Thursday, May 04, 2023

by Physician Office Resource

Within the right atrium is a group of cells called the sinus node, the heart’s natural pacemaker. It’s here where signals are produced to start each heartbeat. When a heart is functioning properly, the signal travels from the sinus node through both atria, and through a pathway between the atria and ventricles known the atrioventricular node. This transmission of electrical signals allows the heart to contract and pump blood through the body.

But what happens when those electrical signals are not functioning properly? When faulty electrical signals are sent, a heart experiences arrhythmia, making the heartbeat too fast, too slow, or irregular in nature. 

Atrial Fibrillation (AFib) is the most common type of heart arrythmia and occurs when the two atria of the heart beat in an irregular way thus inhibiting the flow of blood to the ventricles. Symptoms of AFib include irregular heartbeat, heart palpitations, lightheadedness, extreme fatigue, shortness of breath, and chest pain. Chronic AFib is a progressive disorder that can lead to heart failure and increases a person’s risk for stroke. The CDC reports that AFib causes about 1 in 7 strokes.¹   

Today, an estimated 6 million people in the US suffer with atrial fibrillation. The CDC expects that number to grow to 12.1 million by the year 2030. In 2019 AFib was mentioned on 183,321 death certificates and was the underlying cause of death in 26,535 of those deaths.¹ 

In this article we’ll review current treatments for AFib including drug therapy and cardiac catheter ablation; in addition to new findings from a study published by the New England Journal of Medicine titled, “Progression of Atrial Fibrillation after Cryoablation or Drug Therapy” that focuses on the benefits of treating AFib patients with a cardiac catheter ablation rather than with drug therapy. 

Drug Therapy 

When a patient is first treated for AFib, they are often prescribed three types of medications to help prevent and control irregular heartbeats and stoke²:

• Heart rate controllers
• Heart rhythm controllers
• Blood Thinners 

Heart Rate Controllers

Heart rate controllers usually consist of two different classes of drugs, Beta blockers and calcium channel blockers. 

Beta Blockers are a class of drug that prevent the stimulation of the adrenergic receptors, thus blocking the effects of the hormone epinephrine (adrenaline). Because of this block, the heart begins to beat slower and with less force. Some examples of beta blockers include²:

• Metoprolol
• Propranolol
• Timolol
• Nadolol
• Atenolol
• Bisoprolol
• Carvedilol 

Calcium Channel Blockers are medications that lower blood pressure by preventing calcium to enter the heart and artery cells. By blocking calcium and its effects of causing the heart and arteries to contract with greater force, heart rate slows and blood pressure lowers. 

Depending on heath and conditions being treated, there are short-acting and long-acting forms of calcium channel blockers available. Short-acting medications work quicker but don’t last very long. Long-acting medications release at a slower rate thus providing a longer lasting effect. Some examples of calcium blockers that are used to treat AFib include:

• Diltiazem
• Verapamil 

Heart Rhythm Controllers

Known as a chemical/pharmacological cardioversion, heart rhythm controllers are drugs used to restore normal heart rhythm. Drugs used in this therapy fall in to two classifications: sodium channel blockers and potassium channel blockers. 

Sodium Channel Blockers are a class I antiarrhythmic that inhibit sodium influx through cell membranes. This inhibition of sodium lowers the heart’s ability to conduct electricity. Examples of this drug include:

• Flecainide
• Propafenone
• Quinidine 

Potassium Channel Blockers are a Class III Antiarrhythmic that prolongs the action potential duration by inhibiting repolarizing potassium channel blockers.³ This prolongs the length of time that the cell is unexcitable. Examples of this drug include:

• Amiodarone
• Sotalol
• Dofetilide
• Dronedarone 

Blood Thinners

Because blood clots and stroke are closely associated with AFib, physicians often prescribe blood thinners to reduce the risk of occurrence and damage caused by those conditions. Examples of blood thinners include:

• Warfarin
• Apixaban
• Dabigatran
• Edoxaban
• Rivaroxban 

With the heart rate and rhythm controlled, most people begin to feel better. But what about disease progress? Yes, the medications are treating the symptoms of AFib, but the actual disease can still progress and affect other cells of the heart and AFib can return. Other treatment options for AFib include Electrical Cardioversion Therapy and Cardiac Ablation. 

Electrical Cardioversion

Electrical cardioversion is a method in which the heart rhythm is rest by sending electric shocks through the heart. Even with electrical cardioversion, patients are often still prescribed heart rate and rhythm controllers and blood thinners to help prevent future episodes. 

Cardiac Ablation

Normally last in line in the treatment of AFib, a cardiac catheter ablation involves utilizing heat or extreme cold to create a pattern of scars (known as a maze procedure) in the atria. Scar tissue does not send electrical signals, so the scars act as barriers to the cells that are sending rogue signals that cause AFib. 

The Case for Cardiac Catheter Ablation First over Drug Treatment

As mentioned previously, a cardiac catheter ablation is often last in line in treatment of patients with AFib. However, a recent study published in the New England Journal of Medicine titled, “Progression of Atrial Fibrillation after Cryoablation or Drug Therapy,” concluded that treating patients with cardiac catheter ablation first rather than with drugs can stop the disease from getting worse.⁴ 

Dr. Jason G. Andrade, principle investigator of the study said, “If we perform the procedure earlier, the thinking was that maybe we could change that disease trajectory. We could prevent people from having these more advanced forms of atrial fibrillation, and so the procedure will not only work better, but it will change how people are living with the disease and lead to a much better long-term outcomes”⁵ 

Their study included two randomized groups out of a cohort of 303 people who were treated for AFib to compare the disease progression. One group would be treated with medicine first and the second group would receive a cardiac catheter ablation first. Patients of both groups received an implanted cardiac monitor after treatment to track changes over a three-year period. 

One of the most striking findings of this study showed a 75% reduction in the progression of AFib in patients who received a cardiac catheter ablation over those who only received drug treatment. Dr. Andrade went on to say, “By doing the procedure, you really got at the source of the problem and prevented people from developing more advanced forms of the disease over several years of follow-up. We know that the more advanced forms of atrial fibrillation have higher rates of stroke, are more likely to cause heart failure, and result in premature mortality. We’ve now shown for the first time that an intervention in the form of catheter ablation changes the disease trajectory and prevents patients from going on to have those more advanced forms of atrial fibrillation.”⁵ 

The study also showed that patients who received the ablation experienced fewer serious adverse events at a rate of 4.5% compared to those who received only drug treatment at 10.1%. 

This is the second of such a study performed on treating AFib with a catheter ablation over drug therapy. The authors of this study suggested that more research on the topic will be coming.

Drug therapy will always be essential in the treatment of AFib. However, based on this study’s findings, I believe this will help flip the trend to patients receiving cardiac catheter ablations sooner rather than later. 

References

1. https://www.cdc.gov/heartdisease/atrial_fibrillation.htm
2. https://www.heart.org/en/health-topics/atrial-fibrillation/treatment-and-prevention-of-atrial-fibrillation/atrial-fibrillation-medications
3. https://www.cvpharmacology.com/antiarrhy/potassium-blockers
4. https://www.nejm.org/doi/full/10.1056/NEJMoa2212540
5. https://thedailyscan.providencehealthcare.org/2023/01/surgery-first-vs-drugs-for-a-fib-could-stop-diseases-progress-nejm-study/