In rare cases, endomyocardial biopsy guided by the results of other diagnostic modalities may be helpful in the diagnosis of myocarditis, ARVC or cardiac masses.

The discovery of mutations in genes associated with specific cardiac ion channels or cardiomyopathies has spurred interest in genetic testing to diagnose, risk stratify and guide the management of SCA survivors and their families. However, there are major caveats to the use of genetic testing, not least is the poor negative predictive value (a negative test does not exclude the presence of an inheritable arrhythmic syndrome) and the low yield (and unfavorable cost-effectiveness) of routine indiscriminate genetic testing without a defined clinical phenotype. Hence, genetic testing can only be recommended as an adjunct to phenotypic testing in SCA survivors. The result of the genetic testing (guided by the clinical phenotype) can be used to identify other family members who have inherited that particular mutation and at risk of developing the disease (cascade screening). This is the primary purpose of conducting targeted genetic testing.

An underlying structural heart disease can be uncovered in the majority of SCA survivors from routine diagnostic testing. For the minority of patients without evident structural heart disease, a systematic use of invasive and non-invasive clinical testing, in particular provocative drug testing and advanced cardiac imaging can uncover a diagnosis and direct genetic testing to identify genetically-mediated arrhythmia syndromes.