The ICD is meant to maintain a normal heartbeat rate, and prevent irregular beats. The irregularity can cause the heart to go into an arrhythmia or cardiac arrest. The underlying cause is an electrical impulse disarry possibly due to obstruction of electrical pathways to the heart cells. The disarry can be due to an enlarged heart chamber, damaged heart muscle, etc. Many people lead a normal or near normal life with an ICD.
An EF is an esitmate of the fraction of blood pumped out of the left ventricle with each heartbeat (normal is 50 to 70%). Usually, the problem is due to damaged heart cells that weaken chamber contraction to pump blood. You have a history of blocked coronary vessels, and the blockage may have caused heart cell damage by lack of blood/oxygen to the heart tissues for a period of time.
EECP helps some individuals (70%) if one has blocked vessels...but medication to dilate vessels is the first option. Stem cell therapy could help restore damaged heart muscle...I don't have any information on the status of research or therapy.
It is difficult to establish a prognosis for a heart condition because there are so many variables that include the general health otherwise, life style, diet, exercise. etc.
Six years ago I had enlarged left ventricle, an EF of 19 to 29%. Currently with medication my heart is normal size and EF is 55%.