Nitrate’s Effect on Activity Tolerance in Heart Failure with Preserved Ejection Fraction (NEAT-HFpEF) Trial: Rationale and Design

HEART FAILURE WITH PRESERVED EJECTION FRACTION

The prevalence of heart failure (HF) with preserved ejection fraction (HFpEF) is increasing¹. In patients with HFpEF, the burden of symptoms, functional decline, and mortality is high², and health-related quality of life is poor³. Physicians caring for these patients currently have limited therapeutic options beyond diuresis and management of comorbid conditions. Hence there remains an immediate and critical need for therapies to alleviate symptoms and meaningfully improve quality of life for patients with HFpEF.

ROLE OF NITRATE THERAPY IN HEART FAILURE

Long acting nitrates are used as the cornerstone of anti-anginal therapy and have demonstrated beneficial effects for treatment of patients with heart failure and reduced ejection fraction (HFrEF). In randomized studies, sustained increases in treadmill exercise time^{4, 5} and peak oxygen consumption⁶ have been observed at 3 months after initiation of nitrate therapy in patients with HFrEF, including those already treated with angiotensin converting enzyme inhibitors (ACEI)⁵. Attenuation of pathological left ventricular (LV) remodelling and improved LV systolic function have also been reported⁵. Although no study has directly examined the effects of nitrate monotherapy on survival in HF, symptom relief is a key management goal in patients with HFpEF, whose primary chronic symptom is often exercise limitation⁷.

Practice guidelines for the management of chronic HF from the American College of Cardiology/American Heart Association (ACC/AHA)⁸ and Heart Failure Society of America (HFSA)⁹ advocate a potential role for nitrates in diminishing symptoms in HFpEF but acknowledge the lack of supportive data and the risk of excessive nitrate-induced hypotension in elderly HFpEF patients. Therefore, it is desirable that a randomized, controlled evaluation of the efficacy and tolerance of nitrate therapy in HFpEF is performed in order to support its therapeutic application.

To address this lack of data and current clinical equipoise for nitrate therapy in HFpEF, the Nitrate’s Effect on Activity Tolerance in Heart Failure with Preserved Ejection Fraction (NEAT-HFpEF) trial (http://clinicaltrials.gov NCT02053493) is being conducted within the National Heart, Lung, and Blood Institute-sponsored HF clinical research network. Cognizant of the primary goal to reduce symptom burden and improve quality of life, NEAT-HFpEF will simultaneously assess a new paradigm of using patient-centric data, i.e. data emanating from and of immediate relevance to patients’ daily living, as the primary efficacy endpoint. Thus NEAT-HFpEF is expected to provide important information regarding nitrate’s safety and therapeutic benefit as well as the feasibility of a novel endpoint, with potential for wider application to future HF studies.

RATIONALE FOR NITRATE THERAPY IN HFPEF

Hemodynamic Effects

A fundamental hemodynamic derangement in HFpEF is pathologic elevation in LV filling pressure, at rest or on exertion^{7, 10}. Commonly used organic nitrates, isosorbide dinitrate (ISDN), isosorbide-5-mononitrate (ISMN), and nitroglycerin, reduce ventricular preload by increasing peripheral venous capacitance, reducing LV filling pressure and wall stress^{11, 12}. At higher doses, dilatation of pulmonary and systemic resistance vessels occurs¹³, particularly in patients with high arterial pressures¹⁴. Coronary artery disease is prevalent in HFpEF, and symptoms of angina may occur in patients without angiographically apparent coronary disease¹⁵. Nitrate-induced coronary vasodilatation may improve subendocardial perfusion, which could benefit HFpEF patients for whom ischemia is a contributory factor. Nitrate induced pre-load reduction may also be beneficial in HFpEF where the steep diastolic pressure-volume relationship confers marked increases in LV filling pressures, even at low stroke volumes (SV) and low work rate, prompting early cessation of exercise⁷. Preload reduction may therefore be expected to improve exercise capacity in HFpEF. Furthermore, nitrates may reduce wave reflections in the arterial tree^{16, 17}, which increase left ventricular late systolic load and wall stress¹⁸ and impair diastolic relaxation¹⁹.

