Introduction

Definition of heart enlargement 

An enlarged heart, also known as cardiomegaly, is an important sign (not a disease) that indicates the need for further testing to diagnose what is causing the enlargement.¹

Overview of heart failure 

Heart failure occurs when the heart is unable to pump the amount of blood it should. When heart failure sets in, breathing becomes difficult because in certain cases, fluid can back up into the lungs.²

Importance of understanding the relationship between heart enlargement and heart failure progression 

Cardiomegaly should be taken seriously and it can lead to chronic conditions. Having an enlarged heart hinders blood pumping, and can progress onto causing heart failure and, consequently, other complications.³

Anatomy of the heart

Basic structure and function of the heart 

The heart pumps blood throughout the body, supplying cells with nutrition and oxygen while expelling waste products like carbon dioxide. It consists of:

• Walls that can relax and contract to pump blood
• 4 chambers or cavities with two atria (upper section) and two ventricles (lower section)
• Blood veins that move blood throughout the body from the heart and vice versa
• A system of electrical conduction that works through the brain and neurological system to regulate the heart's beating

Types of heart enlargement 

Left ventricular hypertrophy 

Left ventricular hypertrophy (LVH) means the enlargement of the left ventricle. A condition like hypertension can overwork the ventricle and cause it to thicken by creating pressure inside it. The left ventricle may harden, weaken, and lose its elasticity as a result.⁵

Right ventricular hypertrophy 

The enlargement of the right ventricle is referred to as right ventricular hypertrophy (RVH). The primary distinction between RVH and LVH is that the former is more frequently linked to severe and chronic lung conditions. Because the right ventricle is far smaller than the left ventricle in this instance, the enlargement is less obvious.⁶

Atrial enlargement

The enlargement of the atria also occurs due to the inability to adapt to a pressure change which can cause injuries and scarring. Not only that, but it can also be a problem that arises when the atrium pumps blood to the aorta or an issue with the mitral valve, which is the valve that connects the left atrium and the left ventricle.⁷

In the case of the right atrium, the enlargement is most often due to situations in other parts of the heart or the lungs.⁸

Causes of heart enlargement

Hypertension 

Hypertension is a common condition and can become serious if not treated in time. High blood pressure is often asymptomatic, which is why it’s important to have regular check-ups.⁹

In hypertension, there is added pressure on the heart which means it has to work harder, causing it to enlarge.¹⁰

Heart valve disease 

This occurs when one or more heart valves do not open or close properly.¹¹

The heart, can compensate for the malfunctioning valves by working harder, for years or even decades. But as a consequence, the heart begins to enlarge.¹²

Cardiomyopathy 

Cardiomyopathy is a condition that affects the myocardium, which is the muscular tissue of the heart. Cardiomyopathy causes this tissue to stiffen and enlarge, compromising the pumping of blood to the rest of the body. Fluid can then accumulate in the chambers, leading to cardiomegaly.^1,13 

Coronary artery disease

An enlarged heart is most commonly caused by coronary artery disease (CAD).The coronary arteries are the vessels which provide the heart with oxygenated blood.When plaque (a buildup of lipids, cholesterol, and other chemicals) accumulates on the artery walls, the arteries narrow and blood flow is decreased.^3,14,15

Other contributing factors 

• Myocarditis: Viral infection in the heart that can result in congestive heart failure
• Cardiac ischemia: Reduced blood flow to the heart is known as cardiac ischaemia. Moreover, it may result in angina (chest pain)
• Previous heart attack: After a heart attack, the myocardium weakens and occasionally the heart must grow in order to pump blood to the rest of the body
• Thyroid disease: Thyroid diseases can affect many metabolic functions in the heart, causing cardiomegaly and other conditions 
• Lack of exercise: Sedentary lifestyles can lead to coronary diseases and high blood pressure
• Old age: As we age, arteries lose elasticity, becoming stiffer and potentially causing hypertension¹⁵

Mechanisms of heart enlargement

Physiological vs. pathological enlargement 

Adaptation vs. maladaptation 

The heart hypertrophy(growth) changes can be temporary, such as during pregnancies or physical activities (adaptive hypertrophy), but they can also become chronic (maladaptive hypertrophy) if the heart fails to adapt to a sustained workload.¹⁶

Cellular and molecular changes in cardiac tissue 

Myocyte hypertrophy 

Hypertrophy in myocytes (muscle cells), refers to the increase in the width and length of these cells, which also leads to an increase in the size of the heart. This change occurs as a consequence of the heart's need to pump more blood.¹⁷

Fibrosis and remodelling 

Cardiac remodelling is explained as a change in the size, shape, or structure of any of the cardiac chambers. Changes occur in the myocytes and the extracellular matrix. Myocytes, due to fibroblasts, will excessively synthesize collagen and other components that will accumulate in the extracellular matrix, leading to a process called fibrosis. All these factors affect the structure of the heart, making it stiffer and compromising its ability to pump blood.¹⁸

