welcome to HCM,
as per the details u have submitted,
it is clearly showing that your father is getting dangerous ventricular arrythmias , thats why the ICD (implantable cardioverter defib) is giving shocks to regularize the heart rythm.. so i advise you to consult a cardiologist
and take the opinion in this regard..
he will be monitored throgh a holter monitoring system ...and he will be treated accordingly..
coming to the ejection fraction
, your father has low ejection fraction before surgery , becoz of weak ventricular myocardium , which has became weak due to reduced blood supply by heart attack
, now he has underwent bypass, and ejection farction has improved...
hope i have cleared ur querries...