- Atrial fibrillation (A-fib) is a cardiovascular condition that causes an irregular and often rapid heartbeat.
- The episodes of atrial fibrillation tend to increase in duration and frequency over time, and disease progression is associated with an increased risk of adverse cardiovascular events.
- Treatments for atrial fibrillation include antiarrhythmic medications and catheter ablation, a procedure to destroy dysfunctional tissue, to restore normal heart rhythms.
- A recent randomized clinical trial showed that the use of cryoballoon ablation, a type of catheter ablation, as an initial treatment was associated with lower rates of progression of atrial fibrillation than antiarrhythmic drugs.
Studies suggest that around 1 to 2% of individuals in the United States have atrial fibrillation (A-fib). A-fib can become more severe over time, progressing from short episodes to more persistent forms characterized by longer and more frequent episodes. Studies suggest that persistent A-Fib is associated with an increased risk of stroke, heart failure, and mortality.
A recent study published in The New England Journal of Medicineshows that cryoballoon ablation was associated with a lower rate of progression from short episodes to persistent A-fib.
In an interview with Medical News Today, the study’s author Dr. Jason Andrade, a cardiac electrophysiologist at Vancouver General Hospital, said:
“Until now, we did not have any intervention proven to modify the progression of the disease. In contrast to medications, we see that ablation is able to modify the pathophysiology of the disease. This was a finding that was observed despite selecting a population at low objective risk of progression.
“This finding built on our previous work, which demonstrated that first-line ablation led to less short-term recurrence, a lower burden of AF [A-fib], higher likelihood of symptom resolution, greater improvement in quality of life, and lower subsequent healthcare utilization.”
The heart has four chambers- two upper chambers called the atria, and two lower chambers called the ventricles. The atria and ventricles contract alternately to pump blood to the body during each cardiac cycle.
The sinoatrial node or sinus node, a cluster of muscle cells located in the right atrium, helps maintain a normal heart rhythm and acts as the natural pacemaker. The sinus node generates electrical impulses that travel through a pathway of specialized muscle cells in the atria and the ventricles.
As the electrical impulses travel through the atria and down to the ventricles, these impulses cause the sequential contraction of these chambers. This results in the pumping of blood from the atria to the ventricles and then from the ventricles to the body. The rhythmic firing of the cells in the sinus node helps maintain a normal resting heart rate of 60 to 100 beats per minute in healthy individuals.
The disruption of these electrical impulses leads to an abnormal rate or rhythm of a person’s heartbeat, known as arrhythmia. A-fib, one of the most common forms of arrhythmia, is characterized by the contraction of the atria in a disorganized fashion.
In A-fib, the heart receives electrical impulses from sources other than the sinoatrial node. The resulting disordered electrical impulses lead to the rapid and chaotic contraction or quivering (fibrillation) of the atria.
The irregular heart rhythms in A-fib can lead to the formation of blood clots in the atria, which can travel and obstruct blood vessels, causing a stroke or embolism. In addition, patients with A-fib are at increased risk of heart failure and cardiovascular mortality.
A-fib is a progressive condition, with episodes becoming more frequent and longer with time. The condition can be classified according to the duration of an episode.
Paroxysmal A-fib refers to episodes that spontaneously stop within seven days. On the other hand, episodes that last longer than seven days are known as persistent atrial fibrillation. In long-standing persistent A-fib, episodes occur uninterrupted for more than 12 months.
The authors of the present study note that an estimated 8 to 15% of individuals with paroxysmal A-fib cases tend to develop persistent A-fib within the first 12 months. Moreover, individuals with persistent A-fib are at a greater risk of heart failure and thromboembolism, the obstruction of blood vessels due to a blood clot.
Studies suggest that treatments that can help control the heart rhythm in patients with A-fib in the early stages after diagnosis can reduce the risk of adverse cardiovascular outcomes.
Antiarrhythmic drugs that normalize the heart rhythm are the first line of treatment for patients with symptomatic A-fib. However, these drugs can have significant side effects and are associated with the recurrence of the condition.
Changes in the structure and electrical properties of heart muscles upon the initiation of A-fib are considered to lead to the development of persistent A-fib. However, antiarrhythmic drugs are not able to reverse changes in the heart muscle structure that lead to the progression of the condition to sustained forms.
Catheter ablation for A-fib
Catheter ablation has been conventionally used as the second line of treatment in patients who show side effects or do not respond to antiarrhythmic drugs. However, catheter ablation is now considered an alternative first-line treatment for A-fib.
