Three independent studies have identified genetic factors that influence heart rate and other electrocardiogram measurements. The studies, online this week in Nature Genetics, offer new insight into common genetic variants that influence electrical activity in the heart.
Cardiac conduction is the rate by which the heart conducts electrical impulses. The electrocardiogram (ECG) is a common clinical test that is used to evaluate the function of the cardiac conduction system and assess heart rate variability. Heart rate is usually expressed as beats per minute, while the other measurements obtained from the ECG define time intervals of specific steps in the cardiac cycle. In a normally beating heart, an electrical signal initially spreads from the right atrium to the left atrium, which is represented by the P wave on the ECG. Consequently, the electrical signal leads to ventricular contraction, which corresponds to the QRS duration. The PR interval is the length of time from the beginning of the P-wave to the beginning of the QRS duration.
Hilma Holm and colleagues analyzed approximately 20,000 individuals of European ancestry and identified one variant at the gene MYH6 that is associated with heart rate. They also found that variants at the genes TBX5 and SCN10A were both associated with PR interval and QRS duration. John Chambers and colleagues carried out an analysis of 6543 Indian Asians and found that the same variant in SCN10A also is associated with PR interval in the Indian Asian population. The team performed replication testing in 6243 Indian Asians and 5370 Europeans and confirmed that the variant at SCN10A is associated with prolonged cardiac conduction, Finally, Arne Pfeufer and colleagues report a meta-analysis of 28,517 European individuals and identified nine loci associated with PR interval, which include TBX5 and SCN10A.