Right ventricular hypertrophy
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Right ventricular hypertrophy (RVH) is a condition defined by an abnormal enlargement of the cardiac muscle surrounding the
right ventricle A ventricle is one of two large chambers toward the bottom of the heart that collect and expel blood towards the peripheral beds within the body and lungs. The blood pumped by a ventricle is supplied by an atrium, an adjacent chamber in the uppe ...
. The right ventricle is one of the four chambers of the heart. It is located towards the lower-end of the heart and it receives blood from the right atrium and pumps blood into the lungs. Since RVH is an enlargement of muscle it arises when the muscle is required to work harder. Therefore, the main causes of RVH are pathologies of systems related to the right ventricle such as the
pulmonary artery A pulmonary artery is an artery in the pulmonary circulation that carries deoxygenated blood from the right side of the heart to the lungs. The largest pulmonary artery is the ''main pulmonary artery'' or ''pulmonary trunk'' from the heart, and ...
, the
tricuspid valve The tricuspid valve, or right atrioventricular valve, is on the right dorsal side of the mammalian heart, at the superior portion of the right ventricle. The function of the valve is to allow blood to flow from the right atrium to the right ven ...
or the airways. RVH can be benign and have little impact on day-to-day life or it can lead to conditions such as heart failure, which has a poor prognosis.


Signs and symptoms


Symptoms

Although presentations vary, individuals with right ventricular hypertrophy can experience symptoms that are associated with pulmonary hypertension, heart failure and/or a reduced cardiac output. These include: * Difficulty breathing on exertion * Chest pain ( angina) on exertion * Fainting ( syncope) on exertion * General fatigue/lethargy * Dizziness * Feeling of fullness in the upper abdominal area * Discomfort or pain in the right upper abdomen * Reduced appetite * Swelling (
oedema Edema, also spelled oedema, and also known as fluid retention, dropsy, hydropsy and swelling, is the build-up of fluid in the body's tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels tight, the area ma ...
) of the legs, ankles or feet * Racing heart beat (palpitations) People may rarely present with the symptoms of Ortner's syndrome, which include cough, haemoptysis and hoarseness.


Signs

On physical examination, the most prominent features are due to the development of right-sided heart failure. These can include a raised jugular venous pressure,
ascites Ascites is the abnormal build-up of fluid in the abdomen. Technically, it is more than 25 ml of fluid in the peritoneal cavity, although volumes greater than one liter may occur. Symptoms may include increased abdominal size, increased weight, a ...
, left parasternal heave and a tender, enlarged
liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...
on palpation. On inspection, patients may be chronically ill, cyanotic, cachectic and occasionally jaundiced. On auscultation, an accentuated second pulmonary sound (S2), a third heart sound termed a ‘right ventricular gallop’, as well as a systolic murmur over the
tricuspid The tricuspid valve, or right atrioventricular valve, is on the right dorsal side of the mammalian heart, at the superior portion of the right ventricle. The function of the valve is to allow blood to flow from the right atrium to the right ven ...
area accentuated by inspiration may be present. On occasion, the systolic murmur can be transmitted and auscultated over the liver. Less typically, diastolic murmur may also be heard as a result of pulmonary insufficiency.