However, nitrate-induced hemodynamic effects may also be blunted or deleterious in HFpEF. While nitrates reduce arterial impedance and increase SV without causing hypotension in patients with HFrEF, a steeper end-systolic pressure volume relationship in HFpEF means SV increases less and systolic LV pressure decreases more in response to a decrease in preload or afterload^20–22. In fact, Schwartzenberg et al. observed a reduction in SV among 35% of HFpEF patients following infusion of sodium nitroprusside, suggesting greater vulnerability to excessive preload reduction²². Because deficient SV reserve contributes to exercise limitation in patients with HFpEF²³ excessive venodilation from nitrates might offset any beneficial effects on filling pressures, coronary vasodilation or relief of pericardial constraint²⁴. Moreover, HFpEF patients are frequently elderly and may have autonomic dysfunction, chronotropic incompetence and altered baroreflex sensitivity, all of which may exaggerate hypotension with load changes and thus heighten nitrate intolerance²⁵. Finally, whether the potentially favorable effects of nitrates on wave reflections reported in unselected hypertensive subjects also occur in patients with HFpEF is unknown.

Endothelial Effects of Nitrates

Nitrate vasorelaxant responses are thought to be mediated by the formation of nitric oxide (NO) or a closely related entity²⁶. NO activates soluble guanylyl cyclase (sGC) in vascular smooth muscle, prompting synthesis of the second messenger cyclic guanosine monophosphate (cGMP). Downstream activation of cGMP effector proteins, including cGMP-dependent protein kinase (PKG), leads to a reduction in intracellular calcium, and thus to vasodilation. Endothelial-dependent vasodilation is impaired in patients with HFpEF, compared with healthy age-matched controls, and correlates with greater symptoms and poorer exercise capacity²³. Exogenous NO delivery or enhancement of endogenous NO biosynthesis may therefore improve endothelial function, as has been observed in HFrEF²⁷.

However, nitrates could also paradoxically worsen endothelial function. Studies in normal humans and experimental animals have shown endothelial dysfunction resulting from chronic nitrate therapy, attributed to the generation of reactive oxygen species (ROS) and local endothelin activation^{28, 29}.

Myocardial Effects of Nitrates

Increased NO bioavailability with nitrates, and thus cGMP/PKG signaling, may acutely improve LV diastolic function and ameliorate myocardial hypertrophic remodeling. Low PKG activity has been implicated in the development of myocardial hypertrophy, delayed relaxation and increased passive stiffness³⁰. Van Heerebeek et al. confirmed both low cGMP content and low PKG activity in myocardial tissue obtained from HFpEF patients, compared with samples from patients with HFrEF and aortic stenosis³¹. cGMP-phosphodiesterase (PDE5) expression, a mediator of cGMP hydrolysis, was similar between groups. This observation may provide insight into the lack of effect of PDE5 inhibition in HFpEF³² as enhanced cGMP hydrolysis does not appear to mediate the unique reduction in myocardial cGMP in HFpEF³¹. Rather, nitrotyrosine content (reflecting oxidative/nitrosative stress) was highest in HFpEF³¹, suggesting that a reduction in NO-stimulated cGMP synthesis due to ROS scavenging of NO and oxidation of the NO target, soluble guanylyl cyclase, underlies low myocardial cGMP content and reduced PKG activity in HFpEF. Activation of cGMP-PKG may also acutely improve diastolic function via phosphorylation of titin³³. Acute titin phosphorylation via exogenous administration of PKG results in dramatic reduction in cardiomyocyte stiffness in vitro³¹. While direct augmentation of PKG improves myocardial diastolic properties in vivo, whether chronic nitrate therapy will enhance cGMP, PKG activity and myocardial diastolic function in HFpEF is unclear.

NITRATE RESISTANCE

Therapeutic responses to nitrates are variable and larger doses are needed to elicit hemodynamic and endothelial responses in patients with HFrEF compared to patients without HF (‘nitrate resistance’)³⁴. Furthermore, early systemic effects, including reflex neurohumoral activation and volume expansion, may lead to reversal of initial hemodynamic benefits (‘nitrate pseudotolerance’)³⁴.

