Cardiomyopathy has a base rate in the study population of 0.3%, 0.06% for sudden cardiac arrest. No mention of test sensitivity/specificity, adverse effects of whatever treatments, etc.

Getting the test can be a challenge. An ECG is very basic technology at this point, but getting one performed and interpreted is expensive. Your doctor won’t typically order one (so insurance can cover it) unless you’re having some issue that needs the test as a standard step. And hospitals won’t just perform a test you want even if you are willing to pay. So if you just want an ECG as a preventative diagnostic test, you’re out of luck.