Causes

RVH usually occurs due to chronic lung disease or structural defects in the heart. One of the most common causes of RVH is pulmonary hypertension (PH), defined as increased blood pressure in the vessels supplying blood to the lungs. PH leads to increased pulmonary artery pressure. The
right ventricle A ventricle is one of two large chambers toward the bottom of the heart that collect and expel blood towards the peripheral beds within the body and lungs. The blood pumped by a ventricle is supplied by an atrium, an adjacent chamber in the uppe ...
tries to compensate for this increased pressure by changing its shape and size. Hypertrophy of individual
myocytes A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells. A skeletal muscle cell is long and threadlike with many nuclei and is called a muscl ...
results in an increase in right ventricular wall thickness. The worldwide incidence of PH is 4 per million people. RVH occurs in approximately 30% of these cases. PH is broadly split into five categories by the
World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of ...
, based on the underlying cause. The incidence of RVH varies between the groups. Common causes of PH include
chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce ...
(COPD),
pulmonary embolism Pulmonary embolism (PE) is a blockage of an artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream ( embolism). Symptoms of a PE may include shortness of breath, chest pain particularly upon breathin ...
, and other restrictive lung diseases. RVH often occurs as a result of these disorders. RVH is seen in 76% of patients with advanced COPD and 50% of patients with restrictive lung disease. RVH also occurs in response to structural defects in the heart. One common cause is
tricuspid insufficiency Tricuspid regurgitation (TR), also called tricuspid insufficiency, is a type of valvular heart disease in which the tricuspid valve of the heart, located between the right atrium and right ventricle, does not close completely when the right ventr ...
. This is a disorder where the
tricuspid valve The tricuspid valve, or right atrioventricular valve, is on the right dorsal side of the mammalian heart, at the superior portion of the right ventricle. The function of the valve is to allow blood to flow from the right atrium to the right ven ...
fails to close properly, allowing backward flow of blood. Other structural defects which lead to RVH include
tetralogy of Fallot Tetralogy of Fallot (TOF), formerly known as Steno-Fallot tetralogy, is a congenital heart defect characterized by four specific cardiac defects. Classically, the four defects are: *pulmonary stenosis, which is narrowing of the exit from the r ...
,
ventricular septal defect A ventricular septal defect (VSD) is a defect in the ventricular septum, the wall dividing the left and right ventricles of the heart. The extent of the opening may vary from pin size to complete absence of the ventricular septum, creating one ...
s,
pulmonary valve stenosis Pulmonary valve stenosis (PVS) is a heart valve disorder. Blood going from the heart to the lungs goes through the pulmonary valve, whose purpose is to prevent blood from flowing back to the heart. In pulmonary valve stenosis this opening is too n ...
, and
atrial septal defect Atrial septal defect (ASD) is a congenital heart defect in which blood flows between the atria (upper chambers) of the heart. Some flow is a normal condition both pre-birth and immediately post-birth via the foramen ovale; however, when this d ...
s. RVH is also associated with
abdominal obesity Abdominal obesity, also known as central obesity and truncal obesity, is a condition when excessive visceral fat around the stomach and abdomen has built up to the extent that it is likely to have a negative impact on health. Abdominal obesity has ...
, elevated fasting blood glucose, high
systolic blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...
, and fractional shortening of the left ventricular mid-wall. Other risk factors for RVH include smoking,
sleep apnea Sleep apnea, also spelled sleep apnoea, is a sleep disorder in which pauses in breathing or periods of shallow breathing during sleep occur more often than normal. Each pause can last for a few seconds to a few minutes and they happen many tim ...
, and strenuous activity. These increase the risk of heart and lung disease and hence RVH.


Pathophysiology

Right ventricular hypertrophy can be both a physiological and pathophysiological process. It becomes pathophysiological (damaging) when there is excessive hypertrophy. The pathophysiological process mainly occurs through aberrant signalling of the neuroendocrine hormones; angiotensin II, endothelin-1 and the catecholamines (e.g.
noradrenaline Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter. The name "noradrenaline" (from Latin '' ad'', ...
).


Angiotensin-II and endothelin-1

Angiotensin-II and endothelin-1 are hormones that bind to the angiotensin (AT) and endothelin (ET) receptors. These are
G-protein G proteins, also known as guanine nucleotide-binding proteins, are a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior. Their act ...
coupled receptors that act via internal signalling pathways. Through several intermediates, these pathways directly or indirectly increase
reactive oxygen species In chemistry, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen (). Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen. The reduction of molecular oxygen () p ...
(ROS) production causing accumulation in myocardial cells. This can subsequently induce necrotic cell death,
fibrosis Fibrosis, also known as fibrotic scarring, is a pathological wound healing in which connective tissue replaces normal parenchymal tissue to the extent that it goes unchecked, leading to considerable tissue remodelling and the formation of perma ...
, and mitochondrial dysfunction. This has been demonstrated in animal studies. Protein Kinase C (PKC) is an intermediate molecule in the signalling pathway and mice lacking PKC shown resistance to heart failure compared to mice overexpressing PKC which shown heart dysfunction. Targeting the renin–angiotensin (RAAS) system (using angiotensin-converting enzyme inhibitors and angiotensin-receptor blockers) are a well-recognized clinical approach for reversing maladaptive cardiac hypertrophy independently of blood pressure.


Catecholamines

Catecholamine A catecholamine (; abbreviated CA) is a monoamine neurotransmitter, an organic compound that has a catechol (benzene with two hydroxyl side groups next to each other) and a side-chain amine. Catechol can be either a free molecule or a su ...
s levels increase due to increased sympathetic nervous system activity. Catecholamines can act on the alpha-adrenergic receptors and beta-adrenergic receptors which are G-protein coupled receptors. This binding initiates the same intracellular signalling pathways as angiotensin and endothelin. There is also activation of cAMP and an increase in intracellular Ca2+ which leads to contractile dysfunction and fibrosis.


Others

Hormones are not the only cause of RVH. Hypertrophy can also be caused by mechanical forces, mTOR pathways, nitric oxide and
immune cell White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from multi ...
s. Immune cells can cause hypertrophy by inducing inflammation.


