The purpose of this prospective, non-randomized, single arm, event-based, multicenter trial is to assess: (1) the diagnostic accuracy of the device, (2) the compliance of the prescribing physician, (3) the experience of the implanting physician, (4) the experience of the emergency department physician and (5) the patient compliance for Emergency and See Doctor alerts. The adequacy of the training program for the prescribing physician, implanting physician, emergency department physician, and patients will be assessed.~A minimum of 500 patients who have had prior ACS events and who remain at high risk for recurrent ACS events will be enrolled in the PAS, for the purpose of accruing 314 adjudicated True Positive (TP) or False Positive (FP) ACS events. These ACS events will contribute to the Positive Predictive Value (PPV) and false positive rate (FPR) endpoints of the study. The PAS will be completed once the 314 ACS events have been collected and adjudicated.
500 Patients (minimum) will be enrolled following commercial implant. Will be treated by their physicians using the standard of care.~Standard of care for the Guardian includes an in-office initial programming visit 7-14 days following implant and every 6 months.