I'll make a linguist's answer since I do not belong to the medical profession.
I've done a search on the question and I have noticed that it is more often called torsades de pointes than torsade de pointes. I expect some justify the plural because several torsades are shown on the ECG. It most likely does not affect the choice between de and des.1
I thought at first the pointes were referring to the peaks shown on the ECG, I was totally wrong, the ultimate findings in my research show that the name torsade de pointes was given because:
This was symbolically termed torsade de pointes, or "twisting of the point" about the isoelectric axis, because it reminded the authors of the torsade de pointes movement in ballet.2
This strengthens my conviction that we are referring to some pointes (no definite article) and not to all (des (de+les)).
1 e.g Torsades de pointes on Site de formation à la lecture de l'ElectroCardioGramme.
2 Numerous references can be found on the Internet. Here's one in a research paper.
And to finish on a more literary note I point to this poem I stumbled upon doing my research, published in the Journal of the American Medical Association: Torsades de Pointes