A new algorithm for optimization of rate-adaptive pacing improves exercise tolerance in patients with HFpEF

Anti-bradycardia pacing-impact on patients with HFpEF: a systematic review

Heart failure with preserved ejection fraction (HFpEF) has become an emerging concern. The protective effect of bradycardia in patients with reduced ejection fraction using beta-blockers or ivabradine does not improve symptoms in HFpEF. This review aims to assess current data regarding the impact of anti-bradycardia pacing in patients with HFpEF. A search was conducted on PubMed, ScienceDirect, Springer, and Wiley Online Library, selecting studies from 2013 to 2023. Relevant and eligible prospective studies and randomized controlled trials were included. Functional status, quality of life, and echocardiographic parameters were assessed. Six studies conformed to the selection criteria. Four were prospective studies with a total of 90 patients analyzed. Two were randomized controlled trials with a total of 129 patients assessed. The 6-min walk test (6MWT) and the Minnesota Living with Heart Failure Questionnaire (MLHFQ) score improved in all prospective studies. My-PACE trial showed improvements in MLHFQ score (p < 0.001), significant relative lowering in NT-proBNP levels (p = 0.02), and an increased mean daily activity in the personalized accelerated pacing group compared to usual care. RAPID-HF trial proved that pacemaker implantation to enhance exercise heart rate (HR) did not improve exercise capacity and was associated with increased adverse events. HFpEF requires a more individualized approach and quality of life management. This review demonstrates that higher resting HR by atrial pacing may improve symptoms and even outcomes in HFpEF, while a higher adaptive rate during exertion has not been proven beneficial.

Characterization and prognostic importance of chronotropic incompetence in heart failure with preserved ejection fraction

BACKGROUND

Exercise intolerance is the primary symptom of patients with heart failure with preserved ejection fraction (HFpEF). Chronotropic incompetence has been considered to be common and contribute to poor exercise capacity in HFpEF. However, clinical characteristics, pathophysiology, and outcomes of chronotropic incompetence in HFpEF remain poorly understood.

METHODS

Patients with HFpEF (n = 246) underwent ergometry exercise stress echocardiography with simultaneous expired gas analysis. The patients were divided into two groups based on the presence of chronotropic incompetence, which was defined by heart rate reserve <0.80.

RESULTS

Chronotropic incompetence was common in HFpEF (n = 112, 41 %). Compared to HFpEF patients with a normal chronotropic response (n = 134), those with chronotropic incompetence had higher body mass index, a higher prevalence of diabetes, more frequent β-blocker use, and worse New York Heart Association class. During peak exercise, patients with chronotropic incompetence demonstrated less increase in cardiac output and arterial oxygen delivery (cardiac output × saturation × hemoglobin × 1.34 × 10), higher metabolic work (peak oxygen consumption [VO2]/watt), an inability to increase arteriovenous oxygen difference, and poorer exercise capacity (lower peak VO2) than those without. Chronotropic incompetence was associated with higher rates of a composite of all-cause mortality or worsening HF events (hazard ratio, 2.66, 95 % confidence intervals, 1.16-6.09, p = 0.02).

CONCLUSION

Chronotropic incompetence is common in HFpEF, and is associated with unique pathophysiologic characteristics during exercise and clinical outcomes.

Relationships among norepinephrine levels, exercise capacity, and chronotropic responses in heart failure patients

In heart failure (HF) patients, the pathophysiological mechanisms of severe exercise intolerance and impaired exercise capacity are related to both central and peripheral abnormalities. The central abnormalities in HF patients include impaired cardiac function and chronotropic incompetence (CI). Indeed, CI, the inability to adequately increase heart rate (HR) from rest to exercise often exhibited by HF patients, is related to activation of the sympathetic nervous system (SNS) yielding a rise in circulating norepinephrine (NE). CI may result from downregulation of β-adrenergic receptors, β-blocker usage, high baseline HR, or due to a combination of factors. This paper discusses the role of elevated NE in altering chronotropic responses in HF patients and consequently resulting in impaired exercise capacity. We suggest that future research should focus on the potential treatment of CI with rate-adaptive pacing, using a sensor to measure physical activity, without inducing deleterious hormonal activation of the sympathetic system.

Rate adaptive pacing in people with chronic heart failure increases peak heart rate but not peak exercise capacity: a systematic review

Rate adaptive cardiac pacing (RAP) allows increased heart rate (HR) in response to metabolic demand in people with implantable electronic cardiac devices (IECD). The aim of this work was to conduct a systematic review to determine if RAP increases peak exercise capacity (peak VO₂) in line with peak HR in people with chronic heart failure. We conducted a systematic literature search from 1980, when IECD and RAP were first introduced, until 31 July 2021. Databases searched include PubMed, Medline, EMBASE, EBSCO, and the Clinical Trials Register. A comprehensive search of the literature produced a total of 246 possible studies; of these, 14 studies were included. Studies and subsequent analyses were segregated according to comparison, specifically standard RAP (RAPON) vs fixed rate pacing (RAPOFF), and tailored RAP (TLD RAPON) vs standard RAP (RAPON). Pooled analyses were conducted for peak VO₂ and peak HR for RAPON vs RAPOFF. Peak HR significantly increased by 15 bpm with RAPON compared to RAPOFF (95%CI, 7.98-21.97, P < 0.0001). There was no significant difference between pacing mode for peak VO₂ 0.45 ml kg^-1 min^-1 (95%CI, - 0.55-1.47, P = 0.38). This systematic review revealed RAP increased peak HR in people with CHF; however, there was no concomitant improvement in peak VO₂. Rather RAP may provide benefits at submaximal intensities by controlling the rise in HR to optimise cardiac output at lower workloads. HR may be an important outcome of CHF management, reflecting myocardial efficiency.

