急性冠脉综合征 (Acute Coronary Syndrome)

 

1. Introduction

Acute Coronary Syndrome (ACS),  is used to describe a spectrum of conditions resulting in acute myocardial ischemia. Acute myocardial ischemia is chest pain due to insufficient blood supply to the heart muscle, which results from coronary artery disease (CAD), which is also referred to as coronary heart disease (CHD).

ACS is comprised of 3 categories of disease; these categories are stratified by risk and ECG pattern:

· ST segment elevation myocardial infarction (STEMI)

· High-Risk unstable angina (UA) or Non-ST segment elevation myocardial infarction (NSTEMI)

· Intermediate / Low-Risk Unstable Angina (UA)

ACS is often the first presentation of CAD, which is the leading cause of morbidity and mortality in the industrialized world. By the age of 60, every fifth man and one in 17 women have some form of this disease. It has been estimated that one third of the 13 million individuals living with CAD in North America present to the emergency department (ED) with ACS each year.

Figure A:  Acute Coronary Syndromes

 
 

2. Treatment of Acute Coronary Syndromes (Algorithm)

The AHA Acute Coronary Syndromes Algorithm to allow for the maximum benefit for myocardial salvage. The new algorithm provides for early management of UA and STEMI to improve patient outcome.

1. The following treatments are used for ACS:

· Oxygen

· Aspirin

· Nitroglycerin

· Morphine

· Fibrinolytic (thrombolytic) therapy

· Heparin

The primary goal in the treatment of ACS is prompt identification and treatment. STEMI is the ACS category that carries the highest risk and acute treatment involves early reperfusion therapy.

Reperfusion therapy is central to the treatment of ACS, particularly STEMI. It involves the attempt to re-open an occluded coronary artery using fibrinolytic (thrombolytic) therapy, percutaneous coronary intervention (PCI), or bypass surgery.

PCI: This involves performing a coronary angiogram to determine the anatomical location of the occluded vessel, followed by balloon angioplasty and frequently stent placement.

Fibrinolytic or Thrombolytic therapy: These medications must be administered within 12 hours of the onset of symptoms. The effectiveness of these therapies is highest in the first 2 hours. After 12 hours, the risk associated with these therapies outweighs any benefit.

 

3. Conditions that can lead to ACS

Unstable Angina (UA): The definition of unstable angina is largely based on clinical presentation. Whereas stable angina manifests as a reproducible, deep, poorly localized chest or arm discomfort (rarely described as pain), UA is defined as angina with at least one of the following key features:  

· Severe pain that is new in onset

· Occurring with a crescendo pattern (i.e., more severe, prolonged, or frequent than previously)

· Occurring at rest or with minimal exertion and lasting >20 minutes (if not interrupted by nitroglycerin administration)

The initial goal of treatment of UA involves relief of chest pain using morphine, oxygen, nitrates, and aspirin (MONA). Definitive treatment of UA often involves heparin or low molecular weight heparin (LMWH).

Microemboli: This are composed of cholesterol, calcium, and platelets from proximal atherosclerotic plaques. When they become dislodged from a plaque, they can occlude the coronary microvasculature, leading to small elevations of cardiac troponin.

Occlusive Thrombus: A thrombus or blood clot that forms within the wall of a coronary vessel can grow to entirely or partially occlude the flow of blood to the heart. When myocardial demand exceeds myocardial supply, myocardial ischemia occurs, which can lead to STEMI.

Unstable Plaque: Rupture of an unstable atherosclerotic plaque can lead to ACS by occluding a downstream coronary vessel.

 

4. Signs and Symptoms of Ischemia

It is essential that first responders recognize the type of chest pain that represents ACS. Although some patients may describe actual chest pain, others may describe a feeling of tightness or pressure. The following symptoms may indicate ACS:

· An uncomfortable feeling of pressure, tightening, fullness, squeezing, or pain in the center of the chest. These feelings typically last for several minutes or more.

· Discomfort originating in the chest, but spreading to the shoulders, neck, one or both arms, or jaw.

· Discomfort originating in the chest, but spreading to the back or between shoulder blades

· Chest discomfort accompanied by lightheadedness, fainting, sweating, or nausea

· Unusual episodes of shortness of breath – these episodes may arise suddenly, and may occur with or without chest pain

After identification of ischemia, field personnel should follow the guidelines in Box 2 of the Acute Coronary Syndromes Algorithm while preparing the patient for transport to an ED.

