STEMI Systematic Review Research Paper

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door to balloon time is an important determinant of the prognosis of STEMI patients. To reduce D2B times, most centers implement a pre-hospital triage which involves the use of pre-hospital ECG to allow direct transfer of patients with confirmed STEMI to the PCI lab. Since most health facilities do not have PCI laboratories, a quick decision needs to be made regarding fibrinolytic therapy or transfer to a PCI facility. The most important factor determining this decision is the time taken from the onset of symptoms to arrival at a hospital facility and the predicted time duration for effective transfer. Through this systemic review, we sought to analyze the role of pre-hospital management in door to balloon time (D2B), door to needle (D2N) time and the long-term mortality of STEMI patients.

Since pre-hospital delay is responsible for the greatest time loss, and is indeed the most variable factor, we tried to determine the role of symptom to balloon time (S2B), or first emergency contact to balloon time (E2B) rather than door to balloon times as an important determinant to PPCI or thrombolysis.

METHOD: A total of fifty studies, of world's literature, were identified regarding STEMI. Thirty articles met our inclusion criteria and were used. The MOOSE guidelines were used to assist the review. Relevant data was used to create tables and figures, which summarized the effects of pre-hospital management.

RESULTS: All studies provided positive evidence towards a pre-hospital ECG improving D2B times and improving the overall mortality of STEMI patients. EMS transport helped in reducing D2B times when compared to private transporters due to the use of a pre-hospital ECG. However, the D2B time only accounted for 29.7% of the total time to treatment.

CONCLUSION: Since majority of the time is spent at the scene and during transport, a preferable measurement would be S2B or E2B.

BACKGROUND INFORMATION:

Myocardial infarction is an irreversible change caused by acute ischemic necrosis of an area of the myocardium. This ischemic necrosis is the result of a critical imbalance between coronary blood supply and myocardial oxygen demand. It is the most common cause of death in the United States and a leading cause of death in most developed nations. Most patients who have fallen victims to an MI are elderly; however, due to an inclining trend towards a sedentary lifestyle amongst most people, MI is beginning to appear in younger patients as well (Boon, Colledge & Walker, 2010).

The pathophysiology behind ischemic necrosis is coronary artery atherosclerosis with plaque rupture and superimposed thrombus formation. Rarely, infarction may also result from prolonged vasospasm, hypotension, excessive metabolic demand, embolic occlusion, vasculitis, aortic dissection or aortitis (Boon et al., 2010).

Transmural involvement is the more common type of infarction. In this type, more than fifty percent of the myocardial wall undergoes ischemic necrosis. Symmetrically peaked T. waves are characteristic of a transmural infarction. The T. waves are replaced with ST-segment elevation after several minutes. This type of infarction results from a complete thrombotic occlusion of a coronary artery. If the occlusion is not immediately relieved, pathological Q. waves may develop. The development of a Q. wave reflects a dead zone that has undergone irreversible injury. Subendocardial infarction is the other type of MI that involves lesser than fifty percent of the myocardium. (Boon et al., 2010)

MI is considered as part of a spectrum referred to as Acute Coronary Syndrome, ACS. This continuum represents ongoing myocardial ischemia and is divided into three broad categories: unstable angina, non-ST-segment elevation myocardial infarction (NSTEMI), and ST-segment elevation myocardial infarction ( STEMI). (Boon et al., 2010)

Unstable angina is caused by the formation of a non-occlusive thrombus in an area that is already affected with atherosclerosis. In this type, symptoms occur at rest with an increase in frequency, intensity and duration of episodes. Patients with unstable angina are at a high risk of developing MI. (Boon et al., 2010)

NSTEMI, also known as Non-Q wave infarction develops from high-grade but non-occlusive thrombi. ECG changes in NSTEMI include ST-segment depression and/or T. wave inversion without the evolution of pathological Q. waves. There may be some loss of R. waves in leads facing the infarct. ST-segment elevation myocardial infarction reflects active and ongoing transmural myocardial injury. Patients who do not develop a STEMI are diagnosed either with unstable angina or an NSTEMI. Both these conditions may or may not have ECG changes, such as ST-segment depression or morphological T-wave changes. (Boon et al., 2010)

The division of patients with either STEMI or NSTEMI also has prognostic significance.

