Genetic Testing of Some Patients With Early-Onset AF Advised

Genetic testing may be considered in patients with early-onset atrial fibrillation (AF), particularly those with a positive family history and lack of conventional clinical risk factors, because specific genetic variants may underlie AF as well as “potentially more sinister cardiac conditions,” a new white paper from the Canadian Cardiovascular Society suggested.

“Given the resources and logistical challenges potentially imposed by genetic testing (that is, the majority of cardiology and arrhythmia clinics are not presently equipped to offer it), we have not recommended routine genetic testing for early-onset AF patients at this time,” lead author Jason D. Roberts, MD, associate professor of medicine at McMaster University in Hamilton, Ontario, Canada, told Medscape Medical News.

“We do, however, recommend that early-onset AF patients undergo clinical screening for potential coexistence of a ventricular arrhythmia or cardiomyopathy syndrome through careful history, including family history, and physical examination, along with standard clinical testing, including ECG, echocardiogram, and Holter monitoring,” he said.

The white paper was published online on March 27 in the Canadian Journal of Cardiology.

Routine Testing Unwarranted

The Canadian Cardiovascular Society reviewed AF research in 2022 and concluded that a guideline update was not yet warranted. One area meriting consideration but lacking sufficient evidence for a formal guideline was the clinical application of AF genetics.

Therefore, the society formed a writing group to assess the evidence linking genetic factors to AF, discuss an approach to using genetic testing for early-onset patients with AF, and consider the potential value of genetic testing in the foreseeable future.

The resulting white paper reviews familial and epidemiologic evidence for a genetic contribution to AF. As an example, the authors pointed to work from the Framingham Heart Study showing a statistically significant risk for AF among first-degree relatives of patients with AF. The overall odds ratio (OR) for AF among first-degree relatives was 1.85. But for first-degree relatives of patients with AF onset at younger than age 75 years, the OR increased to 3.23.

Other evidence included the identification of two rare genetic variants: KCNQ1 in a Chinese family and NPPA in a family with Northern European ancestry. In case-control studies, a single gene, titin (TTN), was linked to an increased burden of loss-of-function variants in patients with AF compared with controls. The variant was associated with a 2.2-fold increased risk for AF.

The two main classes of AF variants identified in candidate gene approaches were linked to ion channels and ventricular cardiomyopathy. For example, loss-of-function SCN5A variants are implicated in Brugada syndrome and cardiac conduction system disease, whereas gain-of-function variants cause long QT syndrome type 3 and multifocal ectopic Purkinje-related premature contractions. Each of these conditions was associated with an increased prevalence of AF.

Similarly, genes implicated in various other forms of ventricular channelopathies also have been implicated in AF, as have ion channels primarily expressed in the atria and not the ventricles, such as KCNA5 and GJA5.

Nevertheless, in most cases, AF is diagnosed in the context of older age and established cardiovascular risk factors, according to the authors. The contribution of genetic factors in this population is relatively low, highlighting the limited role for genetic testing when AF develops in the presence of multiple conventional clinical risk factors.

Cardiogenetic Expertise Required

“Although significant progress has been made, additional work is needed before [beginning] routine integration of clinical genetic testing for early-onset AF patients,” Roberts said. The ideal clinical genetic testing panel for AF is still unclear, and the inclusion of genes for which there is no strong evidence of involvement in AF “creates the potential for harm.”

Specifically, “a genetic variant could be incorrectly assigned as the cause of AF, which could create confusion for the patient and family members and lead to inappropriate clinical management,” said Roberts.

“Beyond cost, routine introduction of genetic testing for AF patients will require allocation of significant resources, given that interpretation of genetic testing results can be nuanced,” he noted. “This nuance is anticipated to be heightened in AF, given that many genetic variants have low-to-intermediate penetrance and can manifest with variable clinical phenotypes.”

“Traditionally, genetic testing has been performed and interpreted, and results communicated, by dedicated cardiogenetic clinics with specialized expertise,” he added. “Existing cardiogenetic clinics, however, are unlikely to be sufficient in number to accommodate the large volume of AF patients that may be eligible for testing.”

Careful Counseling

Jim W. Cheung, MD, chair of the American College of Cardiology Electrophysiology Council, told Medscape Medical News that the white paper is consistent with the latest European Heart Rhythm Association/Heart Rhythm Society/Asia Pacific Heart Rhythm Society/Latin American Heart Rhythm Society expert consensus statement published in 2022.

Overall, the approach suggested for genetic testing “is a sound one, but one that requires implementation by clinicians with access to cardiogenetic expertise,” said Cheung, who was not involved in the study. “Any patient undergoing genetic testing needs to be carefully counseled about the potential uncertainties associated with the actual test results and their implications on clinical management.”

Variants of uncertain significance that are detected with genetic testing “can be a source of stress for clinicians and patients,” he said. “Therefore, patient education prior to and after genetic testing is essential.”

Furthermore, he said, “in many patients with early-onset AF who harbor pathogenic variants, initial imaging studies may not detect any signs of cardiomyopathy. In these patients, regular follow-up to assess for development of cardiomyopathy in the future is necessary.”

The white paper was drafted without outside funding. Roberts and Cheung reported no relevant financial relationships.