Neurohormonal activation 

Neurohumoral activation is basically the increase in activity of the sympathetic nervous system (SNS), the renin-angiotensin-aldosterone system (RAAS), vasopressin, and atrial natriuretic peptide (ANP). All of these activities, except for ANP, can lead to heart enlargement.¹⁹

Impact of heart enlargement on cardiac function

Changes in cardiac output 

Hypertrophy generates a higher pressure output, which means that the heart will pump harder. As we mentioned earlier, this can be beneficial in certain short-term situations. However, if it persists over time, the efficiency of the heart will eventually fail.²⁰

Impaired diastolic function

Diastole is the first part of the heartbeat when the chambers of the heart relax and fill with blood. When these chambers are unable to relax, diastolic dysfunction occurs. The thickening of any of these chambers during heart enlargement makes them stiff, which hinders diastole.^21,22

Systolic dysfunction and its consequences 

Systole is the process in which the heart chambers contract to pump blood. Systolic dysfunction reduces this ejection of blood from the dilated left ventricle. This dilation of the ventricle causes increased wall tension and higher oxygen consumption.^23,24

Increased oxygen demand and reduced supply

When the heart increases in size, it also requires more oxygen and nutrients for its myocytes, which necessitates the formation of new blood vessels(angiogenesis). If the angiogenesis does not occur or fails to compensate, cardiac myocytes will experience hypoxia.¹⁶

Relationship between heart enlargement and heart failure

How enlargement worsens heart failure symptoms 

Fluid retention 

Difficulties in pumping blood can cause the heart to accumulate fluid in the sac surrounding it, leading to pericardial effusion, which further hinders the ejection of blood, as well as in other places such as the lungs and limbs.¹

Exercise intolerance 

An enlarged heart under normal conditions can cause problems when performing even minimal exertion. Therefore, exercising, which already places more demand on the heart, increases the likelihood of developing heart failure if one has an elongated heart.²⁵

The cycle of worsening heart function and further enlargement 

The associated complications will largely depend on which part of the heart is being enlarged. If the heart is allowed to continue growing, blood clots can form, blocking blood flow and causing a heart attack, stroke, or pulmonary embolism (clot in the lung). It could also lead to heart failure, improper closure of the valves (heart murmur), or even sudden cardiac death.³

Clinical implications for diagnosis and treatment

The diagnostic process begins with a conversation with your doctor about your family history and symptoms. Tests are often conducted to assess and rule out associated conditions:³

• Chest X-ray and/or cardiac MRI to obtain images of your chest and heart
• Cardiac CT scan to create a video of your heart and blood flow
• Transthoracic echocardiogram to check the size and function of your heart
• Electrocardiogram (ECG) to analyze the heart's electrical activity
• Exercise stress test to evaluate the heart's response to certain exercises
• Genetic testing to determine if you have an underlying genetic problem 

Management and treatment strategies

Importance of early detection and intervention

This sign, although it can become chronic, can be effectively manage symptoms if addressed in a timely manner. A diagnosis will greatly increase your chances of achieving a positive outcome.³

Pharmacological treatments 

The most commonly used medications are:³

• Diuretics can reduce the amount of sodium and fluids in the body. This relieves pressure on the heart
• Anticoagulants 
• Antiarrhythmics to ensure a regular heart rhythm
• Beta-blockers to improve heart function and control blood pressure
• Angiotensin-converting enzyme (ACE) inhibitors and Angiotensin II receptor blockers (ARBs) to reduce blood pressure

Non-pharmacological interventions 

Lifestyle modifications 

The most common recommendations are to try to lose weight if you are overweight, quit smoking, reduce alcohol consumption, decrease salt intake, and manage fluid intake.^3,26

Monitoring and managing underlying conditions

To help monitor and manage underlying conditions, the following methods are often used:³

• A pacemaker is used to help the heart beat at a normal rhythm and rate
• An implantable cardioverter-defibrillator (ICD) is used
• Repair or replacement of a damaged heart valve
• Coronary bypass surgery or stent placement

Summary

Heart enlargement is an important sign for detecting underlying health problems. There are several types, and the most common causes include hypertension, heart valve diseases, cardiomyopathy, and coronary artery disease.

Cardiomegaly can be physiological (temporary) or pathological (chronic) and involves cellular changes such as myocyte hypertrophy and fibrosis. It affects cardiac function leading to increased oxygen demand and worsening heart failure.

If left untreated, it might result in fatalities or major side effects like heart attacks. Tests are used to make the diagnosis and to select the medication. Lifestyle modifications and underlying condition monitoring are used to treat the patients.