This study evaluates whether a rigorously controlled high-normal level of serum-potassium (4.5-5.0 mEq/L) using dietary recommendations, potassium supplements and mineralocorticoid receptor antagonists will results in a lower incidence of cardiac arrhythmias in patients with an ICD. Patients will be randomized to this treatment or a control arm, where patients will receive usual guideline recommended follow-up.

There is solid evidence that potassium-sparing drugs increase survival and ameliorates symptoms in heart failure patients and post-hoc studies have suggested that high-normal levels of blood potassium levels (p-K) markedly decreases the risk of malignant arrhythmias in cardiovascular patients.

This trial will randomize patients implanted with implantable cardioverter defibrillators (ICDs), who remain at high risk of life-threatening cardiac arrhythmias, to a standard therapy or standard therapy plus a regimen to keep high-normal p-K levels. The study will enroll 1,000 patients from the outpatient pacemaker clinics at Rigshospitalet and Gentofte hospital. Using a planned regime to increase p-K using inexpensive drugs and potassium supplements, the patients enrolled and followed with regular controls as well as continuous monitoring using existing home monitoring systems over a period of 4 years for the primary endpoint of appropriate ICD therapy and all cause mortality. Including analysis, the trial will be running for 5 years

Inclusion Criteria:

• Implantable cardioverter defibrillator (ICD) or cardiac resynchronization pacemaker with ICD (CRT-D).
• Age >18 years

Exclusion Criteria:

• Estimated glomerular filtration rate (eGFR) <30 ml/h
• Pregnancy
• Lack of ability to understand and sign informed consent