Jacob R Gordon, Stanton College Preparatory School, Jacksonville, Florida, USA
Summary
In recent decades, the global prevalence of ischemic heart disease (IHD) has dramatically increased. IHD, also known as coronary artery disease (CAD), is a condition that occurs when plaque builds up in the coronary arteries, partially blocking them and reducing the amount of blood flowing to the heart's muscle cells (cardiomyocytes), leading to a variety of symptoms. As the world has developed, our lifestyle has changed in a way that has elevated our risk for IHD. Many risk factors of IHD that we did not contend with now jeopardize our health. These factors include a sedentary lifestyle, obesity, along with poor sleep quality and duration, all of which have become much more common in recent decades. This article will explore the development and symptoms of IHD, its diagnosis, and treatment, and how these factors relate to public health.
Ischemic heart disease (IHD) led to the deaths of 8.9 million people in 2019 alone, accounting for 16% of deaths globally that year (World Health Organization, 2020). In 2019, IHD was the leading cause of death in high-income, upper-middle-income, and lower-middle-income countries and the third leading cause of death in low-income countries (World Health Organization, 2020). From 2020 to 2030, the prevalence of IHD is projected to increase from 1,655 per 100,000 to 1,855 per 100,000 (Khan et al., 2020). IHD is a condition where plaque forms in the coronary artery, decreasing circulation to the myocardium, or heart muscle. This is clinically relevant because IHD can present as a myocardial infarction (heart attack) or as ischemic cardiomyopathy (damage to the heart due to a lack of blood supply) (Khan et al., 2020). IHD is also known as coronary artery disease (CAD) due to the accumulation of cholesterol in the coronary arteries, and it can also be referred to as atherosclerotic cardiovascular disease (ACD) due to its association with atherosclerosis.
Figure 1: A diagram showing the locations and regions of the coronary arteries (Anatomy and function of the coronary arteries, 2020).
The coronary arteries travel along the surface of the heart (Figure 1), carrying various blood components, including a lipid called cholesterol. As cholesterol moves through the coronary arteries, it can accumulate in damaged segments of the arterial wall. White blood cells then migrate to the cholesterol deposit and begin an inflammatory process called atherosclerosis. The most common cause of IHD is atherosclerosis; however, IHD has also been connected to vasospasm and coronary microvascular dysfunction, where vessels that branch off the coronary arteries narrow (Severino et al., 2020). As more cholesterol and white blood cells accumulate, the mass of cholesterol and white blood cells expands into the lumen of the artery (Figure 2) (Khan Academy Medicine, 2014). As the lumen diameter decreases, so does the amount of blood reaching the myocardium (heart muscle). This causes a constellation of symptoms, some of which occur in the cardiac conduction system.
The cardiac conduction system is a group of structures (Figure 3) that send electrical signals through the heart controlling its contractions. This system includes the sinoatrial (SA) and atrioventricular (AV) nodes. Because the SA and AV nodes receive their blood supply from the right coronary artery, IHD patients can present with arrhythmias (abnormal electrical signals) that can impact how the heart contracts, worsening blood flow throughout the rest of body. If the patient has a myocardial infarction (MI) in their left coronary artery, they may experience reflex tachycardia, which is an increase in heart rate to compensate for decreased perfusion. Patients who have an MI in their right coronary artery can also experience sinus bradycardia (low heart rate with normal electrical activity) or an AV block (a block of the electrical signal that controls heart contraction) (Cleveland Clinic, 2021). Patients presenting with IHD can also have lower extremity swelling due to fluid buildup (edema), low blood pressure (hypotension), fluid buildup in the lungs (pulmonary edema), or even an abnormal heart sound called S4 if the left ventricle fails (Ninja Nerd, 2022).
Figure 2: An illustration of an artery cross-section (Wilcox, B. 2015).
Figure 3: A diagram of the cardiac conduction system with major features labeled.(File:Conductionsystemoftheheartwithouttheheart-en.svg).
Not all IHD patients experience an MI - many can present with a condition called ischemic cardiomyopathy, where the myocardium begins to die as a result of decreased blood flow. An ischemic myocardium causes a sudden elevation of catecholamines, a type of hormone and neurotransmitter that is responsible for various processes in the body. An example of a catecholamine is epinephrine, a hormone that increases heart rate. This surge of catecholamines leads to oxidative stress and calcium overload in the mitochondria, causing cell death through necrosis and apoptosis (Liaudet et al., 2014; Santulli et al. 2015; Schömig, 1990). This significantly reduces the ability of the left ventricle to pump blood through the body, causing systolic heart failure, also called heart failure with reduced ejection fraction (HFrEF) (Bhandari et al., 2022; Johns Hopkins, 2022).
Coronary angiography is an invasive diagnostic tool, and the current gold standard for diagnosing IHD. Recently, less invasive tests, such as MRI, CT, and PET scans have recently been proven effective at detecting blockages and observing function, making them possible tools to diagnose IHD (Sirajuddin et al., 2021). Other methods for diagnosing IHD include ECGs, echocardiograms, cardiac stress tests, and chest x-rays. (Centers for Disease Control and Prevention, 2021).
IHD treatment is primarily focused on risk factor modification such as lipid management, hypertension control, diabetes management, physical activity, weight regulation, and smoking cessation. Patients may be prescribed aspirin or clopidogrel to prevent a heart attack. Some patients are also given a beta blocker or calcium-channel blocker to provide relief from symptoms. Metoprolol succinate, carvedilol, or bisoprolol may be used if the patient has HFrEF. ACE-inhibitors may also be given to those with diabetes, hypertension, or other conditions (Devitt, 2013). Medications used can vary, depending on each patient’s severity, comorbidities, current prescriptions, and other factors.
It is currently unclear how effective public health campaigns can be in modifying a population’s risk factors for IHD. Some studies suggest that blood pressure and cholesterol can be decreased by campaigns, while others report little to no reduction in risk factors (Ebireri et al., 2016). With more research, public health organizations may be able to identify the most effective ways to reduce rates of IHD.
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