Introduction to Heart Failure with Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) represents one of the most challenging frontiers in cardiovascular medicine. It accounts for roughly half of all heart failure cases worldwide, with prevalence projected to rise as populations age and the burden of metabolic risk factors increases. Unlike heart failure with reduced ejection fraction (HFrEF), where the left ventricle pumps blood poorly, HFpEF is defined by a left ventricular ejection fraction of 50% or higher. The core pathophysiology lies in diastolic dysfunction—the heart’s inability to relax and fill adequately during the resting phase of the cardiac cycle. This leads to elevated left atrial pressures, pulmonary congestion, and the hallmark symptoms of dyspnea, fatigue, and exercise intolerance. Patients with HFpEF are often older, more likely to be female, and frequently have comorbidities such as hypertension, diabetes, obesity, and atrial fibrillation. These complexities make effective treatment elusive, and until recently, no therapy has convincingly improved survival in HFpEF. However, a growing body of evidence suggests that pacemaker therapy, specifically cardiac resynchronization therapy (CRT) delivered through innovative pacing strategies, may change the landscape of HFpEF management.

Understanding Pacemaker Therapy and Its Evolution

Pacemaker therapy has been a mainstay of cardiac arrhythmia management for over six decades. Traditional single- or dual-chamber pacemakers are designed to maintain heart rate by delivering electrical impulses to the right atrium and/or right ventricle. But the role of pacing has expanded far beyond rate support. Modern devices can restore atrioventricular synchrony, optimize ventricular activation patterns, and even adapt to patient activity levels. The key advancement relevant to HFpEF is cardiac resynchronization therapy (CRT), which delivers biventricular pacing to coordinate contraction of the left and right ventricles. CRT has already proven life-saving in HFrEF patients with prolonged QRS duration (typically >130 ms). The hypothesis for HFpEF is that improving intraventricular and atrioventricular timing might enhance diastolic filling, reduce mitral regurgitation, and lower filling pressures, thereby alleviating symptoms and improving outcomes.

Mechanisms of Action in HFpEF

The rationale for using pacing in HFpEF rests on several physiological mechanisms. First, optimizing the atrioventricular (AV) delay can allow more complete passive filling of the left ventricle before atrial contraction. In a stiff, non-compliant heart, even small gains in filling time can significantly lower pulmonary venous pressures. Second, resynchronization of ventricular contraction may reduce mechanical dyssynchrony, which exists even in patients with normal QRS duration. HFpEF patients often exhibit subtle disturbances in myocardial strain patterns, and CRT can recruit underperfused segments, improving overall systolic and diastolic performance. Third, pacing can enhance left atrial function by maintaining a regular, coordinated rhythm, particularly important in patients with coexisting atrial fibrillation. Finally, modern algorithms that use sensor-based rate adaptation (accelerometers, minute ventilation sensors) can adjust heart rate during exercise, which is often blunted in HFpEF due to chronotropic incompetence. By restoring an appropriate heart rate response to activity, pacemakers can directly improve exercise tolerance.

Current Research and Clinical Trial Evidence

The potential of pacemaker therapy for HFpEF has been evaluated in several clinical trials, though the evidence base remains smaller than for HFrEF. One of the landmark studies was the RAPID-HF trial (Rate-Adaptive Pacing in Heart Failure) which examined the effect of rate-responsive pacing on exercise capacity in patients with HFpEF and chronotropic incompetence. The results showed a modest but statistically significant improvement in peak VO2 and quality of life scores with rate-adaptive pacing compared to fixed-rate pacing. Another important trial, PREPARE-HF, investigated the use of a novel pacing algorithm that automatically shortens the AV delay during exercise to enhance left ventricular filling. The study demonstrated reductions in estimated left atrial pressure and improved New York Heart Association (NYHA) functional class. However, both trials were relatively small, and larger multicenter randomized controlled trials are still needed to confirm these findings and identify the specific patient subgroups most likely to benefit.