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Patients with Q. wave and ST-segment changes in general have a larger area of infarction and therefore have a higher in-hospital mortality rate than with patients with NSTEMI and non-Q wave infarction. After a period of years, following an infarction, the mortality rate of NSTEMI increases, approaching that of STEMI. Therefore, it can be said that initial mortality of STEMI is higher than NSTEMI and so is the initial prognosis at the time of infarction. (Boon et al., 2010)

The recognition of symptoms of ACS is crucial for timely assessment and arrival to the hospital. It is not unusual for some patients to wait up to a few hours before calling for assistance. Reasons for this delay may be uncertainty of the severity of a specific set of signs and symptoms or fear of criticism for a false alarm. (Boon et al., 2010)

Over the last 30 years, the paradigm for the diagnosis and treatment of ACS has switched from management of complications of the disease in the critical care unit (CCU) to the detection and reversal of the pathophysiological process starting in the pre-hospital arena and continuing to the ED with the rapid transfer of selected patients to the cardiac catheterization suite.

Currently, two modes of treatment for STEMI patients are in practice. First is fibrinolytic therapy, where certain drugs are used to break up thrombus that occludes the vessel wall. The efficacy of this therapy diminishes with time. The recommended delay should not exceed beyond thirty minutes. (Harding, Mangini & Taunton, 2010)

Percutaneous coronary intervention is another mode of therapy for STEMI patients. This mode is regarded to be better in terms of clinical outcome and the thirty day patient mortality and morbidity. PCI is a non-surgical procedure in which a cardiac catheter with a balloon is inflated into a blocked artery. This restores the arterial lumen. The balloon is removed and a stent is placed in order to keep the lumen patent. According to current guidelines, the time for PCI should not exceed beyond 90 minutes from the onset of symptoms. (Harding et al., 2010)

Many health care setups do not contain facilities for PCI. These patients could be transferred to a hospital that contains a PCI laboratory or they could be managed using fibrinolytic therapy. The delay that maybe created in the transfer needs to be carefully analyzed by the emergency facility. In any case, this delay should not exceed beyond ninety minutes. Based on several researches, the ACC/ACH has also devised guidelines that minimize this delay. (Harding et al., 2010)

The management and outcome of patients with STEMI greatly depends on door to balloon, D2B or D2N time, which in turn depends on several factors, such as: time lapse from the onset of symptoms to Emergency Medical Service, EMS, call; time lapse from the EMS call to its arrival; and the time from first medical contact to balloon inflation.

The door to balloon time can also differ for patients arriving through private transport or through an emergency medical service. Several studies reveal that even though private transport can be quicker, the door to balloon time is considerably shorter for patients using an EMS. A pre- hospital ECG is one factor that shortens this time. Communicating necessary findings on an ECG or characteristic symptoms through a paramedic to the emergency facility minimizes ER stay, allowing quicker transport to a PCI facility. Also, direct arrival of an EMS service to a PCI laboratory enables to shorten the delay caused from transporting a STEMI patient from a STEMI referring facility to a STEMI accepting hospital that contain PCI facilities. (Boon et al., 2010)

Helicopter Emergency Medical Service, HEMS, can be used for faster transport, in cases where land EMS cannot reach on time. Data on the usefulness of this mode of transport is relatively less as compared to land EMS.

REVIEW OF CURRENT GUIDELINES:

Due to the crucial role of door to balloon time in the prognosis of patients with STEMI, and compiling clinical studies regarding different protocols, clinical guidelines have changed almost annually for the past few years. The advantage of these guidelines and updates is that they have critically analyzed and compiled extensive amount of information available through research and clinical trials, and have provided evidence-based recommendations necessary for management.

Current guidelines state that patients who develop symptoms of ACS should be immediately transferred to the emergency department or to a facility that is capable of acquiring a 12 lead ECG….....

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