Introduction

Diabetes mellitus is one of the most common chronic conditions worldwide. It is characterised by elevated sugar levels in the blood affecting the whole body, including the heart. 

Heart enlargement, also called cardiomegaly, is a condition in which there is an increase in heart size with consequences that can be fatal. 

Uncontrolled diabetes mellitus with persistently elevated blood glucose levels causes changes in the physiology of the body, which can dramatically alter the function and structure of the heart and worsen complications of heart enlargement. 

Pathophysiology of uncontrolled diabetes mellitus

Diabetes mellitus(DM) is characterised by an uncontrolled blood glucose level. Under normal conditions, the pancreas secretes insulin, a hormone that regulates blood sugar levels. In DM, there is no or inadequate secretion of this hormone. 

Diabetes mellitus is classified into many subtypes, including:¹ 

• Type 1 DM
• Type 2 DM
• Maturity-onset diabetes of the young (MODY)
• Gestational diabetes
• Neonatal diabetes  
• Steroid-induced diabetes

Type 1 and Type 2 are the most prevalent, with different presentations and treatments, and both can develop chronically elevated blood sugar levels or hyperglycemia, leading to potential health issues.

Here are some mechanisms through which uncontrolled chronic DM can lead to health issues: 

Chronic hyperglycemia

People with hyperglycemia often present with excessive urination, the urge to drink water, an exaggerated appetite, and weight loss.

However, with longstanding hyperglycemia, elevated blood glucose can be harmful as it affects the body and alters function systemically. Hyperglycemia can also affect the eyes, causing diabetic retinopathy, the heart, causing cardiomyopathy, and the blood vessels, affecting all organs.

Metabolic disturbances

Metabolic disturbances in uncontrolled diabetes, including the elevation of free fatty acids, alteration of lipid metabolism, and oxidative stress, affect bodily functions and can exacerbate heart enlargement. 

In uncontrolled diabetes mellitus, there is an elevated breakdown of fat, contributing to high levels of free fatty acids. These are taken up by the heart and other organs, leading to lipotoxicity and impairment of the heart's functions.

Dyslipidemia or altered lipid metabolism often coexists with diabetes and is distinguished by elevated levels of triglycerides and cholesterol. These contribute to the development of atherosclerosis, a buildup of triglycerides, cholesterol, and other substances in the arterial wall, leading to systemic vascular impairment. This can advance structural heart damage and aggravate heart enlargement. 

Impact of uncontrolled diabetes on the heart

Diabetic cardiomyopathy

Diabetic cardiomyopathy is described as the structural and functional alterations that occur in the muscle of the heart, called the myocardium, associated with diabetes and that are not caused by other conditions such as coronary artery disease or hypertension.

Diabetes causes an increase in left ventricular mass, also known as left ventricular hypertrophy, which can cause dramatic heart dysfunction in the long term.

Obesity, often associated with DM, leads to a condition called myocardial lipotoxicity in which there is the deposition of lipids and cholesterol in the heart, which contributes to the development and severity of diabetic cardiomyopathy.²  

Hypertension

High blood pressure and DM usually coexist as they share common risk factors and pathophysiological mechanisms, especially those related to insulin resistance and obesity. 

Hypertension and diabetes share synergistic effects on the heart, and when left untreated, they can lead to detrimental outcomes. In addition, high blood pressure is a major risk factor for the vascular complications associated with DM, as hypertension itself is marked with vascular injury and dysfunction, which can lead to cardiomyopathy.³

Autonomic nervous system dysfunction 

The autonomic nervous system is an essential element of the nervous system that controls the balance and regulation of involuntary physiological processes such as heart rate and blood pressure. 

Uncontrolled diabetes mellitus is a risk factor for cardiac autonomic neuropathy, and its consequences can be mortal.⁸ 

The impaired cardiac autonomic nervous system function can lead to various cardiac disorders, which include arrhythmias, resting tachycardia, and fatal myocardial infarction.⁴ 

Complications of heart enlargement in uncontrolled diabetes

Heart failure

Heart failure is a condition in which the heart muscle, called the myocardium, fails to pump sufficient blood to meet the requirements of the body. In DM, it is primarily due to diabetic cardiomyopathy and structural changes in the cardiac muscles, which lead to its weakness and dysfunction of both systolic and diastolic functions.