Prolonged exposure is widely recognized to induce true nitrate tolerance^{34, 35}. This is thought to involve vascular processes such as impaired nitrate biotransformation, increased ROS production with impaired clearance, sGC desensitization to NO, enhanced sensitivity to endogenous vasoconstrictors, and increased cGMP phophodiesterase activity, all of which inactivate nitrate vasodilator effects³⁴. The extent of tolerance is somewhat dose-related and low-doses or intermittent dosing regimens with low-nitrate or nitrate-free intervals may be sufficient to prevent its occurrence^{35, 36}. Although, a combination of hydralazine and nitrates is suggested to reduce nitrate tolerate and is utilized in HFrEF, the additional vasodilation and afterload reduction imparted by hydralazine may prove excessive in HFpEF due to the aforementioned differences in pressure-volume relationships, and may mask a beneficial effect of lone nitrate therapy in HFpEF. Furthermore, tolerance differs between nitrate preparations, as once daily ISMN was shown to be devoid of tolerance in patients with coronary artery disease^{37, 38}. Therefore, once daily lone ISMN therapy has been selected for NEAT-HFpEF.

ASSESSMENT OF SYMPTOM BURDEN IN HF

To determine whether nitrates are effective at reducing symptom burden, selection of an appropriate “functional” end-point is preferable to conventional disease-related outcomes. Functional performance refers to the ability to perform day-to-day activities to: “meet basic needs, fulfil usual roles, and maintain health and wellbeing.”³⁹ Such activities often require much less than maximal exertion and may not be accurately summarized by the peak exertional measures used in recent HF trials. Likewise, intermittent evaluation of submaximal exercise capacity, such as the 6MWD, provides low density data which are subject to coaching effects and may underestimate the true burden of disease, for example when patients voluntarily reduce activity to avoid symptoms. Accelerometer-assessed activity is a novel endpoint which may circumvent these limitations by providing high density, quantitative data from continuous assessment of physical activity during usual daily life.

Prior recent studies in patients with HFrEF, have demonstrated correlations between accelerometer data and New York Heart Association (NYHA) functional class⁴⁰, 6 minute walk distance (6MWD)^{41, 42}, peak oxygen consumption^{40, 43}, and estimated (Seattle Heart Failure Model) or observed mortality risks^{44, 45}. Studies have also shown increases in accelerometer-assessed activity after cardiac resynchronization therapy, confirming its ability to reflect therapeutic response^{41, 46, 47}. Validity, analytical issues, and compliance with externally worn accelerometer devices have been addressed in clinical trials for patients with COPD, among whom age and activity level are likely comparable to elderly patients with HFpEF^48–51. Notably, patients who may be too frail to undergo comprehensive cardiopulmonary exercise testing will still be eligible for a study using accelerometry, thereby addressing concerns about the spectrum of disease severity in recent HFpEF trials^{32, 52}.

Importantly, cardiopulmonary diseases, or even therapy, are not the only determinants of physical activity. Behavioral and psychological factors as well as the patient’s immediate environment and social support, may have an impact on habitual physical activity. Thus, while accelerometer-assessed physical activity represents a novel, feasible, and patient-centric method to detect a clinically relevant response to nitrate therapy in ambulatory patients with HFpEF, whether enhanced exercise capacity will translate into increased daily physical activity in HFpEF patients remains uncertain .

RATIONALE AND DESIGN OF NEAT-HFPEF

NEAT-HFpEF is a multicenter, randomized (1:1), double-blind, placebo-controlled, crossover study designed to test the hypothesis that once daily extended-release ISMN, at a maximally tolerated dose (30–120mg), improves daily physical activity in patients with HFpEF. Daily activity will be assessed by two hip-worn tri-axial accelerometers and the primary endpoint will be a within-patient comparison of 14-day averaged arbitrary accelerometer units (AAU₁₄) achieved during the ISMN treatment phase, compared with placebo. Because the ability to carry out usual daily activities is a pervasive marker of symptom burden, and yet may be highly variable between patients, the novel endpoint and crossover design used in NEAT-HFpEF are uniquely suited to address the primary hypothesis while taking heed of nitrate pharmacology and pragmatic sample size.

