Morning pulmonary artery pressure measurements by CardioMEMS are most stable and recommended for pressure trends monitoring

Heart failure (HF) has become a major socio-economic burden as it is characterised by episodes with acute decompensation, requiring hospitalisation, and is associated with increased morbidity and mortality [1, 2]. The CardioMEMS system, an implantable wireless pulmonary artery (PA) pressure monitor, was shown to reduce hospitalisations by improving HF management in the CHAMPION trial [3]. Since the 2016 European Society of Cardiology guidelines on HF [4], ambulatory haemodynamic monitoring may be considered (IIb indication) in symptomatic patients with previous HF hospitalisation. Subsequent analyses and data obtained in the clinical setting showed an improved quality of life and reduced morbidity and mortality using ambulatory haemodynamic monitoring [5‐8].

Currently, HF patients with a CardioMEMS sensor are instructed by the manufacturer to measure PA pressures in the morning. However, it has not yet been investigated whether morning indeed yields the most precise PA pressure measurements, while some patients may prefer a different time for practical reasons, or may vary the time of their measurement considerably. Additionally, while daily patterns of PA pressures measured in a consistent manner are currently not available, CardioMEMS provides the opportunity to study them. Previous studies on PA pressures in HF suggest the existence of diurnal rhythms [9, 10]. Given the emerging importance of these circadian rhythms in cardiovascular pathophysiology [11], we aimed to define the most optimal time of day for measuring PA pressures in HF patients.

In this study, we provided more scientific evidence supporting the current CardioMEMS recommendations to measure PA pressures in the morning. The present data demonstrate the stability of morning PA pressures, suggesting that any observed differences in morning values are more likely reflecting clinically relevant changes in heart failure status, rather than merely natural diurnal variation. Changes in evening PA pressures could be attributed to circadian fluctuations and apparently correct themselves overnight, at least in clinically stable patients.

While diurnal properties of PA pressures were previously explored [9, 10], this is the first study to directly assess its clinical relevance in an ambulatory setting. We sought to determine the most optimal time of day for PA pressure measurements based on intra- and inter-day variation. In order to do so, we opted for a translational set-up by omitting time points during the night (between 12 am and 6 am), when maximal PA pressures were previously noted [9].

In most of the subjects, PA pressure increased in the evening. The evening rise of PA pressure is in line with other studies [9, 10], and ascribed to its diurnal nature. Furthermore, over the course of 5 days, PA pressure exhibited different degrees of time-of-day-dependent variation. Morning measurements were consistently stable in the vast majority of patients, while noticeable fluctuations were usually observed in the evening. Diastolic PA pressure varied more than systolic PA pressure, regardless of the time of day. Pronounced variation in the evenings could be explained by patients’ daily activities, e.g. food and fluid daily intake variation, effect of different medications, as well as physical activity. All of these factors influence important physiological processes directly and via sympathetic nerve system or renin-angiotensin-aldosterone system (RAAS) activation, and can cause PA pressures to fluctuate [12].

Collectively, our data offers a 2-fold evidence to support the current CardioMEMS recommendations to measure PA pressures in the morning. Firstly, we show that PA pressures exhibit a diurnal rhythm, with lowest pressures measured in the morning, and reaching their peak in the evening. Therefore, by measuring PA pressures consistently in the mornings, any changes in pressures could be ascribed to a change in the patient’s condition. For example, if the pressure would first be measured in the morning (= lowest PA pressure), with a follow-up measurement in the evening (= highest PA pressure), it could indicate a deterioration of the patient’s condition, while it actually only reflects a mere circadian fluctuation. If the pressure is always measured in the morning, any deviating recording of PA pressures would be a clear indication that an intervention is needed. Secondly, as previously mentioned, PA pressures may be affected by patient’s activity during the day, including exercise, and food, fluid, and medication intake. The susceptibility of PA pressures to these daily changes could explain why evening PA pressures were least stable in the majority of subjects during a course of five days. Combined with their diurnal properties, highest and least consistent PA pressures are observed in the evening. Thus, morning PA pressure measurements are more reliable and better reflect the true changes in the patient’s condition (e.g. worsening of heart failure), rather than showing the influence of daily activities (e.g. food intake, exercise, etc.) which will reset until the next day. In conclusion, morning PA pressure measurements, as opposed to evening measurements that are prone to external influences, will give a clear indication for intervention if relevant increase in values is observed.

Given the pronounced variation in ambulatory PA pressures during the day, standardised morning PA pressure measurements will improve reliability and interpretation of the values provided by the CardioMEMS sensor (see Take-home Fig. 3). Clinicians will be able to ascertain which changes of the PA pressures indicate true alterations in the patient’s health status (e.g. worsening of HF) and which merely reflect natural diurnal properties.