Physical Activity and Ventricular Arrhythmias

In this study, participants will be randomly assigned to either take part in the exercise program or serve as control and live as usual. At baseline study visit, study researchers will review medical records to collect various information, including the reason for needing an ICD, the type and settings of the ICD, medication use and medical history etc. All participants will undergo blood collection, complete a questionnaire to assess quality of life and undergo examination with echocardiography and ECG. The ICD will be programmed accordingly to international guidelines regarding ICD-therapy and optimal monitoring, before each participant complete an exercise treadmill test to determine VO2 peak. They will wear a Holter monitor to record heart activity 48 hours before the test and 24 hours after the test. All participants will then be observed for 2 months before being randomly assigned to either intervention or control. During this observation period, they will wear a fitness activity tracker wristband to evaluate degree of physical activity and a Holter monitor to register number of premature ventricular contractions. Participants taking part in the interval training group will perform aerobic interval training 4 x 4 minutes intervals, 3 times a week for 12 weeks (week 1-12), whereas participants taking part in the control group will carry on with usual daily life with no lifestyle recommendations. All participants will then undergo a new period of observation (week 13-20) and repeat the tests and examinations performed at baseline and during the observation period prior to intervention/control.