• The primary efficacy objective is to determine that the Guardian System reduces the composite of Cardiac or unexplained death, new Q-wave MI and time to door for a confirmed occlusive event at a medical facility >2 hours [ Time Frame: Due to Bayesian statistical analysis, the study data will be analyzed after subject enrollment reaches 600, 900, 1200, etc. ] [ Designated as safety issue: No ]
  
• The primary safety objective is to demonstrate that the proportion of implanted subjects who are free from system-related complications at six months post programming is at least 90%. [ Time Frame: Due to Bayesian statistical analysis, the study data will be analyzed after subject enrollment reaches 600, 900, 1200, etc. ] [ Designated as safety issue: Yes ]
  

• - Reduction of the incidence of cardiac death or unexplained death during follow-up - Reduction of the incidence of "New" Q-wave myocardial infarction in one or more distributions during follow-up - Reduction of the time to door for confirmed STEMI [ Time Frame: Due to Bayesian statistical analysis, the study data will be analyzed after subject enrollment reaches 600, 900, 1200, etc ] [ Designated as safety issue: No ]
  

There are over one million acute myocardial infarctions (AMI) each year in the United States with more than 400,000 of these resulting in death. Early identification of AMI, and prompt treatment has been shown to significantly improve clinical outcomes. Experimental and clinical studies have shown that most of the irreversible damage to the myocardium occurs during the first two hours after coronary occlusion. Milavetz et al. demonstrated that successful reperfusion therapy within two hours was associated with the greatest degree of myocardial salvage. According to Boersma, et al., restoration of flow, regardless of the method used, can abort infarction within the first 30 minutes after coronary occlusion, and the benefit of fibrinolytic therapy compared with placebo is considerably higher in patients treated within 2 hours after symptom onset than in those treated later.2 Further, evidence exists that expeditious restoration of flow in the obstructed infarct artery after the onset of symptoms in patients with the most severe type of MI, ST elevation MI (STEMI) is a key determinant of short and long-term outcomes regardless of whether reperfusion is accomplished by fibrinolysis or percutaneous coronary intervention (PCI). , , Therefore, the early arrival at the hospital for a reliable diagnosis and initiation of treatment is paramount to improve the outcomes of myocardial infarction. However, despite efforts at educating the public over the past decade, the mean time from AMI symptom onset to arrival at a hospital for treatment has remained, disappointingly, at 2.5-3.0 hours.1,4,7

The largest proportion of the total pre-hospital delay is the interval between the onset of symptoms and the decision to seek medical treatment. Finnegan et al. described that the reasons for delay in seeking medical evaluation generally stem from patient misconceptions about symptom experience, expectations, and attribution. In many cases, patients expect the type of heart attack that they often see in movies or on television: the kind of crushing chest pain that drops a person to the ground. The reality is that many heart attacks are much "quieter," causing only mild chest pain or discomfort or other symptoms such as shortness of breath or diaphoresis.

If patients would take action during the first hour following symptom onset, many lives and significant cost could be saved. It is technically possible to monitor EKGs and detect an acute infarction, even if the patient is unaware that he or she is experiencing a heart attack. However, currently available systems have limitations in the home environment. Twelve lead EKG systems require a clinically trained individual to place them. Holter monitors suffer from limitations in the ability to detect ST deviation due to low compliance and are limited in practice to 24 to 72 hours of monitoring. Systems using surface leads are all subject to noise and other artifacts from patient movement and body orientation, particularly if the patient is ambulatory.

A potentially ideal solution is to implant a device that measures heart signals from inside the heart and will alert the patient when it detects electrogram characteristics set by the physician as worthy of medical evaluation.