Introduction
Acute
coronary syndrome (ACS) is any constellation of symptoms compatible with acute
myocardial ischemia usually caused by the sudden reduction in coronary blood
flow from atherosclerotic plaque rupture or erosion and
subsequent thrombosis. ACS with persistent ST-segment elevation is
ST-segment elevation myocardial infarction or STEMI. It presents with elevated
levels of cardiac biomarkers. It usually has a
completely occluded vessel resulting in transmural myocardial ischemia and
infarction. It is increasingly recognized as more
appropriately corresponding to occlusion MI (OMI).
Please see Myocardial Infarction
with ST-Segment Elevation disease management chart for further
information.
ACS without persistent ST-segment
elevation or non-ST elevation ACS (NSTE-ACS) is comprised of unstable angina
(UA) and non-ST-segment elevation MI (NSTEMI). UA is
characterized by ischemic discomfort that presents with normal cardiac biomarkers
in the blood, with or without ischemia-related ECG
changes. NSTEMI is characterized by elevated levels of cardiac
biomarkers. It may have a partially occluded coronary artery resulting in
subendocardial ischemia. This is increasingly recognized as more
appropriately corresponding to non-occlusion MI (NOMI).
Acute Coronary Syndromes w.out Persistent ST-Segment Elevation_Disease Background 1Epidemiology
It is estimated that around 17.9 million people died of cardiovascular disease (CVD) in 2019, corresponding
to 32% of all deaths in the world. Among these, as much as 85% were due to ACS
and stroke. The annual incidence of UA in industrialized countries is about 6/10,000
people in the general population. In the Unites States alone, there are as much
as 1.4 million hospital admissions a year due to NSTE-ACS. More than 780,000
people will experience ACS with 70% suffering with NSTEMI. The median age of
presentation of ACS is 68 years old with males outnumbering females by 3:2
ratio. These things being considered, heart disease is the leading cause of
mortality and morbidity in the United States.
In Malaysia, ischemic heart disease was the
principal cause of death in 2024, accounting for as many as 17,421 deaths or
13.0% of the medically certified deaths, with the incidence of ACS being roughly
141 per 100,000 population per year. Just like in Malaysia, ischemic heart
disease was identified as the leading cause of mortality in the Philippines
from 2013 to 2018. In the Philippines, males are more commonly noted to suffer
ACS with a mean age group of 66 years old. It was the main cause of death for
men (15.3%) and the second after pneumonia for women. Based on the National
Cardiovascular Disease Database – Acute Coronary Syndrome (NCVD-ACS) Registry
2020-2021, 50.3% had STEMI, 30.4% had NSTEMI, and 19.3% had UA.
Pathophysiology
The hallmark of ACS is the mismatch between
myocardial oxygen supply and demand, usually caused by reduced coronary blood
flow, resulting in myocardial ischemia and injury. The most
common cause of this mismatch is coronary artery obstruction caused by an
atherosclerotic plaque. However, other causes include vasospasms (such as in
Prinzmetal angina), coronary embolism, coronary arteritis, and even non-coronary
conditions such as hypotension, hypertension, hypertrophic cardiomyopathy,
severe anemia, and severe aortic stenosis.
Acute Coronary Syndromes w.out Persistent ST-Segment Elevation_Disease Background 2Risk Factors
Established risk factors include smoking,
dyslipidemia, hypertension, diabetes, and history of coronary artery disease
(CAD). Other risk factors include older age, male sex, family history of
premature CVD in first-degree relatives <55 years old in males and <65
years old in females, sedentary lifestyle, obesity, previous atheromatous CVD,
and other disorders of circulation (eg valvular heart disease, arrhythmias,
cardiomyopathies).
Please see the discussion on Evaluation
for Risk Stratification.