Stent implants should supply sufficient blood to the deficit area from blocked vessels, and there should not be any angina! Heart attacks do not any specific pain or location of pain, in fact there a heart attack can happen without any symptoms. It is termed a silent heart attack...I had that happen and the only sympoms I had was congested heart failure.
The high number with blood pressure is the amount of resistence the heart has to pump against such as constricted (narrow) blood vessels. The lower number is the pressure when in the filling stage. You are correct 45 is too low, and a very low pressure can cause on to faint or feel light headed. There may be a medication problem, or no problem just an artefact.