Resistant hypertension (RH) is a chronic condition in which blood pressure is persistently elevated, despite concurrent treatment with three or more antihypertensive agents. It is associated with increased cardiovascular morbidity and mortality, and its effective treatment is costly and invasive. RH has been a hot topic of late, with more than a dozen prevalence studies published in the past five years alone. An estimated 15–30% of treated hypertensive patients are considered resistant. The real trouble, however, is that RH is notoriously difficult to confirm; inadequate dosing, white coat effects, and medication non-adherence all preclude its diagnosis, and tend not to be routinely assessed in research or clinical practice.
Non-adherence is particularly challenging. Reasons why a patient with a chronic asymptomatic condition like RH might not adhere to their medication are diverse and multifaceted; yet it is essential to understand the function of non-adherence behaviour if you hope to change it.
To learn more about the extent of and reasons for non-adherence for RH, we conducted a systematic review and meta-analysis (Durand et al., 2017). Of 68,313 participants, 31.2% were non-adherent, suggesting that at least one-third of patients may be inappropriately classed as resistant. Further subgroup analyses revealed that adherence rates varied depending on the clinical setting (with poorest adherence observed for patients in specialist hypertension clinics) and the measure used to assess adherence. In fact, when we meta-analysed studies that used direct measures only (e.g. bioassays of blood or urine), the overall non-adherence figure was closer to 50%.
What was particularly interesting, and honestly quite disappointing, about our findings was that, of 24 included studies, only six examined patient-level predictors of adherence. Of these six, all investigated demographic and/or biological factors (e.g., age, sex, income, heart rate or blood pressure); however, no study in our review examined psychological factors associated with adherence for RH. This is a major limitation of the existing literature that needs to be addressed.
Ultimately we ended up knowing a little more and a lot less about non-adherence for RH. The simple fact is that a patient cannot be described as resistant to a treatment he or she is not taking; however, extant research has neglected intensive study of non-adherent patients, leaving “pseudo-resistant” patients at increased risk of cardiovascular events and diseases. My PhD research, supervised by Dr Gerry Molloy (NUI Galway), will use established psychological theory to identify reasons why these patients do not adhere; with the ultimate goal of informing targeted behaviour-change interventions to improve adherence and cardiovascular health [watch this space].
This research is conducted as part of a Health Research Board-funded project investigating RH in general practice in Ireland, led by Professor Andrew Murphy (NUI Galway). This project aims to use international best practice guidelines to identify the prevalence and prognosis of RH in primary care in Ireland.
PhD Candidate, Medication Adherence across the Lifespan (MEDAL) Group,
School of Psychology, NUI Galway
Research funded by the Health Research Board Patient-Oriented Research Award
Durand, H., Hayes, P., Morrissey, E. C., Newell, J., Casey, M., Murphy, A. W., & Molloy, G. J. (2017). Medication adherence among patients with apparent treatment-resistant hypertension: Systematic review and meta-analysis. Journal of Hypertension, 35. Epub ahead of print. http://dx.doi.org/10.1097/HJH.0000000000001502