Heart failure presents with symptoms like shortness of breath, swelling in the lower part of the body, fatigue, and weakness. Heart failure can be fatal when left without treatment for the long term. In people living with DM, there is a 2.5 times higher risk of developing heart failure than in non-diabetic people, and the incidence is higher when diabetes is uncontrolled.⁵ 

Arrhythmias

An arrhythmia is a condition that occurs when there is a disruption in the normal electrical signals to the heart. It can lead to an irregular heartbeat and an unsteady pattern of the heart. The most common symptoms are tachycardia ( fast heartbeat) and bradycardia (slow heartbeat). Arrhythmia can be dramatic and lead to sudden cardiac arrest and death. 

Due to the long-term damage to the heart and excessively high glycemia, arrhythmia incidence is greater in uncontrolled diabetics than in healthy individuals.⁶  

Reduced cardiac output

Cardiac output means the quantity of blood pumped from the heart in one minute. Its normal range is between 5-6 litres per minute for a person at rest. The cardiac output must be within this range to provide the body with blood that is rich in oxygen. 

People with uncontrolled diabetes have reduced cardiac output due to the effect of diabetes on the heart directly and also due to consequential fluid loss from the kidneys because of elevated blood sugar levels.⁷

Diagnostic methods for assessing heart enlargement in diabetics

Several diagnostic methods can help in the early detection of heart conditions, monitoring of disease progression, treatment planning, and assessment of the prognosis of the condition. 

Here are the most used approaches:

Echocardiography

It is a pain-free and secure examination during which a healthcare professional uses ultrasound sound waves to examine the heart structure and motions. It evaluates the measurements of the heart chambers and wall thickness, and estimates the pumping capacity of the heart.  

MRI and CT imaging 

These are advanced imaging techniques that allow detailed cardiac structure images. They also involve perfusion studies for detailed visualisation of the blood vessels of the heart. 

Electrocardiogram

ECG or electrocardiogram is a pain-free test, and it’s particularly useful for estimating the rate and rhythm of the heart. 

Biomarkers

A biomarker is a substance that indicates a normal or abnormal process or a disease. 

Biomarkers are crucial in the diagnosis and follow-up of heart enlargement in diabetic patients. The principal biomarkers in heart enlargement include: natriuretic peptides, BNP, and NT-proBNP. 

Management strategies to prevent or mitigate heart enlargement

Blood sugar control

Glucose is the sugar that supplies the required energy to cells in the body. However, elevated glucose levels have detrimental effects on the body, especially the heart, as discussed above. It is important to maintain glucose levels within suitable levels and target an optimum level of Hba1c. 

Glycemic control can be achieved with lifestyle modifications such as eating healthy and less sugary foods, regularly exercising, weight management, and medications such as metformin and GLP-1 receptor agonists.

Targeting an optimal glucose level in the blood will eventually help to prevent heart problems.

Regular cardiovascular screening

People with diabetes mellitus need regular cardiovascular screening with specialised health providers to detect early heart problems or follow up on heart conditions. 

Cardiovascular screening also includes blood pressure control, which in many cases coexists with diabetes. As with diabetes, blood pressure can be controlled with diet, regular exercise, weight management and medication. 

Pharmacological interventions

Medicative management of heart enlargement plays an important role in minimising complications and improving the quality of life of individuals. Depending on the cause of heart enlargement, here are the most commonly prescribed drugs to prevent or mitigate heart enlargement complications: 

• Diuretics: To reduce the amount of water in the body, which helps in reducing elevated blood pressure
• Beta-blockers, angiotensin-converting enzyme inhibitors: To lower blood pressure and improve heart function
• Blood thinning medications and statins: Reduce blood clot formation, which is important to reduce cholesterol levels

Summary

Diabetes mellitus is one of the most prevalent chronic diseases worldwide. High blood sugar causes multiple complications, and one of its serious complications is its effect on the heart, which leads to heart enlargement, which, if left untreated, can be fatal. 

High sugar in the blood affects the normal functioning of the heart by altering the functional structure of the myocardium and the blood vessels of the heart. It is worth noting that high blood pressure mainly coexists with high blood sugar, and together they accelerate the deterioration of the heart function. Thus, to improve the function of the heart, other risk factors should be appropriately managed as well.

Diabetes complications can be successfully avoided through lifestyle modifications, such as a diet not rich in sugar and regular physical activity. Pharmacological treatment is also essential in some cases to obtain the highest glycemic control. 

Finally, patient education should remain at the centre of the intervention as a well-informed person actively contributes to the outcome of the management and the improved quality of life in the long term.