Introduction 

The heart beats through a steady, regular pattern of electrical impulses. The upper chambers (the atria) hold the small specialised tissues that generate the electrical impulse. This tissue is called the pacemaker. This stimulates the atria to contract. The atria control these impulses to ensure they are sent out simultaneously throughout the heart. However, the heart’s electrical rhythm can become fast and chaotic, causing a chain reaction throughout the heart. The atrial contractions are disrupted, so they cannot pump blood to the ventricles. As a result, the ventricles contract irregularly, thus creating an irregular heartbeat. This is known as atrial fibrillation (Afib). It can be classified by duration and persistence, giving us four main categories.¹ 

• Paroxysmal Afib - episodes may last for a few seconds to a week  and may resolve within 24 hours  either spontaneously or through treatment; however, they may recur 
• Persistent Afib - episodes last longer than 7 days and may not resolve on their own, and  require medical intervention to restore a regular heart rhythm 
• Long-standing Persistent Afib - continues for more than 12 months
• Permanent Afib - reestablishing a regular heart rate is no longer pursued, as all attempts are unsuccessful 

The forms of Afib can have various consequences, which can be life-threatening. In this article, we will discuss the effects of persistent Afib and its role in stroke, heart failure, and thromboembolism risks. 

Stroke Risk in Persistent Atrial Fibrillation

Stroke risk is five times higher in people with persistent Afib. The chaotic contractions mean the movement of the blood is not normal, resulting in stagnant blood in the left atrial appendage (LAA). The LAA is an extension of the left atrium where blood can collect. The LAA varies in structure between individuals. Through 4D MRI and CT scans, studies have shown a decrease in blood flow velocity in patients with persistent Afib due to their LAA shape and function.² The slow-moving blood causes blood clots to form in the LAA. These clots can be pumped to the brain. As a result, the blood vessels in the brain are interrupted, causing an ischemic stroke. The geometry and blood flow of the atrium can be used to determine the risk of stroke in individuals with Afib. 

Stroke risk is assessed through the CHA₂DS₂-VASc score.⁹ Here, all contributing factors are considered to calculate the risk for cardiovascular disease in Afib patients. A high CHA₂DS₂-VASc score calls for anticoagulant intervention. It allows for immediate risk stratification, which tells doctors how severe the risk of stroke is. The score goes into further detail by sectioning the female gender, coronary, and vascular diseases. This ensures that Afib patients are given guided treatment based on their risks.³ 

Heart Failure and Persistent Atrial Fibrillation

Persistent Afib causes oxidative stress, which means the cells are not receiving enough oxygen. This leads to a calcium overload, which triggers the inflammation cascade. As a result, the heartbeat loses its rhythm, which has several consequences that facilitate heart failure: 

Impaired ventricular filling:

The atria quiver instead of contracting normally. Hence, the ventricles receive less blood. Consequently, the heart cannot pump the required volume of blood, which worsens its function. If left untreated, heart failure can occur. 

Irregular and Rapid Ventricular Rhythm:

Afib causes a rapid and chaotic heart rate. This gives the ventricles less time to fill with blood between heartbeats. Thus, it reduces the cardiac output and puts strain on the heart.

Tachycardia-Induced Cardiomyopathy:

Tachycardia results when the heart beats at a fast pace, putting the heart under a lot of stress. The heart muscles weaken and enlarge, which can cause heart failure. 

Neurohumoral Activation:

The neurohumoral system includes a complex network of nervous and hormonal factors that regulate the body’s functions:

• Heart rate 
• Blood pressure 
• Fluid balance 

In Afib, this system is stimulated and produces elevated levels of heart rate-increasing hormones, such as angiotensin II and norepinephrine. Furthermore, blood pressure rises, and the heart changes in size, shape, and function. These alterations contribute to the development of heart failure.⁴

The condition may be reversed, and the structural and electrical remodelling of the heart that occurs in heart failure causes the atria to enlarge and become stiff. This new environment promotes and sustains Afib. In heart failure, the atria are enlarged and suffer from increased pressure. This scars the atria, impairing the electrical impulses, triggering Afib development.⁴

Heart failure and Afib share similar risk factors, such as diabetes, obesity, and hypertension (high blood pressure). This links them in a vicious cycle, where one can worsen the other. This complex relationship is not fully understood. Further research is being done to develop effective strategies to treat both conditions simultaneously.⁴

