Ventricular Arrhythmias Incidence According to Sleep Apnea Syndrome in Implantable Cardioverter-Defibrillator (ICD) Patients

Inclusion Criteria: * Patients who are at risk of sudden death due to ventricular arrhythmia and who satisfy at least one of the following criteria are eligible for enrolment: * Class I indications for ICD * Survival of at least one episode of cardiac arrest due to VT or VF not due to a transient or reversible cause, or presumed to be due to VF when electrophysiological testing is precluded by other medical conditions; or * Spontaneous sustained ventricular tachycardia, or * Syncope of undetermined origin with clinically relevant haemodynamically significant sustained VT or VF induced at electrophysiological study when drug therapy is ineffective, not tolerated or not preferred, or * Class IIa Indication for ICD * Non-sustained VT with coronary disease, prior myocardial infarction, left ventricular dysfunction (≤ 40%) and inducible VF or sustained VT at electrophysiological study. * With prior myocardial infarction and LVEF less than 30 % (without prior life-threatening arrhythmia or sustained VT). * Patients candidate for cardiac resynchronization therapy (CRT) need to be in functional Class III or IV of the NYHA classification. Patients will be included only after having granted their informed consent to participate in the study, preceded by the delivery of appropriate information Exclusion Criteria: * VT/VF is associated with drug toxicity, electrolyte imbalance, hypoxia, electrocution or other reversible cause; * VT/VF occurred during the acute phase of infarction (\< 1 week) or during an unstable ischemic phase; * Incessant VT/VF; * Implanted pacemaker that is not going to be explanted or otherwise disabled; * Inability or refusal to provided informed consent * Tricuspid valvular disease or tricuspid mechanical heart valve (lead contraindication); * Unable to understand the purpose and plan of the study; * Geographically unstable or not available for follow-up as defined in the investigational plan; * Reduced life expectancy (≤ 1 year) for other than cardiovascular reasons; * Patient participating in another clinical study; * Patient of minor age (\< 18 years); * Pregnancy (Women of childbearing potential are required to have a negative pregnancy test within seven days prior to enrollment).