Monitoring and management of patients with chronic atrial fibrillation: Is there added value in the identification of clinical phenotypes?

Chronic atrial fibrillation (AF) remains a major public health problem, with serious, global financial impact. Permanent (or chronic) AF is distinguished from acute paroxysmal or persistent AF in that cardioversion is no longer feasible and treatment therefore centres on ventricular rate control – and related stroke prevention – based on current AF guidelines,1-3 as well as individualized risk factors. In this issue of the European Journal of Cardiovascular Nursing, Ball et al. favour us with their analysis of post-discharge electrocardiogram (ECG) Holter monitoring of intended AF control in chronic AF patients, with the objectives of a) enhancing therapeutic monitoring and b) classifying chronic AF phenotypes that are potentially predictive of future adverse events, such as thrombo-embolism and progressive cardiac dysfunction.4 The authors hypothesized that they would identify a significant proportion of those with marked variation from physician-designated rate or rhythm control in the early discharge period.4 As readers, we are left with three take-home messages: 1) 24-hour Holter monitoring may be a useful post-discharge monitoring strategy, 2) there may be distinct phenotypes among those who have chronic AF, and 3) out of hospital monitoring and timely treatment decision making can be improved. Before we endeavour to unpack the implications of this interesting paper, we first recap, briefly, some key highlights of Ball and colleagues’ methodological approach and results: as part of the multi-centre, Standard versus Atrial Fibrillation Specific Management Study (SAFETY) trial,5 24-h Holter monitoring data (seven to 14 days post-discharge) among those nominated for rhythm (n= 44) and rate (n= 89) control were analysed according to heart rate, rhythm and average inter-individual variability (i.e. hour-to-hour differences in heart rate values). Those in the upper quartile of the 24-h heart rate variability frequency distribution were classified as ‘persistently labile’ (35%, n= 33) and the majority (59%, n= 78) were considered ‘stable’. Based upon discrete sub-analysis of heart rate lability – occurring discretely in either daytime- or night time-specific hours – an additional 16% were classified as ‘periodically labile’. Ball et al. argue4 that the importance of identifying AF phenotypes is their potentially predictive value, particularly given the inherent, well-documented difficulties in achieving therapeutic rate and rhythm control.6 We are definitely inclined to agree when it comes to what we see as being of key interest to clinicians: the identification of those patients with persistently labile chronic AF. Here, the value proposition lies in the potential to carve out opportunities to design clinical interventions for people most at risk for progressive cardiac dysfunction. But, our enthusiasm must be expressed in equal measure with our reservations about outcome data collection in this case. Given groups were identified by 24-h Holter monitoring at just one point in time; it seems clear that more research is required to help elucidate those with labile chronic AF. From a measurement perspective, it is our position that there are potentially several ways to enhance precision of estimates of the proportion of those who are truly persistently labile. Indeed, Ball et al. duly acknowledge the potential for over (and under)-estimation of lability by virtue of their reliance on a single 24-h window.4 At a minimum, subsequent validation work will require longer recording periods (via long-term monitoring technologies) to allow for comprehensive examination of trends in day-to-day heart rate variability. In contrast to the persistently labile phenotype, we find the periodically labile designation somewhat less compelling in terms of prognostic utility. Those deemed periodically labile were classified as such if they were found to be in the upper quartile of the heart rate variability distribution during either night or daytime periods, but not both. Given this team’s conservative rate control cut-off of ⩽ 90 beats/min4 – due to concerns regarding their sample’s high risk for tachycardia-mediated cardiomyopathy – external validation is required to determine whether or not residing in the upper-quartile of heart rate variability (cut-off: 4.22 beats/min) sometime during a period of 12 h (on average) is of consequence, particularly in the daytime hours among those with less clinically complex profiles than those enrolled in this study. While we appreciate the conservative approach of Ball et al., recent guidelines have liberalized rate control to a target of < 100 beats/min, based on randomized controlled trial data demonstrating no significant differences in symptomatology and quality of life outcomes, between traditionally strict (i.e. < 80 beats/min) and more lenient rate targets.3 By virtue of this editorial, we likely raise more questions than answers. This team is to be applauded for sparking what we hope will be ongoing debate and research into how best to identify and target interventions for those with persistently labile chronic AF. Their paper makes a potentially important contribution to the body of work in AF patients, particularly with respect to community-based monitoring and pre-emptive intervention. Early identification of patients who may experience persistently labile heart rates in the context of chronic atrial fibrillation, early after discharge from hospital, may benefit from adjustment to their therapeutic management. In terms of implications for future research, several new avenues of exploration are possible. As alluded to above, the utility of post-discharge Holter monitoring may be worth examining in terms of frequency, duration, cost-effectiveness and patient satisfaction. Certainly, more research needs to be done before we can adopt the proposed three chronic AF phenotypes suggested. In particular, it would be important to explore the proposed distinction between persistently labile and periodically labile and whether there is a clinically meaningful difference between them. If not, the resulting two phenotypes (stable and persistently labile) may give clearer direction to nurses who are monitoring patients after discharge from hospital. Finally, as with all research related to chronic conditions, future work should include investigation of patients’ preferences regarding treatment options and goals, monitoring, and self-management. These future considerations open the door to both qualitative and quantitative inquiry by nurse scientists and their colleagues. The authors declare that there is no conflict of interest. This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

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