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?
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?
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.
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?
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.
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