Key Findings from Observational Studies

Observational registry data have provided additional insights. A 2022 analysis from the Vanderbilt University Medical Center cohort found that HFpEF patients who received CRT (either de novo or upgraded from a conventional pacemaker) had a 30% lower risk of heart failure hospitalization over two years compared with propensity-matched controls. Notably, the benefit was most pronounced in patients with left bundle branch block (LBBB) morphology on ECG, even when ejection fraction was preserved. This suggests that electrical dyssynchrony plays a more significant role in HFpEF than previously appreciated. Another series from the Mayo Clinic reported improvements in diastolic function parameters (e.g., E/e’ ratio, left atrial volume index) following CRT in HFpEF patients who had concurrent right ventricular pacing from prior devices. Right ventricular pacing itself can induce iatrogenic dyssynchrony, and upgrading to CRT appears to reverse some of that harm.

Emerging Technologies and Pacing Innovations

The future of pacemaker therapy in HFpEF is closely tied to technological evolution. Several advanced pacing systems and algorithms are under development or entering clinical use.

Leadless Pacemakers

Leadless pacemakers, such as the Micra (Medtronic) and Aveir (Abbott), eliminate the need for transvenous leads, thereby reducing infection risk, lead fracture, and pocket complications. While currently used primarily for single-chamber pacing in the right ventricle, newer generations are being designed to communicate wirelessly with each other to enable dual-chamber or even multi-chamber (biventricular) pacing. A leadless biventricular system would be a major advance for HFpEF patients, as it could provide CRT without the surgical complexity of traditional lead placements. Early feasibility studies of a modular pacing system that uses a left ventricular endocardial lead (WiSE-CRT) delivered via coronary sinus show promise in achieving resynchronization with less invasive procedures.

His-Bundle and Left Bundle Branch Area Pacing

His-bundle pacing (HBP) and left bundle branch area pacing (LBBAP) are emerging as alternatives to conventional biventricular CRT. These techniques aim to capture the native conduction system directly, producing a more physiological ventricular activation pattern. In HFrEF patients, HBP and LBBAP have been shown to offer comparable or superior echocardiographic and clinical outcomes compared to standard CRT. Early data in HFpEF are limited, but retrospective studies suggest that LBBAP may improve left ventricular filling times and reduce mitral regurgitation. Because HFpEF patients often have narrower QRS complexes than HFrEF patients, the ability of conduction system pacing to correct subtle dyssynchrony without a right ventricular lead might be particularly attractive. Several ongoing trials, including the HIS-SYNC and LBBP-RESYNC studies, are evaluating the efficacy of conduction system pacing specifically in the HFpEF population.

Adaptive Pacing Algorithms and Closed-Loop Stimulation

Manufacturers are developing algorithms that use real-time hemodynamic data to adjust pacing parameters. For example, the Adaptive CRT algorithm from Medtronic automatically adapts the pacing mode (left ventricle only vs. biventricular) and AV delay based on intrinsic conduction and device- measured RV impedance variations that correlate with stroke volume. In HFrEF, Adaptive CRT has been shown to increase the percentage of biventricular pacing while reducing unnecessary right ventricular pacing. For HFpEF, such algorithms could be programmed to prioritize AV delay optimization and rate response that best suits the patient’s diastolic profile. Closed-loop stimulation (CLS) uses a transgenic impedance sensor to detect myocardial contractility changes and adjust pacing rate accordingly. CLS has been used effectively in patients with vasovagal syncope and may offer a more physiological rate response for HFpEF patients with chronotropic incompetence.

Patient Selection: Who Stands to Benefit?

Identifying the right candidates for pacemaker therapy in HFpEF is perhaps the most pressing challenge. Not every patient with HFpEF will benefit, and inappropriate implantation exposes patients to procedural risks without reward.

