Myocardial Infarction Clinical Keys

Yasmine S. Ali, MD          November 13, 2020

Myocardial infarction (MI) is one of the leading causes of death worldwide for men and women of all races. More than 800,000 MIs occur in the United States each year. Commonly referred to as "heart attack," MI is the irreversible death (necrosis) of heart muscle secondary to prolonged lack of oxygen supply (ischemia). MI usually results from an imbalance in oxygen supply and demand, which is most often caused by plaque rupture with thrombus formation in an epicardial coronary artery, resulting in an acute reduction of blood supply to a portion of the myocardium.

In response to the ongoing COVID-19 pandemic, the American College of Cardiology (ACC) released guidance regarding cardiac implications. Among the recommendations was a reminder to providers that classic symptoms and typical presentation of acute MI may be overshadowed in the context of COVID-19, leading to underdiagnosis.

Which of the following is most accurate regarding the presentation of MI?

Your Peers Chose: 

In some individuals, the only reported symptom of MI is epigastric pain[*]

 78%

Most MIs occur in the evening, typically after the final meal of the day

 5%

Pain that radiates above the chest and into the neck, shoulder, and jaws strongly suggests a diagnosis other than MI

 14%

 A positive family history requires at least two male or female relatives aged 60 years or younger who experienced an MI

 3%

Patients with typical acute MI usually present with chest pain and may have prodromal symptoms of fatigue, chest discomfort, or malaise in the days preceding the event; alternatively, typical STEMI may occur suddenly without warning.

The typical chest pain of acute MI is usually intense and unremitting for 30-60 minutes. It is retrosternal and often radiates up to the neck, shoulder, and jaw and down to the left arm. The chest pain is usually described as a substernal pressure sensation that is also perceived as squeezing, aching, burning, or even sharp. In some patients, the symptom is epigastric, with a feeling of indigestion or of fullness and gas. This may be the only reported symptom of MI in some patients.

MI occurs most often in the early morning hours. Mechanisms that may explain this circadian variation include the morning increase in sympathetic tone leading to increases in blood pressure, heart rate, coronary vascular tone, and myocardial contractility; the morning increase in blood viscosity, coagulability, and platelet aggregability; and the increased morning levels of serum cortisol and plasma catecholamines leading to sympathetic overactivity, thereby resulting in increased myocardial demand.

A high index of suspicion for MI should be maintained, especially when evaluating women, patients with diabetes, older patients, patients with dementia, patients with a history of heart failure, cocaine users, patients with hypercholesterolemia, and patients with a positive family history for early coronary disease. A positive family history includes any first-degree male relative aged 45 years or younger or any first-degree female relative aged 55 years or younger who experienced an MI or required coronary revascularization.

Symptoms of MI include the following:

• Anxiety, commonly described as a sense of impending doom

• Pain or discomfort in the arms, left shoulder, back, neck, jaw, or stomach

• Lightheadedness, with or without syncope

• Cough

• Nausea, with or without vomiting

• Profuse sweating

• Shortness of breath

• Wheezing

• Rapid or irregular heart rate

• Fullness, indigestion, or choking feeling

Which of the following is most accurate regarding the physical examination findings associated with MI?

Your Peers Chose: 

In patients with acute inferior-wall MI with right ventricular involvement, distention of neck veins is commonly described as a sign of failure of the right ventricle

 66%[*]

Decreased blood pressure excludes a diagnosis of acute MI

 4%

Fever associated with MI typically occurs after the initial 48 hours, and increased body temperature is typically correlated with decreased left ventricular function

 9%

A new mitral regurgitation murmur (typically holosystolic near the apex) in patients with MI indicates the presence of left bundle branch block

 21%

Physical examination findings for MI vary; one patient may be comfortable in bed, with normal examination results, whereas another patient may be in severe pain, with significant respiratory distress and a need for ventilatory support.

In patients with acute inferior-wall MI with right ventricular involvement, distention of neck veins is commonly described as a sign of failure of the right ventricle. Impaired right ventricular function also leads to systemic venous hypertension, edema, and hepatomegaly.

In general, the patient's blood pressure is initially elevated (hypertension due to peripheral arterial vasoconstriction resulting from an adrenergic response to pain, anxiety, and ventricular dysfunction). Alternatively, hypotension can also be seen. Usually, this indicates either right ventricular MI or severe left ventricular dysfunction due to a large infarct area or impaired global cardiac contractility.

Fever is usually present within 24-48 hours, with the temperature curve generally parallel to the time course of elevations of the blood creatine kinase level. Left ventricular function and peak body temperature or determined markers of inflammation are not significantly correlated.

On palpation, lateral displacement of the apical impulse, dyskinesis, a palpable S₄ gallop, and a soft S₁ sound may be found. These signs indicate diminished contractility of the compromised left ventricle. Paradoxical splitting of S₂ may reflect the presence of left bundle branch block or prolongation of the pre-ejection period with delayed closure of the aortic valve, despite decreased stroke volume. A new mitral regurgitation murmur (typically holosystolic near the apex) indicates papillary muscle dysfunction or rupture, or mitral annular dilatation; it may be audible even when cardiac output is substantially decreased.

Which of the following is most accurate regarding the definition of MI, according to the Joint European Society of Cardiology/ACC/American Heart Association/World Heart Federation Task Force?

