Thrombosis and Ischemia

The cardiovascular system supplies blood to all regions of the body and can be categorized into two main components: the heart and the peripheral vascular system.

The peripheral vascular system is an intricate network of blood vessels responsible for circulating blood throughout the body. The first portion of this system brings deoxygenated blood from the body back to the heart, where it is pumped to the lungs to offload carbon dioxide and take in oxygen. Next, the oxygenated blood is returned to the heart and pumped to the rest of the body, offloading oxygen along the way. Five types of blood vessels are involved in this process. The first are arteries, or large, high-pressure blood vessels that transport blood from the heart to the various regions of the body.¹ All arteries carry oxygenated blood, except for the pulmonary arteries, which carry deoxygenated blood from the heart to the lungs. As the arteries branch off to deliver blood to various tissues, the vessels become smaller, transforming into arterioles. Deoxygenated blood is returned through a low-pressure system. This begins with venules, which converge into veins and ultimately deliver blood to the heart. The exception is the same: pulmonary veins carry oxygenated blood from the lungs to the heart. Finally, at the cellular level are capillaries, a network of vessels connecting arterioles to venules, and the location of gas and nutrient exchange. Blood flows from the arterioles, through the capillaries, then into the venules.

The heart consists of four chambers: two upper chambers, the left and right atrium, and two lower chambers, the left and right ventricles. The right atria delivers blood to the right ventricle, which pumps blood through the pulmonary artery to the lungs. After offloading carbon dioxide and loading oxygen, blood is returned to the left atria via the pulmonary veins. Finally, blood is pumped into the left ventricle, then systemic circulation via arteries.

As blood travels throughout the body, clots (thrombi) can form in the vessels and restrict blood flow. Restricted blood flow prevents oxygenated blood from reaching the target cells and if left untreated will result in tissue death. This condition is known as ischemia. In the section below we will describe some of the common conditions that can arise from blocked blood vessels.

A myocardial infarction (MI), otherwise known as a heart attack, occurs when blood flow to the heart is entirely or partially obstructed, resulting in oxygen deprivation within the heart muscle. Approximately 5-30% of patients experiencing an MI will die before arriving at the hospital.²

An ischemic stroke occurs when the blood vessels supplying oxygen and nutrients to the brain become occluded (blocked). Early identification and treatment for an ischemic stroke is essential to improving a patient’s prognosis. While MIs and ischemic strokes most commonly present in arteries, blood clots can also occur in veins.^2,3

A deep vein thrombosis (DVT) occurs when a blood clot forms in a vein, often in the legs. A major concern of blood clots in the peripheral system is that they can become dislodged while still intact and travel to the heart, lungs, and brain where they become lodged in vital vessels.⁴ Clots that travel between regions of the body are called emboli. Pulmonary and cardiac embolisms occur in the lungs and heart, respectively, while a cerebral embolism occurs in the brain. All pose a significant threat to life.

As previously stated, the restriction of blood flow to cells can result in tissue death and be lethal if left untreated. Genetic factors, such as a family history of similar conditions, can predispose patients to the aforementioned condition. However, smoking, obesity, a sedentary lifestyle, certain medications, and coronary artery disease are all major, yet modifiable, risk factors for developing a clot.⁵  

 

1. Tucker WD, Arora Y, Mahajan K. Anatomy, Blood Vessels. [Updated 2023 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470401/
2. Ojha N, Dhamoon AS. Myocardial Infarction. [Updated 2023 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537076/
3. John Hopkins Medicine. Types of Stroke. John Hopkins Medicine. Retrieved January 25, 2024 from https://www.hopkinsmedicine.org/health/conditions-and-diseases/stroke/types-of-stroke
4. Penn Medicine. Pulmonary Embolism. Penn Medicine. Retrieved January 25, 2024 fromhttps://www.pennmedicine.org/for-patients-and-visitors/patient-information/conditions-treated-a-to-z/pulmonary-embolus
5. Centers for Disease Control and Prevention. Heart Disease and Stroke. (Updated September 8, 2022). Centers for Disease Control and Prevention. Retrieved January 25, 2024 from https://www.cdc.gov/chronicdisease/resources/publications/factsheets/heart-disease-stroke.htm