Introduction

Heart enlargement (Cardiomegaly) happens when the heart grows bigger making it hard to pump blood effectively. It's not a disease itself, but it can show up because of other heart problems. These include high blood pressure, heart muscle disorders, too much body fat, damaged heart valves, and blocked coronary arteries. When the heart can't pump blood right, it causes poor blood flow and unusual heartbeats. This can lead to life-threatening problems like heart failure. When this happens, doctors suggest implanting pacemakers. These helps to maintain a stable heartbeat and boost the heart’s pumping capacity. A pacemaker is a little device that regulates the heartbeat. It can prevent fatal problems like sudden heart failure and make the heart work much better. Doctors can spot a bigger heart using visuals from chest X-rays, CT scans, or MRIs. They also use electrocardiograms, echocardiograms, and heart catheterization to check.

This article explores how pacemakers can help manage heart enlargement as time passes. They do this by improving heart function and making patients' lives better, but new studies show we need to do more research in this area. They point out that using pacemakers for a long time might have potential risks and worsen heart enlargement.

Pacemakers: Overview 

The heart has its own electrical system (sinoatrial node) that works as a natural pacemaker. This system sends signals throughout the heart making it beat in sync and with a steady rhythm. When the heart can't pump enough blood to the body because of irregular heartbeats or heart failure, artificial pacemaker implantation becomes necessary. A pacemaker is a tiny battery-operated device that doctors use to correct heart rhythm problems. These problems happen when the heart beats too slow, too fast, or in an unusual pattern. The pacemaker sends electrical signals to the heart to keep it beating at a steady and regular rate. This helps the heart chambers beat in coordination with each other, which allows the heart to pump blood more efficiently.¹ 

The two main categories of pacemakers are temporary and permanent.

A temporary pacemaker

It is generally used as a short-term solution and is inserted through a vein into the neck or groin region. The device remains outside the body, connected to the heart by a thin wire. Temporary pacemakers are often used in emergencies, until the heart condition improves.

A permanent pacemaker

It is developed for long-term use. It remains inside the body, inserted under the skin, usually in the chest or abdominal area. This type of pacemaker is used for patients with chronic arrhythmias or heart conditions that require continuous support to maintain normal heart function.

Different types of permanent pacemakers  

Doctors suggest a specific type of pacemaker to a patient depending on the heart problem. 

Types of permanent pacemakers include:²

Single-chamber, dual-chamber, leadless pacemakers, and biventricular pacemakers. 

• Single-chamber pacemaker: this type of pacemaker uses a single wire or lead attached to any one chamber of the heart 
• Dual-chamber pacemaker: this type of pacemaker has two wires attached to the two chambers of the heart 
• Leadless pacemakers: a small device attached to the inner wall of the heart with no wires or leads; hence, it is called a leadless or wireless pacemaker. It is inserted using a catheter-based insertion method, in which a thin flexible tube is inserted into the blood vessel to implant the pacemaker properly 
• Biventricular pacemakers: biventricular pacemakers, used during cardiac resynchronization therapy (CRT), have three leads: two connected to the ventricles (lower chambers of the heart) and one connected to the right atrium. It is the right choice for heart failure patients

Mechanism by which pacemakers affect the heart enlargement 

The connection between pacemaker use and cardiac enlargement depends on the underlying cause of the heart enlargement and the type of pacemaker used. 

Several mechanisms through which pacemakers can affect heart enlargement include the following:

Restoring the heart rhythm

Pacemakers work by sending impulses or signals to the heart to fix abnormal heartbeat and help it to beat at normal rate and rhythm. By this, pacemakers help reduce the strain on the heart and let the heart pump blood more efficiently.^3,4  