Catheter ablation involves the use of cold or high temperatures to destroy a small portion of the heart tissue responsible for irregular rhythms. By destroying the defective region, catheter ablation, unlike antiarrhythmic medications, addresses the underlying cause of A-fib.
During this procedure, a thin, flexible tube, i.e., a catheter, is inserted into the blood vessels and guided to the heart. Electrodes at the tip of the catheters are then used to identify the region responsible for the disorganized heart rhythm. During radiofrequency ablation, radiofrequency waves are delivered through the tip of the catheter to generate heat and destroy the defective tissue.
Cryoballoon ablation, in contrast, uses cold temperatures to freeze the tissue and destroy the targeted region. Once the catheter reaches the heart, a tiny balloon at the tip of the catheter is inflated using a refrigerant. This balloon can then be used to freeze and destroy the target tissue.
Cryoballoon ablation is a newer method of catheter ablation and is associated with a lower risk of complications than radiofrequency ablation. Cryoballoon ablation is also less reliant on operator skill than radiofrequency ablation.
Previous studies have shown that catheter ablation can lead to a greater reduction in the recurrence of episodes of arrhythmia and hospitalization in patients with A-fib. Additionally, in a previous randomized clinical trial, the study authors had shown that cryoballoon ablation led to a significant reduction in the recurrence of A-fib episodes compared to antiarrhythmic drugs.
In the present randomized clinical trial, the researchers compared the ability of cryoballoon ablation and antiarrhythmic drugs to reduce the risk of progression of paroxysmal AF to persistent AF over a 3-year follow-up period.
The present study consisted of 303 adults with paroxysmal A-fib who were randomly assigned to receive either cryoballoon ablation or antiarrhythmic drug therapy. Among the 303 patients, 154 participants received cryoballoon ablation, whereas the remaining 149 individuals received antiarrhythmic drug therapy. The researchers implanted a cardiac monitor after the initiation of treatment to continuously track changes in heart rhythm over the follow-up period of 36 months.
During the three-year follow-up period, a smaller fraction of patients in the cryoballoon ablation group experienced an episode of persistent A-fib than the antiarrhythmic drug therapy group. Specifically, 3 out of 154 patients (1.9%) in the cryoballoon ablation group and 11 out of the 149 (7.4%) patients in the antiarrhythmic drug therapy group had a persistent atrial fibrillation episode.
The researchers also evaluated the number of patients who experienced an atrial tachyarrhythmia event between 90 days after the initiation of the treatment and the end of the follow-up period. Atrial tachyarrhythmia describes heart rates greater than 100 beats per minute caused by irregular electrical impulses originating in the atria. Such events can occur due to A-fib as well as other conditions.
In the present study, a lower percentage of patients who underwent cryoballoon ablation surgery (56.5%) had an atrial tachyarrhythmia event during the follow-up period than those using antiarrhythmic drugs (77.2%). Catheter cryoballoon ablation was also associated with a lower average amount of time in A-fib and better quality of life during the follow-up period.
In addition, a lower percentage of patients in the cryoballoon ablation group were hospitalized than those in the antiarrhythmic treatment group. Notably, there was an absence of difference in the risk of serious adverse effects in the cryoballoon ablation and the antiarrhythmic drug therapy groups.
In sum, these results suggest that cryoballoon ablation could be more effective at preventing the progression of A-fib and reducing the risk of hospitalization. These results are consistent with other studies conducted on patients with a higher risk of disease progression.
The present study used a younger population and had the advantage of continuous monitoring. Dr. Shephal Doshi, cardiac electrophysiologist and director of cardiac electrophysiology and pacing at Providence Saint John’s Health Center in Santa Monica, CA, said:
“This study is extremely important and that there was high-quality data in terms of follow-up as all patients had an implantable loop recorder which truly identified the arrhythmia burden and incidence of arrhythmia. This allowed for excellent follow-up and showed that catheter ablation in this group of patients was clearly superior to drug therapy, even with a longer-term follow-up of 3 years.
“There have been other recent studies that have used 1-year follow-up, but this study stands out, with longer duration follow-up where all patients have an implantable loop monitor which recorded the rhythm and rate for any abnormalities 24 hours a day seven days a week,” Dr. Doshi explained.
“This study was specific to cryoablation, but many expect that ablation, in general, is superior to antiarrhythmic drugs, with other forms of ablation such as radiofrequency and likely pulse field ablation shown to be safe and effective in clinical trials,” he added.