Not everyone who has HCM needs a device to shock the heart. An EP Study along with 48-72 hour Holters should be done to see if you are having arrhythmia problems first. A family history of sudden death is also important. Try and keep in mind that no doctor can tell you when you will develop heart failure which is a chronic condition. Some people live years with this disease and some do not, it just depends, especially on your age. (the disease tends to get worse during growth spurts such as through childhood and adolesence)
Difibulator is a device that shocks with an electrical impulse to restart heartbeats when the heart stops beating.
Major heart failure is not a arrhythmetic problem, but it has more to do with the inability of the heart to adequately pump blood into the system to meet blood/oxygen demand. HOCM can cause a deficit of blood supply due to thickened heart chambers that reduces (obstruction, restriction) filling capactity and the pumping function is compromised and the reduction of blood supply causes heart failure.
Sometimes the thickened chamber walls may cause interruption to impulse pathways causing arrhythmia and secondary to heart failure. Treatment (medication) for heart failure is to reduce the heart's workload, blood volume, increase contractions, etc. There is an interventional process that removes some of the excessive mass of the heart walls tha can be beneficial.