Study protocol and dose-titration schedule

Approximately 110 patients with chronic stable HF and preserved ejection fraction (EF≥50%) will be enrolled. Specific entry criteria stipulate that activity limitation is primarily due to HF symptoms (Table). Eligible participants undergo baseline assessment (echocardiography, blood sampling for biomarkers including cGMP and N-terminal pro-brain type natriuretic peptide [NT-proBNP], 6MWD, symptom questionnaires: Minnesota Living with Heart Failure Questionnaire [MLWHFQ] and the Kansas City Cardiomyopathy Questionnaire [KCCQ]) followed by training in accelerometer use. Participants are subsequently randomized to one of two treatment groups, placebo first with crossover to ISMN or ISMN first with crossover to placebo, stratified by clinical site (permuted block randomization) to ensure equal distribution of participants per arm per site.

Table.

NEAT-HFpEF Eligibility criteria

Inclusion criteria

Age ≥ 50 years Symptoms of dyspnea (II–IV) without non-cardiac or ischemic etiology EF ≥ 50% One of the following within the last 12 months Previous hospitalization for HF or Catheterization documented elevated filling pressures at rest (LVEDP≥15 or PCWP≥20) or with exercise (PCWP≥25) or Elevated NT-proBNP (> 400 pg/ml) or BNP (> 200 pg/ml) or Echo evidence of diastolic dysfunction / elevated filling pressures (at least two) ■ E/A > 1.5 + decrease in E/A of > 0.5 with Valsalva ■ Deceleration time ≤ 140 ms ■ PVs<PVd (sinus rhythm) ■ E/e’≥15 ■ LA enlargement (≥ moderate) ■ PASP > 35 mmHg ■ Evidence of LVH LV mass/BSA ≥ 96 (♀) or ≥ 116 (♂) g/m2 RWT ≥ 0.43 (♂ or ♀) Posterior wall thickness ≥ 0.9 (♀) or 1.0 (♂) cm No chronic nitrate therapy or not using (≤ 1× week) intermittent sublingual GTN Ambulatory (not wheelchair/scooter dependent) Heart failure is primary factor limiting activity as indicated by answering # 2 to the following question: My ability to be active is most limited by: Joint, foot, leg, hip or back pain Shortness of breath and/or fatigue and/or chest pain Unsteadiness or dizziness Lifestyle, weather, or I just don’t like to be active Does not regularly swim or do water aerobics as primary form of exercise

Primary Exclusion Criteria

Recent (< 3 months) hospitalization for heart failure or acute coronary syndrome Previous adverse reaction to the nitrates which necessitated withdrawal of therapy Therapy with phosphodiesterase type 5 (PDE-5) inhibitors Documentation of previous EF < 50% Hemodynamic instability, rare causes of HFpEF, significant primary valve disease or severe hematologic, liver or kidney disease.

All participants enter a 2-week ‘run-in’ phase during which accelerometer data obtained reflects baseline physical activity off nitrates. Thereafter, participants commence once daily placebo or oral ISMN according to the dose titration schedule in Figure 1. At each titration step, study staff will discuss tolerability and determine safety to proceed with up-titration. In the case of drug intolerance, participants will be instructed to down-titrate to the previously tolerated dose or discontinue as necessary. At the end of phase 1, repeat assessment is performed (blood sampling, 6MWD and symptom questionnaires) and all participants receive a new accelerometer device and study drug supply and begin a 2-week drug-free washout phase. Dose-titration is then performed as before. Participants are called weekly and encouraged to be active within the limitations imposed by their HF symptoms. After completion of phase 2 patients undergo a final in-person assessment as at the end of phase 1.

Figure 1.

Study protocol and dose-titration schedule for NEAT-HFpEF. * or maximally tolerated dose; BL, Baseline; WO, Washout; wk, week

Crossover study design considerations

As per the crossover study design, each participant will serve as their own control. Avoiding between-participant variation in estimating the intervention effect enables a smaller sample size and timely completion. External social and behavioral related factors influencing exercise capacity would also be expected to vary little during the trial, thus the within-subject comparisons will remain robust. The modest total treatment duration (4 weeks) was selected to minimize potential bias due to period effects or remodeling (carry-over effect). In particular, nitrates have a rapid onset and offset of action and the 2-week washout phase was determined based on nitrate pharmacokinetics and literature review^{17, 38, 53–55}. The key hypothesis to be tested in NEAT-HFpEF is that nitrate hemodynamic effects provide acute symptom relief in HFpEF and that symptom relief will translate into an increase in activity levels. Importantly, NEAT-HFpEF is not designed to evaluate chronic remodeling effects associated with nitrate therapy and, in the event of a negative outcome, should not preclude further investigation into these.

