PANEL DISCUSSION: I

DR. FURMAN: Dr. Sowton has a question to begin the discussion. DR. SOWTON: My question concerns the toxicity of silver in the heart. I believe the General Electric electrode has silver in contact with the heart, and I wondered if we have any information about toxicity? MR. GREATBATCH: I know of no information in the literature. No one with whom I’ve spoken has given any reason for concern or made any direct criticism of using silver in the heart. My mention of toxicity in the body reflects the work of Cooper at Bristol, England, which is the one reference with which I’m familiar. He claims to have established the fact that silver is toxic in brain tissue. Any concern that I would have personally would be simply that if silver is toxic in one area, one should certainly worry about what it might do in other areas and investigate this possibility. I want to stress that in our work we have no evidence whatsoever to imply criticism of the use of any type of electrode. We are interested from a fundamental point of view in the chemical reactions of all electrodes. Our own personal philosophy of pacemaker design is that we will continue to put nothing in contact with body tissue except silicone rubber and platinum metal, but this does not imply criticism of what anyone else might do. DR. FURMAN: I have another question for you. Dr. Marchand discussed the aging or wearing of some of the electrodes that had been in place for a long period of time; he demonstrated increased thresholds after two and one-half and three years. Do you feel that perhaps one explanation might be the dissolution of some non-noble metal, even when it is the nominal cathode. MR. GREATBATCH: ere again we have no hard evidence to indicate that this could be the case. With the platinum metals, none of the corrosion tests and polarization tests that we have been able to run have shown that any type of corrosion or other changes occur at the platinum surface. I don’t believe that we have been able to observe any reaction at all on platinum in any of Dr. Chardack’s cases. With platinum, we feel conservatively safe. In regard to what might happen to other materials in the body, I would hope that the sort of research we are currently conducting will someday result in the ability to look at any electrode for 2 milliseconds and then tell you specifically what will happen to it in the body in eight years. We’re a long way from that, but it’s what we would like to do. At the moment, I can’t really answer your question either way. DR. FURMAN: Can one of Dr. Marchand’s colleagues recall specifically what electrodes were referred to in this aging process. DR. OBEL: They were platinum electrodes. DR. FURMAN: Your observations, then, have led you to believe that this aging or wearing process to which you alluded can be seen in platinum electrodes as well as in non-noble metals. DR. OBEL: They were mainly platinum electrodes, both endocardial and epicardial, and occasionally a combination of the two. We don’t accept that this was the cause of the rise in threshold, of course. MR. GREATBATCH: With electrodes, we must always consider the property of