A Single Center Prospective Study in an Estimated 570 Patients Who Underwent Genetic Screening at UZ Brussel in the Context of a Primary Cardiac Arrhythmia. Patients Showing a Variant Class 3,4 or 5 in SCN4A or CLCN1 Will Undergo a Clinical and Electrophysiological Review After IC.

"we will perform questionnaire, clinical neurological exam, nEMG and if applicable short exercise test on patients with variants in genes associated with mus-cular channelopathies.~Safety Monitoring and reporting: Needle EMG is generally well-tolerated, but transient mild proce-dural pain and discomfort are widespread and the most frequent side effect that patients will ex-perience. Hematomas are infrequent and, in most cases, asymptomatic and selflimiting. Moreover, the bleeding risk is reduced by the investigator's experience, testing superficial muscles (avoiding complications like compartment syndrome), and by not conducting an EMG when patient is treated with anticoagulants. Infectious complications at the site of needle insertion are extremely infre-quent since disposable needle electrodes are used. Needle insertion is avoided in in-jured/potential infected skin and will not be performed in immune-compromised patients and endocarditis risk."