Cellular and molecular pathobiology of heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) affects half of all patients with heart failure worldwide, is increasing in prevalence, confers substantial morbidity and mortality, and has very few effective treatments. HFpEF is arguably the greatest unmet medical need in cardiovascular disease. Although HFpEF was initially considered to be a haemodynamic disorder characterized by hypertension, cardiac hypertrophy and diastolic dysfunction, the pandemics of obesity and diabetes mellitus have modified the HFpEF syndrome, which is now recognized to be a multisystem disorder involving the heart, lungs, kidneys, skeletal muscle, adipose tissue, vascular system, and immune and inflammatory signalling. This multiorgan involvement makes HFpEF difficult to model in experimental animals because the condition is not simply cardiac hypertrophy and hypertension with abnormal myocardial relaxation. However, new animal models involving both haemodynamic and metabolic disease, and increasing efforts to examine human pathophysiology, are revealing new signalling pathways and potential therapeutic targets. In this Review, we discuss the cellular and molecular pathobiology of HFpEF, with the major focus being on mechanisms relevant to the heart, because most research has focused on this organ. We also highlight the involvement of other important organ systems, including the lungs, kidneys and skeletal muscle, efforts to characterize patients with the use of systemic biomarkers, and ongoing therapeutic efforts. Our objective is to provide a roadmap of the signalling pathways and mechanisms of HFpEF that are being characterized and which might lead to more patient-specific therapies and improved clinical outcomes.

Optimizing single-chamber pacing in dogs. Part 2: Rate adaptive pacing

Proper programming of pacemakers for dogs in the rate adaptive mode requires an understanding of the rate requirements for each individual and the interplay of programmable features. The specific advantages and disadvantages of the rate adaptive mode should be considered on a case by case basis. Fundamentally, two components are linked in the implementation of rate adaptive pacing: (1) sensing the need for a change in rate and (2) responding with the appropriate alteration in pacing rate. The programming interaction of these two components are interdependent and affected by the rates programmed. These features may be adjusted manually or automatically. In this review (Part 2 of a two-part review) the considerations required to program each aspect that optimizes the pacing rate profile are reviewed. These include the lower rate, upper sensor rate, activities of daily life rate, sensor threshold, acceleration and deceleration, slope, activities of daily life zone, exertion zone, automatic versus manual adjustments and closed loop stimulation. The programming features of pacemakers manufactured by three companies are summarized (Abbott, formerly St. Jude; Biotronik/Dextronix; Medtronic). Means of assessing the success of pacemaker programing is examined through examples of pacemaker data, Holter analysis, Poincaré plots and tachograms. Finally, the questions and considerations for rate adaptive pacing in dogs that demand investigation are proposed.

Instantaneous and averaged heart rate profiles: Developing strategies for programming pacing rates in dogs

Pacemakers use heart rate histograms (% beats) and sensor indicated rate histograms (% time) to illustrate rate distributions. When programmed to the rate adaptive modes, these data are used to determine the appropriateness of rate response to activity. These histograms are generated from instantaneous heart rate calculations. In humans, such data are compared to known histographic rate profiles. Such rate profiles during 24 h in the dog are not available. Moreover, data representation differ between Holter monitoring and pacemakers making comparisons challenging. The rate distribution in dogs >7-years of age was determined over 24 h using instantaneous and rolling average heart rate. Such data could serve as a guide to programming pacing rates for dogs. Sinus arrhythmia resulted in dissimilar heart rate profiles depending on the method of determining rate. The long intervals of sinus arrhythmia resulted in median values for the percent of time with an instantaneous heart rate of <50 beats/min (bpm) of 15%, whereas a rolling average heart rate of <50 bpm was 0.2%. Based on the cumulative time of the rolling average rate, dogs spent 26.3% of the day between 70-90 bpm with rates <65 bpm and >90 bpm approximating 30% for each. Rates >160 bpm were uncommon (<1%). However, high variability existed between dogs. This study demonstrated the shortcomings of both instantaneous and averaging methods to evaluate heart rate profiles in the dog and that both methods should be incorporated when making pacing rate decisions during programming.

Sensors for rate-adaptive pacing: How they work, strengths, and limitations

Chronotropic incompetence is the inability of the sinus node to increase heart rate commensurate with increased metabolic demand. Cardiac pacing alone may be insufficient to address exercise intolerance, fatigue, dyspnea on exertion, and other symptoms of chronotropic incompetence. Rate-responsive (adaptive) pacing employs sensors to detect physical or physiological indices and mimic the response of the normal sinus node. This review describes the development, strengths, and limitations of a variety of sensors that have been employed to address chronotropic incompetence. A mini-tutorial on programming rate-adaptive parameters is included along with emphasis that patients' lifestyles and underlying medical conditions require careful consideration. In addition, special sensor applications used to respond prophylactically to physiologic signals are detailed and an in-depth discussion of sensors as a potential aid in heart failure management is provided.