After adjusting for risk factors and potential confounders, researchers found that bradycardia was not associated with an increased risk for cardiovascular disease or mortality, according to a retrospective analysis.
They defined bradycardia as a heart rate of less than 50 beats per minute and said the condition is typically found in athletic adults.
Lead researcher Ajay Dharod, MD, of the Wake Forest School of Medicine in Winston Salem, North Carolina, and colleagues published their results online in JAMA: Internal Medicine on Jan. 19.
“Our results may be reassuring to most adults found to have asymptomatic bradycardia,” they wrote. “In contrast, the association of bradycardia with mortality among participants prescribed drugs that may slow [heart rate] may have clinical relevance. Further work is needed in other cohorts and trial databases to see whether these findings can be replicated and if confirmed, to determine whether this association is causally linked to [heart rate] or to use of these agents.”
For this analysis, they evaluated adults who did not have clinical cardiovascular disease before enrolling in the MESA (Multi-Ethnic Study of Atherosclerosis) study, a population-based cohort trial. The MESA participants were selected from Forsyth County, North Carolina; Manhattan, New York; Bronx, New York; Baltimore, Maryland; St. Paul, Minnesota; Chicago, Illinois; and Los Angeles, California.
The researchers had data on 6,733 participants who had an ECG tracing during their initial examination, which took place between 2000 and 2002. During the examination, participants completed a questionnaire regarding their demographic data, education, health habits, medical conditions, prescription medication usage, weight, waist circumference and height. Participants with atrial flutter, atrial fibrillation or a pacemaker at baseline were excluded.
Participants were followed for cardiovascular events and mortality at 9- to 12-month intervals and received calls asking about hospital admissions, cardiovascular outpatient diagnoses and procedures and deaths.
The mean age of participants was 62 years old, while 47 percent were male, 38 percent were white, 12 percent were Chinese, 28 percent were black and 22 percent were Hispanic.
Among participants who were not taking heart rate-modifying drugs, the mean heart rate was 63 beats per minute. Among participants who were taking heart rate-modifying drugs, the mean heart rate was 60 beats per minute.
The researchers found that participants taking heart rate-modifying drugs tended to be older and have a higher burden of cardiovascular disease risk factors and were more likely to have major ECG abnormalities.
After a median follow-up of 10.1 years, there were 633 incident cardiovascular events. The incidence of cardiovascular disease was lowest among participants with a heart rate of 50 to 59 beats per minute and highest among participants with a heart rate greater than 80 beats per minute.
There were also 697 deaths during the follow-up period: 160 were cardiovascular disease-related deaths, while 537 were not related to cardiovascular disease. The researchers found that mortality was significantly higher in participants with heart rates of less than 50 beats per minute and greater than 80 beats per minute who took heart rate-modifying drugs.
The study had a few limitations, according to the authors, including that they could not determine why participants took heart rate-modifying drugs at baseline. The participants may have taken the medications to treat arrhythmias, heart failure or other conditions. The researchers also could not determine the participants’ heart rate before they received the medications.