Diagnosis

The two main diagnostic tests used to confirm right ventricular hypertrophy are electrocardiography and echocardiography.


Electrocardiography

The use of electrocardiogram (ECG) to measure cardiac chamber hypertrophy is well established but since the left ventricular activity is dominant on the ECG a large degree of RVH is often required for any detectable changes. Nonetheless, the ECG is used to assist with the diagnosis of RVH. A
post mortem An autopsy (post-mortem examination, obduction, necropsy, or autopsia cadaverum) is a surgical procedure that consists of a thorough Physical examination, examination of a Cadaver, corpse by dissection to determine the cause, mode, and manner o ...
study on 51 adult male patients concluded that anatomical RVH may be diagnosed using one or more of the following ECG criteria: *
Right axis deviation The electrical axis of the heart is the net direction in which the wave of depolarization travels. It is measured using an electrocardiogram (ECG). Normally, this begins at the sinoatrial node (SA node); from here the wave of depolarisation travel ...
of more than (or equal to) 110° (see hexaxial reference figure) * R-wave dominant over S-wave in V1 or V2 *
S-wave __NOTOC__ In seismology and other areas involving elastic waves, S waves, secondary waves, or shear waves (sometimes called elastic S waves) are a type of elastic wave and are one of the two main types of elastic body waves, so named because th ...
dominant over R-wave in V6 However, the American Heart Association recommended the use of additional diagnostic tests to diagnose RVH because no single criteria or set of criteria were considered sufficiently reliable.


Echocardiography

Echocardiography can be used to directly visualise right ventricular wall thickness. The preferred technique is the trans-oesophageal approach giving a view of 4 chambers. The normal thickness of a right ventricular free wall ranges from 2-5 millimetres, with a value above 5 mm considered to be hypertrophic.


Treatment

It is important to understand that right ventricular hypertrophy in itself is not the main issue, but what right ventricular hypertrophy represents is. Right ventricular hypertrophy is the intermediate stage between increased right ventricular pressure (in the early stages) and right ventricle failure (in the later stages). As such, management of right ventricular hypertrophy is about either preventing the development of right ventricular hypertrophy in the first place, or preventing the progression towards right ventricle failure. Right ventricular hypertrophy in itself has no (pharmacological) treatment.


Treating the cause

Since the main causes of right ventricular hypertrophy is tricuspid regurgitation or pulmonary hypertension (discussed above), management involves treatment of these conditions. Tricuspid regurgitation is typically treated conservatively by aiming to treat the underlying cause and following up the patient regularly. Surgery is considered in more serious situations where the patient is severely symptomatic. Surgical options include either: replacement of the valve or repair of the valve (termed annuloplasty). When it comes to replacement, there is a choice between a bioprosthetic valve or a mechanical valve, depending upon the specific patient characteristics. Mechanical valve has greater durability, but requires anti-coagulation to reduce the risk of thrombosis. Treatment of pulmonary hypertension will depend on the specific cause of the pulmonary hypertension. On top of this, the following may also be considered: diuretic, oxygen and anti-coagulant therapy.


Managing the complications

After a prolonged period, the right ventricle fails to adapt sufficiently to pump against increased right ventricle pressure, which is termed right ventricular failure. This right ventricular failure is the main complication of right ventricular hypertrophy. The mechanisms underlying the progression from hypertrophy to failure is not well understood, and the best management approach involves reducing/minimising the risk factors of progression. Lifestyle changes can often help to reduce the risk of this progression. Lifestyle changes include: eating less salty food as salt consumption leads to greater fluid retention by the body; smoking cessation; avoiding excessive alcohol consumption as alcohol reduces the force of heart contractions. Once right ventricular hypertrophy progresses to right ventricular failure, the treatment becomes that of heart failure. Briefly, this includes the use of: *
Diuretic A diuretic () is any substance that promotes diuresis, the increased production of urine. This includes forced diuresis. A diuretic tablet is sometimes colloquially called a water tablet. There are several categories of diuretics. All diuretics i ...
s * 3 ACEi *
Beta Blocker Beta blockers, also spelled β-blockers, are a class of medications that are predominantly used to manage abnormal heart rhythms, and to protect the heart from a second heart attack after a first heart attack ( secondary prevention). They are ...
s * Aldosterone * Antongists *
Cardiac glycoside Cardiac glycosides are a class of organic compounds that increase the output force of the heart and decrease its rate of contractions by inhibiting the cellular sodium-potassium ATPase pump. Their beneficial medical uses are as treatments for c ...
s * Vasodilators


References


External links

* {{Circulatory system pathology Cardiomegaly Heart diseases