Your Peers Chose: 

In patients with MI, myocardial injury is only considered acute if there is a rise in high-sensitivity cardiac troponin (cTn) levels, as opposed to a fall in cTn levels

 50%

Identification of a coronary thrombus by angiography distinguishes type 1 and type 2 MI

 31%[*]

 Coronary intervention-related MI requires cTn values > 10 times the 99th percentile upper reference limit

 9%

 Patients with MI may have decreased cTn values and marked increases in ejection fraction due to sepsis caused by endotoxin

 10%

According to the Fourth Universal Definition of Myocardial Infarction, detection of an elevated cTn value above the 99th percentile upper reference limit is defined as myocardial injury. The injury is considered acute if there is a rise in cTn values, a fall in cTn values, or both.

The criteria for type 1 MI includes detection of a rise and/or fall of cTn values with at least one value above the 99th percentile and with at least one of the following:

• Symptoms of acute myocardial ischemia

• New ischemic ECG changes

• Development of pathologic Q waves

• Imaging evidence of new loss of viable myocardium or new regional wall motion abnormality in a pattern consistent with an ischemic etiology

• Identification of a coronary thrombus by angiography including intracoronary imaging or at autopsy

The criteria for type 2 MI includes detection of a rise and/or fall of cTn with at least one value above the 99th percentile and evidence of an imbalance between myocardial oxygen supply and demand unrelated to coronary thrombosis, requiring at least one of the following:

• Symptoms of acute myocardial ischemia

• New ischemic ECG changes

• Development of pathologic Q waves

• Imaging evidence of new loss of viable myocardium or a new regional wall-motion abnormality in a pattern consistent with an ischemic etiology

Coronary intervention–related MI is arbitrarily defined by elevation of cTn values greater than five times the 99th percentile upper reference limit in patients with normal baseline values. Coronary artery bypass grafting–related MI is arbitrarily defined as elevation of cTn values > 10 times the 99th percentile URL in patients with normal baseline cTn values.

Patients may have elevated cTn values and marked decreases in ejection fraction due to sepsis caused by endotoxin, with myocardial function recovering completely with normal ejection fraction once the sepsis is treated.

Which of the following is recommended for the management of patients with acute MI during the COVID-19 pandemic, according to a consensus statement from the Society for Cardiovascular Angiography and Interventions, the ACC, and the American College of Emergency Physicians?

Your Peers Chose: 

A fibrinolysis-first approach is recommended for all patients who present with ST-segment elevation MI (STEMI) during the COVID-19 pandemic

 15%

Direct transport of patients with STEMI to the cardiac catheterization laboratory (CCL) is recommended during the COVID-19 pandemic, as opposed to initial assessment in the emergency department

 18%

Primary percutaneous coronary intervention (PCI) remains the standard of care for patients with STEMI presenting to PCI centers within 90 minutes of first medical contact during the COVID-19 pandemic

 54%[*]

 All patients with COVID-19 who have ST elevation with or without an acute coronary occlusion should undergo reperfusion strategies and/or advanced mechanical support

 13%

According to a consensus statement on the management of acute MI during the COVID-19 pandemic, primary PCI remains the standard of care for patients presenting to PCI centers (≤ 90 minutes of first medical contact) during the COVID-19 pandemic. Each primary PCI center should monitor the ability to provide timely primary PCI on the basis of availability of staff and personal protective equipment; need for additional testing; and need for a designated CCL, which will require terminal cleaning after each procedure. In the absence of these resources, a fibrinolysis-first approach should be considered.

Owing to the logistical issues and time delays secondary to diagnostic uncertainty of STEMI with COVID-19, direct transport of the patient to the CCL is not recommended. The consensus statement recommends initial assessment of all patients with STEMI in the emergency department during the COVID-19 pandemic. The attending interventional cardiologist should be notified without activation of the entire STEMI team until the plan for CCL activation is confirmed.

This consensus statement notes that not all patients with COVID-19 who have ST elevation with or without an acute coronary occlusion will benefit from any reperfusion strategy or advanced mechanical support.

Which of the following is most commonly recognized as an absolute contraindication to fibrinolytic therapy in patients with STEMI?

Your Peers Chose: 

Prior ischemic stroke within the past 6 months

 14%

 Systolic blood pressure > 160 mm Hg or diastolic blood pressure > 100 mm Hg

 8%

 Suspected aortic dissection[*]

 76%

 Current menses

 2%

Absolute contraindications to fibrinolytic therapy in patients with STEMI include the following:

• Any prior intracranial hemorrhage

• Known structural cerebral vascular lesion

• Known intracranial neoplasm (primary or metastatic)

• Ischemic stroke within the past 3 months (except for acute stroke within 4.5 hours)

• Suspected aortic dissection

• Active bleeding or bleeding diathesis (excluding menses)

• Significant closed-head or facial trauma within 3 months

• Intracranial or intraspinal surgery within 2 months

• Severe uncontrolled hypertension (unresponsive to emergency therapy)

• For streptokinase (no longer marketed in the United States), treatment within the previous 6 months

Relative contraindications include the following:

• History of chronic, severe, poorly controlled hypertension

• Systolic blood pressure > 180 mm Hg or diastolic blood pressure > 110 mm Hg

• History of ischemic stroke > 3 months prior

• Dementia

• Known intracranial pathology not covered in absolute contraindications

• Traumatic or prolonged cardiopulmonary resuscitation lasting > 10 minutes

• Recent (within 2-4 weeks) internal bleeding

• Noncompressible vascular punctures

• Pregnancy

• Active peptic ulcer disease

• Current use of anticoagulants

• For streptokinase (no longer marketed in the United States), prior exposure (> 5 days previously) or prior allergic reaction to these agents

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