Ventricular hypertrophy
Encyclopedia
Ventricular hypertrophy is the enlargement of ventricles
(lower chambers) in the heart. Although left ventricular hypertrophy
is more common, enlargement can also occur in the right ventricle, or both ventricles.
The ventricles are the chambers in the heart responsible for pumping blood either to the lungs (right ventricle) or to the rest of the body (left ventricle).
Healthy cardiac hypertrophy (physiologic hypertrophy or "athlete's heart
") is the normal response to healthy exercise or pregnancy, which results in an increase in the heart's muscle mass and pumping ability. Trained athletes have hearts that have left ventricular mass up to 60% greater than untrained subjects. Rowers, cyclists, and cross-country skiers tend to have the largest hearts, with an average left ventricular wall thickness of 1.3 centimeters, compared to 1.1 centimeters in normal adults. Heart wall thickness can be measured by ultrasound; computed tomography is more accurate, though it is more expensive and has risks of exposure to radiation.
Unhealthy cardiac hypertrophy (pathological hypertrophy) is the response to stress or disease such as hypertension, heart muscle injury (myocardial infarction
), or neurohormones. Valvular heart disease
is another cause of pathological hypertrophy. It has also been suggested that the root cause of many heart ailments is cardiac hypertrophy, which in turn is caused by hypoxia due to atmospheric CO, particulate matter, and peroxyl acyl nitrates, which reduces ATP synthesis in cardiac mitochondria. Pathological hypertrophy also leads to an increase in muscle mass, but the muscle does not increase its pumping ability, and instead accumulates myocardial scarring
(collagen). In pathological hypertrophy, the heart can increase its mass by up to 150%.
In most situations, described above, the increase in ventricular wall thickness is a slow process. However, in some instances hypertrophy may be "dramatic and rapid." In the Burmese python, consumption of a large meal is associated with an increase in metabolic work by a factor of seven and a 40% increase in ventricular mass within 48 hours, both of which return to normal within 28 days.
Aerobic
training results in the heart's being able to pump a larger volume of blood through an increase in the size of the ventricles. Anaerobic
training results in the thickening of the myocardial wall to push blood through arteries
compressed by muscular contraction
.
This type of physiologic hypertrophy is reversible and non-pathological, increasing the heart's ability to circulate blood. Chronic hypertension causes pathological ventricular hypertrophy. This response enables the heart to maintain a normal stroke volume despite the increase in afterload. However, over time, pathological changes occur in the heart that lead to a functional degradation and heart failure.
If the precipitating stress is volume overload (as through aerobic exercise, which increases blood return to the heart through the action of the skeletal-muscle pump
), the ventricle responds by adding new sarcomeres in-series with existing sarcomeres (i.e., the sarcomeres lengthen rather than thicken). This results in ventricular dilation while maintaining normal sarcomere lengths - the heart can expand to receive a greater volume of blood. The wall thickness normally increases in proportion to the increase in chamber radius. This type of hypertrophy is termed eccentric hypertrophy.
In the case of chronic
pressure overload (as through anaerobic exercise, which increases resistance to blood flow by compressing arteries), the chamber radius may not change; however, the wall thickness greatly increases as new sarcomeres are added in-parallel to existing sarcomeres. This is termed concentric hypertrophy. This type of ventricle is capable of generating greater forces and higher pressures, while the increased wall thickness maintains normal wall stress. This type of ventricle becomes "stiff" (i.e., compliance is reduced), which can impair filling and lead to diastolic dysfunction.
The axis of the heart shifts toward the hypertrophied ventricle for two reasons:
1. far more muscles exist on the hypertrophied side, which allows excess generation of electrical potentials on this side.
2. more time is required for the depolarization to travel to the hypertrophied ventricle compared with the normal.
Ventricle (heart)
In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...
(lower chambers) in the heart. Although left ventricular hypertrophy
Left ventricular hypertrophy
Left ventricular hypertrophy is the thickening of the myocardium of the left ventricle of the heart.-Causes:While ventricular hypertrophy occurs naturally as a reaction to aerobic exercise and strength training, it is most frequently referred to as a pathological reaction to cardiovascular...
is more common, enlargement can also occur in the right ventricle, or both ventricles.
Physiology
Healthy cardiac hypertrophy (physiologic hypertrophy or "athlete's heart
Athletic heart syndrome
Athletic heart syndrome, also known as athlete's heart or athletic bradycardia, is a medical syndrome in which the human heart is enlarged due to significant amounts of exercise...
") is the normal response to healthy exercise or pregnancy, which results in an increase in the heart's muscle mass and pumping ability. Trained athletes have hearts that have left ventricular mass up to 60% greater than untrained subjects. Rowers, cyclists, and cross-country skiers tend to have the largest hearts, with an average left ventricular wall thickness of 1.3 centimeters, compared to 1.1 centimeters in normal adults. Heart wall thickness can be measured by ultrasound; computed tomography is more accurate, though it is more expensive and has risks of exposure to radiation.
Unhealthy cardiac hypertrophy (pathological hypertrophy) is the response to stress or disease such as hypertension, heart muscle injury (myocardial infarction
Myocardial infarction
Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...
