| Ventricular hypertrophy | |
|---|---|
| Classification and external resources | |
| ICD-10 | I51.7 |
| ICD-9 | 429.3 |
Ventricular hypertrophy is the enlargement of ventricles (lower chambers) in the heart.[1][2] Although left ventricular hypertrophy is more common, enlargement can also occur in the right ventricle, or both ventricles.
Contents |
Physiology
The ventricles are the chambers in the heart responsible for pumping blood either to the lungs (right ventricle)[3] or the rest of the body (left ventricle)[4].
Healthy cardiac hypertrophy (physiologic hypertrophy or "athlete's heart") is the normal response to healthy exercise or pregnancy[5], which results in an increase in the heart's muscle mass and pumping ability. Trained athletes have hearts which have left ventricular mass up to 60% greater than untrained subjects. Rowers, cyclists and cross-country skiers tend to have the largest hearts, with a left ventricular wall thickness of 1.3 centimeters, compared to 1.1 centimeters in normal adults. Heart wall thickness can be measured by ultrasound; computer 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 such as hypertension, heart muscle injury (myocardial infarction) or neurohormones. 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[6]. 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%.
Cardiac hypertrophy is "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 "spectacular" 40% increase in ventricular mass within 48 hours, both of which return to normal within 28 days.[7]
Aerobic training results in the heart 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.[8] 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.[9]
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.[10]
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.[10] 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.
References
- ^ Ask the doctor: Left Ventricular Hypertrophy
- ^ Right Ventricular Hypertrophy
- ^ Right ventricle definition - Medical Dictionary definitions on MedTerms
- ^ Left ventricle definition - Medical Dictionary definitions on MedTerms
- ^ Mone SM, Sanders SP, Colan SD (August 1996). "Control mechanisms for physiological hypertrophy of pregnancy". Circulation 94 (4): 667–72. PMID 8772686. http://www.circ.ahajournals.org/cgi/content/full/94/4/667.
- ^ Acharya PV; Irreparable DNA-Damage by Industrial Pollutants in Pre-Mature Aging, Chemical Carcinogenesis and Cardiac Hypertrophy: Experiments and Theory; 1st International Meeting of Heads of Clinical Biochemistry Laboratories, April 1977; Jerusalem, Israel. Work conducted at Industrial Safety and Health Institute and Behavioral Cybernetics Laboratory, University of Wisconsin, Madison.
- ^ Hill JA, Olson EN (March 2008). "Cardiac plasticity". N Engl J Med. 358 (13): 1370–80. doi:. PMID 18367740. http://content.nejm.org/cgi/content/full/358/13/1370.
- ^ McMurray, Robert (1998). Concepts in Fitness Programming. CRC. p. 320. ISBN 978-0849387142.
- ^ Mann DL, Bristow MR (May 2005). "Mechanisms and models in heart failure: the biomechanical model and beyond". Circulation 111 (21): 2837–49. doi:. PMID 15927992. http://www.circ.ahajournals.org/cgi/content/full/111/21/2837.
- ^ a b Hypertrophy
See also
- Cardiac fibrosis
- Cardiology
- Cardiomegaly
- Cardiovascular disease
- Right ventricular hypertrophy
- ECG See diagnosis
External links
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