regard Dr Sieß as a reliable expert witness, and I cannot place any weight upon the opinions expressed in his reports. I do not doubt the accuracy of the purely factual material, however.