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How the Heart Hardens, Biologically

In matters of the heart, a lot can go wrong. As we age, high blood pressure can overburden this tenacious muscle, causing stroke or heart failure. Smoking cigarettes may harm your heart and blood vessels, as well as damaging individual blood cells. Or the natural effects of old age can render the heart simply too weak to do its job, manifesting in tiredness, shortness of breath or even death. But the heart can also harden, its soft muscle changing into bone.

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 Scientists transform scar tissue into beating heart muscle

In an act of transformation worthy of any magician, scientists have converted scar tissue in the hearts of living mice into beating heart cells. If the same trick works in humans (and we’re still several years away from a trial), it could lead us to a long-sought prize of medicine – a way to mend a broken heart.

 The Myocardium: More Than Myocytes

Conventionally, the cardiologist’s view of the myocardium has focused on the cardiac myocyte, leaving the rich population of noncontractile cells in relative neglect. These other cardiac cell types include fibroblasts or myofibroblasts and cells of the microvasculature including endothelial cells, smooth muscle cells, and pericytes

 Time Is Myocardium and Time Is Outcomes

As an interventional cardiologist and a clinical trialist, I am often asked, “what do we need to do to improve mortality by another 1% in the setting of acute myocardial infarction?” Indeed, nearly a decade and a half of effort and many hundreds of millions of dollars have been spent in pursuit of this elusive “1% reduction” in mortality by both the pharmaceutical and the device industry.

Articles of Interest

Making new heart cells

It is literally very difficult to mend a broken heart. Despite its importance, the heart is notoriously bad at regenerating itself after injury. If it is damaged – say, by a heart attack – it replaces the lost muscle with scar tissue rather than fresh cells. That weakens it and increases the chance of heart failure later on in life. No wonder that heart disease is the western world’s leading cause of death and illness.

By the way, doctor: Why don't statins damage the heart muscle?

You're right: the heart is a muscle. However, heart muscle (the medical term is myocardium) is built somewhat differently from the skeletal muscles. If you were to look at a piece of heart muscle under a microscope (particularly an electron microscope) you would see subtle differences between it and a piece of muscle taken from, say, your biceps. This makes sense because the two different types of muscle have very different types of jobs to do. The skeletal muscles need to work sometimes but can rest at other times, whereas the heart muscle (like the muscles that help you breathe) needs to work every minute of your life — without fail.

Evidence that the myocardium is a continuous helical muscle with one insertion

The myocardium in its longitudinal continuity adopts a spiraling spatial configuration, inserted at its end to a nucleus called cardiac fulcrum. The Thebesian veins and hyaluronic acid could have an essential role in the antifriction mechanism, due to the resistance between the sliding myocardial muscle surfaces in their torsion (systole) and detorsion (suction) motions.

Extreme Triathletes Could Be Putting Their Hearts at Risk, Study Finds

People involved in some of the world’s most extreme endurance sports may be at risk of damaging their hearts, according to a new German study of triathletes. The harder the athletes pushed themselves in the past, the greater the likelihood they showed signs of myocardial fibrosis, the scarring of the heart’s ventricles, which has been linked to heart disease.

Heart Muscles and Pumping

The heart wall is composed of heart muscles or the myocardium between an inner layer called the endocardium and an outer layer called the epicardium. The endocardium forms the inner walls and the heart valves. The muscle fibres are arranged differently between these layers, turning almost 90 degrees between the endocardium and the epicardium. This allows them to contract and reduce the volume of the cavity with a twisting motion similar to drying a cloth by wringing.

Hibernating Myocardium and Stunned Myocardium

Hibernating myocardium occurs when heart muscle tissue doesn’t receive adequate blood flow. It receives enough nutrients to stay alive, but it can’t support the heart’s pumping function. This condition occurs in people with coronary artery disease. Treatment to restore blood flow may include angioplasty or coronary artery bypass surgery.

