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Medication adherence in patients with heart failure with preserved ejection fraction is unclear. This study sought to evaluate treatment adherence in the Pirfenidone in Patients with Heart Failure and Preserved Left Ventricular Ejection Fraction (PIROUETTE) trial. Adherence was evaluated through pill counts and diary cards. Univariable and multivariable regression models were used to assess the relationship between adherence and baseline characteristics. Instrumental variable regression was used to estimate the causal effect of pirfenidone treatment duration on myocardial fibrosis. Complete adherence data were available in 54 of 80 participants completing the trial. Mean adherence to study medication was 94.7% and 96.9% in the pirfenidone and placebo groups, respectively. Each additional day of treatment with pirfenidone resulted in a significant decrease in myocardial extracellular volume (–0.004%; 95% confidence interval: -0.007% to -0.001%; P = 0.007). Associations with adherence included older age, higher symptom burden, lower body weight, and smaller right ventricular size. Adherence to study medication in the PIROUETTE trial was very high among patients for whom complete adherence data were available. Importantly, each additional day of treatment reduced myocardial fibrosis. Potential predictors of adherence were identified. Implementation of improved methods for assessing adherence is required. [ABSTRACT FROM AUTHOR]

The myocardial interstitium has emerged as a potential therapeutic target and as a biological entity to improve risk stratification and better guide existing interventions. Clinical trials focusing on the myocardial interstitium are required to establish causality and improve patient outcomes. This review will discuss issues around clinical trials targeting the myocardial interstitium, including antifibrotic therapies, efficacy outcome measurements, mechanistic outcome measurements and mediation analysis, sample size, trial duration, considerations for multicenter trials, stratifying trial recruitment according to the interstitium, and approaches to enrich recruitment, using examples of ongoing clinical trials. • The myocardial interstitium is a potential therapeutic target and a potential risk stratifier that can guide interventions. • Clinical trials focusing on the myocardial interstitium are required to establish causality and improve patient outcomes. • CMR provides quantitative assessment of the myocardial interstitium and many other features of cardiovascular structure and function and thus can be used to stratify recruitment and to evaluate efficacy and mechanism. [ABSTRACT FROM AUTHOR]

Heart failure with preserved ejection fraction (HFpEF) involves multiple pathophysiological mechanisms, which result in the heterogeneous phenotypes that are evident clinically, and which have potentially confounded previous HFpEF trials. A greater understanding of the in vivo human processes involved, and in particular, which are the causes and which are the downstream effects, may allow the syndrome of HFpEF to be distilled into distinct diagnoses based on the underlying biology. From this, specific interventions can follow, targeting individuals identified on the basis of their biological phenotype. This review describes the biological phenotypes of HFpEF and therapeutic interventions aimed at targeting these phenotypes. [ABSTRACT FROM AUTHOR]