Supraventricular extrasystolic activity and the elusive goal of identifying the imminent triggers of atrial fibrillation

Abstract

The concept that supraventricular extrasystoles (SVES) precede and “trigger”atrial fibrillation originated early inthe 20th century. Indeed an early theory proposed that atrial fibrillation wasmaintained bymultipleectopic atrial foci, later supplanted bythe multiple-wavelet,reentrant mechanismfor maintenance of atrial fibrillation. 1 Recent clinical studies have documented the primary role of SVES, generated most commonly in pulmonary veins, 2 in triggering atrial fibrillation. With this background of observations supporting the role of SVES as triggers and given that SVES are ubiquitous, more recent clinical observations have attempted to more accurately define the characteristics of SVES that predict an imminent and potent trigger role. Recent studies 3–6 have implicated frequent SVES and a composite index of SVES greater than 30 per minute plus supraventricular tachycardia (SVT) of 20 beats or more, defined as excessive supraventricular ectopic activity (ESVEA), as predictors of atrial fibrillation. In this issue, Johnson et al 7 report their attempt to evaluate the relative positive predictive values of the components of ESVEA, consisting of frequent SVES and supraventricular tachycardia, with special attention to the relative predictive values of the characteristics of SVT including length, rate, and frequency of the runs. The population was a sample from the Malmo Diet and Cancer study randomly selected from a sub-population with modestly elevated insulin resistance. The parent population had a relatively low incidence of cardiovascular disease. Consequently, this can be considered a study focused on the incidence of lone (idiopathic) atrial fibrillation in an older population (average age at entry 64.4 years). The statistical model that was used adjusted for age, sex, blood pressure, height, weight, smoking, and an index of insulin resistance, omitting physical activity score, education level, and alcohol consumption, which were not found to be associated in a separate analysis. The study population was censored for coronary artery disease and congestive heart failure at entry and during follow-up, but including these variables, which were relatively uncommon in the sub-population, did not alter the results. The assessment of trigger variables was based on a single 24-hour Holter monitor at entry, and the end point at follow-up was the clinical presentation of atrial fibrillation derived from local or national registries. There was no systematic attempt to detect asymptomatic atrial fibrillation by prospective monitoring in this retrospective study. The authors found, in confirmation of previous studies, that frequency of SVES, presence of SVT, and ESVEA were associated with atrial fibrillation and added the finding that frequency of SVT was an independent predictor. The mean follow-up in this study was 10.3 years and the average time to occurrence of atrial fibrillation was 7.1 years. They found no relation between the “duration” of SVT and the occurrence of atrial fibrillation, ostensibly in contradiction with prior reports of a relation between the length of runs and incident atrial fibrillation (with the qualification that lengths of runs measured by number of beats and duration of runs defined by time are not identical measures). It is not clear whether the authors’ analysis of duration involved time or number of beats. Surprisingly, the rate of SVT was not a predictor in this cohort. The additional analysis did not provide significantly greater positive predictive value for incident atrial fibrillation. The hazard ratio for frequent SVT was 1.95, while the hazard ratio for the composite measure ESVEA was 2.95. The authors did not provide a hazard ratio for the addition of frequency of SVT to ESVEA, which may have provided a greater positive predictive value and a more imminent prediction of atrial fibrillation, offering a practical guide for targeting a group for therapeutic intervention and consideration of a prospective study of the efficacy of suppression of supraventricular ectopy for prevention of atrial fibrillation. The relatively long latent period before the occurrence of atrial fibrillation and relatively few cases predicted detracts from the practical value of the predictors analyzed as guides to therapeutic intervention.