I had endocarditis once. I had a picc line for 2 months. I used coke and heroin through it once, but stopped when I learned how crazy dangerous it was. Apparently, when impurities are delivered straight to the heart (the picc line ran into my right heart valve), it can be lethal. To be honest, I forgot the technical reasons, but they made enough sense at the time for me to overcome my desire to use it for such purposes. Something about precipitants causing massive strokes or heart attacks from blockage, as well as serious lung damage, IIRC.
I will say that the rush of injecting straight into the heart was even more intense than a regular injection...but it just wasn't worth dying over.
Now, towards the end, my picc line came out. I had a replacement that did not feed directly into my heart, so I did use those 5CC saline flush syringes to shoot coke. I also almost killed myself because of how easy it was. It really takes the compulsion to a whole different level with that kind of access (just screw it on and push!). I was even able to keep a full 5CC saline flush syringe filled to the top with a heroin-cocaine mixture, and could take that with me in public....... All I had to do was excuse myself for 30 min to go to the bathroom and screw it on. But since I had to carry my antibiotics with me (and had to hook it up while I was out and about), I also had to carry around extra flush syringes, so it made having one filled with drugs too easy.
My advice would not be to do it. It got bad very quick.
I'll give you one example of why it was a bad idea: After I had my temp line removed, I fished it out from the trash, and kept using it since I was so hooked on that particular coke delivery method. The needle was large and dull, and could have seriously messed up my arm. One night, after spending 30 minutes trying to get it in, I accidentally shot the entire dose, which was meant to be spread out over the entire night. I forgot exactly how much it was, but it was around 3 grams. Luckily, the shot missed, otherwise I probably wouldn't be here right now.
Funny story though, I ended up in rehab 2 days after that, and my cocaine "lump" was still slowly absorbing when I got there........ had a decent buzz going for several days lol.