Role of Electromechanical Dyssynchrony

Current guidelines for CRT in heart failure require a left ventricular ejection fraction (LVEF) ≤35% and a QRS duration ≥130 ms with LBBB morphology. For HFpEF patients, who by definition have LVEF ≥50%, these criteria are not met. However, emerging evidence suggests that mechanical dyssynchrony detected by echocardiography or cardiac MRI may identify responders even with a narrow QRS. Techniques such as speckle-tracking strain imaging can quantify septal flash or apical rocking patterns that correlate with response to CRT. The HFA-PEFF (Heart Failure Association Pre-test assessment, Echocardiography & natriuretic peptide, Functional testing, Final etiology) diagnostic algorithm for HFpEF could be extended to include a “dyssynchrony risk score.” Patients with preserved LVEF but evidence of left atrial enlargement, elevated filling pressures, and interventricular or intraventricular mechanical delay may be the most promising candidates.

Chronotropic Incompetence

Chronotropic incompetence (CI)—the failure to achieve at least 80% of the age-predicted maximum heart rate during exercise—affects up to 60% of HFpEF patients. CI is strongly associated with poor exercise capacity and increased mortality. Rate-adaptive pacing is a logical intervention for these patients, and several studies have shown improved functional outcomes. However, the optimal rate-response slope and sensor mix (accelerometer vs. minute ventilation) need individualization. A simple screening tool is the cardiopulmonary exercise test (CPET); if peak heart rate <85% predicted, rate-responsive pacing should be considered. Ambulatory monitoring via implanted loop recorders or cardiac monitors can further help document bradyarrhythmias and the exact degree of CI before committing to a permanent pacemaker.

Atrial Fibrillation and Other Comorbidities

Atrial fibrillation (AF) is present in up to 70% of HFpEF patients. AF can be both a cause and consequence of diastolic dysfunction. Atrial-based pacing strategies that maintain atrioventricular synchrony (such as dual-chamber pacing) are critical in patients with AF who require permanent pacing. Additionally, AV node ablation followed by biventricular pacing (the “ablate and pace” strategy) has been shown to improve symptoms and left ventricular filling in HFpEF patients with refractory rapid AF. However, this procedure should be reserved for those with failed rate control or intolerance of antiarrhythmic drugs. Other comorbidities like hypertension, obesity, and renal dysfunction must be optimized concurrently; pacemaker therapy is not a standalone treatment but an adjunct to comprehensive heart failure management.

Challenges, Complications, and Risk Mitigation

Despite technological advances, pacemaker implantation in HFpEF patients carries unique risks that must be carefully weighed.

Procedural Complications

Standard CRT implantation involves placement of a left ventricular lead via the coronary sinus, which can be technically difficult in patients with tortuous or small veins. Failure rates range from 5% to 10%, even in experienced centers. Leadless systems may reduce some of these challenges but require specialized delivery systems and currently limited options for left ventricular pacing. Pneumothorax, cardiac perforation, pocket hematoma, and infection remain possible. HFpEF patients are often elderly with frail skin and multiple comorbidities, increasing the risk of pocket infections and lead dislodgement. Preoperative antibiotic prophylaxis, minimal handling of lead connectors, and use of antibiotic envelopes (e.g., TYRX) are recommended to reduce infection risk.

Long-Term Device Management

Programming a pacemaker for optimal benefit in HFpEF requires iterative adjustments. The default factory settings may not be ideal; for example, a short AV delay that improves cardiac output at rest may worsen filling at higher heart rates. Remote monitoring systems (CareLink, Home Monitoring, Merlin.net) are essential for tracking atrial and ventricular arrhythmias, device diagnostics (e.g., heart rate variability, thoracic impedance trend for fluid status), and verifying proper rate response. Clinicians must be adept at interpreting these data and reprogramming accordingly. The lack of clear guidelines for CRT programming in HFpEF means that many settings are based on extrapolation from HFrEF experience—an area that demands further research.

Economic Considerations

Pacemaker therapy is expensive. The cost of a CRT device plus implantation and follow-up can exceed $30,000. In an era of value-based care, it is essential to identify which HFpEF patients derive meaningful health gains. Cost-effectiveness analyses assuming modest benefits (improvement in quality of life by 0.1 QALY, reduction in hospitalizations by 20%) suggest that CRT may be cost-effective in subgroups with high baseline morbidity. However, widespread adoption without rigorous patient selection could strain healthcare budgets. Therefore, shared decision-making incorporating patient preferences, life expectancy, and functional goals is critical.