Human Cardiac Muscle under the Microscope

The cardiac muscle is an involuntary, striated muscle that is found in the myocardium, which is the muscle tissue of the heart and forms a thick middle layer between the outer epicardium layer and the inner endocardium layer. Coordinated contractions of cardiac muscle cells in the heart pump blood out of the atria and ventricles to the blood vessels of the left/body/systemic and right/lungs/pulmonary circulatory systems. This complex mechanism illustrates systole of the heart.

Mastering the myocardium: Cardiogenic Shock

The majority of cardiogenic shock is due to underlying acute coronary syndrome (ACS). However, its contribution has declined over the past two decades with a parallel increase of other non-ACS etiologies. A large North American CCU dataset in 2019 showed that only 1/3 of CS was related to ACS, while the remainder included causes such as cardiomyopathies, valvular diseases, and arrhythmias. The main causes of cardiogenic shock can be broken down into ACS vs. non-ACS etiologies.

Myocardial Stunning

Myocardial Stunning = temporary cardiac muscle dysfunction secondary to an insult (ischaemia, hypoxia, very high afterload).

Myocardium of the Heart

This class gave me a greater appreciation of the elegance of the heart and the mechanisms behind its continuous beating. I was fascinated by the spread of electrical signal and its motion through the myocardium. The depolarization starting at the sinoatrial node, which spreads to the atrioventricular node then through the bundle of His and out to the Purkinje fibers is a highly linear path, simple yet powerful. While the lecture on the heart and studying plastic models in lab fascinated me, it was the opportunity to dissect the heart that truly solidified by understanding of it.

New Research in the Anatomy of the Myocardium

Briefly, the myocardium consists of three regions: 1) the free wall of the right ventricle; 2) the free wall of the left ventricle and 3) the interventricular septum. The wall of the right ventricle is formed by the right segment of the basal loop whereas that of the left is formed by both the basal loop (left segment) and the descending and ascending segments of the apical loop; hence, the smaller structural thickness of the right ventricular wall.

Properties of Cardiac Muscle

Some of the key properties of cardiac muscle that make it extremely essential for the functioning of the human heart are- automaticity, excitability, conductivity, contractility, elasticity, interconnected structure, metabolic efficiency, and adaptability.

Recent Advances on Myocardium Physiology, Volume II

Myocardium has evolved to contract in a rhythmic fashion to provide blood from the heart to the body. The mechanical activities of myocardium originate in sarcomeres, composed of three filaments [i.e., thick and thin filaments, and the giant elastic protein titin (connectin)].

The Heart Wall

The myocardium forms the bulk of the heart wall and consists of involuntary striated cardiac muscle. It is the contractile layer responsible for generating force to pump blood throughout the body.

Time is Myocardium, but Who Does Best?

Time is myocardium. This is the edict underpinning the clinical paradigm of rapid revascularisation following acute myocardial infarction (AMI) in order to limit the extent of myocardial necrosis and prevent death. There is established recognition that despite timely revascularisation, adverse clinical outcomes still occur due to the phenomena of cardiac remodeling and infarct expansion in the months following AMI.

Resources

30 Facts About Myocardium

Composed mainly of cardiac muscle cells, the myocardium is thicker in the left ventricle than the right, reflecting its role in pumping blood to the entire body. Unlike skeletal muscles, cardiac muscle cells are interconnected, allowing for synchronized contractions. This unique structure and function make the myocardium essential for maintaining life.

Physiopedia

Cardiac muscle (or myocardium) makes up the thick middle layer of the heart. It is one of three types of muscle in the body, along with skeletal and smooth muscle.

StatPearls

Cardiac muscle also called the myocardium, is one of three major categories of muscles found within the human body, along with smooth muscle and skeletal muscle. Cardiac muscle, like skeletal muscle, is made up of sarcomeres that allow for contractility. However, unlike skeletal muscle, cardiac muscle is under involuntary control.

Truman State University

The myocardium is a smooth muscle which allows it to function autonomically. The muscle cells are connected together by intercalated disks and are composed of sarcomeres (actin and myosin filaments). Mechanically, contraction of sarcomeres occur when there is an influx of calcium (Ca++) ions into the myocardial cells that bind to troponin proteins on the actin filaments. This results in a release of ATP which produces shortening of the sarcomeres and muscle contraction.