Ventricular hypertrophy

DiseaseDisorder infobox
Name = Ventricular hypertrophy
ICD10 = ICD10|I|51|7|i|30
ICD9 = ICD9|429.3
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Ventricular hypertrophy is the enlargement of ventricles (lower chambers) in the heart. [ [http://www.clevelandclinic.org/heartcenter/pub/guide/askdoctor/lvh.htm Ask the doctor: Left Ventricular Hypertrophy ] ] [ [http://www.echoincontext.com/int2/skillI2_03.asp Right Ventricular Hypertrophy] Although left ventricular hypertrophy is more common, enlargement can also occur in the right ventricle, or both ventricles.

Physiology

The ventricles are the chambers in the heart responsible for pumping blood either to the lungs (right ventricle) [ [http://www.medterms.com/script/main/art.asp?articlekey=9124 Right ventricle definition - Medical Dictionary definitions of popular medical terms easily defined on MedTerms ] ] or the rest of the body (left ventricle) [ [http://www.medterms.com/script/main/art.asp?articlekey=9127 Left ventricle definition - Medical Dictionary definitions of popular medical terms easily defined on MedTerms ] ] .

Healthy cardiac hypertrophy (physiologic hypertrophy or "athlete's heart") is the normal response to healthy exercise or pregnancy [ [http://www.circ.ahajournals.org/cgi/content/full/94/4/667 Control Mechanisms for Physiological Hypertrophy of Pregnancy - Mone et al. 94 (4): 667 - Circulation ] ] , 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. Pathological hypertrophy also leads to an increase in muscle mass, but the muscle does not increase its pumping ability, and instead accumulates scar tissue (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. [ [http://content.nejm.org/cgi/content/full/358/13/1370 Joseph A. Hill and Eric N. Olson, Cardiac Plasticity,] New England Journal of Medicine, March 27, 2008, 358:1370-1380]

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. [cite book
last = McMurray
first = Robert
title = Concepts in Fitness Programming
publisher = CRC
date = 1998
pages = 320
isbn = 978-0849387142] 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. [ [http://www.circ.ahajournals.org/cgi/content/full/111/21/2837 Mechanisms and Models in Heart Failure: The Biomechanical Model and Beyond - Mann and Bristow 111 (21): 2837 - Circulation ] ]

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. [ [http://www.cvphysiology.com/Heart%20Failure/HF009.htm 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. [ [http://www.cvphysiology.com/Heart%20Failure/HF009.htm 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.

References

ee also

* Cardiac fibrosis
* Cardiology
* Cardiomegaly
* Cardiovascular disease
* Right ventricular hypertrophy

External links

* [http://library.med.utah.edu/kw/ecg/ecg_outline/Lesson8/ Tutorial at University of Utah]