The following is not a theory and not intended to form part of a theory. It is just a discussion of an idea.

I was working on this idea for a while which seemed like a dead end, but I thought I’d post it up here just for the sake of it. Others may have their own ideas which could mesh.

Suppose for a moment that the Zodiac was suggesting an ECG with that card symbol in a stylized sense. I realize it is not a precise match which is why I say "stylized".

Based on this supposition, I wondered if the letters used to describe the different wave forms could have been intended as a clue.

The pattern corresponds with the QT interval, comprising the QRS complex and the ST segment. So we have QRST, although in the case of the Zodiac symbol the ST segment has strangely been doubled. It is possible that the Zodiac was suggesting that the QRST wave sequence had been lengthened considerably due either to an illness or the taking of psychotropic drugs. The only way a patient would present with such an abnormally long wave sequence would be due to very high doses of certain psychotropic drugs or some kind of chronic ventricular tachycardia disease.

Those who believe that the Zodiac may have been into Satanism will love this ECG idea, because I recall reading somewhere that the letters "QRST" are part of some Satanic alphabet and together mean "Christ Cursed" or some such nonsense. I am not at all familiar with Satanism so I’ll leave this for others to wrangle over.

I did wonder if the Zodiac may have worked in a hospital as an orderly, security guard, groundsman or wards man, laundry worker or in the morgue and was trying to leave a vague clue in this regard. It is possible that he was also an occasional patient at a hospital. The Zodiac seems to have been interested in circuitry so it is logical to assume that if he had ever spent time in a hospital environment the gadgetry would have intrigued him.

An electrocardiograph is a representation of a graphical wave form that relates to the human circulation system. The technology of electrocardiograms involves a particular kind of radial vector analysis and an understanding of how this relates to the corresponding circuitry. I have never delved into it as it is all very complicated (and boring!), but I wondered if perhaps there could be some relationship to the codes/ciphers, bomb diagrams and maps. The symbol could have been providing a unique scale reference for a particular map, for instance. Again I will leave that for others to wrangle over. I scratched my head at it, even though the whole idea seemed plausible and probably not too far-fetched.

Here’s a brief but good outline of ECG. https://en.wikipedia.org/wiki/Electrocardiography Scroll through all of the images on this page.

More stuff here: http://jhcedecg.blogspot.com.au/p/ecg-reference-notes.html

More detailed stuff here: http://www.duhs.edu.pk/curriculum/downloads/lec6-sem2-CVSWK3-20140920.pdf