Future Directions and Unanswered Questions

The pacemaker field is moving rapidly. Several frontiers may reshape how HFpEF is managed over the next decade.

Integration with Implantable Sensors and Artificial Intelligence

Future pacemakers are likely to incorporate multiple sensors: left atrial pressure (e.g., the CardioMEMS system), pulmonary artery pressure, lung impedance, and even biomarkers such as BNP levels via nanoscale sensors. Closed-loop control algorithms powered by artificial intelligence could continuously optimize pacing parameters based on real-time hemodynamic data. For example, if left atrial pressure rises during exercise, the pacemaker could automatically shorten the AV delay or increase the pacing rate to promote filling and reduce congestion. Early proof-of-concept studies using the Hemodynamic Monitoring System in heart failure patients (including HFpEF) have shown that hemodynamic-guided management reduces hospitalizations by nearly 40%. Merging such sensors with pacing capabilities is the logical next step.

Personalized Pacing Algorithms Through Digital Twins

The concept of a “digital twin” of the patient’s cardiovascular system can be used to simulate different pacing strategies before implementation. Using a 3D heart model derived from MRI and computational fluid dynamics, clinicians could predict which AV delay and pacing site configuration yields maximal diastolic filling and lowest filling pressures. This approach is being explored in research settings and may eventually become part of routine clinical workflow. Early results from the ENRICH study using patient-specific computational modeling to guide CRT implantation show higher responder rates than empirical approaches.

Gene Therapy and Biological Pacemaking

While still preclinical, biological pacemakers that use gene therapy to convert ventricular myocytes into pacemaker cells could eliminate the need for hardware entirely. In small animal models, injection of TBX18—a transcription factor that induces sinoatrial node properties—has generated stable heart rates. For HFpEF, a biological pacemaker could theoretically be tuned to provide optimal rate and conduction without foreign materials. However, long-term safety, controllability, and scalability remain major hurdles, making this a distant future.

Large Pragmatic Trials and Reimbursement Landscape

To move pacemaker therapy from niche to standard of care for HFpEF, large pragmatic trials incorporating registry-based randomization are needed. The CRT for HFpEF trial expected to launch later this decade will enroll patients with preserved LVEF and evidence of dyssynchrony (either ECG or echocardiographic) and randomize them to CRT-OFF (backup pacing only) vs. CRT-ON (optimized biventricular pacing). The primary endpoint will be a composite of cardiovascular death and heart failure hospitalization. Pending positive results, reimbursement bodies such as the Centers for Medicare and Medicaid Services (CMS) in the US and the National Institute for Health and Care Excellence (NICE) in the UK may update their guidelines to include HFpEF-specific indications. Until then, strong advocacy by professional societies and local clinical champions will be necessary to support off-label use in select high-need patients.

Conclusion

Pacemaker therapy for heart failure with preserved ejection fraction is an area of intense investigation and gradual clinical translation. Far from the simplistic notion of “a device to speed up the heart,” modern pacing systems offer sophisticated tools to restore atrioventricular synchrony, optimize ventricular filling, correct mechanical dyssynchrony, and provide physiologically appropriate heart rate response. While the evidence base today supports benefits primarily in subgroups—those with chronotropic incompetence, left bundle branch block, or significant electrical dyssynchrony—ongoing trials and technological innovations will likely broaden the therapeutic window. Leadless and conduction system pacing, adaptive algorithms driven by hemodynamic sensors, and computational modeling promise a future where each HFpEF patient receives a tailor-made pacing prescription. The journey from proof-of-concept to guideline-recommended therapy will require meticulous patient selection, responsible cost management, and a continued commitment to high-quality clinical research. For the millions of patients living with HFpEF, pacemaker therapy represents a beacon of hope—not as a panacea, but as an increasingly precise tool to restore cardiac harmony and improve quality of life.