By Michael H. Crawford, MD
SOURCE: Murakoshi N, Xu D, et al. Prognostic impact of supraventricular premature complexes in community-based health checkups: The Ibaraki Prefectural Health Study. Eur Heart J 2015;36:170-178.
Atrial premature complexes (APCs) are commonly observed on routine ECGs and believed to be harbingers of atrial fibrillation, especially in patients with cardiovascular disease. However, little is known about the long-term prognosis of APCs in the general population. Thus, these investigators from Japan analyzed the database of a large community-based cohort from 1993 to 2008 to determine the risks of APCs seen on the subjects’ baseline ECGs. There were 63,197 subjects without heart disease or atrial fibrillation (AF) who were followed for at least 1 year (20,492 men and 42,705 women, mean age 58 years at baseline). The primary endpoint was mortality and the secondary endpoint was AF. The mean follow-up was 14 years, but if censured by AF occurrence on the yearly follow-up exam, it was 6 years. In addition to analyzing the raw data, the data were adjusted for age and other potential confounders such as blood pressure, body mass index, alcohol use, and other ECG findings. Also, a propensity-matched analysis was done matching subjects with APCs to those without.
Results: APCs were observed in 6%, and these subjects were more likely to be older and have other risk factors for AF and mortality. APCs were significantly associated with death from stroke, cardiovascular death, and all-cause mortality in women, but only cardiovascular death in men. AF occurred in 1 per 1000 person years, and APCs were a significant predictor of AF (hazard ratio [HR], 4.87 men and 3.87 women). In the propensity score-matched subjects, APCs were significantly associated with AF and cardiovascular death in all subjects and stroke death in women, but not all-cause mortality. The authors concluded that in a general population free of AF or cardiovascular disease, the presence of APCs on a routine ECG is associated with AF and cardiovascular death.
This study affirms what has been seen in smaller studies of higher-risk patients, that APCs predict future AF. Why APCs would predict cardiovascular death in a general population is not clear from this study. It could be simply that by being associated with AF, you are more likely to have a stroke or develop heart failure. On the other hand, APCs may be markers of underlying cardiovascular disease. This makes sense since in the baseline data, APC subjects were older and had more risk factors for cardiovascular disease. That APCs are strong predictors of AF is not surprising. Pathophysiology studies show that APCs originating in the pulmonary vein orifices can trigger AF. Also, when the number of APCs per ECG was evaluated, more APCs increased the risk of AF. This is remarkable given that we are talking about a routine ECG, approximately 15 seconds of monitoring. Since APCs are frequently seen on ambulatory ECG monitoring done for a variety of reasons, one wonders if there is some threshold for APCs 24 hours above which the risk of AF and cardiovascular disease increases significantly in a general population.
In addition to the limitations of an ECG as a monitoring device for APCs, it was also the way AF was confirmed. Thus, asymptomatic intermittent AF was unlikely to be detected. Also, the subjects were not extensively evaluated for cardiovascular disease on the yearly exams, so some subclinical disease may have been present and unaccounted for in the propensity analysis. In addition, there were twice as many women as men in the study. The authors don’t offer an explanation for this, but since subjects with known cardiovascular disease were excluded in this older middle-aged population, many men may have been excluded. The main clinical message of this study is that patients with APCs on a routine ECG should undergo screening for heart disease and asymptomatic intermittent AF.