Why are beta-blockers used for heart enlargement?

Beta-blocker medications perform four primary functions that are crucial for people living with heart failure:

• They help the heart relax more easily, reducing the workload on the heart muscle
• They lessen the impact of harmful stress chemicals, such as adrenaline, that are often elevated in heart failure
• They gradually improve the heart’s ability to pump blood, which supports long-term heart function. Over time, this improves the heart's ability to pump blood

Even if you don't have noticeable symptoms, beta-blockers are often prescribed for people with heart failure. People with systolic heart failure– a condition where the heart doesn’t pump effectively– are given beta-blockers because these medicines help improve survival, especially in those with more severe symptoms.

Although there are many types of beta-blockers, only three have been approved by the US Food and Drug Administration (FDA) for the treatment of heart failure. The commonly recommended beta-blockers for heart failure are:

• Bisoprolol
• Carvedilol
• Metoprolol¹

How do beta-blockers work in patients with cardiomegaly?

Adrenaline (epinephrine) and noradrenaline (norepinephrine) are two hormones your body produces that help regulate the stress response. In threatening situations, these hormones prepare your body to fight or flee. However, even everyday stress can trigger their release, leading to consistently high hormone levels. As a result, your body may sustain elevated levels of noradrenaline and adrenaline over time.

These hormones trigger the stress response by attaching proteins called receptors in your heart, blood vessels, and muscles. When noradrenaline and adrenaline bind to these receptors, the cells respond in a specific way.

Although there are several different types of receptors, beta-blockers specifically target beta-1 (B1), beta-2 (B2), and beta-3 (B3) receptors. Most B1 receptors are found in the cells of your heart and kidney heart pumps blood. When triggered, they increase your heart rate and how forcefully your heart pumps blood. When stimulated, the kidneys also release an enzyme called renin into the bloodstream.

B2 receptors are mostly found in the tissues of your nervous system, blood vessels, and respiratory system (including your windpipe and airway tubes). Once activated, B2 receptors carry out the following functions:

• Relax your blood vessels and airways to help lower blood pressure and make breathing easier
• Stimulate the liver to convert stored glycogen (a form of sugar) into glucose for quick energy
• Increase heart rate and the force of heart contractions
• Causes muscle tremors

Most B3 receptors are found in your bladder and fat cells. When activated, they cause mild muscle tremors, relax the bladder, and help break down fat.

Beta-blockers work by preventing noradrenaline and adrenaline from attaching to these receptors. This helps keep your blood vessels wide and your heartbeat steady, reducing blood pressure and strain on the heart.¹

What are the common side effects of beta-blockers?

Like all medications, beta-blockers can cause side effects. These vary from person to person, but some are more common than others.

Common side effects may include

• Cold hands or feet
• Feeling tired or fatigued
• Weight gain
• Light-headedness or dizziness

Less common side effects may include

• Depression
• Shortness of breath
• Difficulty sleeping

Special considerations

If you have asthma, it is usually advised to avoid beta-blockers, especially those that affect both the heart and lungs, as they may trigger or worsen asthma symptoms.

For people with diabetes, beta-blockers may mask signs of low blood sugar, such as a rapid heartbeat. If you have diabetes and are prescribed a beta-adrenergic blocker, regular monitoring of your blood sugar levels is important.

Some beta-blockers may also affect blood fat levels by slightly increasing triglycerides (a type of fat in the blood) and lowering HDL (the “good” cholesterol).² 

Use with caution

Beta-blockers may not be suitable for everyone. In certain health conditions, they can worsen symptoms or lead to complications. These include:

• Moderate to severe asthma: Beta-blockers that affect both the heart and lungs (non-selective beta-blockers) can trigger breathing difficulties or asthma attacks. In mild cases, doctors may prescribe beaa-1 selective beta-blockers to minimise this risk. However, for more severe respiratory conditions, beta-blockers are often avoided altogether
• Certain heart rhythm disorders (arrhythmias): Some types of arrhythmias may be aggravated by beta-blockers. Your doctor will assess whether this type of medication is appropriate based on your heart rhythm
• Low blood pressure or a slow heartbeat: Because beta-blockers lower both heart rate and blood pressure, they can worsen existing low readings, potentially causing symptoms such as dizziness or fainting
• Raynaud’s disease: This condition affects blood circulation, especially the fingers and toes. Beta-blockers may worsen these symptoms by further narrowing blood vessels
• Low blood sugar (hypoglycemia): In people with diabetes, especially Type 1, beta-blockers can mask many warning signs of low blood sugar, such as a fast heart rate. However, they do not affect all symptoms, for example, sweating, may still occur and should be taken seriously³

When should you contact your doctor about side effects?

Your healthcare provider can advise when to seek medical attention while taking beta-blockers. In general, contact your doctor if you notice any sudden changes in symptoms, especially those related to your heart or circulation. Examples of symptoms that require medical attention include:

1. Feeling short of breath
2. Experiencing chest pain or discomfort
3. Noticing heart palpitations (such as fluttering, rapid beats, or skipped beats)
4. Fainting suddenly or having repeated episodes of dizziness or light-headedness³ 

Summary

Beta-blockers are commonly used to manage heart conditions, but like all medicines, they can cause side effects and interact with other substances.

It's crucial to discuss any medical concerns you may have, the medications or supplements you take, and your use of alcohol, tobacco, or recreational substances with your doctor before starting beta-blockers.

Make sure to contact your doctor straight away if you experience any unsettling side effects. Your doctor can recommend an alternative medicine and help you safely reduce the beta-blocker dose.