There are several management strategies to counteract these two conditions. Restoring rhythm control is key. This can be done through the following methods:

• Catheter ablation is a minimally invasive treatment. It uses heat or cold energy to scar the heart’s tissue. This aims to disrupt the already disrupted electrical signals, returning them to a normal rhythm. A thin, flexible tube is inserted into a blood vessel and guided to the heart. This delivers the heat or cold energy to the heart tissue, causing the irregular heartbeat. The scars created block the irregular signals.⁵
• Antiarrhythmic drugs are used to treat abnormal heart rhythms. It does so by suppressing irregular electrical signals in the heart. They also prevent rapid electrical impulses from travelling along the heart tissues.
• Rate vs rhythm control is a technique used to manage Afib.⁷ The rate control aims to keep a stable heart rate. Meanwhile, rhythm control focuses on restoring and maintaining a normal heart rhythm. This primarily involves medication such as:
  • Beta-blockers⁶
  • Calcium channel blockers 
  • Digoxin, which slows down the heart rate⁸

Thromboembolism Risks Beyond Stroke

Thromboembolism is the blocking of a blood vessel by a dislodged blood clot. Afib increases the risks of these events:

• Systemic embolism occurs when a blood clot or other substance travels through the bloodstream. It lodges in a blood vessel, obstructing blood flow to organs or tissues. This has serious risks of stroke or heart attack
• Venous thromboembolism (VTE) can occur.¹⁰ This blood clot forms in a vein, causing deep vein thrombosis, leading to a pulmonary embolism (PE). This blood clot starts in a leg vein and travels up to the lungs, obstructing a blood vessel. In the case of PE, the pulmonary artery is blocked

The duration of Afib impacts the risks of thromboembolism. The disruption of the heart’s regular function influences events leading to blood clot formation. Anticoagulants are used to combat this ¹⁰ 

• Heparin is used to prevent blood clots
• Warfarin is a long-term anticoagulant that prevents blood clots
• Direct oral anticoagulants are alternatives to warfarin and are easier to use
• Compression stockings apply pressure on the legs to promote blood flow, preventing blood clots
• Encouraging patients to walk and move soon after a procedure
• Hydration prevents the blood from becoming too thick
• Filters can be placed in the veins to stop clots from reaching the lungs

Management and Prevention Strategies

The management and prevention of Afib ranges from lifestyle changes to invasive procedures. An individual can integrate several lifestyle changes to manage and prevent Afib: 

• Regular exercise 
• Balanced diet 
• Stress management
• Quitting smoking 
• Limited alcohol consumption 

Managing other health conditions that contribute to Afib is also key. A person must control their blood pressure, high cholesterol, and diabetes.

It is crucial to catch this condition early to prevent further diseases. Doctors will conduct a series of physical exams in the initial diagnosis, including:

• Listening to the heart rhythm 
• Taking blood pressure 
• Checking the size of the thyroid gland
• Swelling in the legs or feet 
• Listening to the lungs to detect heart failure or infection

Further scans are done:

• ECG- records the heart’s electrical signals 
• An echocardiogram can reveal any blood flow problems due to irregular muscle contractions. 
• Blood tests can reveal any imbalances in the blood, which can cause Afib 
• Cardiac MRI can detect any irregularities in the heart’s structure or function 

Various treatments include:

• Electrical cardioversion resets the heart's rhythm, using low-energy shocks; however, this may be a temporary solution
• A permanent pacemaker can be placed if the heart rate is too slow 
• Pulmonary vein isolation ablation uses catheters to deliver energy around the pulmonary veins. This can improve the response to Afib medications and, in some cases, provide a permanent solution

There is great potential for advancements in AFib treatment. Artificial intelligence (AI) can produce algorithms to analyse ECG to detect AFib. It uses a predictive modelling system to detect any signs of AFib that would otherwise go overlooked. In addition to this, AI can use genomic data and biomarkers to tailor treatments to individuals with AFib.¹¹  This can revolutionise therapies by creating targeted treatment strategies. 

Conclusion

Persistent Afib is a serious condition that increases the risk of many life-threatening complications. Therefore, an early diagnosis is crucial to understand the risks and their appropriate management. Further advances in anticoagulation therapy to reduce its side effects and gene-based coagulation therapy are in production. This provides a new pathway of personalised treatment for individuals. As a result, guided management of Afib can increase the recovery rates.