Can i use a continuous hr monitoring device like fitbit to predict chances of a cardiac arrest or similar issues.

No: If you are concerned about this you should speak with your physician. If you are asymptomatic with no family history of heart problems your risk of a cardiac arrest at age 34 is negligible. Heart attacks rarely occur below age 40, with some exceptions. Other causes of "cardiac arrest " occur but are NOT at all common, such as: cardiomyopathy, myocarditis and conduction(electrical)problems.