 

ACS patients can be classified into three categories based on the appearance of the ECG:

· ST segment elevation

· ST segment depression

· Non-diagnostic / normal ECG

 

5. EMS Assessment, Care, and Hospital Preparation

Field personnel should follow these steps when treating an ACS patient:

• Monitor the ABCs of ACLS Survey
  • Monitor vital signs and cardiac rhythms
  • Administer CPR if needed
  • Defibrillate if necessary
• Administer aspirin, nitroglycerin, and morphine (if patient in discomfort and not responsive to nitrates)
• Consider oxygen delivery if O2 saturation below 94%
• Obtain and interpret 12-lead ECG
  • ACS patients can be classified into three categories based on the appearance of the ECG:
    • ST segment elevation
    • ST segment depression
    • Non-diagnostic / normal ECG
• Complete fibrinolytic checklist (if needed)
• Notify hospital

EMS providers must be aware of the cautions, indications, actions, and treatment of the adverse effects that may result from these medications.

Aspirin: 325 mg of aspirin (ASA) should be administered to patients to chew. ASA has better absorption rates when it is chewed rather than swallowed, especially when accompanied by morphine administration. Note: Relative contraindications for oral ASA administration include: aspirin or salicylate allergy, history of gastrointestinal (GI) bleed, kidney disease, hyperuricemia, and gout. Patients with vomiting or nausea may be given an ASA suppository. Patients with upper GI disorders such as peptic ulcer may be given ASA suppositories.

Nitroglycerin: Three sublingual nitroglycerin tablets should be administered at 3 to 5 minute intervals for the treatment of ongoing ACS symptoms. Nitroglycerin should only be administered if the patient is hemodynamically stable; the administration of nitroglycerin is contraindicated if systolic blood pressure (SBP) is less than 90 mm Hg or 30 mm Hg below the patient’s baseline. Heart rate should be between 50 and 100 beats per minute (bpm).

Because nitroglycerin is a venodilator it should be administered with the following cautions in mind:

· Inferior MI and RV infarction: Patients that have acute RV infarction are heavily dependent on the maintenance of RV filling pressures to regulate both blood pressure and cardiac output. Vasodilators and other nitrates are contraindicated in these instances.

· Patients with hypotension, bradycardia, or tachycardia: Contraindications to the use of nitroglycerine are hypotension (SBP<90 mm Hg), tachycardia (HR>100bpm), or bradycardia (< 50 bpm).

· Viagra or phosphodiesterase inhibitor use: Nitroglycerin should not be used in patients with known or suspected vardenafil or sildenafil use within the past 24 hours or tadalafil use within the past 48 hours.

Oxygen: Must be administered to all ACS patients. Oxygen has been shown to reduce ST segment elevation during anterior infarction.

Morphine: Morphine should be administered in cases of ACS that do not respond to sublingual nitroglycerin. Morphine treat ACS in several ways:

· Produces CNS analgesia, which reduces the adverse effects that result from catecholamine release, heightened myocardial oxygen demand, and neurohumoral activation.

· Decreases systemic vascular resistance (SVR), which decreases left ventricular (LV) afterload.

· Redistributes blood volume in ACS cases where there is accompanying pulmonary edema.

· Causes venodilation, which reduces left ventricular preload and oxygen demand.

 

6. Immediate ED Assessment and General Treatments

A 12-lead ECG should be obtained within 10 minutes of ED arrival. A focused cardiovascular history and physical exam is crucial to the accurate diagnosis and the subsequent delivery of appropriate care for an ACS patient. Focus should be given to the chest pain location, pattern, and severity, accompanying symptoms, duration, and alleviating measures. The goal for all STEMI patients is to receive fibrinolytic therapy within 30 minutes of ED arrival and PCI within 90 minutes of ED arrival.