ENDPOINTS

Primary Endpoint

As outlined above, the primary endpoint for NEAT-HFpEF will be a within-patient comparison of accelerometer-assessed physical activity averaged over 14-days between the ISMN and placebo phases.

Technical details

Patient factors

Each patient will wear two external, hip worn (belt-attached) accelerometer devices (Figure 2) throughout the study duration, which will also provide variability data. The devices will not display activity or step counts to the patient. Device settings are pre-programmed and the accelerometers will remain switched on throughout the entire measurement period to minimize patient handling. Baseline training and weekly study calls will address participant-specific strategies to enhance steadfast use including during sleep. Participants will be advised to remove the belt only during bathing or swimming.

Figure 2.

The NEAT-HFpEF accelerometer device.

Accelerometer measures

The tri-axial accelerometer (piezoelectric) sensor measures physical activity in terms of acceleration (movement) values along the vertical (x), anteroposterior (y) and mediolateral (z) axes over time. The accelerometer unit samples these measurements 16 times per second, and the raw output generated, i.e. the change in voltage vector from one sample to the next is converted into a digital series of numbers known as Kionix-based arbitrary accelerometer units (AAU; Kionix is the integrated circuit accelerometer supplier) according to the formula: $\sqrt{{(x_1-x_2)}^2+{(y_1-y_2)}^2+{(z_1-z_2)}^2}$where subscript₁ = time point 1, subscript₂ = time point 2, and time points one and two are 1/16^th of a second apart. Data are continuously recorded and cumulative AAUs are stored in 15-minute epochs (assigned recording periods) providing a total of 96 data points per day. In NEAT-HFpEF these AAU data points will be averaged over a period of 14 days (area under the curve integration) to provide a single measure of AAU₁₄, reflecting the average accelerometer-assessed physical activity during habitual free-living conditions, for each individual, for each phase. All raw data collected will be available for analysis, irrespective of activity level. This is important as some commercially available devices eliminate data corresponding to walking speeds less than approximately 1.5 miles per hour and would therefore be unsuitable for sedentary persons with HFpEF.

At present, there are no consistent cutoffs for classifying accelerometer-assessed activity units into recognized intensity levels for direct clinical interpretation⁵⁶. Furthermore, NEAT-HFpEF represents the first study within a dedicated HFpEF population to use accelerometer-assessed physical activity as a primary endpoint. Therefore, in addition to within-patient comparisons with and without nitrate therapy, NEAT-HFpEF will also define the typical AAU₁₄ value and standard deviation relevant for an HFpEF population and future studies.

Secondary Endpoints

NEAT-HFpEF is powered to detect a clinically meaningful change in the 6MWD, the KCCQ score, and the MLHFQ score. Perceived dyspnea and effort (Borg) scores during 6MWD, and changes in plasma NTproBNP concentration will also be assessed. Additional accelerometer endpoints will include: hours active, the slope of daily-averaged AAU during study drug administration, and area under the curve for daily-averaged AAU during study drug administration. Patient preference for study phase will also be assessed via a standardized questionnaire.

Tertiary Endpoints

Tertiary endpoints will include the quotients of 6MWD and associated Borg score (integrated measure of performance and symptoms), plasma cGMP concentration and, where available, accelerometer assessed dose-response to nitrate therapy.

Subgroup Analysis

Prespecified subgroup exploratory analyses include comparison of nitrate efficacy according to treatment (or absence of treatment) with agents reported to reduce nitrate tolerance (renin angiotensin aldosterone antagonists^{35, 57}, carvedilol⁵⁸, statins⁵⁹, or hydralazine^{35, 60}), plasma NT-proBNP level, systolic blood pressure, and presence or absence of coronary artery disease. An analysis confined to patients on “on drug” will also be performed.

