The researchers hope that the new biomarkers will help doctors to identify which patients with atrial fibrillation are most and least likely to benefit from ablation therapy, a procedure that deliberately destroys malfunctioning heart tissue.
The study - by a team at the Intermountain Medical Center in Murray, UT - was recently presented at the American College of Cardiology's Scientific Session in Washington, D.C. The research paper is also published in the Journal of the American College of Cardiology.
In A-fib, the atria - the two upper chambers of the heart - beat in an irregular way and disrupt blood flow into the lower chambers (the ventricles).
A-fib can occur all the time, or it can occur in brief episodes. It is a major cause of stroke.
The Centers for Disease Control and Prevention (CDC) estimate that A-fib affects between 2.7 and 6.1 million people in the United States.
People with A-fib usually experience one or more of the symptoms, which can include: irregular heartbeat, heart palpitations, fatigue, light-headedness, chest pain, and shortness of breath. Others may have A-fib without realizing it, because it can sometimes occur with no symptoms.
Ablation does not work for all A-fib patients
Ablation is a procedure that is used to treat A-fib when medication or electrical cardioversion to reset the heartbeat do not work.
Fast facts about A-fib
- The risk for A-fib rises with age
- Other risk factors include: high blood pressure, obesity, diabetes, and European ancestry
- A-fib increases risk for stroke by four to five times.
The procedure uses a radio-frequency, laser, or cryotherapy catheter to destroy the areas of heart tissue that are sending abnormal electrical signals that disrupt the heartbeat.
If ablation is successful, the heartbeat returns to a normal pattern.
However, in around 30 to 40 percent of cases, A-fib returns following ablation, which means that some patients undergo the procedure several times.
MicroRNAs are small, noncoding molecules that influence gene expression. Since their discovery around 20 years ago, they have been identified as key players in cardiovascular processes linked to several heart conditions, including heart failure, high blood pressure, and arrhythmias.
Also, since researchers have discovered that microRNAs are present in the bloodstream, they have been investigating their potential to serve as biomarkers to screen for patients at higher risk of heart attack, heart failure, and other heart conditions.
MicroRNAs as predictors of ablation success
For the new study, researchers at the Intermountain Medical Center Heart Institute set out to identify which microRNAs might indicate A-fib patients whose ablations are likely to work the first time.
They assessed 140 patients who underwent ablation to treat A-fib. The treatment was successful in 85 patients, but 55 experienced a return of irregular heartbeat within a year of treatment.
The researchers chose to investigate microRNAs that influence inflammation, fibrosis (scarring), and electrical activity in the heart.
From these, the team found three microRNAs whose pre-ablation levels varied between the two groups: they were significantly lower in those patients who later experienced A-fib recurrence.
The three molecules the researchers identified - microRNA21, microRNA150, and microRNA328 - have already been linked to remodeling and adverse electrical healing, a type of atrial scarring that results from ablation.
Dr. T. Jared Bunch, senior study investigator and medical director of Heart Rhythm Services for Intermountain Healthcare, explains that: "Our genetic makeup is important in how we respond and heal from procedures. MicroRNA particles are a direct result of our genetic makeup," and concludes:
"As we try to identify treatments that are tailored to an individual person, microRNA has the promise to help us determine who may be a better candidate for ablation versus other therapies."
He and his colleagues hope that their findings will help doctors to decide which A-fib patients are most and least likely to benefit from ablation therapy, which is costly and not without risk.