 

Patient Assessment (Under 10 Minutes)

Patient assessment for the should include the following:

· Connect patient to cardiorespiratory monitor

· Establish IV access

· Obtain and review 12-lead ECG

· Complete of fibrinolytic checklist along with checking for contraindications

· Obtain a blood sample for initial cardiac marker, electrolyte, and coagulation levels (the results from blood sample studies should not delay reperfusion therapy except in cases in which they are clinically necessary)

· History and a physical exam

· Obtain and review a portable chest x-ray (this should occur within 30 minutes of ED arrival and should not delay fibrinolytic therapy for the treatment of STEMI)

Treatment (MONA)

The following treatments should be administered if no contraindications exist:

· Morphine (if patient is in pain and no response to nitrates)

· Oxygen (if oxygen saturation below 94 % or patient shows signs of heart failure)

· Nitroglycerin

· Aspirin

 

7. ACS Classification

ACS classification is based upon the pattern on 12-lead ECG:

1.) ST Segment Elevation Myocardial Infarction (STEMI) is diagnosed if there is ST segment elevation greater than 1 mm (0.1 mV) in 2 or more contiguous precordial leads or two or more adjacent limb leads or by new and presumed new left bundle branch block.

2.) High-Risk Unstable Angina (UA) / Non-ST Segment Elevation Myocardial Infarction (NSTEMI) is diagnosed if there is ST segment depression of 0.5 mm (0.005 mV) or greater dynamic T-wave inversion, associated with chest pain or discomfort. Also included in this category is non-persistent or transient ST segment elevation of 0.5 mm or greater.

3.) Intermediate / Low-Risk Unstable Angina (UA) Patients with normal ECGs are included in this category, along with patients with ST segment deviation of less than 0.5 mm (0.05 mV) or T-wave inversion of 2 mm or 0.2 mV or less.

Note: A small percentage of patients with normal ECGs may be having an acute myocardial infarction. If a patient continues to experience ischemic symptoms, but the ECG is non-diagnostic, the ECG should be repeated.

 

STEMI:

STEMI is the category of ACS with the highest risk. Patients with STEMI generally have complete blockage of an epicardial coronary artery. In cases of STEMI, EARLY reperfusion therapy is critical. Rapid reperfusion times correspond to lower mortality rates. There are two types of reperfusion therapy: fibrinolytic therapy and PCl.

Unstable Angina (UA):

· High risk UA

· Intermediate risk UA

· Low risk UA

 

8. Early Reperfusion Therapy

Patients with STEMI must be rapidly identified and screened for indications and contraindications to fibrinolytic therapy. A fibrinolytic checklist should be used if required. The physician who first treats a patient with STEMI should interpret the 12-lead ECG readings and determine the risk of reperfusion therapy. After this the physician must then direct administration of fibrinolytic therapy or PCI.

Patients meeting the criteria for fibrinolytic therapy should be treated in under 30 minutes of arrival at the hospital

Patients that meet the criteria for PCI should be treated in under 90 minutes of arrival at the hospital.

 

9. Fibrinolytic Therapy

Fibrinolytic therapy is administered to patients who have more than 1 mm ST segment elevation in two contiguous leads on ECG. Reperfusion occurs in approximately 50% of patients who receive fibrinolytic therapy. Tissue plasminogen activator (tPA) reteplase, and streptokinase are three examples of fibrinolytic medications. Streptokinase was the first fibronlytic indicated for STEMI and it remains a mainstay in reperfusion therapy.

Patients may be screened for fibrinolytic therapy with the following checklist:

 

Figure B: Fibrinolytic Therapy Checklist

 

PCl

Primary PCl is another reperfusion therapy used as an alternative to fibrinolytics. PCl is used on patients who do not reperfuse in response to fibrinolytic therapy. PCl has been shown to produce better patient outcomes than fibrinolytic therapy.

 

10. Adjunctive Treatment

Adjunctive treatment for STEMI is used in addition to MONA and fibrinolytic therapy. Adjunctive treatment for STEMI includes:

· Heparin

· IV nitroglycerin

· Clopidogrel

· Beta blockers

· Angiotensin converting enzyme (ACE) inhibitors

· HMG coenzyme inhibitor therapy

IV Nitroglycerin: Although IV nitroglycerin has not been shown to significantly reduce the mortality of STEMI patients, however it can be used to treat conditions that accompany STEMI. IV Nitroglycerin may be indicated in the following cases:

· STEMI complicated by hypertension

· Pulmonary edema complicating STEMI

· Continued chest discomfort that is unresponsive to spray nitroglycerin and morphine or SL

IV Heparin: Heparin may be administered as an adjunct to PCI and fibrinolytic therapy.