Reducing sympathetic nervous system activation

The sympathetic nervous system (SNS) activates the reflex actions of the cardiovascular system, therefore increasing heart rate and contractility⁵ as a compensatory response to maintain blood flow when the heart becomes weak. This is particularly observed during conditions like exercise, cardiomyopathy, myocardial infarction(MI), and heart failure (HF). In cardiomyopathy, the heart's ability to pump blood diminishes, leading to enlargement to maintain efficient blood flow. Similarly, cardiac remodelling occurs after a myocardial infarction, due to the damage of the heart muscle. While this compensatory response⁶ to the SNS can be beneficial for a short period, prolonged activation is harmful to the heart. It worsens contractile function and potentially leads to heart failure.⁷ 

In such conditions when the SNS is overactive, pacemakers help to regulate the heart rate by providing consistent electrical impulses, reducing the dependency on sympathetic stimulation to maintain sufficient blood flow and normal heart rate. 

With time, excessive sympathetic stimulation can lead to cardiac hypertrophy.⁸ Pacemakers can help reduce the workload on the heart and limit further thickening of the heart muscle (hypertrophy), which eventually enhances overall cardiac performance. 

Enhancing cardiac output

Modern cardiac pacemakers have a special feature called the “rate response” function, which enables the device to alter the heart rate based on the level of activity of the patient.⁹

For instance, more oxygen and blood is required during physical activities like exercise or stress. The rate response function helps the pacemaker to increase the heart rate to meet these needs, as it would happen with a normal healthy heart. It enhances blood flow, ensures adequate oxygen delivery, lessens the workload on the heart, and helps prevent further damage. 

Long-term impact of pacemakers on heart enlargement

This section attempts to provide a summary of main results from the findings of the recent research studies.

• In many cases, a pacemaker is implanted in the patient suffering from bradycardia or heart failure in order to prevent any further damage to the heart. The studies show that patients with right ventricular pacing (RVP) are at a significant risk of developing heart failure within the first six months of the implantation period. The study points out the importance of assessing clinical signs and left ventricular (LV) function before and after the pacemaker implantation. This may be crucial for detecting heart failure at its early stages. It has been concluded in this article, that not all pacemaker patients experience heart failure; however, those with a history of MI and chronic kidney disease (CKD) are more susceptible. This study also recommends that the implantation of CRT would be appropriate, instead of an RVP-only device to treat advanced atrioventricular (AV) block¹⁰
• Another real-world study shows that individuals with high RVP (≥40%) face a high risk of mortality, especially older people (＞67 years) compared to younger persons (＜67 years)¹¹
• A case study reports a 70-year-old woman with heart block developed pacing-induced cardiomyopathy (PICM) following the implantation of a dual chamber pacemaker. This study examines how dual chamber pacemaker implantation can cause ventricular dyssynchrony, leading to structural changes in the heart muscle as time goes by. These changes may result in further cardiac enlargement and worsen the heart condition¹² 
• A study on implanting the leadless micra pacemaker shows that patients with enlarged right atrium (diameter and area over 4 cm and 17 cm² respectively) tend to have longer procedure times, exceeding 60 minutes for the micra pacemaker implantation. This study recommends that patients with larger right atrial diameters are better suited to undergo conventional pacemaker implantation¹³ 
• A study conducted on 322 patients aged 65 and older who received a dual chamber pacemaker explores the risk factors and prognosis for new-onset of atrial fibrillation (AF). In a total of 322 patients, about 24.5% experienced a new-onset of AF in the follow-up period. Elderly age, high blood pressure, and enlarged left atrium were the major risk factors identified. These findings suggest that careful monitoring and effective management of these parameters would be beneficial for elderly patients after pacemaker implantation¹⁴  

Summary

Pacemaker implantation is important in the management of arrhythmias and improvement of symptoms in patients with heart enlargement. However, they also confer risks that may worsen existing conditions. Studies have proven an increased prevalence of heart failure shortly after implantation, increased death rate, and structural changes in the anatomy of enlarged hearts, possibly leading to hypertrophic cardiomyopathy and also observed increased possibility for atrial fibrillation. Thus, it requires constant observation and proper management strategies for the best patient outcome. However, future work is required to overcome the shortcomings of a pacemaker.