My Husband Had A Non Conclusive Stress Test A Month

My husband had a non conclusive stress test a month ago because of increasing of tachycardia. He is on Toprol and takes a baby aspirin. Yesterday he had an echocardiagram which cardiologist recommended. My husband said he did not want anything with a radioactive type dye due to his hx. of radiation for prostate cancer many years ago. During echo stress test the tech injected something into him several times saying it was to make the pictures clearer. He suddenly experienced an odd feeling while on treadmill.Pulse jumped to 212 and despite several attempts by MD to inject with meds to get it down, his pulse did not go below 152. He was feeling better and I was told to take him directly to local ER and after an hour or so all was OK. He was told he had cardiac arrythmia. Did this dye cause his pulse to jump that high? what was in the dye used? Why did she do repeated injections? Was she really trying to get a clearer picture or was she trying to force an increase in his heart rate to see what would show up on the ultrasound? we are awaiting an appt to see his cardiologist next week