The Management of Subclinical Atrial Fibrillation: The Pathway to True Medical Expertise

To become a medical expert, one must go beyond the proficient application of guideline-based care and become an expert at the management of uncertainty. Every day in clinical practice, we are confronted with management dilemmas for which evidence-based medicine [1] cannot give clear guidance. Navigating these routine situations requires the clinician to draw on their experience and the available medical literature; then weigh therapeutic options in terms of their perceived risks and benefits, the degree of uncertainty in these estimates and with a shared decision-making framework that includes patients’ perspectives [2]. It is important that clinicians acknowledge when decisions are made in this fashion, rather than those based on high-quality medical evidence, so that they recognize the knowledge gap and remain receptive to new information. It is even more critical that practice-guidelines and consensus statements highlight these differences, to avoid giving the broader medical community the impression that no new medical evidence is needed.

In the 2019 American Heart Association scientific statement on subclinical atrial fibrillation, Noseworthy and colleagues have done an excellent job to review the medical literature and highlight knowledge gaps pertaining to the role of oral anticoagulation for stroke prevention in this population. [3] They make a clear distinction between clinical and subclinical atrial fibrillation, highlight the prevalence of the latter, and discuss a reasonable approach to anticoagulation use in subclinical atrial fibrillation. This discussion is both thoughtful and comprehensive, but perhaps deserving of two minor clarifications. First, it should be noted that pacemaker patients make up a large proportion of patients identified with subclinical atrial fibrillation, and they are typically elderly [4]. There are good data from the AVERROES trial to show that patients over age 75 years, treated with either aspirin or apixaban have an approximately three-fold increase in major bleeding compared to younger patients [5], which in the context of the lower absolute risk of stroke seen with subclinical atrial fibrillation [4] substantially changes the risk-benefit balance. As Noseworthy states, the CHA2DS2-VASc score also predicts bleeding events, thus the performance of this score may be quite different than in clinical atrial fibrillation.

Elderly patients with subclinical atrial fibrillation are also at risk of stroke from a variety of mechanisms, with data from ASSERT suggesting that only between 25-50% appearing to be embolic in origin [6]. Thus, it is probably overstated to say that any subclinical atrial fibrillation in a patient with a history of stroke requires anticoagulation, although this may be reasonable in those with a clear embolic-appearing stroke [7], or an unclassified ischemic stroke with longer episodes of temporally-associated subclinical atrial fibrillation [8].

In addition to addressing the controversy of anticoagulation in patients with subclinical atrial fibrillation, this scientific statement does an excellent job at describing the looming challenges and opportunities in this field. The statement highlights that the progression of subclinical atrial fibrillation is a strong predictor of incident heart failure [9], which might be amenable to preventive strategies. The writing group has also stressed the important implications that this field, and the ongoing clinical trials [10, 11] have for the controversial topic of population-based atrial fibrillation screening [12]. With the advent of sensitive tools that can screen non-invasively for atrial fibrillation over extended periods of time, understanding the impact of treating short-lasting, low-burden subclinical atrial fibrillation becomes critical if we are to determine what screening strategies may be effective.

Subclinical atrial fibrillation is a good example of a condition with broad clinical implications, for which there are major management uncertainties. This American Heart Association scientific statement does an exemplary job of highlighting these issues, and proposing a path forward, while stressing the need for new medical knowledge. Highlighting and describing knowledge gaps is a more effective strategy than proposing guidelines with weak recommendations based on low-quality evidence [13], as the latter strategy often leads clinicians to believe that best practice is understood, and further evidence unnecessary. Expert clinicians are often those with the reputation for knowing all of the answers. However, the true expert is one who is able to recognize, profess the limits of their knowledge, while remaining receptive to new information which pushes back these limits.