), or neurohormones. Valvular heart disease
Valvular heart disease
Valvular heart disease is any disease process involving one or more of the valves of the heart . Valve problems may be congenital or acquired...
is another cause of pathological hypertrophy. It has also been suggested that the root cause of many heart ailments is cardiac hypertrophy, which in turn is caused by hypoxia due to atmospheric CO, particulate matter, and peroxyl acyl nitrates, which reduces ATP synthesis in cardiac mitochondria. Pathological hypertrophy also leads to an increase in muscle mass, but the muscle does not increase its pumping ability, and instead accumulates myocardial scarring
Myocardial scarring
Myocardial scarring is fibrous tissue that replaces normal tissue destroyed by injury or disease pertaining to the muscular tissue of the heart....
(collagen). In pathological hypertrophy, the heart can increase its mass by up to 150%.
In most situations, described above, the increase in ventricular wall thickness is a slow process. However, in some instances hypertrophy may be "dramatic and rapid." In the Burmese python, consumption of a large meal is associated with an increase in metabolic work by a factor of seven and a 40% increase in ventricular mass within 48 hours, both of which return to normal within 28 days.
Aerobic
Aerobic exercise
Aerobic exercise is physical exercise of relatively low intensity that depends primarily on the aerobic energy-generating process. Aerobic literally means "living in air", and refers to the use of oxygen to adequately meet energy demands during exercise via aerobic metabolism...
training results in the heart's being able to pump a larger volume of blood through an increase in the size of the ventricles. Anaerobic
Anaerobic exercise
Anaerobic exercise is exercise intense enough to trigger anaerobic metabolism. It is used by athletes in non-endurance sports to promote strength, speed and power and by body builders to build muscle mass...
training results in the thickening of the myocardial wall to push blood through arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
compressed by muscular contraction
Muscle contraction
Muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same...
.
This type of physiologic hypertrophy is reversible and non-pathological, increasing the heart's ability to circulate blood. Chronic hypertension causes pathological ventricular hypertrophy. This response enables the heart to maintain a normal stroke volume despite the increase in afterload. However, over time, pathological changes occur in the heart that lead to a functional degradation and heart failure.
If the precipitating stress is volume overload (as through aerobic exercise, which increases blood return to the heart through the action of the skeletal-muscle pump
Skeletal-muscle pump
The skeletal-muscle pump is a collection of skeletal muscles that aid the heart in the circulation of blood. It is especially important in increasing venous return to the heart, but may also play a role in arterial blood flow.-Arterial blood pumping:...
), the ventricle responds by adding new sarcomeres in-series with existing sarcomeres (i.e., the sarcomeres lengthen rather than thicken). This results in ventricular dilation while maintaining normal sarcomere lengths - the heart can expand to receive a greater volume of blood. The wall thickness normally increases in proportion to the increase in chamber radius. This type of hypertrophy is termed eccentric hypertrophy.
In the case of chronic
Chronic (medicine)
A chronic disease is a disease or other human health condition that is persistent or long-lasting in nature. The term chronic is usually applied when the course of the disease lasts for more than three months. Common chronic diseases include asthma, cancer, diabetes and HIV/AIDS.In medicine, the...
pressure overload (as through anaerobic exercise, which increases resistance to blood flow by compressing arteries), the chamber radius may not change; however, the wall thickness greatly increases as new sarcomeres are added in-parallel to existing sarcomeres. This is termed concentric hypertrophy. This type of ventricle is capable of generating greater forces and higher pressures, while the increased wall thickness maintains normal wall stress. This type of ventricle becomes "stiff" (i.e., compliance is reduced), which can impair filling and lead to diastolic dysfunction.
The axis of the heart shifts toward the hypertrophied ventricle for two reasons:
1. far more muscles exist on the hypertrophied side, which allows excess generation of electrical potentials on this side.
2. more time is required for the depolarization to travel to the hypertrophied ventricle compared with the normal.
See also
- Cardiac fibrosisCardiac fibrosisCardiac fibrosis refers to an abnormal thickening of the heart valves due to inappropriate proliferation of cardiac fibroblasts.Fibrocyte cells normally secrete collagen, and function to provide structural support for the heart...
- CardiologyCardiologyCardiology is a medical specialty dealing with disorders of the heart . The field includes diagnosis and treatment of congenital heart defects, coronary artery disease, heart failure, valvular heart disease and electrophysiology...
- CardiomegalyCardiomegalyCardiomegaly is a medical condition wherein the heart is enlarged. It is generally categorized in the following manner:* Cardiomegaly due to dilation* Cardiomegaly due to ventricular hypertrophy** Left ventricular hypertrophy...
- Cardiovascular diseaseCardiovascular diseaseHeart disease or cardiovascular disease are the class of diseases that involve the heart or blood vessels . While the term technically refers to any disease that affects the cardiovascular system , it is usually used to refer to those related to atherosclerosis...
- Right ventricular hypertrophyRight ventricular hypertrophyRight ventricular hypertrophy is a form of ventricular hypertrophy affecting the right ventricle.Blood travels through the right ventricle to the lungs via the pulmonary arteries. If conditions occur which decrease pulmonary circulation, meaning blood does not flow well from the heart to the...
- ECG See diagnosis