I've been dealing with this all summer with my 7 year old male basset,Artie. Our vet decided that the best
course of action would be to administer one shot, then wait six weeks, under strict activity restrictions before
doing the usual treatment of two shots over two days followed by six more weeks of restriction. Thank God he did. One week after the first shot, my female 8 year old went to the bridge and that night there was a severe thunderstorm. Artie is petrified of thunder. This combined stress was all it took for him to suffer a collapse from an inflamed pulmonary artery. He was placed on prednisone for about four weeks before the second round of heartworm shots. That second round was three weeks ago and he has been fine this time. In fact, they did a series of chest x-rays before the second round and said his lungs looked even better than thay had before treatment began.
Our vet never mentioned doxycycline or infection form the dead heartworms. The dead/dying heartworms can break off and cause problems such as Artie had which is why the strict activity restrictions are needed. Its not easy to do , but it can be done. Artie is a very anxious and high energy guy and had been used to two mile walks to burn it off. He's only now starting to be restless and grumpy from the lack of activity, but plenty of belly rubs and brushing seem to be placating him for now. As far as keeping him calm, our vet okayed calms forte for situations which cause added stress such as thunderstorms, fireworks, etc. We had some work done in the house and I gave it to him then as well, and it helped as he's not thrilled about men he doesn't know and it worked wonders. The first two or three days after the treatment, he did alot of whining and really had trouble finding a spot to be comfortable in. He took rimadyl for five days each time and absolutely would not allow anyone to touch the area where they shaved him for the injections. Other than that one collapse, this seemed to be his only real problem.
I hope this information is of some help to you. It can be very frightening, but if your Elvis can handle the activity restrictions I'll bet he'll do fine. Hope it all goes well for you both!
Bridget