STATISTICAL CONSIDERATIONS

Analyses will be conducted on a modified intention-to-treat basis and include all randomized participants who complete both phases. The primary endpoint is based on the within-patient comparison of AAU₁₄ achieved during the maximally-tolerated dose period of ISMN versus placebo, i.e. using accelerometer data obtained during weeks 5–6 versus weeks 11–12. For missing data corresponding to periods when the device-belt is not worn (bathing or water activities) the imputation approach of Catellier et al. will be used to create a pseudo-complete dataset⁶¹. The imputation plan will also account for potential differences in activity between weekdays and weekends. The primary analysis will involve a mixed model with fixed effect terms for the sequence, period (study phase) and treatment⁶². A random effect term will be included to account for the correlated measurement within each participant⁶³. Baseline characteristics (demographics, echocardiographic data, biomarkers, and questionnaire scores) will be used for adjusted and subgroup analyses. Data from the first phase (baseline to maximum tolerated dose) and second phase (washout to maximum tolerated dose) will be presented separately in a sensitivity analysis, thereby including any patients who may have only completed one phase. For secondary and tertiary endpoints, continuous outcomes will be assessed using mixed models, as for the primary analysis; binary outcomes will be assessed using chi-square tests and Fisher’s exact test, for unadjusted comparisons.

Sample Size and Power

As the primary endpoint has not previously been examined in the proposed study population, the justification for sample size is based on two key secondary endpoints: the overall summary score from the KCCQ and 6MWD.

Data from the recently completed Xanthine Oxidase Inhibition for Hyperuricemic Heart Failure Patients (EXACT-HF) trial⁶⁴ suggest the within-patient standard deviation (SD) for KCCQ overall summary score is approximately 17 points. A clinically significant difference is considered to be 5 points and a moderately large clinical difference, 10points^{65, 66} Assuming a two-sided type I error (α) of 0.05, based on a crossover ANOVA⁶³ and a 17-point SD in KCCQ summary score, a total of 94 participants (47 per sequence), would have 80% power to detect a difference of 5 points in KCCQ summary score. 6MWD data from the RELAX trial³² suggest the within-patient SD is ≈ 90 meters. Based on a clinically meaningful difference of 43 meters⁶⁷, a sample size greater than 60 participants (30 per sequence) would have greater than 90% power to detect this difference in this 2*2 crossover design. The NEAT-HFpEF sample size is larger than that used in previous crossover studies which established nitrate efficacy for HFrEF and angina^{5, 53–55, 68–70}.

We have also previously measured accelerometer-assessed activity as the AAU₁₄ at baseline, 3 months and 6 months in 49 elderly sedentary volunteers receiving no intervention⁷¹. The average within-patient SD between baseline (mean 4462 AAU) and 3 months (mean 4496 AAU) was 337 AAU. If the baseline AAU₁₄ and the within-patient variability in HFpEF patients are similar to those observed in healthy elderly sedentary persons, NEAT-HFpEF would have 90% power to detect a difference between the intervention and placebo phases of 114 AAU (approximately 2.5% of the baseline measurement).

SAFETY

Potential inadvertent unblinding of treatment due to nitrate-related side effects including headache, and rarely, lightheadedness and syncope is recognized., Once daily extended release ISMN has been chosen as the study drug for NEAT-HFpEF, with gradual up-titration from a low dose at weekly intervals in order to minimize the risk of severe side effects and enhance tolerability. ISMN is the active metabolite of ISDN and at 60 or 120mg dose has a plasma elimination half-life of approximately 6 hours³⁸, thus the dosing regimen in NEAT-HFpEF will provide a low-nitrate interval per 24 hours. Co-administration of phosphodiesterase-5 inhibitors will be prohibited due to the risk of excessive hypotension.

CONCLUSIONS

While expert consensus guidelines recommend consideration of nitrates in HFpEF, there are currently no data supporting this recommendation. The NEAT-HFpEF trial will address this critical question and determine whether nitrate pharmacodynamic effects may be leveraged for acute symptom relief among ambulatory patients with HFpEF. Moreover, in using accelerometer-assessed activity as the primary endpoint, NEAT-HFpEF will ascertain the true impact of nitrate therapy on patients’ physical activity during daily living and establish the clinical utility of this novel and patient-centric endpoint for future HF trials.